add STRPOP (RedisLabsModules#12)

Includes test and documentation.

README.md

@@ -114,6 +114,15 @@ Credit: Meni Katz
 
 **Reply:** Integer, the length of the String after it was modified.
 
+## `STRPOP key`
+
+Gets the value at `key`, deletes `key`, then returns the value.
+It is equivalent to an atomic [GET](https://redis.io/commands/get) and [DEL](https://redis.io/commands/del).
+
+ * An error is returned if the key exists and does not hold a string.
+
+**Reply:** String, the value at `key` or NULL if `key` didn't exist.
+
 # rxhashes
 
 This module provides extended Redis Hashes commands.

src/rxstrings.c

@@ -463,6 +463,49 @@ int SetRangeRandCommand(RedisModuleCtx *ctx, RedisModuleString **argv,
   return REDISMODULE_OK;
 }
 
+/*
+* STRPOP key
+* Gets the value at key, deletes the key, then return the value.
+* Equivalent to an atomic GET and DEL.
+* An error is returned if there is a value stored that is not a string.
+* String Reply: the value of key, or nil if key does not exist.
+*/
+int StrPopCommand(RedisModuleCtx *ctx, RedisModuleString **argv, int argc) {
+  if (argc != 2) {
+    return RedisModule_WrongArity(ctx);
+  }
+  RedisModule_AutoMemory(ctx);
+
+  /* Obtain key */
+  RedisModuleKey *key =
+      RedisModule_OpenKey(ctx, argv[1], REDISMODULE_READ | REDISMODULE_WRITE);
+
+  if (RedisModule_KeyType(key) == REDISMODULE_KEYTYPE_EMPTY) {
+    RedisModule_ReplyWithNull(ctx);
+    return REDISMODULE_OK;
+  }
+
+  /* Key must be a string */
+  if (RedisModule_KeyType(key) != REDISMODULE_KEYTYPE_STRING) {
+    RedisModule_ReplyWithError(ctx, REDISMODULE_ERRORMSG_WRONGTYPE);
+    return REDISMODULE_ERR;
+  }
+
+  /* GET the string */
+  size_t dmaLen;
+  char* valPtr = RedisModule_StringDMA(key, &dmaLen, REDISMODULE_READ);
+  RedisModuleString* valStr = RedisModule_CreateString(ctx, valPtr, dmaLen);
+
+  /* DELete the key */
+  if (RedisModule_DeleteKey(key) != REDISMODULE_OK) {
+    RedisModule_ReplyWithError(ctx, "ERR DeleteKey failed");
+    return REDISMODULE_ERR;
+  }
+
+  RedisModule_ReplyWithString(ctx, valStr);
+  return REDISMODULE_OK;
+}
+
 int testCheckAnd(RedisModuleCtx *ctx) {
   RedisModuleCallReply *r;
 
@@ -549,6 +592,22 @@ int testSetRangeRand(RedisModuleCtx *ctx) {
   return 0;
 }
 
+int testStrPop(RedisModuleCtx *ctx) {
+  RedisModuleCallReply *r;
+
+  r = RedisModule_Call(ctx, "set", "cc", "foo", "abcdef");
+  RMUtil_AssertReplyEquals(r,"OK");
+  r = RedisModule_Call(ctx, "strpop", "c", "foo");
+  RMUtil_AssertReplyEquals(r,"abcdef");
+  r = RedisModule_Call(ctx, "exists", "c", "foo");
+  RMUtil_Assert(RedisModule_CallReplyInteger(r) == 0);
+  r = RedisModule_Call(ctx, "strpop", "c", "bar");
+  RMUtil_Assert(RedisModule_CallReplyType(r) == REDISMODULE_REPLY_NULL);
+  r = RedisModule_Call(ctx, "FLUSHALL", "");
+
+  return 0;
+}
+
 int TestModule(RedisModuleCtx *ctx, RedisModuleString **argv, int argc) {
   RedisModule_AutoMemory(ctx);
 
@@ -564,6 +623,7 @@ int TestModule(RedisModuleCtx *ctx, RedisModuleString **argv, int argc) {
   RMUtil_Test(testChop);
   RMUtil_Test(testPrepend);
   RMUtil_Test(testSetRangeRand);
+  RMUtil_Test(testStrPop);
 
   RedisModule_ReplyWithSimpleString(ctx, "PASS");
   return REDISMODULE_OK;
@@ -589,6 +649,10 @@ int RedisModule_OnLoad(RedisModuleCtx *ctx) {
                                 "write fast deny-oom", 1, 1,
                                 1) == REDISMODULE_ERR)
     return REDISMODULE_ERR;
+  if (RedisModule_CreateCommand(ctx, "strpop", StrPopCommand,
+                                "fast deny-oom", 1, 1,
+                                1) == REDISMODULE_ERR)
+    return REDISMODULE_ERR;
   if (RedisModule_CreateCommand(ctx, "rxstrings.test", TestModule, "write", 0,
                                 0, 0) == REDISMODULE_ERR)
     return REDISMODULE_ERR;