Direct redis-cli repl prints to stderr, because --rdb can print to stdout. fflush stdout after responses (#9136)

1. redis-cli can output --rdb data to stdout
   but redis-cli also write some messages to stdout which will mess up the rdb.

2. Make redis-cli flush stdout when printing a reply
  This was needed in order to fix a hung in redis-cli test that uses
  --replica.
   Note that printf does flush when there's a newline, but fwrite does not.

3. fix the redis-cli --replica test which used to pass previously
   because it didn't really care what it read, and because redis-cli
   used printf to print these other things to stdout.

4. improve redis-cli --replica test to run with both diskless and disk-based.

Co-authored-by: Oran Agra <oran@redislabs.com>
Co-authored-by: Viktor Söderqvist <viktor@zuiderkwast.se>
(cherry picked from commit 1eb4baa5b8e76adc337ae9fab49acc2585a0cdd0)

2 files changed, 25 insertions, 8 deletions

diff --git a/src/redis-cli.c b/src/redis-cli.c
index d4d5e7459..06ccf1563 100644
--- a/src/redis-cli.c
+++ b/src/redis-cli.c
@@ -1312,6 +1312,7 @@ static int cliReadReply(int output_raw_strings) {
     if (output) {
         out = cliFormatReply(reply, config.output, output_raw_strings);
         fwrite(out,sdslen(out),1,stdout);
+        fflush(stdout);
         sdsfree(out);
     }
     freeReplyObject(reply);
@@ -6990,7 +6991,7 @@ static void latencyDistMode(void) {
 #define RDB_EOF_MARK_SIZE 40
 
 void sendReplconf(const char* arg1, const char* arg2) {
-    printf("sending REPLCONF %s %s\n", arg1, arg2);
+    fprintf(stderr, "sending REPLCONF %s %s\n", arg1, arg2);
     redisReply *reply = redisCommand(context, "REPLCONF %s %s", arg1, arg2);
 
     /* Handle any error conditions */
@@ -7050,7 +7051,7 @@ unsigned long long sendSync(redisContext *c, char *out_eof) {
     }
     *p = '\0';
     if (buf[0] == '-') {
-        printf("SYNC with master failed: %s\n", buf);
+        fprintf(stderr, "SYNC with master failed: %s\n", buf);
         exit(1);
     }
     if (strncmp(buf+1,"EOF:",4) == 0 && strlen(buf+5) >= RDB_EOF_MARK_SIZE) {
diff --git a/tests/integration/redis-cli.tcl b/tests/integration/redis-cli.tcl
index 7e8b41fca..d58229bb4 100644
--- a/tests/integration/redis-cli.tcl
+++ b/tests/integration/redis-cli.tcl
@@ -283,9 +283,9 @@ start_server {tags {"cli"}} {
         assert_equal {key:2} [run_cli --scan --quoted-pattern {"*:\x32"}]
     }
 
-    test "Connecting as a replica" {
+    proc test_redis_cli_repl {} {
         set fd [open_cli "--replica"]
-        wait_for_condition 500 500 {
+        wait_for_condition 500 100 {
             [string match {*slave0:*state=online*} [r info]]
         } else {
             fail "redis-cli --replica did not connect"
@@ -294,14 +294,30 @@ start_server {tags {"cli"}} {
         for {set i 0} {$i < 100} {incr i} {
            r set test-key test-value-$i
         }
-        r client kill type slave
-        catch {
-            assert_match {*SET*key-a*} [read_cli $fd]
+
+        wait_for_condition 500 100 {
+            [string match {*test-value-99*} [read_cli $fd]]
+        } else {
+            fail "redis-cli --replica didn't read commands"
         }
 
-        close_cli $fd
+        fconfigure $fd -blocking true
+        r client kill type slave
+        catch { close_cli $fd } err
+        assert_match {*Server closed the connection*} $err
     }
 
+    test "Connecting as a replica" {
+        # Disk-based master
+        assert_match "OK" [r config set repl-diskless-sync no]
+        test_redis_cli_repl
+
+        # Disk-less master
+        assert_match "OK" [r config set repl-diskless-sync yes]
+        assert_match "OK" [r config set repl-diskless-sync-delay 0]
+        test_redis_cli_repl
+    } {}
+
     test "Piping raw protocol" {
         set cmds [tmpfile "cli_cmds"]
         set cmds_fd [open $cmds "w"]