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HIREDIS OVERVIEW # HIREDIS
----------------
Hiredis is a minimalistic C client library for the Redis Database. Hiredis is a minimalistic C client library for the [Redis](http://redis.io/) database.
It is minimalistic because it just adds minimal support for the protocol, but It is minimalistic because it just adds minimal support for the protocol, but
at the same time it uses an high level printf-alike API in order to make it at the same time it uses an high level printf-alike API in order to make it
much higher level than otherwise suggested by its minimal code base and the much higher level than otherwise suggested by its minimal code base and the
lack of explicit bindings for every Redis command. lack of explicit bindings for every Redis command.
Hiredis only supports the new Redis protocol, so you can use it with any Apart from supporting sending commands and receiving replies, it comes with
a reply parser that is decoupled from the I/O layer. It
is a stream parser designed for easy reusability, which can for instance be used
in higher level language bindings for efficient reply parsing.
Hiredis only supports the binary-safe Redis protocol, so you can use it with any
Redis version >= 1.2.0. Redis version >= 1.2.0.
HIREDIS API The library comes with multiple APIs. There is the
----------- *synchronous API*, the *asynchronous API* and the *reply parsing API*.
Hiredis exports only three function calls: ## SYNCHRONOUS API
redisReply *redisConnect(int *fd, char *ip, int port); To consume the synchronous API, there are only a few function calls that need to be introduced:
redisReply *redisCommand(int fd, char *format, ...);
void freeReplyObject(redisReply *r);
The first function is used in order to create a connection to the Redis server: redisContext *redisConnect(const char *ip, int port);
void *redisCommand(redisContext *c, const char *format, ...);
void freeReplyObject(void *reply);
redisReply *reply; ### Connecting
int fd;
reply = redisConnect(&fd,"127.0.0.1",6379); The function `redisConnect` is used to create a so-called `redisContext`. The context is where
Hiredis holds state for a connection. The `redisContext` struct has an `error` field that is
non-NULL when the connection is in an error state. It contains a string with a textual
representation of the error. After trying to connect to Redis using `redisConnect` you should
check the `error` field to see if establishing the connection was successful:
to test for connection errors all it is needed to do is checking if reply redisContext *c = redisConnect("127.0.0.1", 6379);
is not NULL: if (c->error != NULL) {
printf("Error: %s\n", c->error);
if (reply != NULL) { // handle error
printf("Connection error: %s\n", reply->reply);
freeReplyObject(reply);
exit(1);
} }
When a reply object returns an error, the reply->type is set to the value ### Sending commands
`REDIS_REPLY_ERROR`, and reply->reply points to a C string with the description
of the error.
In the above example we don't check for reply->type as `redisConnect()` can There are several ways to issue commands to Redis. The first that will be introduced is
only return `NULL` or a reply object that is actually an error. `redisCommand`. This function takes a format similar to printf. In the simplest form,
it is used like this:
As you can see `redisConnect()` will just set (by reference) the `fd` variable reply = redisCommand(context, "SET foo bar");
to the file descriptor of the open socket connected to our Redis server.
Calls to `redisCommand()` will require this file descriptor as first argument. The specifier `%s` interpolates a string in the command, and uses `strlen` to
determine the length of the string:
SENDING COMMANDS reply = redisCommand(context, "SET foo %s", value);
----------------
Commands are sent using a printf-alike format. In the simplest form it is When you need to pass binary safe strings in a command, the `%b` specifier can be
like that: used. Together with a pointer to the string, it requires a `size_t` length argument
of the string:
reply = redisCommand("SET foo bar"); reply = redisCommand(context, "SET foo %b", value, valuelen);
But you can use "%s" and "%b" format specifiers to create commands in a Internally, Hiredis splits the command in different arguments and will
printf-alike fashion: convert it to the protocol used to communicate with Redis.
One or more spaces separates arguments, so you can use the specifiers
reply = redisComand("SET foo %s", somevalue); anywhere in an argument:
If your arguments are binary safe, you can use "%b" that receives the pointer
to the buffer and a size_t integer with the length of the buffer.
reply = redisCommand("SET %s %b", "foo", somevalue, somevalue_length);
Internally Hiredis will split the command in different arguments and will
convert it to the actual protocol used to communicate with Redis.
Every space will separate arguments, so you can use interpolation.
The following example is valid:
reply = redisCommand("SET key:%s %s", myid, value); reply = redisCommand("SET key:%s %s", myid, value);
USING REPLIES ### Using replies
-------------
`redisCommand()` returns a reply object. In order to use this object you The return value of `redisCommand` holds a reply when the command was
need to test the reply->type field, that can be one of the following types: successfully executed. When the return value is `NULL`, the `error` field
in the context can be used to find out what was the cause of failure.
Once an error is returned the context cannot be reused and you should set up
a new connection.
The standard replies that `redisCommand` are of the type `redisReply`. The
`type` field in the `redisReply` should be used to test what kind of reply
was received:
* `REDIS_REPLY_STATUS`:
The command replied with a status reply. The status string can be accessed using `reply->str`.
The length of this string can be accessed using `reply->len`.
* `REDIS_REPLY_ERROR`: * `REDIS_REPLY_ERROR`:
The command returned an error string, that can be read accessing to The command replied with an error. The error string can be accessed identical to `REDIS_REPLY_STATUS`.
the reply->reply field.
* `REDIS_REPLY_STRING`:
The command returned a string, that can be read accessing to the
reply->reply field. The string is always null-terminated, but when you
need to work with binary-safe strings you can obtain the exact length
of the reply with: `sdslen(reply->reply)`.
* `REDIS_REPLY_ARRAY`:
The command returned an array of reply->elements elements.
Every element is a redisReply object, stored at redis->element[..index..]
Redis may reply with nested arrays but this is fully supported.
* `REDIS_REPLY_INTEGER`: * `REDIS_REPLY_INTEGER`:
The command replies with an integer. It's possible to access this integer The command replied with an integer. The integer value can be accessed using the
using the reply->integer field that is of type "long long". `reply->integer` field of type `long long`.
* `REDIS_REPLY_NIL`: * `REDIS_REPLY_NIL`:
The command replies with a NIL special object. There is no data to access. The command replied with a **nil** object. There is no data to access.
FREEING REPLIES * `REDIS_REPLY_STRING`:
--------------- A bulk (string) reply. The value of the reply can be accessed using `reply->str`.
The length of this string can be accessed using `reply->len`.
* `REDIS_REPLY_ARRAY`:
A multi bulk reply. The number of elements in the multi bulk reply is stored in
`reply->elements`. Every element in the multi bulk reply is a `redisReply` object as well
and can be accessed via `reply->elements[..index..]`.
Redis may reply with nested arrays but this is fully supported.
Replies should be freed using the `freeReplyObject()` function. Replies should be freed using the `freeReplyObject()` function.
Note that this function will take care of freeing sub-replies objects Note that this function will take care of freeing sub-replies objects
contained in arrays and nested arrays, so there is no need for the user to contained in arrays and nested arrays, so there is no need for the user to
free the sub replies (it is actually harmful and will corrupt the memory). free the sub replies (it is actually harmful and will corrupt the memory).
AUHTOR ## AUTHORS
------
Hiredis was written by Salvatore Sanfilippo (antirez at gmail) and is Hiredis was written by Salvatore Sanfilippo (antirez at gmail) and
released under the BSD license. Pieter Noordhuis (pcnoordhuis at gmail) and is released under the BSD license.