21.8. Function STREAM-ELEMENT-TYPE

21.8. Function `STREAM-ELEMENT-TYPE`
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21.8. Function `STREAM-ELEMENT-TYPE`

21.8.1. Binary input from *STANDARD-INPUT*

STREAM-ELEMENT-TYPE is SETFable. The STREAM-ELEMENT-TYPE of STREAMs created by the functions OPEN, EXT:MAKE-PIPE-INPUT-STREAM EXT:MAKE-PIPE-OUTPUT-STREAM, EXT:MAKE-PIPE-IO-STREAM, SOCKET:SOCKET-ACCEPT, SOCKET:SOCKET-CONNECT can be modified, if the old and the new STREAM-ELEMENT-TYPEs are either

both equivalent to CHARACTER or (UNSIGNED-BYTE 8) or (SIGNED-BYTE 8); or
both equivalent to (UNSIGNED-BYTE n) or (SIGNED-BYTE n), with the same n.

Functions STREAM-ELEMENT-TYPE and (SETF STREAM-ELEMENT-TYPE) are GENERIC-FUNCTIONs, see Chapter 30, Gray streams.

Warning

CLISP expects to be able to do CHARACTER i/o on standard streams like *TERMINAL-IO*, *STANDARD-OUTPUT*, *STANDARD-INPUT*, *ERROR-OUTPUT*, *QUERY-IO* et al, thus is is a very bad idea to change their STREAM-ELEMENT-TYPE even when you can. Use EXT:MAKE-STREAM instead, see Section 21.8.1, “Binary input from *STANDARD-INPUT*”.

21.8.1. Binary input from `STANDARD-INPUT`

Note that you cannot change STREAM-ELEMENT-TYPE for some built-in streams, such as terminal streams, which is normally the value of *TERMINAL-IO*. Since *STANDARD-INPUT* normally is a SYNONYM-STREAM pointing to *TERMINAL-IO*, you cannot use READ-BYTE on it.

Since CGI (Common Gateway Interface) provides the form data for METHOD="POST" on the stdin, and the server will not send you an end-of-stream on the end of the data, you will need to use (EXT:GETENV "CONTENT_LENGTH") to determine how much data you should read from stdin. CLISP will detect that stdin is not a terminal and create a regular FILE-STREAM which can be passed to (SETF STREAM-ELEMENT-TYPE). To test this functionality interactively, you will need to open the standard input in the binary mode:

(let ((buf (MAKE-ARRAY (PARSE-INTEGER (EXT:GETENV "CONTENT_LENGTH"))
                       :element-type '(UNSIGNED-BYTE 8))))
  (WITH-OPEN-STREAM (in (EXT:MAKE-STREAM :INPUT :ELEMENT-TYPE '(UNSIGNED-BYTE 8)))
    (READ-SEQUENCE buf in))
  buf)

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