twitter-server: add scope separator character to metric_metadata resp…

…onse

Problem
metric_metadata.json does not return the scope separating character and consequently consumers of the endpoint would have to infer the character from full metric names.

Solution
Expose the scope separating character as a top level "separator_char" field in metrics_metadata.json.

Result
Consumers of the metric_metadata.json endpoint can now determine the scope separating character via the top level field.

JIRA Issues: CSL-10255

Differential Revision: https://phabricator.twitter.biz/D591106

CHANGELOG.rst

@@ -7,6 +7,9 @@ Note that ``PHAB_ID=#`` and ``RB_ID=#`` correspond to associated messages in com
 Unreleased
 ----------
 
+* Add separator_char field to the top level of the Metrics Metadata endpoint and bump the
+  endpoints version number to 2.1. ``PHAB_ID=D591106``
+
 20.12.0
 -------
 

server/src/main/scala/com/twitter/server/handler/MetricMetadataQueryHandler.scala

@@ -2,6 +2,7 @@ package com.twitter.server.handler
 
 import com.twitter.finagle.Service
 import com.twitter.finagle.http.{MediaType, Request, Response, Uri}
+import com.twitter.finagle.stats.metadataScopeSeparator
 import com.twitter.io.Buf
 import com.twitter.server.util.HttpUtils.newResponse
 import com.twitter.server.util.{JsonConverter, MetricSchemaSource}
@@ -95,8 +96,9 @@ class MetricMetadataQueryHandler(source: MetricSchemaSource = new MetricSchemaSo
       content = Buf.Utf8(
         JsonConverter.writeToString(
           Map(
-            "@version" -> 2.0,
+            "@version" -> 2.1,
             "counters_latched" -> latched,
+            "separator_char" -> metadataScopeSeparator(),
             "metrics" -> metrics
           )))
     )

server/src/test/scala/com/twitter/server/handler/MetricMetadataQueryHandlerTest.scala

@@ -307,8 +307,9 @@ class MetricMetadataQueryHandlerTest extends FunSuite {
       val responseStart =
         """
           | {
-          |   "@version" : 2.0,
+          |   "@version" : 2.1,
           |   "counters_latched" : true,
+          |   "separator_char" : "/",
         """.stripMargin
       test(testName + " when using latched counters") {
         assertJsonResponse(
@@ -320,8 +321,9 @@ class MetricMetadataQueryHandlerTest extends FunSuite {
       val responseStart =
         """
           | {
-          |   "@version" : 2.0,
+          |   "@version" : 2.1,
           |   "counters_latched" : false,
+          |   "separator_char" : "/",
         """.stripMargin
       test(testName + " when using unlatched counters") {
         assertJsonResponse(