channel_read - read a message from a channel


#include <magenta/syscalls.h>

mx_status_t mx_channel_read(mx_handle_t handle, uint32_t options,
                            void* bytes, mx_handle_t* handles,
                            uint32_t num_bytes, uint32_t num_handles,
                            uint32_t* actual_bytes, uint32_t* actual_handles);


channel_read() attempts to read the first message from the channel specified by handle into the provided bytes and/or handles buffers.

The parameters num_bytes and num_handles are used to specify the size of the read buffers.

Channel messages may contain both byte data and handle payloads and may only be read in their entirety. Partial reads are not possible.

The bytes buffer is written before the handles buffer. In the event of overlap between these two buffers, the contents written to handles will overwrite the portion of bytes it overlaps.


channel_read() returns MX_OK on success, if actual_bytes and actual_handles (if non-NULL), contain the exact number of bytes and count of handles read.


MX_ERR_BAD_HANDLE handle is not a valid handle.

MX_ERR_WRONG_TYPE handle is not a channel handle.

MX_ERR_INVALID_ARGS If any of bytes, handles, actual_bytes, or actual_handles are non-NULL and an invalid pointer.

MX_ERR_ACCESS_DENIED handle does not have MX_RIGHT_READ.

MX_ERR_SHOULD_WAIT The channel contained no messages to read.

MX_ERR_PEER_CLOSED The other side of the channel is closed.

MX_ERR_NO_MEMORY (Temporary) Failure due to lack of memory.

MX_ERR_BUFFER_TOO_SMALL The provided bytes or handles buffers are too small (in which case, the minimum sizes necessary to receive the message will be written to actual_bytes and actual_handles, provided they are non-NULL). If options has MX_CHANNEL_READ_MAY_DISCARD set, then the message is discarded.


num_handles and actual_handles are counts of the number of elements in the handles array, not its size in bytes.


handle_close, handle_duplicate, handle_replace, object_wait_one, object_wait_many, channel_call, channel_create, channel_write.