Added error handling.

Without this fix, a segv will happen in certain error conditions where
the reply_obj == nullptr.

include/redox/client.hpp

@@ -393,7 +393,7 @@ class Redox {
   template <class ReplyT> friend void Command<ReplyT>::free();
 
   // Access to call disconnectedCallback
-  template <class ReplyT> friend void Command<ReplyT>::processReply(redisReply *r);
+  template <class ReplyT> friend void Command<ReplyT>::processReply(redisReply *r, const std::string& errorMessage);
 };
 
 // ------------------------------------------------

include/redox/command.hpp

@@ -105,7 +105,7 @@ template <class ReplyT> class Command {
           bool free_memory, log::Logger &logger);
 
   // Handles a new reply from the server
-  void processReply(redisReply *r);
+  void processReply(redisReply *r, const std::string& errorMessage = std::string());
 
   // Invoke a user callback from the reply object. This method is specialized
   // for each ReplyT of Command.

src/client.cpp

@@ -365,17 +365,27 @@ template <class ReplyT> Command<ReplyT> *Redox::findCommand(long id) {
 template <class ReplyT>
 void Redox::commandCallback(redisAsyncContext *ctx, void *r, void *privdata) {
 
-  Redox *rdx = (Redox *)ctx->data;
-  long id = (long)privdata;
-  redisReply *reply_obj = (redisReply *)r;
+  Redox *rdx = reinterpret_cast<Redox*>(ctx->data);
+  if (rdx == nullptr) {
+    return;
+  }
+
+  redisReply *reply_obj = reinterpret_cast<redisReply*>(r);
 
+  long id = (long)privdata;
   Command<ReplyT> *c = rdx->findCommand<ReplyT>(id);
   if (c == nullptr) {
-    freeReplyObject(reply_obj);
+    if (reply_obj != nullptr) {
+      freeReplyObject(reply_obj);
+    }
     return;
   }
 
-  c->processReply(reply_obj);
+  if (ctx->err) {
+    c->processReply(nullptr, std::string(ctx->errstr));
+  } else {
+    c->processReply(reply_obj);
+  }
 }
 
 template <class ReplyT> bool Redox::submitToServer(Command<ReplyT> *c) {

src/command.cpp

@@ -75,14 +75,19 @@ template <class ReplyT> void Command<ReplyT>::wait() {
   waiting_done_ = {false};
 }
 
-template <class ReplyT> void Command<ReplyT>::processReply(redisReply *r) {
+template <class ReplyT> void Command<ReplyT>::processReply(redisReply *r, const std::string& errorMessage) {
 
   last_error_.clear();
   reply_obj_ = r;
 
   if (reply_obj_ == nullptr) {
     reply_status_ = ERROR_REPLY;
-    last_error_ = "Received null redisReply* from hiredis.";
+    if (errorMessage.empty()) {
+        last_error_ = "Received null redisReply* from hiredis.";
+    }
+    else {
+        last_error_ = errorMessage;
+    }
     logger_.error() << last_error_;
     Redox::disconnectedCallback(rdx_->ctx_, REDIS_ERR);