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tar, tarfs: implement longname support

this allows extracting tar archives that use longnames extension,
where the real filename is stored in a special entry with
linkflag == 'L' before the file entry. also skip longlink entries
with linkflag == 'K'.

--- a/sys/src/cmd/tapefs/tarfs.c

+++ b/sys/src/cmd/tapefs/tarfs.c

@@ -14,6 +14,7 @@

 	Namsiz = 100,

 	Maxpfx = 155,		/* from POSIX */

 	Maxname = Namsiz + 1 + Maxpfx,

+	Maxlongname = 65535,

 	Binsize = 0x80,		/* flag in size[0], from gnu: positive binary size */

 	Binnegsz = 0xff,	/* flag in size[0]: negative binary size */

 };

@@ -30,7 +31,12 @@

 	LF_DIR =	'5',

 	LF_FIFO =	'6',

 	LF_CONTIG =	'7',

+

 	/* 'A' - 'Z' are reserved for custom implementations */

+

+	LF_LONGNAME =	'L',		/* GNU extension */

+	LF_LONGLINK =	'K',

+

 };

 typedef union {

@@ -106,7 +112,9 @@

 void

 populate(char *name)

 {

-	long chksum, linkflg;

+	char longname[Maxlongname+1];

+	char *nextname = nil;

+	long chksum, linkflg, namelen;

 	vlong blkno;

 	char *fname;

 	Fileinf f;

@@ -121,7 +129,9 @@

 		seek(tapefile, Tblock*blkno, 0);

 		if (readn(tapefile, hp->dummy, sizeof hp->dummy) < sizeof hp->dummy)

 			break;

-		fname = tarname(hp);

+		fname = nextname, nextname = nil;

+		if(fname == nil || fname[0] == '\0')

+			fname = tarname(hp);

 		if (fname[0] == '\0')

 			break;

@@ -162,6 +172,16 @@

 		if (linkflg) {

 			/*fprint(2, "link %s->%s skipped\n", fname, hp->linkname);*/

 			f.size = 0;

+		} else if (hp->linkflag == LF_LONGLINK) {

+			;

+		} else if (hp->linkflag == LF_LONGNAME) {

+			namelen = Maxlongname;

+			if(f.size < namelen)

+				namelen = f.size;

+			namelen = readn(tapefile, longname, namelen);

+			if(namelen < 0) namelen = 0;

+			longname[namelen] = '\0';

+			nextname = longname;

 		} else {

 			/* accept this file */

 			f.name = fname;

@@ -169,8 +189,8 @@

 				fprint(2, "%s: null name skipped\n", argv0);

 			else

 				poppath(f, 1);

-			blkno += (f.size + Tblock - 1)/Tblock;

 		}

+		blkno += (f.size + Tblock - 1)/Tblock;

 	}

 }

--- a/sys/src/cmd/tar.c

+++ b/sys/src/cmd/tar.c

@@ -52,6 +52,7 @@

 	Namsiz = 100,

 	Maxpfx = 155,		/* from POSIX */

 	Maxname = Namsiz + 1 + Maxpfx,

+	Maxlongname = 65535,

 	Binsize = 0x80,		/* flag in size[0], from gnu: positive binary size */

 	Binnegsz = 0xff,	/* flag in size[0]: negative binary size */

@@ -72,7 +73,11 @@

 	LF_DIR =	'5',

 	LF_FIFO =	'6',

 	LF_CONTIG =	'7',

+

 	/* 'A' - 'Z' are reserved for custom implementations */

+

+	LF_LONGNAME =	'L',		/* GNU extenstion */

+	LF_LONGLINK = 	'K',

 };

 #define islink(lf)	(isreallink(lf) || issymlink(lf))

@@ -145,7 +150,7 @@

 static int nblock = Dblock;

 static int resync;

 static char *usefile, *arname = "archive";

-static char origdir[Maxname*2];

+static char origdir[Maxlongname+1];

 static Hdr *tpblk, *endblk;

 static Hdr *curblk;

@@ -934,12 +939,11 @@

 static int

 prefix(char *name, char *pfx)

 {

+	char clpfx[Maxlongname+1];

 	int pfxlen = strlen(pfx);

-	char clpfx[Maxname+1];

-	if (pfxlen > Maxname)

-		return 0;

-	strcpy(clpfx, pfx);

+	clpfx[Maxlongname] = '\0';

+	strncpy(clpfx, pfx, Maxlongname);

 	cleanname(clpfx);

 	return strncmp(clpfx, name, pfxlen) == 0 &&

 		(name[pfxlen] == '\0' || name[pfxlen] == '/');

@@ -948,12 +952,13 @@

 static int

 match(char *name, char **argv)

 {

+	char clname[Maxlongname+1];

 	int i;

-	char clname[Maxname+1];

 	if (argv[0] == nil)

 		return 1;

-	strcpy(clname, name);

+	clname[Maxlongname] = '\0';

+	strncpy(clname, name, Maxlongname);

 	cleanname(clname);

 	for (i = 0; argv[i] != nil; i++)

 		if (prefix(clname, argv[i]))

@@ -1045,6 +1050,7 @@

 	case LF_LINK:

 	case LF_SYMLINK1:

 	case LF_SYMLINK2:

+	case LF_LONGLINK:

 		fprint(2, "%s: can't make (sym)link %s\n",

 			argv0, fname);

 		break;

@@ -1201,6 +1207,46 @@

 	}

 }

+static char*

+getname(int ar, Hdr *hp)

+{

+	static char namebuf[Maxlongname+1], *nextname = nil;

+	ulong blksleft, blksread;

+	char *fname, *p;

+	int n;

+

+	if(nextname != nil && nextname[0] != '\0'){

+		fname = nextname, nextname = nil;

+		return fname;

+	}

+	fname = name(hp);

+	if(hp->linkflag == LF_LONGNAME){

+		p = namebuf;

+		for (blksleft = BYTES2TBLKS(arsize(hp)); blksleft > 0;

+		     blksleft -= blksread) {

+			hp = getblkrd(ar, Alldata);

+			if (hp == nil)

+				sysfatal("unexpected EOF on archive reading %s from %s",

+					fname, arname);

+			blksread = gothowmany(blksleft);

+			n = &namebuf[Maxlongname] - p;

+			if(Tblock*blksread < n)

+				n = Tblock*blksread;

+			memmove(p, hp->data, n);

+			p += n;

+			putreadblks(ar, blksread);

+		}

+		*p = '\0';

+		fname = nil;

+		nextname = namebuf;

+	} else {

+		namebuf[Maxlongname] = '\0';

+		strncpy(namebuf, fname, Maxlongname);

+		fname = namebuf;

+	}

+	return fname;

+}

+

 static char *

 extract(char **argv)

 {

@@ -1221,7 +1267,9 @@

 		sysfatal("can't open archive %s: %r", usefile);

 	while ((hp = readhdr(ar)) != nil) {

-		longname = name(hp);

+		longname = getname(ar, hp);

+		if(longname == nil)

+			continue;

 		if (match(longname, argv))

 			extract1(ar, hp, longname);

 		else