Merge pull request #10262 from y-zeng/set_user_agent

Replace the existing user agent string in SetUserAgentPrefix

src/cpp/common/channel_arguments.cc

@@ -133,14 +133,19 @@ void ChannelArguments::SetUserAgentPrefix(
     return;
   }
   bool replaced = false;
+  auto strings_it = strings_.begin();
   for (auto it = args_.begin(); it != args_.end(); ++it) {
     const grpc_arg& arg = *it;
-    if (arg.type == GRPC_ARG_STRING &&
-        grpc::string(arg.key) == GRPC_ARG_PRIMARY_USER_AGENT_STRING) {
-      strings_.push_back(user_agent_prefix + " " + arg.value.string);
-      it->value.string = const_cast<char*>(strings_.back().c_str());
-      replaced = true;
-      break;
+    ++strings_it;
+    if (arg.type == GRPC_ARG_STRING) {
+      if (grpc::string(arg.key) == GRPC_ARG_PRIMARY_USER_AGENT_STRING) {
+        GPR_ASSERT(arg.value.string == strings_it->c_str());
+        *(strings_it) = user_agent_prefix + " " + arg.value.string;
+        it->value.string = const_cast<char*>(strings_it->c_str());
+        replaced = true;
+        break;
+      }
+      ++strings_it;
     }
   }
   if (!replaced) {

test/cpp/common/channel_arguments_test.cc

@@ -243,6 +243,22 @@ TEST_F(ChannelArgumentsTest, SetUserAgentPrefix) {
 
   channel_args_.SetUserAgentPrefix(prefix);
   EXPECT_TRUE(HasArg(arg0));
+
+  // Test if the user agent string is copied correctly
+  ChannelArguments new_channel_args(channel_args_);
+  grpc_channel_args args;
+  SetChannelArgs(new_channel_args, &args);
+  bool found = false;
+  for (size_t i = 0; i < args.num_args; i++) {
+    const grpc_arg& arg = args.args[i];
+    if (arg.type == GRPC_ARG_STRING &&
+        grpc::string(arg.key) == GRPC_ARG_PRIMARY_USER_AGENT_STRING) {
+      EXPECT_FALSE(found);
+      EXPECT_EQ(0, strcmp(arg.value.string, arg0.value.string));
+      found = true;
+    }
+  }
+  EXPECT_TRUE(found);
 }
 
 }  // namespace testing