fix: fix incorrect REST request serialization

[parthea]

Fixes #2548

This PR fixes a bug in the templates when calling the rest_call_method_common shared macro. The value of the is_proto_plus_type argument was set to method.output.ident.is_proto_plus_type but it should be method.input.ident.is_proto_plus_type because is_proto_plus_type is used to serialize the request message (input message rather than output message).

[gemini-code-assist]

Summary of Changes

Hello @parthea, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses a critical bug in the gapic-generator-python templates that led to incorrect serialization of REST requests. The fix ensures that the generator correctly identifies and processes proto-plus types for input messages, preventing serialization errors. It also refines the serialization mechanism in the generated client libraries to use a more appropriate method for converting request objects to JSON.

Highlights

• Bug Fix: Incorrect REST Request Serialization: Resolved an issue where the rest_call_method_common macro was incorrectly using the output message type (method.output.ident.is_proto_plus_type) instead of the input message type (method.input.ident.is_proto_plus_type) for determining proto-plus serialization. This ensures that request messages are serialized correctly.
• Updated Serialization Method: The method for serializing request payloads in generated REST transport files has been updated from json_format.MessageToJson(request) to type(request).to_json(request). This change provides a more direct and potentially more robust way to handle JSON serialization for proto-plus types.
• Template and Golden File Updates: The core fix involves changes to shared macro templates and is reflected in updates to several golden integration test files across different services (Asset, Eventarc, Redis) to align with the new serialization logic.

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[gemini-code-assist]

Code Review

This pull request correctly fixes a bug in the REST request serialization by using the input message's is_proto_plus_type attribute instead of the output message's. The changes in the Jinja2 templates are accurate, and the resulting updates to the golden files are as expected. I've added one comment regarding the use of a bare except in the generated code, which is a pre-existing issue but would be good to address for more robust error handling.

[gemini-code-assist]

The except: on the next line is a bare except, which is a bad practice as it catches all exceptions, including system-exiting ones like SystemExit and KeyboardInterrupt. This can make debugging difficult and hide underlying issues. It would be better to catch a more specific exception, like Exception.

While there's a TODO in the template to remove this try/except block, improving it in the meantime would be beneficial.

This change should be applied to the template file: gapic/templates/%namespace/%name_%version/%sub/services/%service/_shared_macros.j2.

Suggested change in the template:

        except Exception:

[parthea]

Ack. I'm hesitant to change this now but I'll file a bug to follow up on it.

[parthea]

Filed #2550 to fix this throughout the code base

[daniel-sanche]

LGTM