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The socket stream class.





A socket handle.


One of :input , :output , or :io .


An element type.


A positive number or nil .




The socket-stream class implements a buffered stream connected to a socket. The socket handle, specified by :socket , and the direction, specified by :direction , must be passed for a meaningful stream to be constructed. Common Lisp input functions such as read-char will see end-of-file if the other end of the socket is closed.

The :element-type keyword determines the expected element type of the stream traffic. However, stream input and output functions for character and binary data all work in the obvious way on a socket-stream with element-type base-char , (unsigned-byte 8) or (signed-byte 8) . For example, read-sequence can be called with a string buffer and a binary socket-stream : the character data is constructed from the input as if by code-char . Similarly write-sequence can be called with a string buffer and a binary socket-stream : the output is converted from the character data as if by char-code . All standard stream I/O functions have this flexibility. Also, 8-bit binary data can be read and written to a base-char socket-stream .

The :read-timeout initarg specifies the read-timeout in seconds, or is nil , meaning there are no timeouts during reads (this is the default).

The read-timeout property is intended for use when a socket connection might hang during a call to any Common Lisp input function. The read-timeout can be set by make-instance or by open-tcp-stream. It can also be modified by (setf stream:stream-read-timeout) . When read-timeout is nil , there is no timeout during reads and the call may hang. When read-timeout is not nil , and there is no input from the socket for more than read-timeout seconds, any reading function returns end-of-file . The read-timeout does not limit the time inside read , but the time between successful extractions of data from the socket. Therefore, if the reading needs several rounds it may take longer than read-timeout .

Using (setf stream:stream-read-timeout) on the stream while it is inside a read function has undefined effects. However, the setf function can be used between calls to read functions. The read-timeout property of a stream can be read by (stream:stream-read-timeout stream)


The following makes a bidirectional stream connected to a socket specified by handle .

(make-instance 'comm:socket-stream
               :socket handle
               :direction :io
               :element-type 'base-char)

This example creates a socket stream with a read-timeout:

(make-instance 'comm:socket-stream
               :direction :input
               :read-timeout 42)

The following form illustrates character I/O in a binary socket-stream :

(with-open-stream (x 
                    "localhost" 80
                    :element-type '(unsigned-byte 8)))
  (write-sequence (format nil "GET / HTTP/1.0~%~%") x)
  (force-output x)
  (let ((res (make-array 20 :element-type 'base-char)))
    (values (read-sequence res x) res)))

The following form illustrates binary I/O in a base-char socket-stream :

(with-open-stream (x 
                    "localhost" 80
                    :element-type 'base-char))
   (map '(simple-array (unsigned-byte 8) 1)
        (format nil "GET / HTTP/1.0~%~%"))
  (force-output x)
  (let ((res (make-array 20 
                         '(unsigned-byte 8))))
    (values (read-sequence res x) 
            (map 'string 'code-char res))))
See also


LispWorks Reference Manual - 25 Jul 2003

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