Support setlocale via CONFIG operation. (#11059)

Till now Redis officially supported tuning it via environment variable see #1074.
But we had other requests to allow changing it at runtime, see #799, and #11041.

Note that `strcoll()` is used as Lua comparison function and also for comparison of
certain string objects in Redis, which leads to a problem that, in different regions,
for some characters, the result may be different. Below is an example.
```
127.0.0.1:6333> SORT test alpha
1) "<"
2) ">"
3) ","
4) "*"
127.0.0.1:6333> CONFIG GET locale-collate
1) "locale-collate"
2) ""
127.0.0.1:6333> CONFIG SET locale-collate 1
(error) ERR CONFIG SET failed (possibly related to argument 'locale')
127.0.0.1:6333> CONFIG SET locale-collate C
OK
127.0.0.1:6333> SORT test alpha
1) "*"
2) ","
3) "<"
4) ">"
```
That will cause accidental code compatibility issues for Lua scripts and some
Redis commands. This commit creates a new config parameter to control the
local environment which only affects `Collate` category. Above shows how it
affects `SORT` command, and below shows the influence on Lua scripts.
```
127.0.0.1:6333> CONFIG GET locale-collate
1) " locale-collate"
2) "C"
127.0.0.1:6333> EVAL "return ',' < '*'" 0
(nil)
127.0.0.1:6333> CONFIG SET locale-collate ""
OK
127.0.0.1:6333> EVAL "return ',' < '*'" 0
(integer) 1
```

Co-authored-by: calvincjli <calvincjli@tencent.com>
Co-authored-by: Oran Agra <oran@redislabs.com>

4 files changed, 24 insertions, 1 deletions

diff --git a/redis.conf b/redis.conf
index 13b29c428..3bb52e76d 100644
--- a/redis.conf
+++ b/redis.conf
@@ -409,6 +409,11 @@ set-proc-title yes
 #
 proc-title-template "{title} {listen-addr} {server-mode}"
 
+# Set the local environment which is used for string comparison operations, and 
+# also affect the performance of Lua scripts. Empty String indicates the locale 
+# is derived from the environment variables.
+locale-collate ""
+
 ################################ SNAPSHOTTING  ################################
 
 # Save the DB to disk.
diff --git a/src/config.c b/src/config.c
index 0ffe65a61..f98225cbe 100644
--- a/src/config.c
+++ b/src/config.c
@@ -35,6 +35,7 @@
 #include <sys/stat.h>
 #include <glob.h>
 #include <string.h>
+#include <locale.h>
 
 /*-----------------------------------------------------------------------------
  * Config file name-value maps.
@@ -2400,6 +2401,15 @@ static int isValidProcTitleTemplate(char *val, const char **err) {
     return 1;
 }
 
+static int updateLocaleCollate(const char **err) {
+    const char *s = setlocale(LC_COLLATE, server.locale_collate);
+    if (s == NULL) {
+        *err = "Invalid locale name";
+        return 0;
+    }
+    return 1;
+}
+
 static int updateProcTitleTemplate(const char **err) {
     if (redisSetProcTitle(NULL) == C_ERR) {
         *err = "failed to set process title";
@@ -2995,6 +3005,7 @@ standardConfig static_configs[] = {
     createStringConfig("proc-title-template", NULL, MODIFIABLE_CONFIG, ALLOW_EMPTY_STRING, server.proc_title_template, CONFIG_DEFAULT_PROC_TITLE_TEMPLATE, isValidProcTitleTemplate, updateProcTitleTemplate),
     createStringConfig("bind-source-addr", NULL, MODIFIABLE_CONFIG, EMPTY_STRING_IS_NULL, server.bind_source_addr, NULL, NULL, NULL),
     createStringConfig("logfile", NULL, IMMUTABLE_CONFIG, ALLOW_EMPTY_STRING, server.logfile, "", NULL, NULL),
+    createStringConfig("locale-collate", NULL, MODIFIABLE_CONFIG, ALLOW_EMPTY_STRING, server.locale_collate, "", NULL, updateLocaleCollate),
 
     /* SDS Configs */
     createSDSConfig("masterauth", NULL, MODIFIABLE_CONFIG | SENSITIVE_CONFIG, EMPTY_STRING_IS_NULL, server.masterauth, NULL, NULL, NULL),
diff --git a/src/server.c b/src/server.c
index 3456f06c9..b96d95b75 100644
--- a/src/server.c
+++ b/src/server.c
@@ -2440,6 +2440,12 @@ void initServer(void) {
     server.reply_buffer_resizing_enabled = 1;
     resetReplicationBuffer();
 
+    /* Make sure the locale is set on startup based on the config file. */
+    if (setlocale(LC_COLLATE,server.locale_collate) == NULL) {
+        serverLog(LL_WARNING, "Failed to configure LOCALE for invalid locale name.");
+        exit(1);
+    }
+
     if ((server.tls_port || server.tls_replication || server.tls_cluster)
                 && tlsConfigure(&server.tls_ctx_config) == C_ERR) {
         serverLog(LL_WARNING, "Failed to configure TLS. Check logs for more info.");
@@ -6910,7 +6916,6 @@ int main(int argc, char **argv) {
 #ifdef INIT_SETPROCTITLE_REPLACEMENT
     spt_init(argc, argv);
 #endif
-    setlocale(LC_COLLATE,"");
     tzset(); /* Populates 'timezone' global. */
     zmalloc_set_oom_handler(redisOutOfMemoryHandler);
 
diff --git a/src/server.h b/src/server.h
index 685768803..c0f68c73f 100644
--- a/src/server.h
+++ b/src/server.h
@@ -1944,6 +1944,8 @@ struct redisServer {
                                                 is down, doesn't affect pubsub global. */
     long reply_buffer_peak_reset_time; /* The amount of time (in milliseconds) to wait between reply buffer peak resets */
     int reply_buffer_resizing_enabled; /* Is reply buffer resizing enabled (1 by default) */
+    /* Local environment */
+    char *locale_collate;
 };
 
 #define MAX_KEYS_BUFFER 256