From b7f2a1a217b5c5b7b0320bfe0511dfdf2e0eb174 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Viktor=20S=C3=B6derqvist?= <viktor.soderqvist@est.tech>
Date: Mon, 18 Oct 2021 21:21:19 +0200
Subject: [PATCH] Add RedisModule_KeyExists (#9600)

The LRU of the key is not touched. Locically expired keys are
logically not existing, so they're treated as such.
---
 src/module.c                  | 12 ++++++++++++
 src/redismodule.h             |  2 ++
 tests/modules/misc.c          |  9 +++++++++
 tests/unit/moduleapi/misc.tcl |  7 +++++++
 4 files changed, 30 insertions(+)

diff --git a/src/module.c b/src/module.c
index 0cdad7eac..9cf30938d 100644
--- a/src/module.c
+++ b/src/module.c
@@ -2707,6 +2707,17 @@ int RM_SelectDb(RedisModuleCtx *ctx, int newid) {
     return (retval == C_OK) ? REDISMODULE_OK : REDISMODULE_ERR;
 }
 
+/* Check if a key exists, without affecting its last access time.
+ *
+ * This is equivalent to calling RM_OpenKey with the mode REDISMODULE_READ |
+ * REDISMODULE_OPEN_KEY_NOTOUCH, then checking if NULL was returned and, if not,
+ * calling RM_CloseKey on the opened key.
+ */
+int RM_KeyExists(RedisModuleCtx *ctx, robj *keyname) {
+    robj *value = lookupKeyReadWithFlags(ctx->client->db, keyname, LOOKUP_NOTOUCH);
+    return (value != NULL);
+}
+
 /* Initialize a RedisModuleKey struct */
 static void moduleInitKey(RedisModuleKey *kp, RedisModuleCtx *ctx, robj *keyname, robj *value, int mode){
     kp->ctx = ctx;
@@ -10261,6 +10272,7 @@ void moduleRegisterCoreAPI(void) {
     REGISTER_API(ReplyWithLongDouble);
     REGISTER_API(GetSelectedDb);
     REGISTER_API(SelectDb);
+    REGISTER_API(KeyExists);
     REGISTER_API(OpenKey);
     REGISTER_API(CloseKey);
     REGISTER_API(KeyType);
diff --git a/src/redismodule.h b/src/redismodule.h
index 938bacc5c..85c963d58 100644
--- a/src/redismodule.h
+++ b/src/redismodule.h
@@ -610,6 +610,7 @@ REDISMODULE_API int (*RedisModule_WrongArity)(RedisModuleCtx *ctx) REDISMODULE_A
 REDISMODULE_API int (*RedisModule_ReplyWithLongLong)(RedisModuleCtx *ctx, long long ll) REDISMODULE_ATTR;
 REDISMODULE_API int (*RedisModule_GetSelectedDb)(RedisModuleCtx *ctx) REDISMODULE_ATTR;
 REDISMODULE_API int (*RedisModule_SelectDb)(RedisModuleCtx *ctx, int newid) REDISMODULE_ATTR;
+REDISMODULE_API int (*RedisModule_KeyExists)(RedisModuleCtx *ctx, RedisModuleString *keyname) REDISMODULE_ATTR;
 REDISMODULE_API void * (*RedisModule_OpenKey)(RedisModuleCtx *ctx, RedisModuleString *keyname, int mode) REDISMODULE_ATTR;
 REDISMODULE_API void (*RedisModule_CloseKey)(RedisModuleKey *kp) REDISMODULE_ATTR;
 REDISMODULE_API int (*RedisModule_KeyType)(RedisModuleKey *kp) REDISMODULE_ATTR;
@@ -953,6 +954,7 @@ static int RedisModule_Init(RedisModuleCtx *ctx, const char *name, int ver, int
     REDISMODULE_GET_API(ReplyWithLongDouble);
     REDISMODULE_GET_API(GetSelectedDb);
     REDISMODULE_GET_API(SelectDb);
+    REDISMODULE_GET_API(KeyExists);
     REDISMODULE_GET_API(OpenKey);
     REDISMODULE_GET_API(CloseKey);
     REDISMODULE_GET_API(KeyType);
diff --git a/tests/modules/misc.c b/tests/modules/misc.c
index 1c7c47a90..88039c6dd 100644
--- a/tests/modules/misc.c
+++ b/tests/modules/misc.c
@@ -122,6 +122,13 @@ int test_randomkey(RedisModuleCtx *ctx, RedisModuleString **argv, int argc)
     return REDISMODULE_OK;
 }
 
+int test_keyexists(RedisModuleCtx *ctx, RedisModuleString **argv, int argc) {
+    if (argc < 2) return RedisModule_WrongArity(ctx);
+    RedisModuleString *key = argv[1];
+    int exists = RedisModule_KeyExists(ctx, key);
+    return RedisModule_ReplyWithBool(ctx, exists);
+}
+
 RedisModuleKey *open_key_or_reply(RedisModuleCtx *ctx, RedisModuleString *keyname, int mode) {
     RedisModuleKey *key = RedisModule_OpenKey(ctx, keyname, mode);
     if (!key) {
@@ -306,6 +313,8 @@ int RedisModule_OnLoad(RedisModuleCtx *ctx, RedisModuleString **argv, int argc)
         return REDISMODULE_ERR;
     if (RedisModule_CreateCommand(ctx,"test.randomkey", test_randomkey,"",0,0,0) == REDISMODULE_ERR)
         return REDISMODULE_ERR;
+    if (RedisModule_CreateCommand(ctx,"test.keyexists", test_keyexists,"",1,1,1) == REDISMODULE_ERR)
+        return REDISMODULE_ERR;
     if (RedisModule_CreateCommand(ctx,"test.setlru", test_setlru,"",0,0,0) == REDISMODULE_ERR)
         return REDISMODULE_ERR;
     if (RedisModule_CreateCommand(ctx,"test.getlru", test_getlru,"",0,0,0) == REDISMODULE_ERR)
diff --git a/tests/unit/moduleapi/misc.tcl b/tests/unit/moduleapi/misc.tcl
index 3205b1c45..a74c89aec 100644
--- a/tests/unit/moduleapi/misc.tcl
+++ b/tests/unit/moduleapi/misc.tcl
@@ -40,6 +40,13 @@ start_server {tags {"modules"}} {
         assert_equal [r test.dbsize] 0
     }
 
+    test {test module keyexists} {
+        r set x foo
+        assert_equal 1 [r test.keyexists x]
+        r del x
+        assert_equal 0 [r test.keyexists x]
+    }
+
     test {test module lru api} {
         r config set maxmemory-policy allkeys-lru
         r set x foo