Make INFO command variadic (#6891)

This is an enhancement for INFO command, previously INFO only support one argument
for different info section , if user want to get more categories information, either perform
INFO all / default or calling INFO for multiple times.

**Description of the feature**

The goal of adding this feature is to let the user retrieve multiple categories via the INFO
command, and still avoid emitting the same section twice.

A use case for this is like Redis Sentinel, which periodically calling INFO command to refresh
info from monitored Master/Slaves, only Server and Replication part categories are used for
parsing information. If the INFO command can return just enough categories that client side
needs, it can save a lot of time for client side parsing it as well as network bandwidth.

**Implementation**
To share code between redis, sentinel, and other users of INFO (DEBUG and modules),
we have a new `genInfoSectionDict` function that returns a dict and some boolean flags
(e.g. `all`) to the caller (built from user input).
Sentinel is later purging unwanted sections from that, and then it is forwarded to the info `genRedisInfoString`.

**Usage Examples**
INFO Server Replication   
INFO CPU Memory
INFO default commandstats

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

1 files changed, 36 insertions, 29 deletions

diff --git a/src/sentinel.c b/src/sentinel.c
index 98121acde..61408c802 100644
--- a/src/sentinel.c
+++ b/src/sentinel.c
@@ -4099,46 +4099,52 @@ numargserr:
     addReplyErrorArity(c);
 }
 
-#define info_section_from_redis(section_name) do { \
-    if (defsections || allsections || !strcasecmp(section,section_name)) { \
-        sds redissection; \
-        if (sections++) info = sdscat(info,"\r\n"); \
-        redissection = genRedisInfoString(section_name); \
-        info = sdscatlen(info,redissection,sdslen(redissection)); \
-        sdsfree(redissection); \
-    } \
-} while(0)
+void addInfoSectionsToDict(dict *section_dict, char **sections);
 
 /* SENTINEL INFO [section] */
 void sentinelInfoCommand(client *c) {
-    if (c->argc > 2) {
-        addReplyErrorObject(c,shared.syntaxerr);
-        return;
+    char *sentinel_sections[] = {"server", "clients", "cpu", "stats", "sentinel", NULL};
+    int sec_all = 0, sec_everything = 0;
+    static dict *cached_all_info_sectoins = NULL;
+
+    /* Get requested section list. */
+    dict *sections_dict = genInfoSectionDict(c->argv+1, c->argc-1, sentinel_sections, &sec_all, &sec_everything);
+
+    /* Purge unsupported sections from the requested ones. */
+    dictEntry *de;
+    dictIterator *di = dictGetSafeIterator(sections_dict);
+    while((de = dictNext(di)) != NULL) {
+        int i;
+        sds sec = dictGetKey(de);
+        for (i=0; sentinel_sections[i]; i++)
+            if (!strcasecmp(sentinel_sections[i], sec))
+                break;
+        /* section not found? remove it */
+        if (!sentinel_sections[i])
+            dictDelete(sections_dict, sec);
     }
+    dictReleaseIterator(di);
 
-    int defsections = 0, allsections = 0;
-    char *section = c->argc == 2 ? c->argv[1]->ptr : NULL;
-    if (section) {
-        allsections = !strcasecmp(section,"all");
-        defsections = !strcasecmp(section,"default");
-    } else {
-        defsections = 1;
+    /* Insert explicit all sections (don't pass these vars to genRedisInfoString) */
+    if (sec_all || sec_everything) {
+        releaseInfoSectionDict(sections_dict);
+        /* We cache this dict as an optimization. */
+        if (!cached_all_info_sectoins) {
+            cached_all_info_sectoins = dictCreate(&stringSetDictType);
+            addInfoSectionsToDict(cached_all_info_sectoins, sentinel_sections);
+        }
+        sections_dict = cached_all_info_sectoins;
     }
 
-    int sections = 0;
     sds info = sdsempty();
-
-    info_section_from_redis("server");
-    info_section_from_redis("clients");
-    info_section_from_redis("cpu");
-    info_section_from_redis("stats");
-
-    if (defsections || allsections || !strcasecmp(section,"sentinel")) {
+    info = genRedisInfoString(sections_dict, 0, 0);
+    if (sec_all || (dictFind(sections_dict, "sentinel") != NULL)) {
         dictIterator *di;
         dictEntry *de;
         int master_id = 0;
 
-        if (sections++) info = sdscat(info,"\r\n");
+        if (sdslen(info) != 0)
+            info = sdscat(info,"\r\n");
         info = sdscatprintf(info,
             "# Sentinel\r\n"
             "sentinel_masters:%lu\r\n"
@@ -4171,7 +4177,8 @@ void sentinelInfoCommand(client *c) {
         }
         dictReleaseIterator(di);
     }
-
+    if (sections_dict != cached_all_info_sectoins)
+        releaseInfoSectionDict(sections_dict);
     addReplyBulkSds(c, info);
 }