uv_stream_t — Stream handle

Stream handles provide an abstraction of a duplex communication channel. uv_stream_t is an abstract type, libuv provides 3 stream implementations in the form of uv_tcp_t, uv_pipe_t and uv_tty_t.

Data types


Stream handle type.


Connect request type.


Shutdown request type.


Write request type. Careful attention must be paid when reusing objects of this type. When a stream is in non-blocking mode, write requests sent with uv_write will be queued. Reusing objects at this point is undefined behaviour. It is safe to reuse the uv_write_t object only after the callback passed to uv_write is fired.

void (*uv_read_cb)(uv_stream_t* stream, ssize_t nread, const uv_buf_t* buf)

Callback called when data was read on a stream.

nread is > 0 if there is data available or < 0 on error. When we’ve reached EOF, nread will be set to UV_EOF. When nread < 0, the buf parameter might not point to a valid buffer; in that case buf.len and buf.base are both set to 0.


nread might be 0, which does not indicate an error or EOF. This is equivalent to EAGAIN or EWOULDBLOCK under read(2).

The callee is responsible for stopping/closing the stream when an error happens by calling uv_read_stop() or uv_close(). Trying to read from the stream again is undefined.

The callee is responsible for freeing the buffer, libuv does not reuse it. The buffer may be a null buffer (where buf->base == NULL and buf->len == 0) on error.

void (*uv_write_cb)(uv_write_t* req, int status)

Callback called after data was written on a stream. status will be 0 in case of success, < 0 otherwise.

void (*uv_connect_cb)(uv_connect_t* req, int status)

Callback called after a connection started by uv_connect() is done. status will be 0 in case of success, < 0 otherwise.

void (*uv_shutdown_cb)(uv_shutdown_t* req, int status)

Callback called after a shutdown request has been completed. status will be 0 in case of success, < 0 otherwise.

void (*uv_connection_cb)(uv_stream_t* server, int status)

Callback called when a stream server has received an incoming connection. The user can accept the connection by calling uv_accept(). status will be 0 in case of success, < 0 otherwise.

Public members

size_t uv_stream_t.write_queue_size

Contains the amount of queued bytes waiting to be sent. Readonly.

uv_stream_t* uv_connect_t.handle

Pointer to the stream where this connection request is running.

uv_stream_t* uv_shutdown_t.handle

Pointer to the stream where this shutdown request is running.

uv_stream_t* uv_write_t.handle

Pointer to the stream where this write request is running.

uv_stream_t* uv_write_t.send_handle

Pointer to the stream being sent using this write request.

See also

The uv_handle_t members also apply.


int uv_shutdown(uv_shutdown_t* req, uv_stream_t* handle, uv_shutdown_cb cb)

Shutdown the outgoing (write) side of a duplex stream. It waits for pending write requests to complete. The handle should refer to a initialized stream. req should be an uninitialized shutdown request struct. The cb is called after shutdown is complete.

int uv_listen(uv_stream_t* stream, int backlog, uv_connection_cb cb)

Start listening for incoming connections. backlog indicates the number of connections the kernel might queue, same as listen(2). When a new incoming connection is received the uv_connection_cb callback is called.

int uv_accept(uv_stream_t* server, uv_stream_t* client)

This call is used in conjunction with uv_listen() to accept incoming connections. Call this function after receiving a uv_connection_cb to accept the connection. Before calling this function the client handle must be initialized. < 0 return value indicates an error.

When the uv_connection_cb callback is called it is guaranteed that this function will complete successfully the first time. If you attempt to use it more than once, it may fail. It is suggested to only call this function once per uv_connection_cb call.


server and client must be handles running on the same loop.

int uv_read_start(uv_stream_t* stream, uv_alloc_cb alloc_cb, uv_read_cb read_cb)

Read data from an incoming stream. The uv_read_cb callback will be made several times until there is no more data to read or uv_read_stop() is called.

Changed in version 1.38.0: uv_read_start() now consistently returns UV_EALREADY when called twice, and UV_EINVAL when the stream is closing. With older libuv versions, it returns UV_EALREADY on Windows but not UNIX, and UV_EINVAL on UNIX but not Windows.

int uv_read_stop(uv_stream_t*)

Stop reading data from the stream. The uv_read_cb callback will no longer be called.

This function is idempotent and may be safely called on a stopped stream.

int uv_write(uv_write_t* req, uv_stream_t* handle, const uv_buf_t bufs[], unsigned int nbufs, uv_write_cb cb)

Write data to stream. Buffers are written in order. Example:

void cb(uv_write_t* req, int status) {
    /* Logic which handles the write result */

uv_buf_t a[] = {
    { .base = "1", .len = 1 },
    { .base = "2", .len = 1 }

uv_buf_t b[] = {
    { .base = "3", .len = 1 },
    { .base = "4", .len = 1 }

uv_write_t req1;
uv_write_t req2;

/* writes "1234" */
uv_write(&req1, stream, a, 2, cb);
uv_write(&req2, stream, b, 2, cb);


The memory pointed to by the buffers must remain valid until the callback gets called. This also holds for uv_write2().

int uv_write2(uv_write_t* req, uv_stream_t* handle, const uv_buf_t bufs[], unsigned int nbufs, uv_stream_t* send_handle, uv_write_cb cb)

Extended write function for sending handles over a pipe. The pipe must be initialized with ipc == 1.


send_handle must be a TCP socket or pipe, which is a server or a connection (listening or connected state). Bound sockets or pipes will be assumed to be servers.

int uv_try_write(uv_stream_t* handle, const uv_buf_t bufs[], unsigned int nbufs)

Same as uv_write(), but won’t queue a write request if it can’t be completed immediately.

Will return either:

  • > 0: number of bytes written (can be less than the supplied buffer size).
  • < 0: negative error code (UV_EAGAIN is returned if no data can be sent immediately).
int uv_is_readable(const uv_stream_t* handle)

Returns 1 if the stream is readable, 0 otherwise.

int uv_is_writable(const uv_stream_t* handle)

Returns 1 if the stream is writable, 0 otherwise.

int uv_stream_set_blocking(uv_stream_t* handle, int blocking)

Enable or disable blocking mode for a stream.

When blocking mode is enabled all writes complete synchronously. The interface remains unchanged otherwise, e.g. completion or failure of the operation will still be reported through a callback which is made asynchronously.


Relying too much on this API is not recommended. It is likely to change significantly in the future.

Currently only works on Windows for uv_pipe_t handles. On UNIX platforms, all uv_stream_t handles are supported.

Also libuv currently makes no ordering guarantee when the blocking mode is changed after write requests have already been submitted. Therefore it is recommended to set the blocking mode immediately after opening or creating the stream.

Changed in version 1.4.0: UNIX implementation added.

size_t uv_stream_get_write_queue_size(const uv_stream_t* stream)

Returns stream->write_queue_size.

New in version 1.19.0.

See also

The uv_handle_t API functions also apply.