Thanks for your issue. Do you mean to say that other query parameters are correctly converted? It only happens when there's a : in the path?

@johanbrandhorst Yes exactly, Query parameters are correctly converted in other requests.

example:

syntax = "proto3";

  rpc SearchItems(item.SearchItemsRequest) returns (item.SearchItemsResponse) {
    option (google.api.http) = {get: "/item/search-item/{item_no_query}"};
  }

is converted to

{
  "swagger": "2.0",
  "info": {
    "title": "api-rest-gateway/proto/api.proto",
    "version": "version not set"
  },
  "paths": {
    "/item/search-items/{itemNoQuery}": {
      ...
    }
  }
}

Please Note, this is only happening when the ":" is in the middle of the path, if I add the ":" at the end then it works.
example:

syntax = "proto3";

  rpc SearchItems(item.SearchItemsRequest) returns (item.SearchItemsResponse) {
    option (google.api.http) = {get: "/item/search/{item_no_query}:item"};
  }

is converted correctly to
"/item/search/{itemNoQuery}:item"

Thanks for the clarification. This will make it easier to fix. I think if someone wants to pick this up the first step would be to recreate this scenario in a test in https://github.com/grpc-ecosystem/grpc-gateway/blob/main/protoc-gen-openapiv2/internal/genopenapi/template_test.go. Then the fix will probably be somewhere in https://github.com/grpc-ecosystem/grpc-gateway/blob/main/protoc-gen-openapiv2/internal/genopenapi/template.go (

Digged a bit into it. I think the code assumes that a "resource:action" part only occurs on the end. This PR fixes the generation for our use-case, however I'm not sure about the general impact: #3532

updated the PR with a test that should reproduce the issue (and a fix proposal)