fix: Validate paths and check additionalPathTemplates

gax-java/gax-httpjson/src/main/java/com/google/api/gax/httpjson/ProtoMessageRequestFormatter.java

@@ -95,10 +95,29 @@ public String getRequestBody(RequestT apiMessage) {
     return requestBodyExtractor.extract(apiMessage);
   }
 
-  /* {@inheritDoc} */
+  /**
+   * Returns the relative URL path created from the path parameters from the given message. Attempts
+   * to match the with the default PathTemplate. If there is not match, it attempts to match with
+   * the templates in the additionalPathTemplates.
+   *
+   * @param apiMessage Request object to extract fields from
+   * @return Path of a matching valid URL or the default Path URL
+   */
   @Override
   public String getPath(RequestT apiMessage) {
-    return pathTemplate.instantiate(pathVarsExtractor.extract(apiMessage));
+    Map<String, String> pathVarsMap = pathVarsExtractor.extract(apiMessage);
+    String path = pathTemplate.instantiate(pathVarsMap);
+    if (pathTemplate.matches(path)) {
+      return path;
+    }
+    for (PathTemplate additionalPathTemplate : additionalPathTemplates) {
+      String additionalPath = additionalPathTemplate.instantiate(pathVarsMap);
+      if (additionalPathTemplate.matches(additionalPath)) {
+        return additionalPath;
+      }
+    }
+    // If there are no matches, we return the default path
+    return path;
   }
 
   @BetaApi

gax-java/gax-httpjson/src/test/java/com/google/api/gax/httpjson/ProtoMessageRequestFormatterTest.java

@@ -131,6 +131,27 @@ public void getPath() {
     Truth.assertThat(path).isEqualTo("api/v1/names/field_name1/aggregated");
   }
 
+  @Test
+  public void getPath_additionalPaths() {
+    Field fieldWithLongerName = field.toBuilder().setName("field_name1/random_text").build();
+    String path = formatter.getPath(fieldWithLongerName);
+    Truth.assertThat(path).isEqualTo("api/v1/names/field_name1/random_text/aggregated");
+
+    Field fieldWithRandomValues =
+        field.toBuilder().setName("field_name1/random_text/random_text1").build();
+    path = formatter.getPath(fieldWithRandomValues);
+    Truth.assertThat(path)
+        .isEqualTo("api/v1/names/field_name1/random_text/random_text1/aggregated");
+  }
+
+  @Test
+  public void getPath_noMatches() {
+    // If there are no valid matches, it will return with the default path's url
+    Field fieldNotMatching = field.toBuilder().setName("name_does_not_match").build();
+    String path = formatter.getPath(fieldNotMatching);
+    Truth.assertThat(path).isEqualTo("api/v1/names/name_does_not_match/aggregated");
+  }
+
   @Test
   public void getPathTemplate() {
     String path =