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Add section on errors to readme

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Pieter Noordhuis 2010-11-26 15:14:51 +01:00
parent 4eab917a24
commit e24023a46a
1 changed files with 37 additions and 11 deletions
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README.md
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@ -39,7 +39,8 @@ 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 an the connection is in
an error state. The field `errstr` will contain a string with a description of
the error. After trying to connect to Redis using `redisConnect` you should
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:
redisContext *c = redisConnect("127.0.0.1", 6379);
@ -77,8 +78,8 @@ anywhere in an argument:
### Using replies
The return value of `redisCommand` holds a reply when the command was
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.
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.
@ -167,7 +168,7 @@ to the `redisCommand` family, apart from not returning a reply:
After calling either function one or more times, `redisGetReply` can be used to receive the
subsequent replies. The return value for this function is either `REDIS_OK` or `REDIS_ERR`, where
the latter means an error occurred while reading a reply. Just as with the other commands,
the `error` field in the context can be used to find out what the cause of this error is.
the `err` field in the context can be used to find out what the cause of this error is.
The following examples shows a simple pipeline (resulting in only a single call to `write(2)` and
a single call to `write(2)`):
@ -185,10 +186,35 @@ This API can also be used to implement a blocking subscriber:
reply = redisCommand(context,"SUBSCRIBE foo");
freeReplyObject(reply);
while(redisGetReply(context,&reply) == REDIS_OK) {
// consume message
freeReplyObject(reply);
// consume message
freeReplyObject(reply);
}
### Errors
When a function call is not successful, depending on the function either `NULL` or `REDIS_ERR` is
returned. The `err` field inside the context will be non-zero and set to one of the
following constants:
* **`REDIS_ERR_IO`**:
There was an I/O error while creating the connection, trying to write
to the socket or read from the socket. If you included `errno.h` in your
application, you can use the global `errno` variable to find out what is
wrong.
* **`REDIS_ERR_EOF`**:
The server closed the connection which resulted in an empty read.
* **`REDIS_ERR_PROTOCOL`**:
There was an error while parsing the protocol.
* **`REDIS_ERR_OTHER`**:
Any other error. Currently, it is only used when a specified hostname to connect
to cannot be resolved.
In every case, the `errstr` field in the context will be set to hold a string representation
of the error.
## Asynchronous API
Hiredis comes with an asynchronous API that works easily with any event library.
@ -198,15 +224,15 @@ and [libevent](http://monkey.org/~provos/libevent/).
### Connecting
The function `redisAsyncConnect` can be used to establish a non-blocking connection to
Redis. It returns a pointer to the newly created `redisAsyncContext` struct. The `error` field
Redis. It returns a pointer to the newly created `redisAsyncContext` struct. The `err` field
should be checked after creation to see if there were errors creating the connection.
Because the connection that will be created is non-blocking, the kernel is not able to
instantly return if the specified host and port is able to accept a connection.
redisAsyncContext *c = redisAsyncConnect("127.0.0.1", 6379);
if (c->error != NULL) {
printf("Error: %s\n", c->error);
// handle error
if (c->err) {
printf("Error: %s\n", c->errstr);
// handle error
}
The asynchronous context can hold a disconnect callback function that is called when the
@ -216,7 +242,7 @@ have the following prototype:
void(const redisAsyncContext *c, int status);
On a disconnect, the `status` argument is set to `REDIS_OK` when disconnection was initiated by the
user, or `REDIS_ERR` when the disconnection was caused by an error. When it is `REDIS_ERR`, the `error`
user, or `REDIS_ERR` when the disconnection was caused by an error. When it is `REDIS_ERR`, the `err`
field in the context can be accessed to find out the cause of the error.
The context object is always free'd after the disconnect callback fired. When a reconnect is needed,