PATCH: `read -t' tests for available input before reading.

[Peter Stephenson <pws@xxxxxxxxxxxxxxxxxxxxxxxxx>]

I implemented this because I need it for a set of commands which will
mediate between the user and data on the serial port; I would be glad to
consider a better way of doing it, but it does not mean I am willing to
implement random changes to read (particularly after the hassle with this
one).

The -t option to read tests for input before performing the read; if there
is none, read does nothing and returns status 1.  With an ordinary read the
terminal is in canonical mode and nothing happens unless you have typed in
a complete line.

However, it works with the -k option outside zle (which is a different
kettle of fish altogether) to poll for a character being available.  This
is where the fun really started.  Solaris, it eventually transpired, needed
to use the termio mechanism for polling (setting the minimum number of
characters in the termio struct to zero) and wouldn't take any notice of
any other way of doing it.  Cygwin, which I need to use because the rest of
the world has backward ideas about operating systems, has the
infrastructure for this but it doesn't seem to work; the only thing that
works there is setting non-blocking read and attempting to read a
character.

Consequently I have no particular confidence that it will work without
tweaking on other people's systems.  I would hope, however, that one of the
two ways round should work.  I wouldn't expect problems without -k present.

It's quite possible that some of the other options could use `-t' to test
before returning even if the input isn't coming from an fd.  It's also
possible $PENDING in zle could usefully use something like read_poll()
(together with the input queue) if FIONREAD doesn't do the job, so that
you know that at least one character is available.

Index: Doc/Zsh/builtins.yo
===================================================================
RCS file: /cvsroot/zsh/zsh/Doc/Zsh/builtins.yo,v
retrieving revision 1.12
diff -u -r1.12 builtins.yo
--- Doc/Zsh/builtins.yo	2000/06/25 20:17:33	1.12
+++ Doc/Zsh/builtins.yo	2000/06/26 14:48:31
@@ -751,7 +751,7 @@
 alias(r)(fc -e -)
 findex(read)
 vindex(IFS, use of)
-item(tt(read) [ tt(-rzpqAclneE) ] [ tt(-k) [ var(num) ] ] \
+item(tt(read) [ tt(-rzpqAclneEt) ] [ tt(-k) [ var(num) ] ] \
 [ tt(-u)var(n) ] [ var(name)[tt(?)var(prompt)] ] [ var(name) ...  ])(
 Read one line and break it into fields using the characters
 in tt($IFS) as separators, except as noted below.
@@ -821,6 +821,22 @@
 )
 item(tt(-p))(
 Input is read from the coprocess.
+)
+item(tt(-t))(
+Test if input is available before attempting to read; if none is, return
+status 1 and do not set any variables.  This is not available when reading
+from the editor buffer with tt(-z), when called from within completion
+with tt(-c) or tt(-l), with tt(-q) which clears the input queue before
+reading, or within zle where other mechanisms should be used to test for
+input.
+
+Note that read does not attempt to alter the input processing mode.  The
+default mode is canonical input, in which an entire line is read at a time,
+so usually `tt(read -t)' will not read anything until an entire line has
+been typed.  However, when reading from the terminal with tt(-k)
+this is automatically handled; note that only availablity of the first
+character is tested, so that e.g. `tt(read -t -k 2)' can still block on the
+second character.
 )
 enditem()
 
Index: Src/builtin.c
===================================================================
RCS file: /cvsroot/zsh/zsh/Src/builtin.c,v
retrieving revision 1.25
diff -u -r1.25 builtin.c
--- Src/builtin.c	2000/06/23 09:45:39	1.25
+++ Src/builtin.c	2000/06/26 14:48:31
@@ -97,7 +97,7 @@
     BUILTIN("pushln", BINF_PRINTOPTS, bin_print, 0, -1, BIN_PRINT, NULL, "-nz"),
     BUILTIN("pwd", 0, bin_pwd, 0, 0, 0, "rLP", NULL),
     BUILTIN("r", BINF_R, bin_fc, 0, -1, BIN_FC, "nrl", NULL),
-    BUILTIN("read", 0, bin_read, 0, -1, 0, "rzu0123456789pkqecnAlE", NULL),
+    BUILTIN("read", 0, bin_read, 0, -1, 0, "ceklnpqrtzuAE0123456789", NULL),
     BUILTIN("readonly", BINF_TYPEOPTS | BINF_MAGICEQUALS | BINF_PSPECIAL, bin_typeset, 0, -1, 0, "AEFHLRTUZafghiltux", "r"),
     BUILTIN("rehash", 0, bin_hash, 0, 0, 0, "df", "r"),
     BUILTIN("return", BINF_PSPECIAL, bin_break, 0, 1, BIN_RETURN, NULL, NULL),
@@ -3361,6 +3361,94 @@
 /* Read a character from readfd, or from the buffer zbuf.  Return EOF on end of
 file/buffer. */
 
+/**/
+static int
+read_poll(int *readchar, int polltty)
+{
+    int ret = 0;
+    long mode = -1;
+    char c;
+#ifdef FIONREAD
+    int val;
+#endif
+#ifdef HAVE_SELECT
+    fd_set foofd;
+    struct timeval expire_tv;
+#endif
+#ifdef HAS_TIO
+    struct ttyinfo ti;
+#endif
+
+
+#if defined(HAS_TIO) && !defined(__CYGWIN__)
+    /*
+     * Under Solaris, at least, reading from the terminal in non-canonical
+     * mode requires that we use the VMIN mechanism to poll.  Any attempt
+     * to check any other way, or to set the terminal to non-blocking mode
+     * and poll that way, fails; it will just for canonical mode input.
+     * We should probably use this mechanism if the user has set non-canonical
+     * mode, in which case testing here for isatty() and ~ICANON would be
+     * better than testing whether bin_read() set it, but for now we've got
+     * enough problems.
+     *
+     * Under Cygwin, you won't be surprised to here, this mechanism,
+     * although present, doesn't work, and we *have* to use ordinary
+     * non-blocking reads to find out if there is a character present
+     * in non-canonical mode.
+     *
+     * I am assuming Solaris is nearer the UNIX norm.  This is not necessarily
+     * as plausible as it sounds, but it seems the right way to guess.
+     *		pws 2000/06/26
+     */
+    if (polltty) {
+	gettyinfo(&ti);
+	ti.tio.c_cc[VMIN] = 0;
+	settyinfo(&ti);
+    }
+#else
+    polltty = 0;
+#endif
+#ifdef HAVE_SELECT
+    if (!ret) {
+	expire_tv.tv_sec = expire_tv.tv_usec = 0;
+	FD_ZERO(&foofd);
+	FD_SET(readfd, &foofd);
+	if (select(readfd+1, (SELECT_ARG_2_T) &foofd, NULL, NULL, &expire_tv)
+	    > 1)
+	    ret = 1;
+    }
+#else
+#ifdef FIONREAD
+    if (!ret) {
+	ioctl(readfd, FIONREAD, (char *)&val);
+	if (val)
+	    ret = 1;
+    }
+#endif
+#endif
+
+    if (!ret) {
+	/*
+	 * Final attempt: set non-blocking read and try to read a character.
+	 * Praise Bill, this works under Cygwin (nothing else seems to).
+	 */
+	if ((polltty || setblock_fd(0, readfd, &mode))
+	    && read(readfd, &c, 1) > 0) {
+	    *readchar = STOUC(c);
+	    ret = 1;
+	}
+	if (mode != -1)
+	    fcntl(readfd, F_SETFL, mode);
+    }
+#ifdef HAS_TIO
+    if (polltty) {
+	ti.tio.c_cc[VMIN] = 1;
+	settyinfo(&ti);
+    }
+#endif
+    return ret;
+}
+
 /* read: get a line of input, or (for compctl functions) return some *
  * useful data about the state of the editing line.  The -E and -e   *
  * options mean that the result should be sent to stdout.  -e means, *
@@ -3378,6 +3466,9 @@
     char *buf, *bptr, *firstarg, *zbuforig;
     LinkList readll = newlinklist();
     FILE *oshout = NULL;
+    int readchar = -1, val;
+    char d;
+
 
     if ((ops['k'] || ops['b']) && *args && idigit(**args)) {
 	if (!(nchars = atoi(*args)))
@@ -3438,6 +3529,17 @@
     } else
 	readfd = izle = 0;
 
+    if (ops['t'] && !read_poll(&readchar, keys && !zleactive)) {
+	if (ops['k'] && !zleactive && !isem)
+	    settyinfo(&shttyinfo);
+	if (haso) {
+	    fclose(shout);
+	    shout = oshout;
+	    SHTTY = -1;
+	}
+	return 1;
+    }
+
     /* handle prompt */
     if (firstarg) {
 	for (readpmpt = firstarg;
@@ -3453,9 +3555,6 @@
 
     /* option -k means read only a given number of characters (default 1) */
     if (ops['k']) {
-	int val;
-	char d;
-
 	/* allocate buffer space for result */
 	bptr = buf = (char *)zalloc(nchars+1);
 
@@ -3467,7 +3566,11 @@
 		nchars--;
 	    } else {
 		/* If read returns 0, is end of file */
-		if ((val = read(readfd, bptr, nchars)) <= 0)
+		if (readchar >= 0) {
+		    *bptr = readchar;
+		    val = 1;
+		    readchar = -1;
+		} else if ((val = read(readfd, bptr, nchars)) <= 0)
 		    break;
 	    
 		/* decrement number of characters read from number required */
@@ -3544,7 +3647,7 @@
 	buf = bptr = (char *)zalloc(bsiz = 64);
 	/* get input, a character at a time */
 	while (!gotnl) {
-	    c = zread(izle);
+	    c = zread(izle, &readchar);
 	    /* \ at the end of a line indicates a continuation *
 	     * line, except in raw mode (-r option)            */
 	    if (bslash && c == '\n') {
@@ -3645,7 +3748,7 @@
     if (!gotnl) {
 	sigset_t s = child_unblock();
 	for (;;) {
-	    c = zread(izle);
+	    c = zread(izle, &readchar);
 	    /* \ at the end of a line introduces a continuation line, except in
 	    raw mode (-r option) */
 	    if (bslash && c == '\n') {
@@ -3711,7 +3814,7 @@
 
 /**/
 static int
-zread(int izle)
+zread(int izle, int *readchar)
 {
     char cc, retry = 0;
 
@@ -3729,6 +3832,11 @@
 	    return zbuf++, STOUC(*zbuf++ ^ 32);
 	else
 	    return (*zbuf) ? STOUC(*zbuf++) : EOF;
+    }
+    if (*readchar >= 0) {
+	cc = *readchar;
+	*readchar = -1;
+	return STOUC(cc);
     }
     for (;;) {
 	/* read a character from readfd */
Index: Src/utils.c
===================================================================
RCS file: /cvsroot/zsh/zsh/Src/utils.c,v
retrieving revision 1.7
diff -u -r1.7 utils.c
--- Src/utils.c	2000/06/01 09:10:17	1.7
+++ Src/utils.c	2000/06/26 14:48:32
@@ -1249,7 +1249,7 @@
 
 /**/
 int
-setblock_stdin(void)
+setblock_fd(int turnonblocking, int fd, long *modep)
 {
 #ifdef O_NDELAY
 # ifdef O_NONBLOCK
@@ -1267,18 +1267,35 @@
 
 #if NONBLOCK
     struct stat st;
-    long mode;
 
-    if (!fstat(0, &st) && !S_ISREG(st.st_mode)) {
-	mode = fcntl(0, F_GETFL, 0);
-	if (mode != -1 && (mode & NONBLOCK) &&
-	    !fcntl(0, F_SETFL, mode & ~NONBLOCK))
-	    return 1;
-    }
+    if (!fstat(fd, &st) && !S_ISREG(st.st_mode)) {
+	*modep = fcntl(fd, F_GETFL, 0);
+	if (*modep != -1) {
+	    if (!turnonblocking) {
+		/* We want to know if blocking was off */
+		if ((*modep & NONBLOCK) ||
+		    !fcntl(fd, F_SETFL, *modep | NONBLOCK))
+		    return 1;
+	    } else if ((*modep & NONBLOCK) &&
+		       !fcntl(fd, F_SETFL, *modep & ~NONBLOCK)) {
+		/* Here we want to know if the state changed */
+		return 1;
+	    }
+	}
+    } else
 #endif /* NONBLOCK */
+	*modep = -1;
     return 0;
 
 #undef NONBLOCK
+}
+
+/**/
+int
+setblock_stdin(void)
+{
+    long mode;
+    return setblock_fd(1, 0, &mode);
 }
 
 /**/

-- 
Peter Stephenson <pws@xxxxxxxxxxxxxxxxxxxxxxxxx>
Cambridge Silicon Radio, Unit 300, Science Park, Milton Road,
Cambridge, CB4 0XL, UK                          Tel: +44 (0)1223 392070