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**This Readme reflects the latest changed in the master branch. See [v0.13.3](https://github.com/redis/hiredis/tree/v0.13.3) for the Readme and documentation for the latest release.**
# HIREDIS
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
at the same time it uses a high level printf-alike API in order to make it
much higher level than otherwise suggested by its minimal code base and the
lack of explicit bindings for every Redis command.
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.
The library comes with multiple APIs. There is the
*synchronous API*, the *asynchronous API* and the *reply parsing API*.
## Upgrading to `1.0.0`
Version 1.0.0 marks a stable release of hiredis.
It includes some minor breaking changes, mostly to make the exposed API more uniform and self-explanatory.
It also bundles the updated `sds` library, to sync up with upstream and Redis.
For most applications a recompile against the new hiredis should be enough.
For code changes see the [Changelog](CHANGELOG.md).
## Upgrading from `<0.9.0`
Version 0.9.0 is a major overhaul of hiredis in every aspect. However, upgrading existing
code using hiredis should not be a big pain. The key thing to keep in mind when
upgrading is that hiredis >= 0.9.0 uses a `redisContext*` to keep state, in contrast to
the stateless 0.0.1 that only has a file descriptor to work with.
## Synchronous API
To consume the synchronous API, there are only a few function calls that need to be introduced:
```c
redisContext *redisConnect(const char *ip, int port);
void *redisCommand(redisContext *c, const char *format, ...);
void freeReplyObject(void *reply);
```
### Connecting
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 integer `err` field that is non-zero when the connection is in
an error state. The field `errstr` will contain a string with a description of
the error. More information on errors can be found in the **Errors** section.
After trying to connect to Redis using `redisConnect` you should
check the `err` field to see if establishing the connection was successful:
```c
redisContext *c = redisConnect("127.0.0.1", 6379);
if (c == NULL || c->err) {
if (c) {
printf("Error: %s\n", c->errstr);
// handle error
} else {
printf("Can't allocate redis context\n");
}
}
```
*Note: A `redisContext` is not thread-safe.*
### Sending commands
There are several ways to issue commands to Redis. The first that will be introduced is
`redisCommand`. This function takes a format similar to printf. In the simplest form,
it is used like this:
```c
reply = redisCommand(context, "SET foo bar");
```
The specifier `%s` interpolates a string in the command, and uses `strlen` to
determine the length of the string:
```c
reply = redisCommand(context, "SET foo %s", value);
```
When you need to pass binary safe strings in a command, the `%b` specifier can be
used. Together with a pointer to the string, it requires a `size_t` length argument
of the string:
```c
reply = redisCommand(context, "SET foo %b", value, (size_t) valuelen);
```
Internally, Hiredis splits the command in different arguments and will
convert it to the protocol used to communicate with Redis.
One or more spaces separates arguments, so you can use the specifiers
anywhere in an argument:
```c
reply = redisCommand(context, "SET key:%s %s", myid, value);
```
### Using replies
The return value of `redisCommand` holds a reply when the command was
successfully executed. When an error occurs, the return value is `NULL` and
the `err` field in the context will be set (see section on **Errors**).
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`**:
* The command replied with an error. The error string can be accessed identical to `REDIS_REPLY_STATUS`.
* **`REDIS_REPLY_INTEGER`**:
* The command replied with an integer. The integer value can be accessed using the
`reply->integer` field of type `long long`.
* **`REDIS_REPLY_NIL`**:
* The command replied with a **nil** object. There is no data to access.
* **`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->element[..index..]`.
Redis may reply with nested arrays but this is fully supported.
Replies should be freed using the `freeReplyObject()` function.
Note that this function will take care of freeing sub-reply objects
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).
**Important:** the current version of hiredis (0.10.0) frees replies when the
asynchronous API is used. This means you should not call `freeReplyObject` when
you use this API. The reply is cleaned up by hiredis _after_ the callback
returns. This behavior will probably change in future releases, so make sure to
keep an eye on the changelog when upgrading (see issue #39).
### Cleaning up
To disconnect and free the context the following function can be used:
```c
void redisFree(redisContext *c);
```
This function immediately closes the socket and then frees the allocations done in
creating the context.
### Sending commands (cont'd)
Together with `redisCommand`, the function `redisCommandArgv` can be used to issue commands.
It has the following prototype:
```c
void *redisCommandArgv(redisContext *c, int argc, const char **argv, const size_t *argvlen);
```
It takes the number of arguments `argc`, an array of strings `argv` and the lengths of the
arguments `argvlen`. For convenience, `argvlen` may be set to `NULL` and the function will
use `strlen(3)` on every argument to determine its length. Obviously, when any of the arguments
need to be binary safe, the entire array of lengths `argvlen` should be provided.
The return value has the same semantic as `redisCommand`.
### Pipelining
To explain how Hiredis supports pipelining in a blocking connection, there needs to be
understanding of the internal execution flow.
When any of the functions in the `redisCommand` family is called, Hiredis first formats the
command according to the Redis protocol. The formatted command is then put in the output buffer
of the context. This output buffer is dynamic, so it can hold any number of commands.
After the command is put in the output buffer, `redisGetReply` is called. This function has the
following two execution paths:
1. The input buffer is non-empty:
* Try to parse a single reply from the input buffer and return it
* If no reply could be parsed, continue at *2*
2. The input buffer is empty:
* Write the **entire** output buffer to