bug: openapi-to-mcp appends a second ? to a query-suffixed path template

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Assessment

Difficulty
2/5
Estimated time
1-3 hours
Newbie friendliness
83/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Active
Tech stack
lua, openapi
Domain
api, backend-api-design

Research direction

Read apisix/plugins/openapi-to-mcp/tools/handler.lua, focusing on build_path() and _M.call(), where the issue identifies the query suffix and serialized parameters being joined. Check the existing tests added in PR #14154 for query-suffixed templates. Done means the example request uses /b?acl&prefix=logs and the declared parameter reaches the upstream under its own name.

Written by the indexing model from the issue text.

Description

Current Behavior

openapi-to-mcp sends a second literal ? upstream when a path template carries a query
suffix and the operation also declares query parameters.

build_path() returns the template with its substitutions, query suffix included, and
_M.call() then appends the serialized query parameters with its own ?:

local url = base_url .. path
if query then
    url = url .. "?" .. query
end

For a template of /{Bucket}?acl with a declared prefix query parameter, a call with
Bucket=b and prefix=logs is sent as:

/b?acl?prefix=logs

The upstream parses everything after the first ? as the query string, so it sees one
parameter spelled acl?prefix, and the declared prefix parameter never arrives under
its own name. Query-suffixed path templates are used by S3-style documents.

Verified at runtime against the official test harness on master; the output is identical
on #14154, so the behavior is pre-existing and that PR neither introduces nor changes it.
It surfaced while reviewing #14154, which added the first test coverage for query-suffixed
templates: https://github.com/apache/apisix/pull/14154#discussion_r4475591464

Expected Behavior

The template's query suffix and the serialized query parameters should be merged into one
query string joined by &, so the example above is sent as /b?acl&prefix=logs and every
declared parameter reaches the upstream under its own name.

Steps to Reproduce

  1. Serve an OpenAPI document whose path is /{Bucket}?acl, with Bucket as a required
    path parameter and prefix as a query parameter.
  2. Configure an openapi-to-mcp Route using that document.
  3. Call the generated tool with Bucket=b and prefix=logs.
  4. Observe the upstream request path /b?acl?prefix=logs rather than /b?acl&prefix=logs.

Environment

  • APISIX: current master, reproduced at 6205e4a56
  • Component: apisix/plugins/openapi-to-mcp/tools/handler.lua, build_path() and _M.call()
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