feat(memcache): Add support for GETS (#5087)

Support is added for the GETS command. A placeholder CAS token of 0 is
always returned.

Signed-off-by: Abhijat Malviya <abhijat@dragonflydb.io>

Author: abhijat

src/facade/reply_builder.cc

@@ -212,7 +212,7 @@ MCReplyBuilder::MCReplyBuilder(::io::Sink* sink) : SinkReplyBuilder(sink), all_(
 }
 
 void MCReplyBuilder::SendValue(std::string_view key, std::string_view value, uint64_t mc_ver,
-                               uint32_t mc_flag) {
+                               uint32_t mc_flag, bool send_cas_token) {
   ReplyScope scope(this);
   if (flag_.meta) {
     string flags;
@@ -227,7 +227,7 @@ void MCReplyBuilder::SendValue(std::string_view key, std::string_view value, uin
     }
   } else {
     WritePieces("VALUE ", key, " ", mc_flag, " ", value.size());
-    if (mc_ver)
+    if (send_cas_token)
       WritePieces(" ", mc_ver);
 
     if (value.size() <= kMaxInlineSize) {

src/facade/reply_builder.h

@@ -177,7 +177,8 @@ class MCReplyBuilder : public SinkReplyBuilder {
   void SendDeleted();
   void SendGetEnd();
 
-  void SendValue(std::string_view key, std::string_view value, uint64_t mc_ver, uint32_t mc_flag);
+  void SendValue(std::string_view key, std::string_view value, uint64_t mc_ver, uint32_t mc_flag,
+                 bool send_cas_token);
   void SendSimpleString(std::string_view str) final;
   void SendProtocolError(std::string_view str) final;
 

src/server/dragonfly_test.cc

@@ -341,6 +341,9 @@ TEST_F(DflyEngineTest, Memcache) {
   auto resp = RunMC(MP::SET, "key", "bar", 1);
   EXPECT_THAT(resp, ElementsAre("STORED"));
 
+  resp = RunMC(MP::GETS, "key");
+  EXPECT_THAT(resp, ElementsAre("VALUE key 1 3 0", "bar", "END"));
+
   resp = RunMC(MP::GET, "key");
   EXPECT_THAT(resp, ElementsAre("VALUE key 1 3", "bar", "END"));
 
@@ -366,6 +369,9 @@ TEST_F(DflyEngineTest, Memcache) {
 
   resp = RunMC(MP::GET, "unkn");
   EXPECT_THAT(resp, ElementsAre("END"));
+
+  resp = GetMC(MP::GETS, {"key", "key2", "unknown"});
+  EXPECT_THAT(resp, ElementsAre("VALUE key 1 3 0", "bar", "VALUE key2 2 8 0", "bar2val2", "END"));
 }
 
 TEST_F(DflyEngineTest, MemcacheFlags) {

src/server/main_service.cc

@@ -1536,6 +1536,8 @@ void Service::DispatchMC(const MemcacheParser::Command& cmd, std::string_view va
       strcpy(cmd_name, "PREPEND");
       break;
     case MemcacheParser::GET:
+      [[fallthrough]];
+    case MemcacheParser::GETS:
       strcpy(cmd_name, "MGET");
       break;
     case MemcacheParser::FLUSHALL:
@@ -1589,6 +1591,9 @@ void Service::DispatchMC(const MemcacheParser::Command& cmd, std::string_view va
       char* key = const_cast<char*>(s.data());
       args.emplace_back(key, s.size());
     }
+    if (cmd.type == MemcacheParser::GETS) {
+      dfly_cntx->conn_state.memcache_flag |= ConnectionState::FETCH_CAS_VER;
+    }
   } else {  // write commands.
     if (store_opt[0]) {
       args.emplace_back(store_opt, strlen(store_opt));

src/server/string_family.cc

@@ -1366,7 +1366,7 @@ void StringFamily::MGet(CmdArgList args, const CommandContext& cmnd_cntx) {
     DCHECK(dynamic_cast<CapturingReplyBuilder*>(builder) == nullptr);
     for (const auto& entry : res) {
       if (entry) {
-        rb->SendValue(entry->key, entry->value, entry->mc_ver, entry->mc_flag);
+        rb->SendValue(entry->key, entry->value, 0, entry->mc_flag, fetch_mask & FETCH_MCVER);
       } else {
         rb->SendMiss();
       }

tests/dragonfly/memcache_meta.py

@@ -6,7 +6,7 @@
     CacheClient,
     connection_pool_factory_builder,
 )
-from meta_memcache.protocol import RequestFlags, Miss, Value, Success
+from meta_memcache.protocol import RequestFlags, Success
 
 DEFAULT_ARGS = {"memcached_port": 11211, "proactor_threads": 4}
 
@@ -30,3 +30,12 @@ def test_basic(df_server: DflyInstance):
     assert pool.get("key2") is None
     assert pool.delete("key1")
     assert pool.delete("key1") is False
+
+    assert pool.set("cask", "v", 100)
+    value, cas_token = pool.get_cas("cask")
+    assert value == "v" and cas_token == 0
+
+    k = Key("cask")
+    response = pool.meta_multiget([k], RequestFlags(return_cas_token=True, return_value=True))
+    assert k in response
+    assert response[k].flags.cas_token == 0 and response[k].value == "v"

tests/dragonfly/pymemcached_test.py

@@ -1,17 +1,17 @@
 import logging
-import pytest
-from pymemcache.client.base import Client as MCClient
-from redis import Redis
-import socket
 import random
-import time
+import socket
 import ssl
+import time
+
+from pymemcache.client.base import Client as MCClient
 
 from . import dfly_args
 from .instance import DflyInstance
 
 DEFAULT_ARGS = {"memcached_port": 11211, "proactor_threads": 4}
 
+
 # Generic basic tests
 
 
@@ -32,7 +32,7 @@ def test_basic(memcached_client: MCClient):
     # delete
     assert memcached_client.delete("key1")
     assert not memcached_client.delete("key3")
-    assert memcached_client.get("key1") == None
+    assert memcached_client.get("key1") is None
 
     # prepend append
     assert memcached_client.set("key4", "B")
@@ -46,6 +46,8 @@ def test_basic(memcached_client: MCClient):
     assert memcached_client.incr("key5", 1) == 2
     assert memcached_client.decr("key5", 1) == 1
 
+    assert memcached_client.gets("key5") == (b"1", b"0")
+
 
 # Noreply (and pipeline) tests