From 9204a9b2c2f6eb59767ab0bddcde62c75e8c20b0 Mon Sep 17 00:00:00 2001
From: Valentino Geron <valentino@redislabs.com>
Date: Thu, 20 Aug 2020 18:48:09 +0300
Subject: [PATCH] Fix LPOS command when RANK is greater than matches

When calling to LPOS command when RANK is higher than matches,
the return value is non valid response. For example:
```
LPUSH l a
:1
LPOS l b RANK 5 COUNT 10
*-4
```
It may break client-side parser.

Now, we count how many replies were replied in the array.
```
LPUSH l a
:1
LPOS l b RANK 5 COUNT 10
*0
```
---
 src/t_list.c             | 5 +++--
 tests/unit/type/list.tcl | 6 ++++++
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/src/t_list.c b/src/t_list.c
index 7737da771..ecf09cd94 100644
--- a/src/t_list.c
+++ b/src/t_list.c
@@ -571,13 +571,14 @@ void lposCommand(client *c) {
     li = listTypeInitIterator(o,direction == LIST_HEAD ? -1 : 0,direction);
     listTypeEntry entry;
     long llen = listTypeLength(o);
-    long index = 0, matches = 0, matchindex = -1;
+    long index = 0, matches = 0, matchindex = -1, arraylen = 0;
     while (listTypeNext(li,&entry) && (maxlen == 0 || index < maxlen)) {
         if (listTypeEqual(&entry,ele)) {
             matches++;
             matchindex = (direction == LIST_TAIL) ? index : llen - index - 1;
             if (matches >= rank) {
                 if (arraylenptr) {
+                    arraylen++;
                     addReplyLongLong(c,matchindex);
                     if (count && matches-rank+1 >= count) break;
                 } else {
@@ -593,7 +594,7 @@ void lposCommand(client *c) {
     /* Reply to the client. Note that arraylenptr is not NULL only if
      * the COUNT option was selected. */
     if (arraylenptr != NULL) {
-        setDeferredArrayLen(c,arraylenptr,matches-rank+1);
+        setDeferredArrayLen(c,arraylenptr,arraylen);
     } else {
         if (matchindex != -1)
             addReplyLongLong(c,matchindex);
diff --git a/tests/unit/type/list.tcl b/tests/unit/type/list.tcl
index 0e39d7d95..5ea2b9cd1 100644
--- a/tests/unit/type/list.tcl
+++ b/tests/unit/type/list.tcl
@@ -50,6 +50,12 @@ start_server {
         assert {[r LPOS mylist c COUNT 0 MAXLEN 7 RANK 2] == {6}}
     }
 
+    test {LPOS when RANK is greater than matches} {
+        r DEL mylist
+        r LPUSH l a
+        assert {[r LPOS mylist b COUNT 10 RANK 5] eq {}}
+    }
+
     test {LPUSH, RPUSH, LLENGTH, LINDEX, LPOP - ziplist} {
         # first lpush then rpush
         assert_equal 1 [r lpush myziplist1 aa]