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, 48 insertions, 0 deletions

diff --git a/tests/sentinel/tests/13-info-command.tcl b/tests/sentinel/tests/13-info-command.tcl
new file mode 100644
index 000000000..4772a1da8
--- /dev/null
+++ b/tests/sentinel/tests/13-info-command.tcl
@@ -0,0 +1,48 @@
+# Check the basic monitoring and failover capabilities.
+source "../tests/includes/init-tests.tcl"
+
+test "info command with at most one argument" {
+    set subCommandList {}
+    foreach arg {"" "all" "default" "everything"} {
+        if {$arg == ""} {
+            set info [S 0 info]
+        } else {
+            set info [S 0 info $arg]
+        }
+        assert { [string match "*redis_version*" $info] }
+        assert { [string match "*maxclients*" $info] }
+        assert { [string match "*used_cpu_user*" $info] }
+        assert { [string match "*sentinel_tilt*" $info] }
+        assert { ![string match "*used_memory*" $info] }
+        assert { ![string match "*rdb_last_bgsave*" $info] }
+        assert { ![string match "*master_repl_offset*" $info] }
+        assert { ![string match "*cluster_enabled*" $info] }
+    }
+}
+
+test "info command with one sub-section" {
+    set info [S 0 info cpu]
+    assert { [string match "*used_cpu_user*" $info] }
+    assert { ![string match "*sentinel_tilt*" $info] }
+    assert { ![string match "*redis_version*" $info] }
+
+    set info [S 0 info sentinel]
+    assert { [string match "*sentinel_tilt*" $info] }
+    assert { ![string match "*used_cpu_user*" $info] }
+    assert { ![string match "*redis_version*" $info] }
+}
+
+test "info command with multiple sub-sections" {
+    set info [S 0 info server sentinel replication]
+    assert { [string match "*redis_version*" $info] }
+    assert { [string match "*sentinel_tilt*" $info] }
+    assert { ![string match "*used_memory*" $info] }
+    assert { ![string match "*used_cpu_user*" $info] }
+
+    set info [S 0 info cpu all]
+    assert { [string match "*used_cpu_user*" $info] }
+    assert { [string match "*sentinel_tilt*" $info] }
+    assert { [string match "*redis_version*" $info] }
+    assert { ![string match "*used_memory*" $info] }
+    assert { ![string match "*master_repl_offset*" $info] }
+}