Fix RDB check regression caused by PR 12022 (#12051)

The nightly tests showed that the recent PR #12022 caused random failures
in aof.tcl on checking RDB preamble inside an AOF file.

Root cause:
When checking RDB preamble in an AOF file, what's passed into redis_check_rdb is
aof_filename, not aof_filepath. The newly introduced isFifo function does not check return
status of the stat call and hence uses the uninitailized stat_p object.

Fix:
1. Fix isFifo by checking stat call's return code.
2. Pass aof_filepath instead of aof_filename to redis_check_rdb.
3. move the FIFO check to rdb.c since the limitation is the re-opening of the file, and not
  anything specific about redis-check-rdb.

src/anet.c

@@ -697,3 +697,9 @@ int anetSetSockMarkId(char *err, int fd, uint32_t id) {
     return ANET_OK;
 #endif
 }
+
+int anetIsFifo(char *filepath) {
+    struct stat sb;
+    if (stat(filepath, &sb) == -1) return 0;
+    return S_ISFIFO(sb.st_mode);
+}

src/anet.h

@@ -70,5 +70,6 @@ int anetFormatAddr(char *fmt, size_t fmt_len, char *ip, int port);
 int anetPipe(int fds[2], int read_flags, int write_flags);
 int anetSetSockMarkId(char *err, int fd, uint32_t id);
 int anetGetError(int fd);
+int anetIsFifo(char *filepath);
 
 #endif

src/rdb.c

@@ -88,6 +88,11 @@ void rdbReportError(int corruption_error, int linenum, char *reason, ...) {
         /* If we're loading an rdb file form disk, run rdb check (and exit) */
         serverLog(LL_WARNING, "%s", msg);
         char *argv[2] = {"",rdbFileBeingLoaded};
+        if (anetIsFifo(argv[1])) {
+            /* Cannot check RDB FIFO because we cannot reopen the FIFO and check already streamed data. */
+            rdbCheckError("Cannot check RDB that is a FIFO: %s", argv[1]);
+            return;
+        }
         redis_check_rdb_main(2,argv,NULL);
     } else if (corruption_error) {
         /* In diskless loading, in case of corrupt file, log and exit. */

src/redis-check-aof.c

@@ -242,7 +242,7 @@ int checkSingleAof(char *aof_filename, char *aof_filepath, int last_file, int fi
     }
 
     if (preamble) {
-        char *argv[2] = {NULL, aof_filename};
+        char *argv[2] = {NULL, aof_filepath};
         if (redis_check_rdb_main(2, argv, fp) == C_ERR) {
             printf("RDB preamble of AOF file is not sane, aborting.\n");
             exit(1);

src/redis-check-rdb.c

@@ -186,15 +186,9 @@ void rdbCheckSetupSignals(void) {
     sigaction(SIGABRT, &act, NULL);
 }
 
-static int isFifo(char *filename) {
-    struct stat stat_p;
-    stat(filename, &stat_p);
-    return S_ISFIFO(stat_p.st_mode);
-}
-
 /* Check the specified RDB file. Return 0 if the RDB looks sane, otherwise
  * 1 is returned.
- * The file is specified as a filename in 'rdbfilename' if 'fp' is not NULL,
+ * The file is specified as a filename in 'rdbfilename' if 'fp' is NULL,
  * otherwise the already open file 'fp' is checked. */
 int redis_check_rdb(char *rdbfilename, FILE *fp) {
     uint64_t dbid;
@@ -205,11 +199,6 @@ int redis_check_rdb(char *rdbfilename, FILE *fp) {
     static rio rdb; /* Pointed by global struct riostate. */
     struct stat sb;
 
-    if (isFifo(rdbfilename)) {
-        /* Cannot check RDB over named pipe because fopen blocks until another process opens the FIFO for writing. */
-        return 1;
-    }
-
     int closefile = (fp == NULL);
     if (fp == NULL && (fp = fopen(rdbfilename,"r")) == NULL) return 1;