Implement substr command (#212)

The PR implements the SUBSTR command, although it's deprecated it's still available.

The SUBSTR command is a clone of the GETRANGE command, tests have been duplicated and adapted as needed.

Author: danielealbano

src/module/redis/command/module_redis_command_substr.c

@@ -0,0 +1,106 @@
+/**
+ * Copyright (C) 2018-2022 Daniele Salvatore Albano
+ * All rights reserved.
+ *
+ * This software may be modified and distributed under the terms
+ * of the BSD license.  See the LICENSE file for details.
+ **/
+
+#include <stdint.h>
+#include <stdbool.h>
+#include <stddef.h>
+#include <string.h>
+#include <strings.h>
+#include <arpa/inet.h>
+#include <assert.h>
+
+#include "misc.h"
+#include "exttypes.h"
+#include "log/log.h"
+#include "clock.h"
+#include "spinlock.h"
+#include "data_structures/small_circular_queue/small_circular_queue.h"
+#include "data_structures/double_linked_list/double_linked_list.h"
+#include "data_structures/queue_mpmc/queue_mpmc.h"
+#include "slab_allocator.h"
+#include "data_structures/hashtable/mcmp/hashtable.h"
+#include "data_structures/hashtable/mcmp/hashtable_op_get.h"
+#include "data_structures/hashtable/spsc/hashtable_spsc.h"
+#include "protocol/redis/protocol_redis.h"
+#include "protocol/redis/protocol_redis_reader.h"
+#include "protocol/redis/protocol_redis_writer.h"
+#include "module/module.h"
+#include "network/io/network_io_common.h"
+#include "config.h"
+#include "fiber.h"
+#include "network/channel/network_channel.h"
+#include "storage/io/storage_io_common.h"
+#include "storage/channel/storage_channel.h"
+#include "storage/db/storage_db.h"
+#include "module/redis/module_redis.h"
+#include "module/redis/module_redis_connection.h"
+#include "module/redis/module_redis_command.h"
+#include "network/network.h"
+#include "worker/worker_stats.h"
+#include "worker/worker_context.h"
+
+#define TAG "module_redis_command_substr"
+
+MODULE_REDIS_COMMAND_FUNCPTR_COMMAND_END(substr) {
+    bool return_res = false;
+    storage_db_entry_index_t *entry_index = NULL;
+    module_redis_command_substr_context_t *context = connection_context->command.context;
+
+    entry_index = storage_db_get_entry_index_for_read(
+            connection_context->db,
+            context->key.value.key,
+            context->key.value.length);
+
+    if (unlikely(!entry_index)) {
+        return_res = module_redis_connection_send_string_null(connection_context);
+        goto end;
+    }
+
+    off_t range_start = context->start.value;
+    off_t range_end = context->end.value;
+
+    if (range_start < 0) {
+        range_start += (off_t)entry_index->value->size;
+    }
+
+    if (range_end < 0) {
+        range_end += (off_t)entry_index->value->size;
+    }
+
+    if (unlikely(range_end < range_start)) {
+        return_res = module_redis_connection_send_string(connection_context, "", 0);
+        goto end;
+    }
+
+    off_t range_length = range_end - range_start + 1;
+
+    if (unlikely(range_start > entry_index->value->size || range_length <= 0)) {
+        return_res = module_redis_connection_send_string(connection_context, "", 0);
+        goto end;
+    }
+
+    if (unlikely(range_start + range_length > entry_index->value->size)) {
+        range_length = (off_t)entry_index->value->size - range_start;
+    }
+
+    return_res = module_redis_command_stream_entry_range(
+            connection_context->network_channel,
+            connection_context->db,
+            entry_index,
+            range_start,
+            range_length);
+
+end:
+
+    if (likely(entry_index)) {
+        storage_db_entry_index_status_decrease_readers_counter(entry_index, NULL);
+        entry_index = NULL;
+    }
+
+    return return_res;
+}