libdill: Structured Concurrency for C

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NAME

ws_sendl - sends a WebSocket message

SYNOPSIS

#include <libdill.h>

int ws_sendl(
    int s,
    int flags,
    struct iolist* first,
    struct iolist* last,
    int64_t deadline);

DESCRIPTION

WARNING: This is experimental functionality and the API may change in the future.

WebSocket is a message-based protocol defined in RFC 6455. It can be used as a bidirectional communication channel for communication with a web server.

This function works very much like msendl except that it allows message type (text or binary) to be specified explicitly rather that using the type specified at attach time.

This function accepts a linked list of I/O buffers instead of a single buffer. Argument first points to the first item in the list, last points to the last buffer in the list. The list represents a single, fragmented message, not a list of multiple messages. Structure iolist has the following members:

void *iol_base;          /* Pointer to the buffer. */
size_t iol_len;          /* Size of the buffer. */
struct iolist *iol_next; /* Next buffer in the list. */
int iol_rsvd;            /* Reserved. Must be set to zero. */

When receiving, iol_base equal to NULL means that iol_len bytes should be skipped.

The function returns EINVAL error in the case the list is malformed:

• If last->iol_next is not NULL.
• If first and last don't belong to the same list.
• If there's a loop in the list.
• If iol_rsvd of any item is non-zero.

The list (but not the buffers themselves) can be temporarily modified while the function is in progress. However, once the function returns the list is guaranteed to be the same as before the call.

s: The socket handle.

flags: Type of message to send. Either WS_BINARY or WS_TEXT. This will override the type specified when attaching the socket.

first: Pointer to the first item of a linked list of I/O buffers.

last: Pointer to the last item of a linked list of I/O buffers.

deadline: A point in time when the operation should time out, in milliseconds. Use the now function to get your current point in time. 0 means immediate timeout, i.e., perform the operation if possible or return without blocking if not. -1 means no deadline, i.e., the call will block forever if the operation cannot be performed.

This function is not available if libdill is compiled with --disable-sockets option.

RETURN VALUE

In case of success the function returns 0. In case of error it returns -1 and sets errno to one of the values below.

ERRORS

• EBADF: Invalid handle.
• EBUSY: The handle is currently being used by a different coroutine.
• ECANCELED: Current coroutine was canceled.
• ECONNRESET: Broken connection.
• EINVAL: Invalid argument.
• ENOTSUP: The handle does not support this operation.
• EPIPE: Closed connection.
• ETIMEDOUT: Deadline was reached.

EXAMPLE

struct ipaddr addr;
ipaddr_remote(&addr, "www.example.org", 80, 0, -1);
int s = tcp_connect(&addr, -1);
s = ws_attach_client(s, "/", "www.example.org", WS_TEXT, -1);
ws_send(s, WS_TEXT, "Hello, world!", 13, -1);
int flags;
char buf[256];
ssize_t sz = ws_recv(s, &flags, buf, sizeof(buf), -1);
assert(flags & WS_TEXT);
s = ws_detach(s, -1);
tcp_close(s, -1);

SEE ALSO

mrecv(3) mrecvl(3) msend(3) msendl(3) now(3) ws_attach_client(3) ws_attach_client_mem(3) ws_attach_server(3) ws_attach_server_mem(3) ws_detach(3) ws_done(3) ws_recv(3) ws_recvl(3) ws_request_key(3) ws_response_key(3) ws_send(3) ws_status(3)