From 5397f0b03312b8cace07a85333d8f035bdfb8d57 Mon Sep 17 00:00:00 2001
From: John Sully <john@csquare.ca>
Date: Wed, 4 Mar 2020 17:09:12 -0500
Subject: [PATCH] Add extra logging when reporting errors from masters -
 especially in rreplay

---
 src/networking.cpp  | 35 +++++++++++++++++++++++++++++++++++
 src/replication.cpp |  2 ++
 src/server.h        |  1 +
 3 files changed, 38 insertions(+)

diff --git a/src/networking.cpp b/src/networking.cpp
index 00322df72..58bd79bcc 100644
--- a/src/networking.cpp
+++ b/src/networking.cpp
@@ -177,6 +177,7 @@ client *createClient(int fd, int iel) {
     c->bufposAsync = 0;
     c->client_tracking_redirection = 0;
     c->casyncOpsPending = 0;
+    c->master_error = 0;
     memset(c->uuid, 0, UUID_BINARY_LEN);
 
     listSetFreeMethod(c->pubsub_patterns,decrRefCountVoid);
@@ -432,6 +433,34 @@ void addReplyProtoAsync(client *c, const char *s, size_t len) {
     addReplyProtoCore(c, s, len, true);
 }
 
+std::string escapeString(sds str)
+{
+    std::string newstr;
+    size_t len = sdslen(str);
+    for (size_t ich = 0; ich < len; ++ich)
+    {
+        char ch = str[ich];
+        switch (ch)
+        {
+        case '\n':
+            newstr += "\\n";
+            break;
+
+        case '\t':
+            newstr += "\\t";
+            break;
+
+        case '\r':
+            newstr += "\\r";
+            break;
+        
+        default:
+            newstr += ch;
+        }
+    }
+    return newstr;
+}
+
 /* Low level function called by the addReplyError...() functions.
  * It emits the protocol for a Redis error, in the form:
  *
@@ -464,6 +493,12 @@ void addReplyErrorLengthCore(client *c, const char *s, size_t len, bool fAsync)
         serverLog(LL_WARNING,"== CRITICAL == This %s is sending an error "
                              "to its %s: '%s' after processing the command "
                              "'%s'", from, to, s, cmdname);
+
+        if (c->querybuf && sdslen(c->querybuf)) {
+            std::string str = escapeString(c->querybuf);
+            serverLog(LL_WARNING, "\tquerybuf: %s", str.c_str());
+        }
+        c->master_error = 1;
     }
 }
 
diff --git a/src/replication.cpp b/src/replication.cpp
index d7e92d308..2bdc21bf0 100644
--- a/src/replication.cpp
+++ b/src/replication.cpp
@@ -3482,6 +3482,8 @@ void replicaReplayCommand(client *c)
     cFake->flags &= ~(CLIENT_MASTER | CLIENT_PREVENT_REPL_PROP);
     bool fExec = ccmdPrev != serverTL->commandsExecuted;
     cFake->lock.unlock();
+    if (cFake->master_error)
+        addReplyError(c, "Error in rreplay command, please check logs");
     if (fExec || cFake->flags & CLIENT_MULTI)
     {
         addReply(c, shared.ok);
diff --git a/src/server.h b/src/server.h
index 58ea3e620..1e6632576 100644
--- a/src/server.h
+++ b/src/server.h
@@ -1337,6 +1337,7 @@ typedef struct client {
 
     int iel; /* the event loop index we're registered with */
     struct fastlock lock;
+    int master_error;
 } client;
 
 struct saveparam {