DBGP - A common debugger protocol for languages and debugger UI communication
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

:Version: 1.0
:Status: draft 15
:Authors: - Shane Caraveo, ActiveState <shanec@ActiveState.com>
          - Derick Rethans <derick@derickrethans.nl>


.. contents::

1. Description
==============

This document describes a simple protocol for use with language tools
and engines for the purpose of debugging applications.  It does not
describe user interfaces or interactions with the debugger.  The
protocol provides a means of communication between a debugger
engine (scripting engine, vm, etc.) and a debugger IDE (IDE, etc.).
Any references to the debugger IDE UI are recommendations only, and are
provided for additional explanation or as reasoning for specific
design decisions.

1.1 Issues
==========

1. The handling of proxy errors needs to be clarified.  Without both
IDE and debugger engine supporting commands to be received at
arbitrary times, the proxy may have problems sending error or status
information to either one.  See section 5.3.2.  We should think a bit
more about what a proxy might need to do.

2. Requirements
===============

* extensibility, allow for vendor or language specific features
* backwards and forwards compatibility
* firewall and tunneling support
* support for multiple languages
* support for multiple processes or threads
* support for dynamic and possibly for compiled languages

3. Terminology
==============

IDE
    An IDE, or other debugger UI IDE or tool.

debugger engine
    The language engine being debugged.

proxy
    An intermediary demon that acts as a proxy, and may also
    implement support for other features such as just in time
    debugging, ip security, etc.

session
    a single thread in an application.  multiple threads in an
    application will attach separately.

TRUE
    a value defined as TRUE should be a numeric one.

FALSE
    a value defined as FALSE should be a numeric zero.

NUM
    a base 10 numeric value that is stringified.

4. Security
===========

It is expected that implementations will provide security, such as ip
filtering, ssh tunneling, etc.  This protocol itself does not provide
a means of securing the debugging session.

5. Initiating a debugging session
=================================

The debugger engine initiates a debugging session.  The debugger engine
will make a connection to a listening IDE, then wait for the IDE to
initiate commands.  The debugger engine does not step into the first line of
execution until the IDE issues one of the continuation commands.
The first thing that should happen in a debug session is that the IDE
negotiates features using the feature_get and feature_set commands, and sets
any additional data, such as breakpoints.  Debugger engine implementations
should store and data it receives if it is unable to process them prior to
compiling and/or executing code.  Commands such as stack_get should not be
expected to work during this phase, otherwise known as the 'starting' state (see
section 7.1 for status levels).

Likewise, at the end of a debug session, there is a 'stopping' state.  This state
is entered after all execution is complete.  For most debugger engine implementations,
only a 'stop' command can be accepted at this point, however some implementations
may provide additional commands for retrieving various data from the engine for
post debug session processing.

5.1 Standard DBGP port
----------------------

The IDE listens on port 9000 for debugger connections, unless the
IDE is using a proxy, in which case it may listen on any port.  In
that case, the IDE will tell the proxy which port it is listening on, and the
proxy should listen on port 9000.  While this document defines port 9000
as the standard DBGP port, an implementation may support the use of any
port.  Current implementations accept various forms of configuration that
allow this port to be defined.

5.2 Connection Initialization
-----------------------------

When a debugger engine connects to either a IDE or proxy, it must send an
init packet: ::

    <init appid="APPID"
          idekey="IDE_KEY"
          session="DBGP_COOKIE"
          thread="THREAD_ID"
          parent="PARENT_APPID"
          language="LANGUAGE_NAME"
          protocol_version="1.0"
          fileuri="file://path/to/file">


Attributes in the init element can include:
    
    ================ ========================================================
    Attribute        Description
    ================ ========================================================
    appid            defined by the debugger engine
    idekey           defined by the user.  The DBGP_IDEKEY environment
                     variable SHOULD be used if it is available,
                     otherwise setting this value is debugger engine
                     implementation specific.  This value may be empty.
    session          If the environment variable DBGP_COOKIE exists,
                     then the init packet MUST contain a session
                     attribute with the value of the variable.  This
                     allows an IDE to execute a debugger engine, and
                     maintain some state information between the
                     execution and the protocol connection.  This value
                     should not be expected to be set in 'remote'
                     debugging situations where the IDE is not in
                     control of the process.  
    thread           the systems thread id
    parent           the appid of the application that spawned the
                     process.  When an application is executed, it
                     should set it's APPID into the environment.
                     If an APPID already exists, it should first
                     read that value and use it as the PARENT_APPID.
    language         debugger engine specific, must not contain
                     additional information, such as version, etc.
    protocol_version The highest version of this protocol supported
    fileuri          URI of the script file being debugged
    ================ ========================================================

The IDE responds by dropping socket connection, or starting with
debugger commands.

The init packet may have child elements for additional vendor specific
data.  These are entirely optional and must not effect behavior
of the debugger interaction.  Suggested child elements include: ::

    <engine version="1.abcd">product title</engine>
    <author>author</author>
    <company>company</company>
    <license>licensing info</license>
    <url>url</url>
    <copyright>xxx</copyright>

5.3 Just in time debugging and debugger proxies
-----------------------------------------------

Proxies are supported to allow multiuser systems work with a defined
port for debugging.  Each IDE would listen on a unique port and notify the
proxy what port it is listening on, along with a key value that is used by
the debugger engine to specify which IDE it should be connected with.

With the exception of the init packet, all communications
will be passed through without modifications.  A proxy could also implement
support for just in time debugging.  In this case, a debugger engine would
break (perhaps on an error or exception) and connect to the proxy.  The proxy
would then start the IDE (if it is not already running) and initiate a
debugging session with it.

The method for handling just in time debugging is not defined by the protocol
and is implementation specific.  One example of how this may work is that the
proxy has a configuration file that defines key's for each user, along with
the path to the executable that will provide the UI for that user.  The debugger
engine would have to know this key value in advance and provide it to the proxy
in the init packet (see IDE_KEY in section 5.2).  The proxy would know if the
IDE is running, since the IDE should have communicated with the proxy already,
if it has not, the proxy could execute the IDE directly.

To support proxies and jit deamons, the IDE should be configured with
and ip:port pointing to the proxy/jit.  The IDE then makes a
connection to the proxy when it starts and sends the following command: 

    IDE command ::
    
        proxyinit -a ip:port -k ide_key -m [0|1]

    ==  ========================================================
    -p  the port that the IDE listens for debugging on.  The address
        is retrieved from the connection information.
    -k  a IDE key, which the debugger engine will also use in it's
        debugging init command.  this allows the proxy to match
        request to IDE.  Typically the user will provide the
        session key as a configuration item.
    -m  this tells the demon that the IDE supports (or doesn't)
        multiple debugger sessions.  if -m is missing, zero or no
        support is default.
    ==  ========================================================

    IDE command ::
    
        proxystop -k ide_key
    
    The IDE sends a proxystop command when it wants the proxy
    server to stop listening for it.

The proxy should respond with a simple XML statement alerting the
IDE to an error, or the success of the initialization (see section
6.5 for more details on the error element). ::

    <proxyinit success="[0|1]"
               idekey="{ID}"
               address="{IP_ADDRESS}"
               port="{NUM}>
        <error id="app_specific_error_code">
            <message>UI Usable Message</message>
        </error>
    </proxyinit>

Once the IDE has sent this command, and received a confirmation, it
disconnects from the proxy.  The IDE will only connect to the proxy
when it initially wants to start accepting connections from the proxy,
or when it wants to stop accepting connections from the proxy.

The address and port attributes of the returned proxyinit element are the
address and port that the proxy is configured to listen for DBGP connections on.
This information is returned to the IDE so that it may pass this information on
to build systems or the user via some UI.

5.3.1 Init Packet Handling
^^^^^^^^^^^^^^^^^^^^^^^^^^

If a proxy receives the init packet (see section 5.2), it will use the
idekey attribute to pass the request to the correct IDE, or to do some
other operation such as which may be required to implement security or
initiate just in time debugging.  The proxy will add the idekey as a attribute
to the init packet when it passes it through to the IDE.  The proxy may
also add child elements with further information, and must add an
attribute to the init element called 'proxied' with the attribute
value being the ip address of the debugger engine.  This is the only
time the proxy should modify data being passed to the IDE.

5.3.2 Proxy Errors
^^^^^^^^^^^^^^^^^^

If the proxy must send error data to the IDE, it may send an XML
message with the root element named 'proxyerror'.  This message will
be in the format of the error packets defined in 6.3 below.

If the proxy must send error data to the debugger engine, it may
send the proxyerror command defined in section 7 below.

5.3.3 Proxy Ports
^^^^^^^^^^^^^^^^^

The proxy listens for IDE connections on port 9001, and for debugger
engine connections on port 9000.  As with section 5.1, these ports may
be configurable in the implementation.

5.4 Multiple Processes or Threads
---------------------------------

The debugger protocol is designed to use a separate socket connection
for each process or thread.  The IDE may or may not support
multiple debugger sessions.  If it does not, the debugger engine must
not attempt to start debug sessions for threads, and the IDE should
not accept more than one socket connection for debugging.  The
IDE should tell the debugger engine whether it supports multiple
debugger sessions, the debugger engine should assume that the IDE does
not.  The IDE can use the feature_set command with the feature name of
'multiple_sessions' to notify the debugger engine that it supports multiple
session debugging.  The IDE may also query the the debugger engine specifically
for multithreaded debugging support by using the feature_get command with
a feature name of 'language_supports_threads'.

5.5 Feature Negotiation
-----------------------

Although the IDE may at any time during the debugging session send
feature_get or feature_set commands, the IDE should be designed to
negotiate the base set of features up front.  Differing languages and
debugger engines may operate in many ways, and the IDE should be
prepared to handle these differences.  Likewise, the IDE may dictate
certain features or capabilities be supported by the debugger engine.
In any case, the IDE should strive to work with all debugger engines
that support this protocol.  Therefore, this section describes a
minimal set of features the debugger engine must support.  These
required features are outlined here in the form of discussion,
actual implementation of feature arguments are detailed in section 7
under the feature_get and feature_set commands.

Data packet negotiation
^^^^^^^^^^^^^^^^^^^^^^^

IDE's may want to limit the size of data that is retrieved from
debugger engines.  While the debugger engines will define their own
base default values, the IDE should negotiate these terms if it
needs to.  The debugger engine must support these requests from the
IDE.  This includes limits to the data size of a property or
variable, and the depth limit to arrays, hashes, objects, or other
tree like structures.  The data size excludes any the protocol
overhead.

Asynchronous Communications
^^^^^^^^^^^^^^^^^^^^^^^^^^^

While the protocol does not depend on asynchronous socket support,
certain design considerations may require that the IDE and/or debugger
engine treat incoming and outgoing data in an asynchronous fashion.

For ease of design, some implementations may choose to utilize this
protocol in a completely synchronous fashion, and not implement
optional commands that require the debugger engine to behave in an
asynchronous fashion.  One example of this is the break command.

The break command is sent from the IDE while the debugger engine is
in a run state.  To support this, the debugger engine must periodically
peek at the socket to see if there are any incoming commands.  For
this reason the break command is optional.  If a command requires
this type of asynchronous behavior on the part of the debugger
engine it must be optional for the debugger engine to support it.

On the other hand, IDE's MUST at times behave in an asynchronous
fashion.  When an IDE tells the debugger engine to enter a 'run' state,
it must watch the socket for incoming packets for stdout or stderr,
if it has requested the data be sent to it from the debugger engine.

The form of asynchronous communications that may occur in this
protocol are defined further in section 6.2 below.


6. Message Packets
==================

The IDE sends simple ASCII commands to the debugger engine.  The
debugger engine responds with XML data.  The XML data is prepended
with a stringified integer representing the length of the XML data
packet.  The length and XML data are separated by a NULL byte.  The
XML data is ended with a NULL byte.  Neither the IDE or debugger engine
packets may contain NULL bytes within the packet since it is used as
a separator.  Data must be encoded using base64. ::

    IDE:       command [SPACE] [args] -- data [NULL]
    DEBUGGER:  [NUMBER] [NULL] XML(data) [NULL]

Arguments to the IDE commands are in the same format as common command
line arguments, and should be parseable by common code such as getopt,
or Pythons Cmd module: ::

    command -a value -b value ...

All numbers in the protocol are base 10 string representations, unless
the number is noted to be debugger engine specific (eg. the address
attribute on property elements).

6.1 Why not XML both ways?
--------------------------

The primary reason is to avoid the requirement that a debugger
engine has an XML parser available.  XML is easy to generate, but
requires additional libraries for parsing.


6.2 Packet Communications
-------------------------

The IDE sends a command, then waits for a response from the
debugger engine.  If the command is not received in a reasonable
time (implementation dependent) it may assume the debugger engine
has entered a non-responsive state.  The exception to this is when
the IDE sends a 'continuation' command which may not have an immediate response.

'continuation' commands include, but may not be limited to: run, step_into,
step_over, step_out and eval.  When the debugger engine
receives such a command, it is considered to have entered a
'run state'.

During a 'continuation' command, the IDE should expect to possibly receive
stdin and/or stderr packets from the debugger engine prior to
receiving a response to the command itself.  It may also possibly
receive error packets from either the debugger engine, or a proxy
if one is in use, either prior to the 'continuation' response, or in response
to any other command.

Stdout and stderr, if requested by the IDE, may only be sent during
commands that have put the debugger engine into a 'run' state.

If the debugger engine supports asynchronous commands, the IDE may also
send commands while the debugger engine is in a 'run' state.  These
commands should be limited to commands such as the 'break' or 'status'
commands for performance reasons, but this protocol does not impose
such limitations.  The debugger engine MUST respond to these commands
prior to responding to the original 'run' command.

An example of communication between IDE and debugger engines.  (this
is not an example of the actual protocol.) ::

    IDE:  feature_get supports_async
    DBG:  yes
    IDE:  stdin redirect
    DBG:  ok
    IDE:  stderr redirect
    DBG:  ok
    IDE:  run
    DBG:  stdin data...
    DBG:  stdin data...
    DBG:  reached breakpoint, done running
    IDE:  give me some variables
    DBG:  ok, here they are
    IDE:  evaluate this expression
    DBG:  stderr data...
    DBG:  ok, done
    IDE:  run
    IDE:  break
    DBG:  ok, breaking
    DBG:  at breakpoint, done running
    IDE:  stop
    DBG:  good bye


6.3 IDE to debugger engine communications
-----------------------------------------

A debugging IDE (IDE) sends commands to the debugger engine in
the form of command line arguments.  One argument that is included in
all commands is the data length.  The data itself is the last part of
the command line.  The data may be binary data if the encoding argument
is 'binary'. ::

    command [SPACE] [arguments] [SPACE] base64(data) [NULL]

Standard arguments for all commands ::

    -i      Transaction ID
            unique for each command generated by the IDE

6.4 debugger engine to IDE communications
-----------------------------------------

The debugger engine always replies or sends XML data.  The standard
namespace for the root elements returned from the debugger
engine MUST be "urn:debugger_protocol_v1".  Namespaces have been left
out in the examples in this document.  The messages sent by the
debugger engine must always be NULL terminated.  The XML document tag
must always be present to provide XML version and encoding information.

Two base tags are used for the root tags: ::

    data_length
    [NULL]
    <?xml version="1.0" encoding="UTF-8"?>
    <response command="command_name"
              transaction_id="transaction_id"/>
    [NULL]

    data_length
    [NULL]
    <?xml version="1.0" encoding="UTF-8"?>
    <stream type="stdout|stderr">...Base64 Data...</stream>
    [NULL]

For simplification, data length and NULL bytes will be left out of the
rest of the examples in this document.

6.5 debugger engine errors
--------------------------

A debugger engine may need to relay error information back to the IDE in
response to any command.  The debugger engine may add an error element
as a child of the response element.  Note that this is not the same
as getting language error messages, such as exception data.  This is
specifically a debugger engine error in response to a IDE
command.  IDEs and debugger engines may elect to support additional
child elements in the error element, but should namespace the elements
to avoid conflicts with other implementations. ::

    <response command="command_name"
              transaction_id="transaction_id">
        <error code="error_code" apperr="app_specific_error_code">
            <message>UI Usable Message</message>
        </error>
    </response>

6.5.1 Error Codes
-----------------

The following are predefined error codes for the response to commands:

000 Command parsing errors ::

    0 - no error
    1 - parse error in command
    2 - duplicate arguments in command
    3 - invalid options (ie, missing a required option)
    4 - Unimplemented command
    5 - Command not available (Is used for async commands. For instance
        if the engine is in state "run" than only "break" and "status"
        are available). 

100 File related errors ::

    100 - can not open file (as a reply to a "source" command if the
          requested source file can't be opened)
    101 - stream redirect failed 

200 Breakpoint, or code flow errors ::

    200 - breakpoint could not be set (for some reason the breakpoint
          could not be set due to problems registering it)
    201 - breakpoint type not supported (for example I don't support
          'watch' yet and thus return this error)
    202 - invalid breakpoint (the IDE tried to set a breakpoint on a
          line that does not exist in the file (ie "line 0" or lines
          past the end of the file)
    203 - no code on breakpoint line (the IDE tried to set a breakpoint
          on a line which does not have any executable code. The
          debugger engine is NOT required to return this type if it
          is impossible to determine if there is code on a given
          location. (For example, in the PHP debugger backend this
          will only be returned in some special cases where the current
          scope falls into the scope of the breakpoint to be set)).
    204 - Invalid breakpoint state (using an unsupported breakpoint state
          was attempted)
    205 - No such breakpoint (used in breakpoint_get etc. to show that
          there is no breakpoint with the given ID)
    206 - Error evaluating code (use from eval() (or perhaps
          property_get for a full name get))
    207 - Invalid expression (the expression used for a non-eval()
          was invalid) 

300 Data errors ::

    300 - Can not get property (when the requested property to get did
          not exist, this is NOT used for an existing but uninitialized
          property, which just gets the type "uninitialised" (See:
          PreferredTypeNames)).
    301 - Stack depth invalid (the -d stack depth parameter did not
          exist (ie, there were less stack elements than the number
          requested) or the parameter was < 0)
    302 - Context invalid (an non existing context was requested) 

900 Protocol errors ::

    900 - Encoding not supported
    998 - An internal exception in the debugger occurred
    999 - Unknown error 


6.6 file paths
--------------

All file paths passed between the IDE and debugger engine must be in
the URI format specified by IETF RFC 1738 and 2396, and must be
absolute paths.

6.7 Dynamic code and virtual files
----------------------------------

The protocol reserves the URI scheme 'dbgp' for all virtual
files generated and maintained by language engines. Such
virtual files are usually managed by a language engine for
dynamic code blocks, i.e. code created at runtime, without
an association with a regular file. Any IDE seeing an URI
with the 'dbgp' scheme has to use the 'source' command (See
section 7.14) to obtain the contents of the file from the
engine responsible for that URI.

All URIs in that scheme have the form:

    dbgp:engine-specific-identifier

The engine-specific-identifier is some string which the debugger engine
uses to keep track of the specific virtual file.  The IDE must return
the URI to the debugger engine unchanged through the source command to
retrieve the virtual file.

7. Core Commands
================

Both IDE and debugger engine must support all core commands.

7.1 status
----------

The status command is a simple way for the IDE to find out from
the debugger engine whether execution may be continued or not.
no body is required on request.  If async support has been
negotiated using feature_get/set the status command may be sent
while the debugger engine is in a 'run state'.

The status attribute values of the response may be:

    starting:
       State prior to execution of any code
    stopping:
       State after completion of code execution.  This typically
       happens at the end of code execution, allowing the IDE to
       further interact with the debugger engine (for example, to
       collect performance data, or use other extended commands).
    stopped:
       IDE is detached from process, no further interaction is
       possible.
    running:
       code is currently executing.  Note that this
       state would only be seen with async support
       turned on, otherwise the typical state during
       IDE/debugger interaction would be 'break'
    break:
       code execution is paused, for whatever reason
       (see below), and the IDE/debugger can pass
       information back and forth.

The reason attribute value may be:

    - ok
    - error
    - aborted
    - exception

IDE ::

    status -i transaction_id

debugger engine ::

    <response command="status"
              status="starting"
              reason="ok"
              transaction_id="transaction_id">
        message data
    </response>

7.2 Options and Configuration
-----------------------------

The feature commands are used to request feature support from the debugger
engine. This includes configuration options, some of which may be changed via
feature_set, the ability to discover support for implemented commands, and to
discover values for various features, such as the language version or name.

An example of usage would be to send a feature request with the string 'stdin'
to find out if the engine supports redirection of the stdin stream through the
debugger socket. The debugger engine must consider all commands as keys for this
command, but may also have keys that are for features that do not map directly
to commands.

7.2.1 Feature Names
^^^^^^^^^^^^^^^^^^^

The following features strings MUST be available: 

    ========================= ======= ==========================================
    language_supports_threads get     [0|1]
    language_name             get     {eg. PHP, Python, Perl}
    language_version          get     {version string}
    encoding                  get     current encoding in use by
                                      the debugger session
    protocol_version          get     {for now, always 1}
    supports_async            get     {for commands such as break}
    data_encoding             get     optional, allows to turn off
                                      the default base64 encoding of data. This
                                      should only be used for development and
                                      debugging of the debugger engines
                                      themselves, and not for general use. If
                                      implemented the value 'base64' must be
                                      supported to turn back on regular
                                      encoding. the value 'none' means no
                                      encoding is in use. all elements that use
                                      encoding must include an encoding
                                      attribute.
    breakpoint_languages      get     some engines may support more than one
                                      language. This feature returns a string
                                      which is a comma separated list of
                                      supported languages. **If the engine does
                                      not provide this feature, then it is
                                      assumed that the engine only supports the
                                      language defined in the feature
                                      language_name.** One example of this is an
                                      XSLT debugger engine which supports XSLT,
                                      XML, HTML and XHTML. An IDE may need this
                                      information to to know what types of
                                      breakpoints an engine will accept.
    breakpoint_types          get     returns a space separated list with all
                                      the breakpoint types that are supported.
                                      See `7.6 breakpoints`_ for a list of the
                                      6 defined breakpoint types.
    multiple_sessions         get|set {0|1}
    encoding                  get|set {ISO8859-15, UTF-8, etc.}
    max_children              get|set max number of array or object
                                      children to initially retrieve
    max_data                  get|set max amount of variable data to
                              get|set initially retrieve.
    max_depth                 get|set maximum depth that the debugger
                                      engine may return when sending arrays,
                                      hashs or object structures to the IDE.
    ========================= ======= ==========================================

The following features strings MAY be available, if they are not, the IDE should
assume that the feature is not available: 

    ========================= ======= ==========================================
    supports_postmortem       get     [0|1]  This feature lets an IDE know that
                                      there is benefit to continuing interaction
                                      during the STOPPING state (sect. 7.1).
    show_hidden               get|set [0|1]  This feature can get set by the IDE
                                      if it wants to have more detailed internal
                                      information on properties (eg. private
                                      members of classes, etc.)  Zero means that
                                      hidden members are not shown to the IDE.
    notify_ok                 get|set [0|1]  See section 8.5
    ========================= ======= ==========================================

Additionally, all protocol commands supported must have a string,
such as the following examples: ::

    breakpoint_set
    break
    eval

7.2.2 feature_get
^^^^^^^^^^^^^^^^^

arguments for feature_get include: 

    ==      ==========================================
    -n      feature_name
    ==      ==========================================

IDE ::

    feature-get -i transaction_id -n feature_name

debugger engine ::

    <response command="feature_get"
              feature_name="feature_name"
              supported="0|1"
              transaction_id="transaction_id">
        feature setting or available options, such as a list of
        supported encodings
    </response>


7.2.3 feature_set
^^^^^^^^^^^^^^^^^

The feature set command allows a IDE to tell the debugger engine what additional
capabilities it has. One example of this would be telling the debugger engine
whether the IDE supports multiple debugger sessions (for threads, etc.). The
debugger engine responds with telling the IDE whether it has enabled the feature
or not.

Note: The IDE does not have to listen for additional debugger connections if it
does not support debugging multiple sessions. debugger engines must handle
connection failures gracefully.

arguments for feature_set include: 

    ==      ==========================================
    -n      feature_name
    -v      value to be set
    ==      ==========================================

feature_set can be called at any time during a debug session to
change values previously set.  This allows a IDE to change
encodings.

IDE ::

    feature_set -i transaction_id -n feature-name -v value

debugger engine ::

    <response command="feature_set"
              feature="feature_name"
              success="0|1"
              transaction_id="transaction_id"/>


7.5 continuation commands
-------------------------

resume the execution of the application.

run:
    starts or resumes the script until a new breakpoint is reached,
    or the end of the script is reached.

step_into:
    steps to the next statement, if there is a function call
    involved it will break on the first statement in that function

step_over:
    steps to the next statement, if there is a function call on the
    line from which the step_over is issued then the debugger engine
    will stop at the statement after the function call in the same
    scope as from where the command was issued

step_out:
    steps out of the current scope and breaks on the statement after
    returning from the current function. (Also called 'finish' in
    GDB)

stop:
    ends execution of the script immediately, the debugger engine may
    not respond, though if possible should be designed to do so.
    The script will be terminated right away and be followed by a
    disconnection of the network connection from the IDE (and debugger
    engine if required in multi request apache processes).

detach (optional):
    stops interaction with the debugger engine.  Once this command
    is executed, the IDE will no longer be able to communicate with
    the debugger engine.  This does not end execution of the script
    as does the stop command above, but rather detaches from debugging.
    Support of this continuation command is optional, and the IDE should
    verify support for it via the feature_get command.  If the IDE has
    created stdin/stdout/stderr pipes for execution of the script
    (eg. an interactive shell or other console to catch script output),
    it should keep those open and usable by the process until the process
    has terminated normally.

The response to a continue command is a status response (see
status above).  The debugger engine does not send this response
immediately, but rather when it reaches a breakpoint, or ends
execution for any other reason.

IDE ::

    run -i transaction_id

debugger engine ::

    <response command="run"
              status="starting"
              reason="ok"
              transaction_id="transaction_id"/>

7.6 breakpoints
---------------

Breakpoints are locations or conditions at which a debugger engine
pauses execution, responds to the IDE, and waits for further commands
from the IDE.  A failure in any breakpoint commands results in an
error defined in `section 6.5`_.


The following DBGP commands relate to breakpoints:

    ==================  =================================================
    breakpoint_set_     Set a new breakpoint on the session.
    breakpoint_get_     Get breakpoint info for the given breakpoint id.
    breakpoint_update_  Update one or more attributes of a breakpoint.
    breakpoint_remove_  Remove the given breakpoint on the session.
    breakpoint_list_    Get a list of all of the session's breakpoints.
    ==================  =================================================

.. _breakpoint_set: `7.6.1 breakpoint_set`_
.. _breakpoint_get: `7.6.2 breakpoint_get`_
.. _breakpoint_update: `7.6.3 breakpoint_update`_
.. _breakpoint_remove: `7.6.4 breakpoint_remove`_
.. _breakpoint_list: `7.6.5 breakpoint_list`_


There are six different breakpoints *types*:

    ==============  ===========     =========================================
    Type            Req'd Attrs     Description
    ==============  ===========     =========================================
    line            filename,       break on the given lineno in the given
                    lineno          file
    call            function        break on entry into new stack for
                                    function name
    return          function        break on exit from stack for function
                                    name
    exception       exception       break on exception of the given name
    conditional     expression      break when the given expression is true
                                    at the given filename and line number or
                                    just in given filename
    watch           expression      break on write of the variable or address
                                    defined by the expression argument
    ==============  ===========     =========================================


A breakpoint has the following attributes. Note that some attributes are only
applicable for some breakpoint types.

    ==================  ======================================================
    type                breakpoint type (see table above for valid types)
    filename            The file the breakpoint is effective in. This must be
                        a "file://" URI.
    lineno              Line number on which breakpoint is effective. Line
                        numbers are 1-based. If an implementation requires a
                        numeric value to indicate that *lineno* is not set,
                        it is suggested that -1 be used, although this is not
                        enforced.
    state               Current state of the breakpoint. This must be one of
                        *enabled*, *disabled*.
    function            Function name for *call* or *return* type
                        breakpoints.
    temporary           Flag to define if breakpoint is temporary. A
                        temporary breakpoint is one that is deleted after its
                        first use. This is useful for features like "Run to
                        Cursor".  Once the debugger engine uses a temporary
                        breakpoint, it should automatically remove the breakpoint
                        from it's list of valid breakpoints.
    hit_count           Number of effective hits for the breakpoint in the
                        current session.  This value is maintained by the
                        debugger engine (a.k.a.  DBGP client).  A
                        breakpoint's hit count should be increment whenever
                        it is considered to break execution (i.e. whenever
                        debugging comes to this line). If the breakpoint is
                        *disabled* then the hit count should NOT be
                        incremented.
    hit_value           A numeric value used together with the
                        *hit_condition* to determine if the breakpoint should
                        pause execution or be skipped.
    hit_condition       A string indicating a condition to use to compare
                        *hit_count* and *hit_value*. The following values are
                        legal:

                        `>=`
                            break if hit_count is greater than or equal to
                            hit_value [default]
                        `==`
                            break if hit_count is equal to hit_value
                        `%`
                            break if hit_count is a multiple of hit_value
    exception           Exception name for *exception* type breakpoints.
    ==================  ======================================================

Breakpoints should be maintained in the debugger engine at an application
level, not the thread level.  Debugger engines that support thread debugging
MUST provide breakpoint id's that are global for the application, and must
use all breakpoints for all threads where applicable.

As for any other commands, if there is error the debugger engine should
return an error response as described in `section 6.5`_.

.. _`section 6.5`: `6.5 debugger engine errors`_


7.6.1 breakpoint_set
^^^^^^^^^^^^^^^^^^^^

This command is used by the IDE to set a breakpoint for the session.

IDE to debugger engine::

    breakpoint_set -i TRANSACTION_ID [<arguments...>] -- base64(expression)

where the arguments are:

    ==================  =====================================================
    -t TYPE             breakpoint *type*, see below for valid values
                        [required]
    -s STATE            breakpoint *state* [optional, defaults to "enabled"]
    -f FILENAME         the *filename* to which the breakpoint belongs
                        [optional]
    -n LINENO           the line number (*lineno*) of the breakpoint
                        [optional]
    -m FUNCTION         *function* name [required for *call* or *return*
                        breakpoint types]
    -x EXCEPTION        *exception* name [required for *exception* breakpoint
                        types]
    -h HIT_VALUE        hit value (*hit_value*) used with the hit condition
                        to determine if should break; a value of zero
                        indicates hit count processing is disabled for this
                        breakpoint [optional, defaults to zero (i.e.
                        disabled)]
    -o HIT_CONDITION    hit condition string (*hit_condition*); see
                        hit_condition documentation above; BTW 'o' stands for
                        'operator' [optional, defaults to '>=']
    -r 0|1              Boolean value indicating if this breakpoint is
                        *temporary*. [optional, defaults to false]
    -- EXPRESSION       code *expression*, in the language of the debugger
                        engine [required for *conditional* breakpoint types]
    ==================  =====================================================

An example breakpoint_set command for a conditional breakpoint could look
like this::

    breakpoint_set -i 1 -f test.pl -l 20 -- base64($x > 3)

A unique id for this breakpoint for this session is returned by the debugger
engine. This *session breakpoint id* is used by the IDE to identify the
breakpoint in other breakpoint commands.

debugger engine to IDE::

     <response command="breakpoint_set"
               transaction_id="TRANSACTION_ID"
               state="STATE"
               id="BREAKPOINT_ID"/>

where,

    ==================  =====================================================
    BREAKPOINT_ID       is an arbitrary string that uniquely identifies this
                        breakpoint in the debugger engine.
    STATE               the initial state of the breakpoint as set by the
                        debugger engine
    ==================  =====================================================


7.6.2 breakpoint_get
^^^^^^^^^^^^^^^^^^^^

This command is used by the IDE to get breakpoint information from the
debugger engine.

IDE to debugger engine::

    breakpoint_get -i TRANSACTION_ID -d BREAKPOINT_ID 

where,
    
    ==================  =====================================================
    BREAKPOINT_ID       is the unique *session breakpoint id* returned by
                        *breakpoint_set*.
    ==================  =====================================================

debugger engine to IDE::

    <response command="breakpoint_get"
              transaction_id="TRANSACTION_ID">
        <breakpoint id="BREAKPOINT_ID"
                    type="TYPE"
                    state="STATE"
                    filename="FILENAME"
                    lineno="LINENO"
                    function="FUNCTION"
                    exception="EXCEPTION"
                    hit_value="HIT_VALUE"
                    hit_condition="HIT_CONDITION"
                    hit_count="HIT_COUNT">
            <expression>EXPRESSION</expression>
        </breakpoint>
    </response>

where each breakpoint attribute is only required if its value is relevant.
E.g., the <expression/> child element need only be included if there is an
expression defined, the *function* attribute need only be included if this is
a *function* breakpoint.


7.6.3 breakpoint_update
^^^^^^^^^^^^^^^^^^^^^^^

This command is used by the IDE to update one or more attributes of a
breakpoint that was already set on the debugger engine via *breakpoint_set*.

IDE to debugger engine::

    breakpoint_update -i TRANSACTION_ID -d BREAKPOINT_ID [<arguments...>]

where the arguments are as follows.  All arguments are optional, however
at least one argument should be present.  See breakpoint_set_ for a description of
each argument:

    ==  ===============  
    -s  STATE
    -n  LINENO
    -h  HIT_VALUE
    -o  HIT_CONDITION
    ==  ===============  

debugger engine to IDE::

    <response command="breakpoint_update"
              transaction_id="TRANSACTION_ID"/>


7.6.4 breakpoint_remove
^^^^^^^^^^^^^^^^^^^^^^^

This command is used by the IDE to remove the given breakpoint.

IDE to debugger engine::

    breakpoint_remove -i TRANSACTION_ID -d BREAKPOINT_ID

debugger engine to IDE::

    <response command="breakpoint_remove"
              transaction_id="TRANSACTION_ID"/>


7.6.5 breakpoint_list
^^^^^^^^^^^^^^^^^^^^^

This command is used by the IDE to get breakpoint information for all
breakpoints that the debugger engine has.

IDE to debugger engine::

    breakpoint_list -i TRANSACTION_ID

debugger engine to IDE::

    <response command="breakpoint_list"
              transaction_id="TRANSACTION_ID">
        <breakpoint id="BREAKPOINT_ID"
                    type="TYPE"
                    state="STATE"
                    filename="FILENAME"
                    lineno="LINENO"
                    function="FUNCTION"
                    exception="EXCEPTION"
                    hit_value="HIT_VALUE"
                    hit_condition="HIT_CONDITION"
                    hit_count="HIT_COUNT">
            <expression>EXPRESSION</expression>
        </breakpoint>
        <breakpoint ...>...</breakpoint>
        ...
    </response>



7.7 stack_depth
---------------

IDE ::

    stack-depth -i transaction_id

debugger engine ::

    <response command="stack_depth"
              depth="{NUM}"
              transaction_id="transaction_id"/>


7.8 stack_get
-------------

Returns stack information for a given stack depth.  For extended
debuggers, multiple file/line's may be returned by having
child elements of the stack element.  This is to allow
for debuggers, such as XSLT, that have execution and data files.
The filename returned should always be the local file
system path translated into a file URI, and should include the
system name if the engine is not connecting to an ip on the local
box: file://systemname/c|/path.  If the stack depth is
specified, only one stack element is returned, for the depth
requested, though child elements may be returned also.  The
current context is stack depth of zero, the 'oldest' context
(in some languages known as 'main') is the highest numbered
context. 

    ==      ==========================================
    -d      stack depth (optional)
    ==      ==========================================

IDE ::

    stack_get -d {NUM} -i transaction_id

debugger engine ::

    <response command="stack_get"
              transaction_id="transaction_id">
        <stack level="{NUM}"
               type="file|eval|?"
               filename="..."
               lineno="{NUM}"
               where=""
               cmdbegin="line_number:offset"
               cmdend="line_number:offset"/>
        <stack level="{NUM}"
               type="file|eval|?"
               filename="..."
               lineno="{NUM}">
            <input level="{NUM}"
                   type="file|eval|?"
                   filename="..."
                   lineno="{NUM}"/>
        </stack>
    </response>

Attributes for the stack element can include:
    
    =========   ========================================================
    Attribute   Description
    =========   ========================================================
    level       stack depth for this stack element
    type        the type of stack frame.  Valid values are file or eval.
    filename    file URI
    lineno      1-based line offset into the buffer
    where       current command name (optional)
    cmdbegin    line number and text offset from beginning of line
                for the current instruction (optional)
    cmdend      same as cmdbegin, denotes end of current instruction
    =========   ========================================================

The attributes where, cmdbegin and cmdlength are primarily used
for relaying visual information in the IDE.  cmdbegin and cmdend
can be used by the IDE for high lighting the command that is
currently being debugged.  The where attribute contains the name
of the current stack.  This could be the current function name
that the user is stepping through.


7.9 context_names
-----------------

The names of currently available contexts at a given stack depth,
typically Local, Global and Class.  These SHOULD be UI friendly
names.  The id attribute returned with the names is used in other
commands such as context_get to identify the context.  The context
id zero is always considered to be the 'default' context is no
context id is provided.  In most languages, this will the be
'local' context. 

    ==      ========================================================
    -d      stack depth (optional)
    ==      ========================================================

IDE ::

    context_names -d {NUM} -i transaction_id

debugger engine ::

    <response command="context_names"
              transaction_id="transaction_id">
        <context name="Local" id="0"/>
        <context name="Global" id="1"/>
        <context name="Class" id="2"/>
    </response>


7.10 context_get
----------------

Returns an array of properties in a given context at a given
stack depth.  If the stack depth is omitted, the current
stack depth is used.  If the context name is omitted, the context
with an id zero is used (generally the 'locals' context). 

    ==      ========================================================
    -d      stack depth (optional)
    -c      context id  (optional, retrieved by context-names)
    ==      ========================================================

IDE ::

    context_get -d {NUM} -i transaction_id

debugger engine ::

    <response command="context_get"
              context="context_id"
              transaction_id="transaction_id">
        <property ... />
    </response>


7.11 Properties, variables and values
-------------------------------------

Properties that have children may return an arbitrary depth of
children, as defaulted by the debugger engine.  A maximum depth
may be defined by the IDE using the feature_set command with the
max_depth argument.  The IDE may then use the fullname attribute of
a property to dig further into the tree.  Data types are defined
further in section 7.12 below.

The number of children sent is defined by the debugger engine unless
otherwise defined by sending the feature_set command with the
max_children argument. If max_depth > 1, irregardless of the page
argument, the childrens pages are always the first page. Children are
only returned if max_depth > 0 and max_children > 0. ::

    <property
        name="short_name"
        fullname="long_name"
        type="data_type"
        classname="name_of_object_class"
        constant="0|1"
        children="0|1"
        size="{NUM}"
        page="{NUM}"
        pagesize="{NUM}"
        address="{NUM}"
        key="language_dependent_key"
        encoding="base64|none"
        numchildren="{NUM}">
    ...encoded Value Data...
    </property>

Attributes in the property element can include:
    
    =============== ========================================================
    Attribute       Description
    =============== ========================================================
    name            variable name.  This is the short part of the
                    name.  For instance, in PHP:
                    $v = 0; // short name 'v'
                    class:$v; // short name 'v'
    fullname        variable name.  This is the long form of the name
                    which can be eval'd by the language to retrieve
                    the value of the variable.
                    $v = 0; // long name 'v'
                    class::$v; // short name 'v', long 'class::$v'
                    $this->v; // short name 'v', long '$this->v'
    classname       If the type is an object or resource, then the
                    debugger engine MAY specify the class name
                    This is an optional attribute.
    page            if not all the children in the first level are
                    returned, then the page attribute, in combination
                    with the pagesize attribute will define where in
                    the array or object these children should be
                    located. The page number is 0-based.
    pagesize        the size of each page of data, defaulted by the
                    debugger engine, or negotiated with feature_set
                    and max_children
    type            language specific data type name
    facet           provides a hint to the IDE about additional
                    facets of this value.  These are space separated
                    names, such as private, protected, public,
                    constant, etc.
    size            size of property data in bytes
    children        true/false whether the property has children
                    this would be true for objects or array's.
    numchildren     optional attribute with number of children for
                    the property.
    key             language dependent reference for the property.
                    if the key is available, the IDE SHOULD use it
                    to retrieve further data for the property
    address         containing physical memory address
    encoding        if this is binary data, it should be base64 encoded
                    with this attribute set
    =============== ========================================================


7.12 Data Types
---------------

Languages may have different names or meanings for data types,
however the IDE may want to be able to handle similar data types
as the same type.  For this reason, we define a minimal set of
standard data types, and a method for specifying more explicit
facets on those types.  We provide three different type attributes,
and a command to map those types to each other.  The schema type
serves as a hint to the IDE as to how to handle this specific data
type, if it so chooses to, but should not be considered to be
generally supported.  If the debugger engine chooses to support
Schema, it should handle all data validation itself.

language type:
    A language specific name for a data type
common type:
    A name used by the IDE to group data types
    that are similar or the same
schema type:
    The XML Schema data type name as specified
    in the W3C Recommendation, XML Schema
    Part 2: Datatypes located at
    http://www.w3.org/TR/xmlschema-2/
    The use of the schema type is completely
    optional.  The language engine should not
    expect an IDE to support usage of this
    attribute.  The IDE identifies support for
    this in the debugger engine by retrieving
    the data map, which would contain the
    schema type attribute.


7.12.1 Common Data Types
^^^^^^^^^^^^^^^^^^^^^^^^

This is a list of the common data types supported by this protocol.
For ease of documentation, and as hints to the IDE, they are mapped
to one or more schema data types, which are documented at
http://www.w3.org/TR/xmlschema-2/.  Some non-scalar types are also
defined, which do not have direct mappings to the base types defined
by XML Schema.

    ===========     =======================================================
    Common Type     Schema Type
    ===========     =======================================================
    bool            boolean (The value is always 0 or 1)
    int             integer, long, short, byte, and signed or
                    unsigned variants
    float           float, double, decimal
    string          string or other string-like data types, such as
                    dateTime, hexBinary, etc.
    ===========     =======================================================

Data types that do not map to schema:

null:
    For example the "None" of Python or
    the "null" of PHP.  Some languages may not have
    a method to specify a null type.
array:
    for non-associative arrays, such as
    List in Python.  Arrays have integers as keys,
    and the index is put in the name attribute of
    the property element.
hash:
    for associative arrays, such as Dictionaries
    in Python.  The only supported key type is a
    string, which would be in the name attribute of
    the property.
object:
    An instance of a class.
resource:
    Any data type the language supports that does
    not map into one of the common types.  This
    could include pointers in C, various Python
    types such as Method or Class types, or
    file descriptors, database resources, etc. in
    PHP.  Complex types may also be defined by
    using XML Schema, and mapping a type to the
    Schema type.  This is a more specialized use
    of the type mapping, and should be considered
    experimental, and not generally available in
    implementations of this protocol.
undefined:
	This is used when a variable exists in the
	local scope but does not have any value yet.
	This is optional, it is also correct to not
	return the property at all instead.

For the most part, this protocol treats array's and hashes in the
same way, placing the key or index into the name attribute of the
property element.

7.12.2 typemap_get
^^^^^^^^^^^^^^^^^^

The IDE calls this command to get information on how to
map language specific type names (as received in the property
element returned by the context_get, and property_*
commands).  The debugger engine returns all data types that
it supports.  There may be multiple map elements with the same
type attribute value, but the name value must be unique.  This
allows a language to map multiple language specific types into
one of the common data types (eg. float and double can both
be mapped to float). 

IDE ::

    typemap_get -i transaction_id

debugger engine ::

    <response command="typemap_get"
              transaction_id="transaction_id"
              xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
              xmlns:xsd="http://www.w3.org/2001/XMLSchema">
       <map type="common_type"
            name="language_type_name"
            xsi:type="xsd:schema_type_name"/>
    </response>

Using the map element, a language can map a specific data type
into something the IDE can handle in a more generic way.  For
example, if a language supports both float and double, the IDE
does not necessarily need to distinguish between them (but MAY). ::

    <map type="float"
         name="float"
         xsi:type="xsd:float"/>
    <map type="float"
         name="double"
         xsi:type="xsd:double"/>
    <map type="float"
         name="real"
         xsi:type="xsd:decimal"/>

Complex types may be supported if an implementation wishes to.  Any
implementation doing so should work without the other end having
support for this::

    <response command="typemap_get"
              transaction_id="transaction_id"
              xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
              xmlns:xsd="http://www.w3.org/2001/XMLSchema"
              xmlns:mytypes="http://mysite/myschema.xsd">
       <map type="resource"
            name="SpecialDataType"
            xsi:type="mytypes:SpecialDataType"/>
    </response>


7.13 property_get, property_set, property_value
-----------------------------------------------

Gets/sets a property value.  When retrieving a property with the
get method, the maximum data that should be returned is a default
defined by the debugger engine unless it has been negotiated using
feature_set with max_data.  If the size of the properties data is
larger than that, the debugger engine only returns the configured
amount, and the IDE should call property_value to get the entire
data.  This is to prevent large data from slowing down debugger
sessions.  The IDE should implement UI that allows the user to
decide whether they want to retrieve all the data.  The IDE should
not read more data than the length defined in the packet header.
The IDE can determine if there is more data by using the property
data length information.  As per the context_get command, the depth
of nested elements returned is either defaulted by the debugger
engine, or negotiated using feature_set with max_children.

    ==      ========================================================
    -d      stack depth (optional, debugger engine should assume
            zero if not provided)
    -c      context id (optional, retrieved by context-names,
            debugger engine should assume zero if not provided)
    -n      property long name (required)
    -m      max data size to retrieve (optional)
    -t      data type (optional)
    -p      data page (optional, for arrays, hashes, objects, etc.)
    -k      property key as retrieved in a property element,
            optional, used for property_get of children and
            property_value, required if it was provided by the
            debugger engine.
    -a      property address as retrieved in a property element,
            optional, used for property_set/value, required if it
            was provided by the debugger engine.
    ==      ========================================================

IDE ::

    property_get -n property_long_name -d {NUM} -i transaction_id

debugger engine ::

    <response command="property_get"
              transaction_id="transaction_id">
        <property ... />
        ...
    </response>

IDE ::

    property_set -n property_long_name -d {NUM} -i transaction_id
             -l data_length -- {DATA}

debugger engine ::

    <response command="property_set"
          success="0|1"
          transaction_id="transaction_id"/>

IDE ::

    property_value -n property_long_name -d {NUM} -i transaction_id

debugger engine ::

    <response command="property_value"
              size="{NUM}"
              encoding="base64|none"
              transaction_id="transaction_id">
        ...data...
    </response>

When the encoding attribute is not present then the default value of "none"
is assumed.

7.14 source
-----------

The body of the request is the URI (retrieved from the stack info),
the body of the response is the data contents of the URI.  If the
file uri is not provided, then the file for the current context
is returned. 

    ==      ========================================================
    -b      begin line (optional)
    -e      end line (optional)
    -f      file URI
    ==      ========================================================

IDE ::

    source -i transaction_id -f fileURI

debugger engine ::

    <response command="source"
              success="0|1"
              transaction_id="transaction_id">
        ...data source code...
    </response>


7.15 stdout, stderr
-------------------

Body of the request is null, body of the response is true or false.
Upon receiving one of these redirect requests, the debugger engine
will start to copy data bound for one of these streams to the IDE,
using the message packets. 

    ==      ===========================================================
    -c      [0|1|2] 0 - disable, 1 - copy data, 2 - redirection ::
    
                0 (disable)   stdout/stderr output goes to regular
                              place, but not to IDE
                1 (copy)      stdout/stderr output goes to both regular
                              destination and IDE
                2 (redirect)  stdout/stderr output goes to IDE only.

    ==      ===========================================================

IDE ::

    stdout -i transaction_id -c 1

debugger engine ::

    <response command="stdout"
              success="0|1"
              transaction_id="transaction_id"/>


8. Extended Commands
====================

A IDE can query the debugger engine by using the feature_get command
(see above).  The feature strings for extended commands defined in this
specification are the same as the command itself.  For commands not
listed in this specification, the prefix is 'xcmd_name'.  Vendor or language
specific commands may be prefixed with 'xcmd_vendorname_name'.

8.1 stdin
---------

The stdin command has nearly the same arguments and responses as
stdout and stderr from the core commands (section 7).  Since
redirecting stdin may be very difficult to support in some
languages, it is provided as an optional command.  Uses for
this command would primarily be for remote console operations.

If an IDE wishes to redirect stdin, or cancel the stdin redirection,
then it must send the stdin command with the -c argument, without
any data.  After the IDE has redirected stdin, it can send more
stdin commands with the data.  Sending both the -c argument and
data in the same command is invalid.

If the IDE requests stdin, it will *always* be a redirection,
and the debugger engine must not accept stdin from any other
source.  The debugger engine may choose to not allow stdin to be
redirected in certain situations (such as when running under
a web server). 

    ==      ============================================================
    -c      [0|1] 0 - disable, 1 - redirection ::

                0 (disable)   stdin is read from the regular place
                1 (redirect)  stdin is read from stdin packets received
                              from the IDE.

    ==      ============================================================

IDE ::

    stdin -i transaction_id -c 1
    stdin -i transaction_id -- base64(data)

debugger engine ::

    <response command="stdin"
              success="0|1"
              transaction_id="transaction_id"/>


8.2 break
---------

This command can be sent to interrupt the execution of the
debugger engine while it is in a 'run state'.

IDE ::

    break -i transaction_id

debugger engine ::

    <response command="break"
              success="0|1"
              transaction_id="transaction_id"/>


8.3 eval
--------

Evaluate a given string within the current execution context.  A
property element MAY be returned as a child element of the
response, but the IDE MUST NOT expect one.  The string being evaluated
may be an expression or a code segment to be executed.  Languages, such
as Python, which have separate statements for these, will need to handle
both appropriately.  For implementations that need to be more explicit, use
the expr or exec commands below.

IDE ::

    eval -i transaction_id -- {DATA}

debugger engine ::

    <response command="eval"
          success="0|1"
          transaction_id="transaction_id">
          <property .../>
    </response>

8.3.1 expr
^^^^^^^^^^

expr, short for expression, uses the same command and response as eval above,
except that it is limited to evaluating expressions.  Only some languages
support this functionality.  expr should always return a property element
if the expression is evaluated successfully.  This command is specified for
those applications that may need to implement this specific functionality.
General uses of the protocol should not expect to find this command available,
and should rely on eval above.

8.3.2 exec
^^^^^^^^^^

exec, short for execute, uses the same command and response as eval above,
except that it is limited to executing code fragments.  Only some languages
support this functionality.  An IDE should not expect exec to return a value.
This command is specified for those applications that may need to implement
this specific functionality.  General uses of the protocol should not expect
to find this command available, and should rely on eval above.

8.4 spawnpoints
---------------

Spawnpoints are points in (currently Tcl) file where a new debug session
might (i.e. if this position is a point in the code where a new application
is created) get spawned when hit. Spawnpoints are treated much like a
different type of breakpoint: They share many of the same attributes as
breakpoints, using a *type=="spawn"* to distinguish themselves. Spawnpoints
have an equivalent set of commands.  A failure in any spawnpoint commands
results in an error defined in `section 6.5`_.

The following DBGP commands relate to spawnpoints:

    ==================  =================================================
    spawnpoint_set_     Set a new spawnpoint on the session.
    spawnpoint_get_     Get spawnpoint info for the given spawnpoint id.
    spawnpoint_update_  Update one or more attributes of a spawnpoint.
    spawnpoint_remove_  Remove the given spawnpoint on the session.
    spawnpoint_list_    Get a list of all of the session's spawnpoints.
    ==================  =================================================

.. _spawnpoint_set: `8.4.1 spawnpoint_set`_
.. _spawnpoint_get: `8.4.2 spawnpoint_get`_
.. _spawnpoint_update: `8.4.3 spawnpoint_update`_
.. _spawnpoint_remove: `8.4.4 spawnpoint_remove`_
.. _spawnpoint_list: `8.4.5 spawnpoint_list`_


A spawnpoint has the following attributes:

    ==================  ======================================================
    type                always set to "spawn"
    filename            The file the spawnpoint is effective in. This must be
                        a "file://" URI.
    lineno              Line number on which spawnpoint is effective. Line
                        numbers are 1-based. If an implementation requires a
                        numeric value to indicate that *lineno* is not set,
                        it is suggested that -1 be used, although this is not
                        enforced.
    state               Current state of the spawnpoint. This must be one of
                        *enabled*, *disabled*.
    ==================  ======================================================

Spawnpoints should be maintained in the debugger engine at an application
level, not the thread level.  Debugger engines that support thread debugging
MUST provide spawnpoint id's that are global for the application, and must
use all spawnpoints for all threads where applicable.

As for any other commands, if there is error the debugger engine should
return an error response as described in `section 6.5`_.


8.4.1 spawnpoint_set
^^^^^^^^^^^^^^^^^^^^

This command is used by the IDE to set a spawnpoint for the session.

IDE to debugger engine::

    spawnpoint_set -i TRANSACTION_ID [<arguments...>]

where the arguments are:

    ==================  =====================================================
    -f FILENAME         the *filename* to which the spawnpoint belongs
                        [optional]
    -n LINENO           the line number (*lineno*) of the spawnpoint
                        [optional]
    -s STATE            spawnpoint *state* [optional, defaults to "enabled"]
    ==================  =====================================================

A unique id for this spawnpoint for this session is returned by the debugger
engine. This *session spawnpoint id* is used by the IDE to identify the
spawnpoint in other spawnpoint commands.

debugger engine to IDE::

     <response command="spawnpoint_set"
               transaction_id="TRANSACTION_ID"
               state="STATE"
               id="SPAWNPOINT_ID"/>

where,

    ==================  =====================================================
    SPAWNPOINT_ID       is an arbitrary string that uniquely identifies this
                        spawnpoint in the debugger engine.
    STATE               the initial state of the spawnpoint as set by the
                        debugger engine
    ==================  =====================================================


8.4.2 spawnpoint_get
^^^^^^^^^^^^^^^^^^^^

This command is used by the IDE to get spawnpoint information from the
debugger engine.

IDE to debugger engine::

    spawnpoint_get -i TRANSACTION_ID -d SPAWNPOINT_ID 

where,
    
    ==================  =====================================================
    SPAWNPOINT_ID       is the unique *session spawnpoint id* returned by
                        *spawnpoint_set*.
    ==================  =====================================================

debugger engine to IDE::

    <response command="spawnpoint_get"
              transaction_id="TRANSACTION_ID">
        <spawnpoint id="SPAWNPOINT_ID"
                    state="STATE"
                    filename="FILENAME"
                    lineno="LINENO"/>
    </response>


8.4.3 spawnpoint_update
^^^^^^^^^^^^^^^^^^^^^^^

This command is used by the IDE to update one or more attributes of a
spawnpoint that was already set on the debugger engine via *spawnpoint_set*.

IDE to debugger engine::

    spawnpoint_update -i TRANSACTION_ID -d SPAWNPOINT_ID [<arguments...>]

where the arguments are as follows.  Both arguments are optional, however
at least one should be provided. See spawnpoint_set_ for a description of
each option:

    ==================  =====================================================
    -s STATE
    -n LINENO
    ==================  =====================================================

debugger engine to IDE::

    <response command="spawnpoint_update"
              transaction_id="TRANSACTION_ID"/>

8.4.4 spawnpoint_remove
^^^^^^^^^^^^^^^^^^^^^^^

This command is used by the IDE to remove the given spawnpoint.

IDE to debugger engine::

    spawnpoint_remove -i TRANSACTION_ID -d SPAWNPOINT_ID

debugger engine to IDE::

    <response command="spawnpoint_remove"
              transaction_id="TRANSACTION_ID"/>

8.4.5 spawnpoint_list
^^^^^^^^^^^^^^^^^^^^^

This command is used by the IDE to get spawnpoint information for all
spawnpoints that the debugger engine has.

IDE to debugger engine::

    spawnpoint_list -i TRANSACTION_ID

debugger engine to IDE::

    <response command="spawnpoint_list"
              transaction_id="TRANSACTION_ID">
        <spawnpoint id="SPAWNPOINT_ID"
                    state="STATE"
                    filename="FILENAME"
                    lineno="LINENO"/>
        <spawnpoint .../>
        ...
    </response>

8.5 Notifications
-----------------

At times it may be desirable to receive a notification from the debugger
engine for various events.  This notification tag allows for some simple
data to be passed from the debugger engine to the IDE.  Customized
implementations may add child elements for additional data.

As an example, this is useful for handling STDIN.  The debugger engine
interupts all STDIN reads, and when a read is done by the application, it sends
a notification to the IDE.  The IDE is then able to do something to let the user
know the application is waiting for input, such as placing a cursor in the
debugger output window.

A new feature name is introduced: notify_ok.  The IDE will call feature_set
with the notify_ok name and a TRUE value.  This lets the debugger engine know
that it can send notifications to the IDE.  If the IDE has not set this value,
or sets it to FALSE, then the debugger engine MUST NOT send notifications to
the IDE.

The debugger engine MUST NOT expect a notification to cause an IDE to behave
in any particular way, or even to be handled by the IDE at all.

A proxy may also use notifications, during a debug session, to let the IDE know
about events that happen in the proxy.  To do this, the proxy will have to
listen for feature_set commands and keep track of the values set, as well as
passing them through to the debugger engine.

IDE initialization of notifications::

    feature_set -i TRANSACTION_ID -n notify_ok -- base64(1)

debugger engine notifications to IDE::

    <notify name="notification_name">
    TEXT_NODE or CDATA
    <custom.../>
    </notify>


8.5.1 Standard Notifications
^^^^^^^^^^^^^^^^^^^^^^^^^^^^

The following list of notifications are standardized for the protocol. Other
notifications may be added by other implementations.  It is suggested that
notification names not found in this document are preceded with 'XXX' or some
similar tag as a means of preventing name conflicts when new notifications get
added to the protocol in the future.

    ======= =====================================================
    Name    Description
    ======= =====================================================
    stdin   notification occurs when the debugger engine is about
            to read the stdin pipe.
    ======= =====================================================


8.6 interact - Interactive Shell
--------------------------------

The interact command allows an IDE to send chunks of code to be compiled and
executed by the debugger engine.  While this is similar to the eval command,
it has a couple important differences.

First, it buffers code sent to it until a successful compile is achieved.  The
buffering allows the IDE to send a line of code for each call to the interact
command, which reflects a user typing code into a console.  Each line is joined
in the debugger engine with a newline character.  As soon as a successful
compile happens, the code is run and any output returned to the IDE (via
stdout/stderr or otherwise).

Second, it returns a prompt string that can be used by the IDE as an input
prompt for the user.

The interact command can only be called during a break or interactive state.

The debugger engine implementation MAY also be designed to work in
and interactive-only mode, where there is no script being debugged, and
all code is received through the interact command.  This allows the
protocol to be utilized for the purpose of a pure interactive shell
for the language.

Control characters should be sent in the data section of the command, and the
debugger engine should handle the control characters in a way that is expected
by the implementation.  These characters can include Ctrl-C (KeyboardInterupt
in Python) and other such console like controls.  The IDE should not expect
the debugger engine to handle control characters in any specific way.

The IDE can query the debugger engine for interact support using the
feature_get command.

The 'filename' in the stack for an interactive session should be '<console>'
or some other string to denote a console stack level.

The debugger engine is not required to enable debugging of code
received via the interact command, however it should provide access
to other information, such as the variables retrieved via context_get.

IDE to debugger engine::

    interact -i TRANSACTION_ID -m mode -- base64(code)

where,

    ======== ==========================================
    -m mode  a mode of zero tells the interact command
             to clear the buffer and any other state
             that was maintained for previous interact
             commands.  The prompt attribute returned
             should be an empty string.
    ======== ==========================================


debugger engine to IDE::

    <response command="interact"
        transaction_id="TRANSACTION_ID"
        status="STATUS_NAME"
        more="CONTINUE_FLAG"
        prompt="PROMPT" />

where,

    ============= ========================================
    STATUS_NAME   A valid status name from the list of
                  status names in section 7.1.  A new name
                  is added specificaly for this command
                  which is 'interactive'.  The interactive
                  status is returned unless the mode in the
                  command was zero, in which case the
                  status will be up to the debugger engine
                  (typically the last status before running
                  interact), or some error has occurred
                  that causes a different status.
    CONTINUE_FLAG a boolean which is true if the interact
                  command requires more code to compile
                  successfully
    PROMPT        a string containing the prompt for the
                  next line of code
    ============= ========================================




A. ChangeLog
============
2006-01-24

- 7.2.1 Added a description of the breakpoint_types feature.

2006-01-23

- 7.11 Clarified the behavior of paging regarding depths, and that
  paging of arrays/objects/hashes is 0 based.
- draft 15

2004-11-03

- 7.12.1 Added the 'undefined' type.

2004-10-28

- 6 Clarify encoding for data passed in commands with the -- option.
- 7.13 Clarify the default encoding for property values.

2004-05-16

- 5.3 add address and port attributes to the proxyinit element returned to the
  ide by the proxy.

2004-05-12

- 7.2 reorganize the feature names, add a couple missing names
      (supports_postmortem, show_hidden, notify_ok).

2004-04-05

- 8.5 New notification support
- 8.6 New interact command

2004-02-20

- 1.2 moved the change log to appendix A
- 5 massive reorganization of section 5
- 5.3 expanded description of proxies and just in time debugging.
- 5.4 expand description of multisession and multithreaded debugging.
- 7.2 A new feature name, breakpoint_languages, has been added.  This option
  is only required if the engine supports more than one language.
- 7.2 and 7.3 Remove crufty documentation that still referred to old binary
  protocol information.
- 7.6.1 For conditional breakpoints the expression has been moved to the data
  section of the command.
- 8.3 remove the length argument in the eval command, it is unnecessary.
- 8.3 be more explicit about how eval works, add 8.3.1 expr and 8.3.2 exec as
  additional optional commands that can be used in special implementations.
- 8.4 Remove the 'delete' state, this was old and removed in breakpoints.

2004-01-28

- 7.8 Fix cmdbegin/end attributes for stack_get

2004-01-09

- 5.1 New DBGP_IDEKEY environment variable

2004-01-07

- 7.5 renamed the stop and kill commands to detach and stop, added
  some clarification to the description of the commands.

2003-12-16

- 7.6, 8.4 re-write the breakpoint and spawnpoint sections to be clearer

2003-12-09

- 6.7 new section describing dbgp file protocol
- 7.6 better document breakpoints

2003-12-05

- 6 Change the deliminator for command data to '--'.  This conforms to
  standard getopt libraries.
- 7.11 remove the recursive attribute, if an IDE wants to handle
  circular references, it can do so based on the address attribute if
  the engine provides it.

2003-12-02

- 7.6 remove breakpoint_enable/disable, and add breakpoint_update
  command.  Enable/disable states are changed through breakpoint_update.
- 8.4 new (optional) spawnpoint commands

2003-11-25

- 7.6 Change the breakpoint *hits* and *ignore* attributes to *hit_count*,
  *hit_value* and *hit_condition* to add functionality available in VS.NET
  and to simplify usage. Also clarify some other breakpoint attribute legal
  values.

2003-11-24

- 7.5 correct the stop command documentation, stop is 'detach', and
  does not allow for continued interaction.  Document how expressions
  are returned from breakpoint_get.
- 7.8 correct old documentation on the stack element.  Add new
  attributes: where, cmdbegin, cmdlength.  Provide further documentation
  about all the attributes.

2003-11-20

- 5.1 better define session keys vs. ide key for proxy, document how
  proxy works better.
- 7.6 better document attributes and hit option

2003-11-18

- 7.1 Clarify stopping and stopped states
- 7.5 Clarify the stop command
- 7.6 Remove 'temporary' as a status for breakpoints, make it an option
  in the command line.  Remove the 'function' breakpoint type, provide
  two new types, 'call' and 'return'.  Add 'hits' option to allow a
  breakpoint to be ignored a number of times before being used.

2003-11-12

- draft 12
- Rest markup tweaks

2003-11-09

- draft 11
- 7.12 new section inserted as 7.12.  This section specifies common
  data types, and how to map more specific data types to the the common
  types.
- 7.11 two new optional attributes, classname and facet, that provide
  additional hints to the IDE about the nature of the property.  New
  key attribute for language specific keys to properties.
- 6.5 new section, 6.5.1 for defining common error codes.

2003-11-05

- spelling fixes
- 5.1 change proxy options
- 7.6 clarify breakpoint command options
- 7.12 fix old text about context names

2003-10-15

- 6 remove the first NULL in the command structure from IDE to debugger
  engine.  This makes dealing with those commands easier.
- 6.6 NEW File paths must be URI's.
- 7 source command returns the source for the current context if no
  file uri is provided.
- 7 added sub-item numbering
- 7.1 clarify the status values
- 8 added sub-item numbering

2003-10-09

- 7 remove run_to, unnecessary
- 7 remove 'step', there is no generic step command
- 7 clarify continuation commands
- 7 clarify breakpoints

2003-10-07

- more layout changes for reStructuredText

2003-10-06

- reformat to `reStructuredText markup
  <http://docutils.sourceforge.net/spec/rst/reStructuredText.html>`_
- 6 clarify message packets
- 6.3 clarify command packets
- 7 clarify feature_get/set
- 7 allow error results on breakpoints if a type of breakpoint
  is not supported by a debugger engine.
- 7 add recursive attribute to properties, and clarify the
  address attribute and how recursive data is handled.
- 7,8 moved stdin to the optional commands section

2003-10-02

- 5.1 changed proxy error to be the same as that in 6.5
- 5.1 the IDE and proxy ports have been defined to 9000/9001
- 5.3 exclude protocol overhead from data size definition
- 6.2 changed typo 'stdin and stdout' to 'stdout and stderr'
- 6.5 changed error id to error code
- 7 removed comments on 'body' from the run commands
- 7 clarified 'source' command arguments to be optional
- 7 added 'disable' option to stdin/out/err commands
- 7 breakpoint arguments and types have been better defined since
  not all arguments need to be required for all types
- 7 the expression breakpoint type has been removed since it is
  covered by the conditional breakpoint type


2003-09-30

- section numbers added, changes below are marked with the section
  number
- 3 Terminology changed (frontend -> IDE, backend -> debugger engine)
- 5.1 added response packet from proxy to IDE when IDE issues the
  proxyinit command.
- 5.1 the proxy now adds a proxyclientid to the init packet from
  the debugger engine when it passes the packet through to the IDE.
- 5.1 the proxy must be able to send errors to the IDE, for instance,
  if it looses the connection to the debugger engine.
- 5.1 the proxy must be able to send errors to the Debugger, for
  instance, if it looses the connection to the IDE.
- 5.3 added new section to help better define feature negotiation
  with feature_get/set commands.
- 6 packets have been better defined.  This section has also been
  reorganized.
- 6.2 the communication of packets has been rewritten.
- 7 feature_get/set have some modifications.
- 7 context_get and property_* commands have been modified to better
  reflect negotiation of features using the feature_get/set commands.
- 7 property_* commands have been commented a bit more, and an
  additional argument is available for paging arrays, etc.
- 7 The definition of the property tag has been modified
- 7 stdin command has been modified, the debugger engine may choose
  to not redirect stdin.
- 7 status command modified to support the async state
- 7 source command now accepts begin and end line arguments for
  retrieving only parts of a file.
- 7 stack_get now defines an enumeration for the stack
- 8 break command clarified so it can only be sent while the debugger
  engine is in a run state.
- 8 eval can return a property as part of the response


