yenc news/mail decoder.
"Please thake these files as part of the Plan9 distribution of you wish"
-Steve

Notes:
Mon Apr 5 17:38:50 EDT 2004 rsc
    i put this in /n/sources/steve/ydec.
    i don't think it's generally useful enough to put 
    into the distribution.


Reference: /n/sources/patch/sorry/ydec
Date: Mon Apr  5 23:39:10 CES 2004
Reviewed-by: rsc

--- /usr/local/sys/src/cmd/ydec/ydec.c	Thu Jan  1 00:00:00 1970
+++ /usr/local/sys/src/cmd/ydec/ydec.c	Mon Apr  5 23:39:10 2004
@@ -0,0 +1,175 @@
+/* yenc file decoder
+ *
+ * Please read www.exit109.com/~jeremy/news/yenc.html
+ * "Why Yenc is bad for Usenet" before adding an encoder.
+ */
+#include <u.h>
+#include <libc.h>
+#include <bio.h>
+#include <flate.h>
+
+static int Verbose = 0;
+static ulong *Crctab;
+static Biobuf bout;
+
+int
+yydec(char *file, Biobuf *bi)
+{
+	uchar c;
+	char *name, *buf, *p, *q;
+	static int totgot = 0;
+	static int nextpart = 1;
+	unsigned long crc, ecrc;
+	int got, line, part, size, esize, begin, end;
+
+	got = 0;
+	crc = 0;
+	part = 0;
+	name = 0;
+	while((buf = Brdline(bi, '\n')) != nil){
+		if ((p = strchr(buf, '\n')) != nil)
+			*p = 0;	
+		if ((p = strchr(buf, '\r')) != nil)
+			*p = 0;	
+		if (strncmp(buf, "=ybegin ", 8)==0) {
+			if ((p = strstr(buf,"name=")) == nil)
+				sysfatal("%s - no name= in =ybegin\n", file);
+			name = strdup(p+5);
+
+			if ((p = strstr(buf,"size=")) == nil)
+				sysfatal("%s - no size= in =ybegin\n", file);
+			size = atoi(p+5);
+
+			if ((p = strstr(buf,"line=")) == nil)
+				sysfatal("%s - no line= in =ybegin\n", file);
+			line = atoi(p+5);
+
+			if ((p = strstr(buf,"part=")) != nil)
+				part = atoi(p+5);
+			break;
+		}
+	}
+
+	if (part){
+		if ((buf = Brdline(bi, '\n')) == nil)
+			sysfatal("%s - unexpected EOF\n", file);
+		if ((p = strchr(buf, '\n')) != nil)
+			*p = 0;	
+		if ((p = strchr(buf, '\r')) != nil)
+			*p = 0;	
+		if (strncmp(buf, "=ypart ", 7) != 0)
+			sysfatal("%s - no =ypart in multipart file\n", file);
+
+		if ((p = strstr(buf, "end=")) == nil)
+			sysfatal("%s - no end= in =ypart\n", file);
+		end = atol(p+4);
+
+		if ((p = strstr(buf, "begin=")) == nil)
+			sysfatal("%s - no begin= in =ypart\n", file);
+		begin = atol(p+6);
+	}
+
+	if (name == nil)
+		sysfatal("%s - =ybegin not found\n", file);
+
+	if (Verbose && part == 0 || part == 1)
+		fprint(2, "%s %d bytes\n", name, size);
+
+	if (part && part != nextpart)
+		sysfatal("%s - got part=%d, wanted part=%d\n", file, part, nextpart);
+
+	while (1){
+		if ((buf = Brdline(bi, '\n')) == nil)
+			sysfatal("%s - unexpected EOF\n", file);
+		if ((p = strchr(buf, '\n')) != nil)
+			*p = 0;	
+		if ((p = strchr(buf, '\r')) != nil)
+			*p = 0;	
+		if (strncmp(buf, "=yend ", 6) == 0)
+			break;
+		for (p = buf; *p;){
+			c = (uchar)*p++;
+			if (c == '='){
+				if ((c = *p++) == 0)
+					sysfatal("%s - Esc char (=) at end of line\n", file);
+				c = (uchar)(c-64);
+			}
+			c = (uchar)(c-42);
+			Bputc(&bout, c);
+			crc = blockcrc(Crctab, crc, &c, 1);
+			totgot++;
+			got++;
+		}
+	}
+
+	if ((p = strstr(buf, "size=")) != nil){
+		esize = atoi(p+5);
+		if (esize != got) {
+			fprint(2, "%s corrupted size=%d != %d\n", file, esize, got);
+			return 0;
+		}
+	}
+
+	if (! part){
+		if ((p = strstr(buf, "crc32=")) != nil)
+			ecrc = strtoul((p+6), nil, 16);
+		if (crc != ecrc)
+			fprint(2, "%s: %s corrupt crc=%08lux != %08lux\n", argv0, file, crc, ecrc);
+		return 0;
+	}
+
+	/*
+	 * multipart only from here on
+	 */
+	if ((p = strstr(buf, "pcrc32=")) != nil)
+		ecrc = strtoul((p+7), nil, 16);
+	if (crc != ecrc)
+			fprint(2, "%s: %s corrupt part crc=%08lux != %08lux\n", argv0, file, crc, ecrc);
+
+	if (got != (end - begin + 1))
+		sysfatal("%s part=%d wrong size\n", file, part);
+
+	nextpart = part +1;
+	return 0;
+}
+
+void
+usage(void)
+{
+	fprint(2, "usage: %s [-v] [file...]\n", argv0);
+	exits("usage");
+}
+
+void
+main(int argc, char *argv[])
+{
+	Biobuf bin, *bi = &bin;
+
+	Crctab = mkcrctab(0xedb88320UL);
+	Binit(&bin, 0, OREAD);
+	Binit(&bout, 1, OWRITE);
+	argv0 = *argv;
+
+	ARGBEGIN {
+	case 'v':
+		Verbose++;
+		break;
+	default:
+		usage();
+		break;
+	} ARGEND;
+
+	if (argc == 0)
+		yydec(*argv, &bin);
+
+	for (; argc--; argv++){
+		if ((bi = Bopen(*argv, OREAD)) == nil){
+			fprint(2, "%s: %s - cannot read file %r\n", argv0, *argv);
+			continue;
+		}
+		yydec(*argv, bi);
+		Bterm(bi);
+	}
+	Bterm(&bout);
+	exits(0);
+}
--- /usr/local/sys/man/1/ydec	Thu Jan  1 00:00:00 1970
+++ /usr/local/sys/man/1/ydec	Mon Apr  5 23:39:10 2004
@@ -0,0 +1,30 @@
+.TH ydec 1
+.SH NAME
+ydec \- decode \fIyenc\fR encoded files.
+.SH SYNOPSIS
+.B ydec
+[
+.BI -v
+] [
+.B file...
+]
+.SH DESCRIPTION
+.I Ydec
+decodes the given email or news files (or standard input if none)
+to a standard output. If the \fB-v\fR option is supplied it prints some
+information about decoded file on standard error.
+.PP
+Multipart files can be decoded but must be presented in order.
+.PP
+Yenc is a depricated and thus no encoder is supplied,
+for further information see www.exit109.com/~jeremy/news/yenc.html
+"Why Yenc is bad for Usenet".
+.PP
+.SH EXAMPLE
+.EX
+	nntpfs
+	cd /mnt/news/alt/binaries/sounds/mp3/blues
+	ydec 1234*/body | ydec | mp3
+.EE
+.SH SOURCE
+.B /sys/src/cmd/ydec.c