Wrong URI when using auth_request directive

[sriemer]

This is about:

nginx-opentracing/opentracing/src/ngx_http_opentracing_module.cpp

Line 55 in 111a491

{ngx_string("http.url"), ngx_string("$scheme://$http_host$request_uri")},

This uses the unparsed URI. But the parsed URI $scheme://$http_host$uri is required for (auth) subrequests.

Got NGINX Plus R24 and the Instana tracer with patched defaults here (tracing is always on, locations aren't traced).
Test config: nginx-auth-test.conf.txt
Issuing the request: wget -O- 'http://127.0.0.1:8081/private'

Getting spans:

/private (301, port 8081)
 \
   /private (200, port 8081, in reality subrequest to /auth)
    \
      /auth (200, port 8080)
 \
   /private (301, port 8080)

I've implemented this like this now:

--- a/opentracing/src/request_tracing.cpp
+++ b/opentracing/src/request_tracing.cpp
@@ -45,7 +45,23 @@ static void add_script_tags(ngx_array_t *tags, ngx_http_request_t *request,
   auto add_tag = [&](const opentracing_tag_t &tag) {
     auto key = tag.key_script.run(request);
     auto value = tag.value_script.run(request);
-    if (key.data && value.data) span.SetTag(to_string(key), to_string(value));
+    if (key.data && value.data) {
+      // Replace unparsed URI with parsed URI for subrequests
+      // Needed for using `auth_request` directive
+      if (request != request->main && to_string(key) == "http.url") {
+        std::string new_value = to_string(value);
+        size_t uri_pos = new_value.rfind(to_string(request->unparsed_uri));
+        if (uri_pos != std::string::npos) {
+          new_value.replace(uri_pos, new_value.length() - uri_pos,
+              reinterpret_cast<const char *>(request->uri.data), request->uri.len);
+          span.SetTag(to_string(key), new_value);
+        } else {
+          span.SetTag(to_string(key), to_string(value));
+        }
+      } else {
+        span.SetTag(to_string(key), to_string(value));
+      }
+    }
   };
   for_each<opentracing_tag_t>(*tags, add_tag);
 }

Getting spans:

/private (301, port 8081)
 \
   /auth (200, port 8081, subrequest)
    \
      /auth (200, port 8080)
 \
   /private (301, port 8080)

The search for the key and the possible further memory allocation are sub optimal. I haven't found any better possibility yet.

Thoughts on this? Do you have a better idea how to implement this? TIA