[redis proxy]: redis unsupported command message compatibility

Signed-off-by: duanhongyi <duanhongyi@doopai.com>

docs/root/intro/arch_overview/other_protocols/redis.rst

@@ -302,7 +302,7 @@ Envoy can also generate its own errors in response to the client.
   the connection."
   invalid request, "Command was rejected by the first stage of the command splitter due to
   datatype or length."
-  unsupported command, "The command was not recognized by Envoy and therefore cannot be serviced
+  ERR unknown command, "The command was not recognized by Envoy and therefore cannot be serviced
   because it cannot be hashed to a backend server."
   finished with n errors, "Fragmented commands which sum the response (e.g. DEL) will return the
   total number of errors received if any were received."

source/extensions/filters/network/redis_proxy/command_splitter_impl.cc

@@ -839,7 +839,8 @@ SplitRequestPtr InstanceImpl::makeRequest(Common::Redis::RespValuePtr&& request,
   if (handler == nullptr) {
     stats_.unsupported_command_.inc();
     callbacks.onResponse(Common::Redis::Utility::makeError(
-        fmt::format("unsupported command '{}'", request->asArray()[0].asString())));
+        fmt::format("ERR unknown command '{}', with args beginning with: {}",
+                    request->asArray()[0].asString(), request->asArray()[1].asString())));
     return nullptr;
   }
 

test/extensions/filters/network/redis_proxy/command_splitter_impl_test.cc

@@ -173,7 +173,7 @@ TEST_F(RedisCommandSplitterImplTest, InvalidRequestArrayNotStrings) {
 TEST_F(RedisCommandSplitterImplTest, UnsupportedCommand) {
   Common::Redis::RespValue response;
   response.type(Common::Redis::RespType::Error);
-  response.asString() = "unsupported command 'newcommand'";
+  response.asString() = "ERR unknown command 'newcommand', with args beginning with: hello";
   EXPECT_CALL(callbacks_, connectionAllowed()).WillOnce(Return(true));
   EXPECT_CALL(callbacks_, onResponse_(PointeesEq(&response)));
   Common::Redis::RespValuePtr request{new Common::Redis::RespValue()};