tar-tree: Introduce write_entry()

... and use it initially to write global extended header records.
Improvements compared to the old write_header():

  - Uses a struct ustar_header instead of hardcoded offsets.
  - Takes one struct strbuf as path argument instead of a (basedir,
    prefix, name) tuple.
  - Not only writes the tar header, but also the contents of the
    file, if any.
  - Does not write directly into the ring buffer.  This allows the
    code to be layed out more naturally, because there is no more
    ordering constraint.  Before we had to first finish writing the
    extended header, now we can construct the extended and normal
    headers in parallel.
  - The typeflag parameter has been replaced by (reasonable) magic
    values.  path == NULL indicates an extended header, additionally
    sha1 == NULL means it is a global extended header.

Signed-off-by: Rene Scharfe <rene.scharfe@lsrfire.ath.cx>
Signed-off-by: Junio C Hamano <junkio@cox.net>

tar-tree.c

@@ -1,21 +1,16 @@
 /*
- * Copyright (c) 2005 Rene Scharfe
+ * Copyright (c) 2005, 2006 Rene Scharfe
  */
 #include <time.h>
 #include "cache.h"
 #include "diff.h"
 #include "commit.h"
+#include "strbuf.h"
+#include "tar.h"
 
 #define RECORDSIZE	(512)
 #define BLOCKSIZE	(RECORDSIZE * 20)
 
-#define TYPEFLAG_AUTO		'\0'
-#define TYPEFLAG_REG		'0'
-#define TYPEFLAG_LNK		'2'
-#define TYPEFLAG_DIR		'5'
-#define TYPEFLAG_GLOBAL_HEADER	'g'
-#define TYPEFLAG_EXT_HEADER	'x'
-
 #define EXT_HEADER_PATH		1
 #define EXT_HEADER_LINKPATH	2
 
@@ -119,6 +114,127 @@ static void write_blocked(void *buf, unsigned long size)
 	write_if_needed();
 }
 
+/*
+ * pax extended header records have the format "%u %s=%s\n".  %u contains
+ * the size of the whole string (including the %u), the first %s is the
+ * keyword, the second one is the value.  This function constructs such a
+ * string and appends it to a struct strbuf.
+ */
+static void strbuf_append_ext_header(struct strbuf *sb, const char *keyword,
+                                     const char *value, unsigned int valuelen)
+{
+	char *p;
+	int len, total, tmp;
+
+	/* "%u %s=%s\n" */
+	len = 1 + 1 + strlen(keyword) + 1 + valuelen + 1;
+	for (tmp = len; tmp > 9; tmp /= 10)
+		len++;
+
+	total = sb->len + len;
+	if (total > sb->alloc) {
+		sb->buf = xrealloc(sb->buf, total);
+		sb->alloc = total;
+	}
+
+	p = sb->buf;
+	p += sprintf(p, "%u %s=", len, keyword);
+	memcpy(p, value, valuelen);
+	p += valuelen;
+	*p = '\n';
+	sb->len = total;
+}
+
+static unsigned int ustar_header_chksum(const struct ustar_header *header)
+{
+	char *p = (char *)header;
+	unsigned int chksum = 0;
+	while (p < header->chksum)
+		chksum += *p++;
+	chksum += sizeof(header->chksum) * ' ';
+	p += sizeof(header->chksum);
+	while (p < (char *)header + sizeof(struct ustar_header))
+		chksum += *p++;
+	return chksum;
+}
+
+static void write_entry(const unsigned char *sha1, struct strbuf *path,
+                        unsigned int mode, void *buffer, unsigned long size)
+{
+	struct ustar_header header;
+	struct strbuf ext_header;
+
+	memset(&header, 0, sizeof(header));
+	ext_header.buf = NULL;
+	ext_header.len = ext_header.alloc = 0;
+
+	if (!sha1) {
+		*header.typeflag = TYPEFLAG_GLOBAL_HEADER;
+		mode = 0100666;
+		strcpy(header.name, "pax_global_header");
+	} else if (!path) {
+		*header.typeflag = TYPEFLAG_EXT_HEADER;
+		mode = 0100666;
+		sprintf(header.name, "%s.paxheader", sha1_to_hex(sha1));
+	} else {
+		if (S_ISDIR(mode)) {
+			*header.typeflag = TYPEFLAG_DIR;
+			mode |= 0777;
+		} else if (S_ISLNK(mode)) {
+			*header.typeflag = TYPEFLAG_LNK;
+			mode |= 0777;
+		} else if (S_ISREG(mode)) {
+			*header.typeflag = TYPEFLAG_REG;
+			mode |= (mode & 0100) ? 0777 : 0666;
+		} else {
+			error("unsupported file mode: 0%o (SHA1: %s)",
+			      mode, sha1_to_hex(sha1));
+			return;
+		}
+		if (path->len > sizeof(header.name)) {
+			sprintf(header.name, "%s.data", sha1_to_hex(sha1));
+			strbuf_append_ext_header(&ext_header, "path",
+				                 path->buf, path->len);
+		} else
+			memcpy(header.name, path->buf, path->len);
+	}
+
+	if (S_ISLNK(mode) && buffer) {
+		if (size > sizeof(header.linkname)) {
+			sprintf(header.linkname, "see %s.paxheader",
+			        sha1_to_hex(sha1));
+			strbuf_append_ext_header(&ext_header, "linkpath",
+			                         buffer, size);
+		} else
+			memcpy(header.linkname, buffer, size);
+	}
+
+	sprintf(header.mode, "%07o", mode & 07777);
+	sprintf(header.size, "%011lo", S_ISREG(mode) ? size : 0);
+	sprintf(header.mtime, "%011lo", archive_time);
+
+	/* XXX: should we provide more meaningful info here? */
+	sprintf(header.uid, "%07o", 0);
+	sprintf(header.gid, "%07o", 0);
+	strncpy(header.uname, "git", 31);
+	strncpy(header.gname, "git", 31);
+	sprintf(header.devmajor, "%07o", 0);
+	sprintf(header.devminor, "%07o", 0);
+
+	memcpy(header.magic, "ustar", 6);
+	memcpy(header.version, "00", 2);
+
+	sprintf(header.chksum, "%07o", ustar_header_chksum(&header));
+
+	if (ext_header.len > 0) {
+		write_entry(sha1, NULL, 0, ext_header.buf, ext_header.len);
+		free(ext_header.buf);
+	}
+	write_blocked(&header, sizeof(header));
+	if (S_ISREG(mode) && buffer && size > 0)
+		write_blocked(buffer, size);
+}
+
 static void append_string(char **p, const char *s)
 {
 	unsigned int len = strlen(s);
@@ -237,16 +353,12 @@ static void write_extended_header(const char *headerfilename, int is_dir,
 
 static void write_global_extended_header(const unsigned char *sha1)
 {
-	char *p;
-	unsigned int size;
-
-	size = extended_header_len("comment", 40);
-	write_header(NULL, TYPEFLAG_GLOBAL_HEADER, NULL, NULL,
-	             "pax_global_header", 0100600, NULL, size);
-
-	p = get_record();
-	append_extended_header(&p, "comment", sha1_to_hex(sha1), 40);
-	write_if_needed();
+	struct strbuf ext_header;
+	ext_header.buf = NULL;
+	ext_header.len = ext_header.alloc = 0;
+	strbuf_append_ext_header(&ext_header, "comment", sha1_to_hex(sha1), 40);
+	write_entry(NULL, NULL, 0, ext_header.buf, ext_header.len);
+	free(ext_header.buf);
 }
 
 /* stores a ustar header directly in the block buffer */

tar.h

@@ -0,0 +1,25 @@
+#define TYPEFLAG_AUTO		'\0'
+#define TYPEFLAG_REG		'0'
+#define TYPEFLAG_LNK		'2'
+#define TYPEFLAG_DIR		'5'
+#define TYPEFLAG_GLOBAL_HEADER	'g'
+#define TYPEFLAG_EXT_HEADER	'x'
+
+struct ustar_header {
+	char name[100];		/*   0 */
+	char mode[8];		/* 100 */
+	char uid[8];		/* 108 */
+	char gid[8];		/* 116 */
+	char size[12];		/* 124 */
+	char mtime[12];		/* 136 */
+	char chksum[8];		/* 148 */
+	char typeflag[1];	/* 156 */
+	char linkname[100];	/* 157 */
+	char magic[6];		/* 257 */
+	char version[2];	/* 263 */
+	char uname[32];		/* 265 */
+	char gname[32];		/* 297 */
+	char devmajor[8];	/* 329 */
+	char devminor[8];	/* 337 */
+	char prefix[155];	/* 345 */
+};