Add SIMPLE_STRING reply type to the Module API

This commit adds the `SIMPLE_STRING` reply type to the Module API, which is
required for scripts to process correctly the reply type of commands
called inside scripts.

Before this change, commands like `PING` or `SET`, which return `"OK"`
as a simple string reply, would be returned as string replies to scripts.
To allow the support of the Lua engine as an external module, we need to
distinguish between simple string and string replies to keep backward
compatibility.

Signed-off-by: Ricardo Dias <ricardo.dias@percona.com>

Author: rjd15372

src/call_reply.c

@@ -33,6 +33,7 @@
 #define REPLY_FLAG_ROOT (1 << 0)
 #define REPLY_FLAG_PARSED (1 << 1)
 #define REPLY_FLAG_RESP3 (1 << 2)
+#define REPLY_FLAG_SIMPLE_STRING (1 << 3)
 
 /* --------------------------------------------------------
  * An opaque struct used to parse a RESP protocol reply and
@@ -102,7 +103,9 @@ static void callReplyError(void *ctx, const char *str, size_t len, const char *p
 
 static void callReplySimpleStr(void *ctx, const char *str, size_t len, const char *proto, size_t proto_len) {
     CallReply *rep = ctx;
-    callReplySetSharedData(rep, VALKEYMODULE_REPLY_STRING, proto, proto_len, 0);
+    int type = rep->flags & REPLY_FLAG_SIMPLE_STRING ? VALKEYMODULE_REPLY_SIMPLE_STRING
+                                                     : VALKEYMODULE_REPLY_STRING;
+    callReplySetSharedData(rep, type, proto, proto_len, 0);
     rep->len = len;
     rep->val.str = str;
 }
@@ -306,6 +309,7 @@ int callReplyType(CallReply *rep) {
 
 /* Return reply string as buffer and len. Applicable to:
  * - VALKEYMODULE_REPLY_STRING
+ * - VALKEYMODULE_REPLY_SIMPLE_STRING
  * - VALKEYMODULE_REPLY_ERROR
  *
  * The return value is borrowed from CallReply, so it must not be freed
@@ -316,7 +320,9 @@ int callReplyType(CallReply *rep) {
  */
 const char *callReplyGetString(CallReply *rep, size_t *len) {
     callReplyParse(rep);
-    if (rep->type != VALKEYMODULE_REPLY_STRING && rep->type != VALKEYMODULE_REPLY_ERROR) return NULL;
+    if (rep->type != VALKEYMODULE_REPLY_STRING &&
+        rep->type != VALKEYMODULE_REPLY_SIMPLE_STRING &&
+        rep->type != VALKEYMODULE_REPLY_ERROR) return NULL;
     if (len) *len = rep->len;
     return rep->val.str;
 }
@@ -563,3 +569,13 @@ CallReply *callReplyCreateError(sds reply, void *private_data) {
     listAddNodeTail(deferred_error_list, sdsnew(err_buff));
     return callReplyCreate(err_buff, deferred_error_list, private_data);
 }
+
+/* Enable the parsing of simple strings flag.
+ *
+ * This flag enforces the distinction between simple strings and bulk strings
+ * when parsing the CallReply.
+ */
+void enableParseSimpleStringFlag(CallReply *rep) {
+    serverAssert(!(rep->flags & REPLY_FLAG_PARSED));
+    rep->flags |= REPLY_FLAG_SIMPLE_STRING;
+}

src/call_reply.h

@@ -56,5 +56,6 @@ int callReplyIsResp3(CallReply *rep);
 list *callReplyDeferredErrorList(CallReply *rep);
 void freeCallReply(CallReply *rep);
 CallReply *callReplyCreatePromise(void *private_data);
+void enableParseSimpleStringFlag(CallReply *rep);
 
 #endif /* SRC_CALL_REPLY_H_ */

src/module.c

@@ -911,6 +911,9 @@ static CallReply *moduleParseReply(client *c, ValkeyModuleCtx *ctx) {
         listDelNode(c->reply, listFirst(c->reply));
     }
     CallReply *reply = callReplyCreate(proto, c->deferred_reply_errors, ctx);
+    if (ctx && ctx->flags & VALKEYMODULE_CTX_SCRIPT_EXECUTION) {
+        enableParseSimpleStringFlag(reply);
+    }
     c->deferred_reply_errors = NULL; /* now the responsibility of the reply object. */
     return reply;
 }
@@ -6179,6 +6182,7 @@ ValkeyModuleString *VM_CreateStringFromCallReply(ValkeyModuleCallReply *reply) {
     const char *str;
     switch (callReplyType(reply)) {
     case VALKEYMODULE_REPLY_STRING:
+    case VALKEYMODULE_REPLY_SIMPLE_STRING:
     case VALKEYMODULE_REPLY_ERROR: str = callReplyGetString(reply, &len); return VM_CreateString(ctx, str, len);
     case VALKEYMODULE_REPLY_INTEGER: {
         char buf[64];

src/valkeymodule.h

@@ -112,6 +112,7 @@ typedef long long ustime_t;
 #define VALKEYMODULE_REPLY_VERBATIM_STRING 10
 #define VALKEYMODULE_REPLY_ATTRIBUTE 11
 #define VALKEYMODULE_REPLY_PROMISE 12
+#define VALKEYMODULE_REPLY_SIMPLE_STRING 13
 
 /* Postponed array length. */
 #define VALKEYMODULE_POSTPONED_ARRAY_LEN -1 /* Deprecated, please use VALKEYMODULE_POSTPONED_LEN */