main/syscalls/socket_read.md

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# zx_socket_read

## Summary

Read data from a socket.

## Declaration

```c
#include <zircon/syscalls.h>

zx_status_t zx_socket_read(zx_handle_t handle,
                           uint32_t options,
                           void* buffer,
                           size_t buffer_size,
                           size_t* actual);
```

## Description

`zx_socket_read()` attempts to read *buffer_size* bytes into *buffer*. If
successful, the number of bytes actually read are return via
*actual*.

If a NULL *actual* is passed in, it will be ignored.

If the socket was created with `ZX_SOCKET_DATAGRAM`, this syscall reads
only the first available datagram in the socket (if one is present).
If *buffer* is too small for the datagram, then the read will be
truncated, and any remaining bytes in the datagram will be discarded.

Supported *options* are:

* `ZX_SOCKET_PEEK` to leave the message in the socket.

To determine how many bytes are available to read, use the `rx_buf_available`
field of the resulting `zx_info_socket_t`, which you can obtain using the
`ZX_INFO_SOCKET` topic for [`zx_object_get_info()`].

## Rights

*handle* must be of type `ZX_OBJ_TYPE_SOCKET` and have `ZX_RIGHT_READ`.

## Return value

`zx_socket_read()` returns `ZX_OK` on success, and writes into
*actual* (if non-NULL) the exact number of bytes read.

## Errors

`ZX_ERR_BAD_HANDLE`  *handle* is not a valid handle.

`ZX_ERR_BAD_STATE`  writing to *handle*'s peer has been disabled via
[`zx_socket_set_disposition()`] and no pending data remains on *handle*.

`ZX_ERR_WRONG_TYPE`  *handle* is not a socket handle.

`ZX_ERR_INVALID_ARGS` If any of *buffer* or *actual* are non-NULL
but invalid pointers, or if *buffer* is NULL, or if *options* is zero.

`ZX_ERR_ACCESS_DENIED`  *handle* does not have `ZX_RIGHT_READ`.

`ZX_ERR_SHOULD_WAIT`  The socket contained no data to read.

`ZX_ERR_PEER_CLOSED`  The other side of the socket is closed and no data is
readable.

## See also

 - [`zx_socket_create()`]
 - [`zx_socket_set_disposition()`]
 - [`zx_socket_write()`]

[`zx_object_get_info()`]: object_get_info.md
[`zx_socket_create()`]: socket_create.md
[`zx_socket_set_disposition()`]: socket_set_disposition.md
[`zx_socket_write()`]: socket_write.md