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Showing content from http://orthecreedence.github.io/cl-async/tcp-stream below:

TCP stream | Documentation | cl-async (Asynchronous operations for Common Lisp)

A TCP stream wraps a socket, which is returned by tcp-connect:

(let ((socket (tcp-connect "google.com" 80 ... :dont-drain-read-buffer t)))
  (make-instance 'async-io-stream :socket socket))

tcp-connect makes this a bit more convenient as well:

(tcp-connect "google.com" 80 ... :stream t)

The stream we just created is a normal lisp stream which can be operated on via close, read-sequence, write-sequence, etc. One caveat is that the stream does not block when pulling data from it, so reading from the stream should be triggered by the read-cb given to tcp-connect.

See the notes on buffer draining section for an explanation of the :dont-drain-read-buffer parameter.

The base async stream, extended by all other cl-async TCP streams.

The base output stream, can only be used to send data on a socket.

The base input stream, can only be used to recieve data on a socket.

Extends both async-output-stream and async-input-stream, and allows both reading and writing on the underlying socket.

Streams work by sucking the data out of the socket they are set up to wrap. Normally, when a read-cb fires on a socket, cl-async will drain the data received and put it into a byte array it passes to the read-cb.

In the case of streams, cl-async pushes the data onto the stream’s input buffer instead of passing the data to the read-cb directly. The stream is then passed as the second parameter to the read-cb (the first still being the socket object). This is what :dont-drain-read-buffer does for you. Note that if you specify :stream t then dont-drain-read-buffer is assumed to be T unless explicitely stated otherwise.

When the read-cb fires and dont-drain-read-buffer is T, the data param will always be the stream and the socket data can be read via read-sequence or similar. Note that the socket arg (the first arg) to the read-cb is still a socket.

(tcp-connect "musio.com" 80
  (lambda (sock stream)
    (let* ((seq (make-array 4096 :element-type '(unsigned-byte 8)))
           (num-bytes (read-sequence seq stream :end 4096)))
      (format t "~a" (babel:octets-to-string (subseq seq 0 num-bytes)))))
  (lambda (ev) (format t "ev: ~a~%" ev))
  :data (format nil "GET /~C~C" #\return #\newline)
  :stream t
  :read-timeout 5)

Note that you can write the socket returned by (tcp-connect ... :stream t) with write-sequence like any other stream.

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