[Frontend] Add logits_processors as an extra completion argument

[bradhilton]

Adds logits_processors as an extra (optional) argument to ChatCompletionRequest and CompletionRequest:

    logits_processors: Optional[List[Union[str, LogitsProcessorConstructor]]] = Field(
        default=None,
        description=(
            "A list of either qualified names of logits processors, or "
            "constructor objects, to apply when sampling. A constructor is "
            "a JSON object with a required 'qualname' field specifying the "
            "qualified name of the processor class/factory, and optional "
            "'args' and 'kwargs' fields containing positional and keyword "
            "arguments. For example: {'qualname': 'my_module.MyLogitsProcessor',"
            "'args': [1, 2], 'kwargs': {'param': 'value'}}."))

This enables passing built-in or custom logits processors to direct the sampling process.

[github-actions]

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[DarkLight1337]

Hmm, this seems a bit dangerous as it allows the client to execute any Python module server-side. A better solution would be to introduce a registry of logits processors which the client can reference by their key in the registry.

[bradhilton]

Hmm, this seems a bit dangerous as it allows the client to execute any Python module server-side. A better solution would be to introduce a registry of logits processors which the client can reference by their key in the registry.

Great feedback, thank you @DarkLight1337. I added an optional --logits-processor-pattern engine argument for whitelisting matching processor qualified names. It's None by default, disallowing the usage of the logits_processors argument entirely.

[DarkLight1337]

Using a pattern to restrict access also works, thanks for adding this!

[bradhilton]

@DarkLight1337 buildkite/ci/pr/multi-step-tests-4-gpus failed due to a connect timeout. Is this normal test flakiness or cause for concern?

[DarkLight1337]

Let me retry the test.

[bradhilton]

Thanks @DarkLight1337 !