stacklok / toolhive / 21355567264

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Build Type

push

github

Committed by web-flow

Commit Message

Preserve _meta fields in vMCP backend responses (#3354)

* Preserve _meta fields in vMCP backend responses

vMCP was discarding _meta fields from backend MCP server responses,
violating the MCP specification requirement to preserve protocol-level
metadata. This prevented clients from receiving progress tokens, trace
IDs, and custom backend metadata.

Fixes #2640

* fixes from review

* adds license headers

* fixes from review

* fix tests

Fix metadata preservation for IsError=true tool results

When a backend tool returns IsError=true, it's an MCP protocol-level
indication that the tool execution failed, not a transport/network error.
The previous implementation was converting IsError=true into a Go error
and discarding the result (including metadata), which violated the MCP
specification's requirement to preserve _meta fields.

Changes:
- client.go: Return full result (with metadata and IsError flag) instead
  of converting IsError=true to a Go error
- handler_factory.go: Remove ErrToolExecutionFailed handling since we
  no longer return that error for IsError=true results
- meta_integration_test.go: Update test to verify metadata is preserved
  even when IsError=true
- handler_factory_test.go: Update test to return IsError=true result
  instead of ErrToolExecutionFailed error

This allows clients to receive error results with metadata for distributed
tracing and debugging, as intended by the MCP specification.

Fix E2E test: use correct parameter name for yardstick echo tool

The yardstick echo tool expects 'input' parameter, not 'message'.
This was causing the tool to return IsError=true with no metadata,
making the test fail.

Fix E2E test: use only alphanumeric characters for yardstick input

Yardstick echo tool validates input against regex ^[a-zA-Z0-9]+$,
which doesn't allow hyphens. Changed test input from
'test-metadata-preservation' to 'testmetadatapreservation'.

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Co-authored-by: taskbot <taskbot@users.noreply.github.com>

Run Details

208 of 242 new or added lines in 7 files covered. (85.95%)

1 existing line in 1 file now uncovered.

38071 of 63321 relevant lines covered (60.12%)

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