RESP3: initial implementation of the HELLO command.

src/module.c

@@ -4818,6 +4818,25 @@ int moduleUnload(sds name) {
     return REDISMODULE_OK;
 }
 
+/* Helper function for the MODULE and HELLO command: send the list of the
+ * loaded modules to the client. */
+void addReplyLoadedModules(client *c) {
+    dictIterator *di = dictGetIterator(modules);
+    dictEntry *de;
+
+    addReplyArrayLen(c,dictSize(modules));
+    while ((de = dictNext(di)) != NULL) {
+        sds name = dictGetKey(de);
+        struct RedisModule *module = dictGetVal(de);
+        addReplyMapLen(c,2);
+        addReplyBulkCString(c,"name");
+        addReplyBulkCBuffer(c,name,sdslen(name));
+        addReplyBulkCString(c,"ver");
+        addReplyLongLong(c,module->ver);
+    }
+    dictReleaseIterator(di);
+}
+
 /* Redis MODULE command.
  *
  * MODULE LOAD <path> [args...] */
@@ -4865,20 +4884,7 @@ NULL
             addReplyErrorFormat(c,"Error unloading module: %s",errmsg);
         }
     } else if (!strcasecmp(subcmd,"list") && c->argc == 2) {
-        dictIterator *di = dictGetIterator(modules);
-        dictEntry *de;
-
-        addReplyArrayLen(c,dictSize(modules));
-        while ((de = dictNext(di)) != NULL) {
-            sds name = dictGetKey(de);
-            struct RedisModule *module = dictGetVal(de);
-            addReplyMapLen(c,2);
-            addReplyBulkCString(c,"name");
-            addReplyBulkCBuffer(c,name,sdslen(name));
-            addReplyBulkCString(c,"ver");
-            addReplyLongLong(c,module->ver);
-        }
-        dictReleaseIterator(di);
+        addReplyLoadedModules(c);
     } else {
         addReplySubcommandSyntaxError(c);
         return;

src/networking.c

@@ -1998,6 +1998,54 @@ NULL
     }
 }
 
+/* HELLO <protocol-version> [AUTH <user> <password>] */
+void helloCommand(client *c) {
+    long long ver;
+
+    if (getLongLongFromObject(c->argv[1],&ver) != C_OK ||
+        ver < 2 || ver > 3)
+    {
+        addReplyError(c,"-NOPROTO unsupported protocol version");
+        return;
+    }
+
+    /* Switching to protocol v2 is not allowed. But we send a specific
+     * error message in this case. */
+    if (ver == 2) {
+        addReplyError(c,"Switching to RESP version 2 is not allowed.");
+        return;
+    }
+
+    /* Let's switch to RESP3 mode. */
+    c->resp = 3;
+    addReplyMapLen(c,7);
+
+    addReplyBulkCString(c,"server");
+    addReplyBulkCString(c,"redis");
+
+    addReplyBulkCString(c,"version");
+    addReplyBulkCString(c,REDIS_VERSION);
+
+    addReplyBulkCString(c,"proto");
+    addReplyLongLong(c,3);
+
+    addReplyBulkCString(c,"id");
+    addReplyLongLong(c,c->id);
+
+    addReplyBulkCString(c,"mode");
+    if (server.sentinel_mode) addReplyBulkCString(c,"sentinel");
+    if (server.cluster_enabled) addReplyBulkCString(c,"cluster");
+    else addReplyBulkCString(c,"standalone");
+
+    if (!server.sentinel_mode) {
+        addReplyBulkCString(c,"role");
+        addReplyBulkCString(c,server.masterhost ? "replica" : "master");
+    }
+
+    addReplyBulkCString(c,"modules");
+    addReplyLoadedModules(c);
+}
+
 /* This callback is bound to POST and "Host:" command names. Those are not
  * really commands, but are used in security attacks in order to talk to
  * Redis instances via HTTP, with a technique called "cross protocol scripting"

src/sentinel.c

@@ -453,7 +453,8 @@ struct redisCommand sentinelcmds[] = {
     {"role",sentinelRoleCommand,1,"l",0,NULL,0,0,0,0,0},
     {"client",clientCommand,-2,"rs",0,NULL,0,0,0,0,0},
     {"shutdown",shutdownCommand,-1,"",0,NULL,0,0,0,0,0},
-    {"auth",authCommand,2,"sltF",0,NULL,0,0,0,0,0}
+    {"auth",authCommand,2,"sltF",0,NULL,0,0,0,0,0},
+    {"hello",helloCommand,-2,"sF",0,NULL,0,0,0,0,0}
 };
 
 /* This function overwrites a few normal Redis config default with Sentinel

src/server.c

@@ -284,6 +284,7 @@ struct redisCommand redisCommandTable[] = {
     {"object",objectCommand,-2,"rR",0,NULL,2,2,1,0,0},
     {"memory",memoryCommand,-2,"rR",0,NULL,0,0,0,0,0},
     {"client",clientCommand,-2,"as",0,NULL,0,0,0,0,0},
+    {"hello",helloCommand,-2,"sF",0,NULL,0,0,0,0,0},
     {"eval",evalCommand,-3,"s",0,evalGetKeys,0,0,0,0,0},
     {"evalsha",evalShaCommand,-3,"s",0,evalGetKeys,0,0,0,0,0},
     {"slowlog",slowlogCommand,-2,"aR",0,NULL,0,0,0,0,0},

src/server.h

@@ -1459,6 +1459,7 @@ void addReplyAttributeLen(client *c, long length);
 void addReplyPushLen(client *c, long length);
 void addReplyHelp(client *c, const char **help);
 void addReplySubcommandSyntaxError(client *c);
+void addReplyLoadedModules(client *c);
 void copyClientOutputBuffer(client *dst, client *src);
 size_t sdsZmallocSize(sds s);
 size_t getStringObjectSdsUsedMemory(robj *o);
@@ -2093,6 +2094,7 @@ void dumpCommand(client *c);
 void objectCommand(client *c);
 void memoryCommand(client *c);
 void clientCommand(client *c);
+void helloCommand(client *c);
 void evalCommand(client *c);
 void evalShaCommand(client *c);
 void scriptCommand(client *c);