Clarifications and fixes for set-port-buffering.

doc/scsh-manual/syscalls.tex

@@ -957,6 +957,12 @@ this reason, all shells, including sh, csh, and scsh, read stdin unbuffered.
 Applications that can tolerate buffered input on stdin can reset
 \ex{(current-input-port)} to block buffering for higher performance.
 
+\note{So support \texttt{peek-char} a Scheme implementation has to
+  maintain a buffer for all input ports. In scsh, for ``unbuffered''
+  input ports the buffer size is one. As you cannot request less then
+  one character there is no unrequested reading so this can still be
+  called ``unbuffered input''.}
+
 \begin{defundesc}{set-port-buffering}{port policy [size]}\undefined
 This procedure allows the programmer to assign a particular I/O buffering
 policy to a port, and to choose the size of the associated buffer.
@@ -966,7 +972,7 @@ There are three buffering policies that may be chosen:
         \begin{tabular}{l@{\qquad}l}
         \ex{bufpol/block} & General block buffering (general default) \\
         \ex{bufpol/line}  & Line buffering (tty default) \\
-        \ex{bufpol/none}  & Direct I/O---no buffering
+        \ex{bufpol/none}  & Direct I/O---no buffering\footnote{But see the note above}
         \end{tabular}
         \end{inset}
 The line buffering policy flushes output whenever a newline is output;
@@ -975,10 +981,13 @@ Line buffering is the default for ports open on terminal devices.
 \oops{The current implementation doesn't support \ex{bufpol/line}.}
 
 The \var{size} argument requests an I/O buffer of \var{size} bytes.
-If not given, a reasonable default is used; if given and zero,
-buffering is turned off
-(\ie, $\var{size} = 0$ for any policy is equivalent to
-      $\var{policy} = \ex{bufpol/none}$).
+For output ports, \var{size} must be non-negative, for input ports
+\var{size} must be positve. If not given, a reasonable default is
+used. For output ports, if given and zero, buffering is turned off
+(\ie, $\var{size} = 0$ for any policy is equivalent to $\var{policy} =
+\ex{bufpol/none}$). For input ports, setting the size to one
+corresponds to unbuffered input as defined above. If given, \var{size}
+must be zero respectively one for \ex{bufpol/none}.
 \end{defundesc}
 
 \begin{defundesc}{force-output} {[fd/port]}{\undefined}

scsh/newports.scm

@@ -176,35 +176,47 @@
 
 (define (set-port-buffering port policy . maybe-size) 
   (cond ((and (fdport? port) (open-input-port? port))
-	 (let ((size (if (pair? maybe-size) (car maybe-size) 255)))
+	 (let ((size (if (pair? maybe-size) (car maybe-size) 
+			 (if (= policy bufpol/none) 1 255))))
+	   (if (<= size 0) 
+	       (error "buffer size must be at least 1 for input ports" 
+		      port policy size))
 	   (set-input-port-buffering port policy size)))
 	((and (fdport? port) (open-output-port? port))
-	 (let ((size (if (pair? maybe-size) (car maybe-size) 255)))
-	    (if (<= size 0) (error "size must be at least 1"))
+	 (let ((size (if (pair? maybe-size) (car maybe-size) 
+			 (if (= policy bufpol/none) 0 255))))
+	   (if (< size 0) 
+	       (error "buffer size must be at least 0 for output ports" 
+		      port policy size))
 	   (set-output-port-buffering port policy size)))
 	(else
-            (warn "port-type not supported" port))))
+            (error "Not a port" port))))
 
-(define (set-output-port-buffering port policy size) 
+(define (set-output-port-buffering port policy size)
   (cond ((eq? policy bufpol/none)
+	 (if (not (= size 0))
+	     (error "buffer size must be 0 for bufpol/none on output ports" 
+		    port policy size))
 	 (install-nullbuffer port unbuffered-output-fdport-handler))
 	((eq? policy bufpol/block)
-	 (let ((old-size (byte-vector-length (port-buffer port)))
-	       (new-buffer (make-byte-vector size 0)))
-	   (if (< size old-size)
-	       (begin
-		 (really-force-output port)
-		 (obtain-port-lock port)
- 		 (set-port-index! port 0))
-	       (begin 
-		 (obtain-port-lock port)
-		 (copy-bytes! (port-buffer port) 0 new-buffer 0 old-size)))
-	   (install-buffer port new-buffer size)
-	   (release-port-lock port)))
-	((eq? policy bufpol/line)
+	 (if (= size 0)
+	     (install-nullbuffer port unbuffered-output-fdport-handler)
+	     (let ((old-size (byte-vector-length (port-buffer port)))
+		   (new-buffer (make-byte-vector size 0)))
+	       (if (< size old-size)
+		   (begin
+		     (really-force-output port)
+		     (obtain-port-lock port)
+		     (set-port-index! port 0))
+		   (begin 
+		     (obtain-port-lock port)
+		     (copy-bytes! (port-buffer port) 0 new-buffer 0 old-size)))
+	       (install-buffer port new-buffer size)
+	       (release-port-lock port))))
+	 ((eq? policy bufpol/line)
 	 ;(install-nullbuffer port (make-line-output-proc size)))
 	 (error "bufpol/line is currently not supported"))
-	(else (warn "policy not supported " policy))))
+	(else (error "policy not supported " policy))))
 
 (define (install-nullbuffer port handler)
  (really-force-output port)
@@ -253,13 +265,15 @@
 	
 (define (set-input-port-buffering port policy size)
   (cond ((eq? policy bufpol/none)
+	 (if (not (= size 1))
+	     (error "buffer size must be 1 for bufpol/none on input ports" 
+		    port policy size))
 	 (set-input-port-buffering port bufpol/block 1))
 	((eq? policy bufpol/block)
-	 (if (<= size 0) (error "size must be at least 1"))
 	 (install-input-handler port input-fdport-handler size #t))
 	((eq? policy bufpol/line)
 	 (error "bufpol/line not allowed on input"))
-	(else (warn "policy not supported " policy))))
+	(else (error "policy not supported " policy))))
 
 (define (install-input-handler port new-handler size gentle?)
   	 (obtain-port-lock port)