serverGDB Architecture

Jim Blandy set out a proposal for a GDB server architecture based around a formal API.  This propsal presents an alternative design that addressed some of the limitations that Jim identified in Stan's Headless GDB architecture.

One of the limitations that Jim identified was:

Finally, amending GDB to produce two kinds of output increases the complexity of the code.  In contrast, imposing a well-defined interface between GDB's core functionality and its user interface reduces total complexity, by segregating the code into separate modules with well-defined interactions.
 while for Stan's part, he argues that:
[...] the CLI effectively defines a robust protocol - by being text-based, encoding and byte-order issues go away, the command processor already has error-handling built into it, and the user manual constitutes a fairly precise specification of the protocol's "messages".
The architecture below incorporates a design that both addresses Jim's concern of code duplication while at the same time retaining the flexibility of an interface based around the existing command line.

This architecture breaks the rendering of data into two distinct phases:

  1. The GDB core which builds a description of the Reply (data).

  3. The Sever which transforms reply into a form suitable for the corresponding user interface.

  4. For a CLI that would involve the simple display of the reply in textual form.
    For a remote GUI, a Server implementation would serialized the Reply (data) before transmitting it to the remote GUI.
Since the modified GDB would exploit a single set of build operations to construct a results, Jim's concern over the need to maintain parallel code streams each producing similar output is addressed.  Similarly, by initially implementing a GUI Server that serialized replies into text, the benefits that Stan identifies would be present.

Importantly, the architecture is not limited to just a CLI based server.  If the Server was replaced with TK/TCL, for instance, GDB would be able to build TCL data structures directly.

Problems and limitations

This architecture, is not with out potential limitations and risks.  Those immediately identifiable include:

Further reading

Design Patterns, Gamma "Builder", page 97.