From 76ad23d012f194efa1acc0f8356d945b07681851 Mon Sep 17 00:00:00 2001
From: Itamar Haber <itamar@redislabs.com>
Date: Thu, 7 Jun 2018 18:34:58 +0300
Subject: [PATCH] Adds MODULE HELP and implements  addReplySubSyntaxError

---
 src/module.c     | 13 +++++++++++--
 src/networking.c | 12 ++++++++++++
 src/server.h     |  1 +
 3 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/src/module.c b/src/module.c
index cb03ad2cd..e4d6e2cf2 100644
--- a/src/module.c
+++ b/src/module.c
@@ -4499,7 +4499,15 @@ int moduleUnload(sds name) {
  * MODULE LOAD <path> [args...] */
 void moduleCommand(client *c) {
     char *subcmd = c->argv[1]->ptr;
-
+    if (c->argc == 2 && !strcasecmp(subcmd,"help")) {
+        const char *help[] = {
+"list -- Return a list of loaded modules.",
+"load <path> [arg ...] -- Load a module library from <path>.",
+"unload <name> -- Unload a module.",
+NULL
+        };
+        addReplyHelp(c, help);
+    } else
     if (!strcasecmp(subcmd,"load") && c->argc >= 3) {
         robj **argv = NULL;
         int argc = 0;
@@ -4548,7 +4556,8 @@ void moduleCommand(client *c) {
         }
         dictReleaseIterator(di);
     } else {
-        addReply(c,shared.syntaxerr);
+        addReplySubSyntaxError(c);
+        return;
     }
 }
 
diff --git a/src/networking.c b/src/networking.c
index 00558974e..ac28ba2b8 100644
--- a/src/networking.c
+++ b/src/networking.c
@@ -560,6 +560,18 @@ void addReplyHelp(client *c, const char **help) {
     setDeferredMultiBulkLength(c,blenp,blen);
 }
 
+/* Add a suggestive error reply.
+ * This function is typically invoked by from commands that support
+ * subcommands in response to an unknown subcommand or argument error. */
+void addReplySubSyntaxError(client *c) {
+    sds cmd = sdsnew((char*) c->argv[0]->ptr);
+    sdstoupper(cmd);
+    addReplyErrorFormat(c,
+        "Unknown subcommand or wrong number of arguments for '%s'. Try %s HELP.",
+        c->argv[1]->ptr,cmd);
+    sdsfree(cmd);    
+}
+
 /* Copy 'src' client output buffers into 'dst' client output buffers.
  * The function takes care of freeing the old output buffers of the
  * destination client. */
diff --git a/src/server.h b/src/server.h
index c34cdcfbf..26aee8932 100644
--- a/src/server.h
+++ b/src/server.h
@@ -1410,6 +1410,7 @@ void addReplyHumanLongDouble(client *c, long double d);
 void addReplyLongLong(client *c, long long ll);
 void addReplyMultiBulkLen(client *c, long length);
 void addReplyHelp(client *c, const char **help);
+void addReplySubSyntaxError(client *c);
 void copyClientOutputBuffer(client *dst, client *src);
 size_t sdsZmallocSize(sds s);
 size_t getStringObjectSdsUsedMemory(robj *o);