abspath: convert absolute_path() to strbuf

Move most of the code of absolute_path() into the new function
strbuf_add_absolute_path() and in the process transform it to use
struct strbuf and xgetcwd() instead of a PATH_MAX-sized buffer,
which can be too small on some file systems.

Signed-off-by: Rene Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/technical/api-strbuf.txt

@@ -293,6 +293,12 @@ same behaviour as well.
 
 	Set the buffer to the path of the current working directory.
 
+`strbuf_add_absolute_path`
+
+	Add a path to a buffer, converting a relative path to an
+	absolute one in the process.  Symbolic links are not
+	resolved.
+
 `stripspace`::
 
 	Strip whitespace from a buffer. The second parameter controls if

abspath.c

@@ -140,54 +140,16 @@ const char *real_path_if_valid(const char *path)
 	return real_path_internal(path, 0);
 }
 
-static const char *get_pwd_cwd(void)
-{
-	static char cwd[PATH_MAX + 1];
-	char *pwd;
-	struct stat cwd_stat, pwd_stat;
-	if (getcwd(cwd, PATH_MAX) == NULL)
-		return NULL;
-	pwd = getenv("PWD");
-	if (pwd && strcmp(pwd, cwd)) {
-		stat(cwd, &cwd_stat);
-		if ((cwd_stat.st_dev || cwd_stat.st_ino) &&
-		    !stat(pwd, &pwd_stat) &&
-		    pwd_stat.st_dev == cwd_stat.st_dev &&
-		    pwd_stat.st_ino == cwd_stat.st_ino) {
-			strlcpy(cwd, pwd, PATH_MAX);
-		}
-	}
-	return cwd;
-}
-
 /*
  * Use this to get an absolute path from a relative one. If you want
  * to resolve links, you should use real_path.
- *
- * If the path is already absolute, then return path. As the user is
- * never meant to free the return value, we're safe.
  */
 const char *absolute_path(const char *path)
 {
-	static char buf[PATH_MAX + 1];
-
-	if (!*path) {
-		die("The empty string is not a valid path");
-	} else if (is_absolute_path(path)) {
-		if (strlcpy(buf, path, PATH_MAX) >= PATH_MAX)
-			die("Too long path: %.*s", 60, path);
-	} else {
-		size_t len;
-		const char *fmt;
-		const char *cwd = get_pwd_cwd();
-		if (!cwd)
-			die_errno("Cannot determine the current working directory");
-		len = strlen(cwd);
-		fmt = (len > 0 && is_dir_sep(cwd[len - 1])) ? "%s%s" : "%s/%s";
-		if (snprintf(buf, PATH_MAX, fmt, cwd, path) >= PATH_MAX)
-			die("Too long path: %.*s", 60, path);
-	}
-	return buf;
+	static struct strbuf sb = STRBUF_INIT;
+	strbuf_reset(&sb);
+	strbuf_add_absolute_path(&sb, path);
+	return sb.buf;
 }
 
 /*

strbuf.c

@@ -568,6 +568,31 @@ void strbuf_humanise_bytes(struct strbuf *buf, off_t bytes)
 	}
 }
 
+void strbuf_add_absolute_path(struct strbuf *sb, const char *path)
+{
+	if (!*path)
+		die("The empty string is not a valid path");
+	if (!is_absolute_path(path)) {
+		struct stat cwd_stat, pwd_stat;
+		size_t orig_len = sb->len;
+		char *cwd = xgetcwd();
+		char *pwd = getenv("PWD");
+		if (pwd && strcmp(pwd, cwd) &&
+		    !stat(cwd, &cwd_stat) &&
+		    (cwd_stat.st_dev || cwd_stat.st_ino) &&
+		    !stat(pwd, &pwd_stat) &&
+		    pwd_stat.st_dev == cwd_stat.st_dev &&
+		    pwd_stat.st_ino == cwd_stat.st_ino)
+			strbuf_addstr(sb, pwd);
+		else
+			strbuf_addstr(sb, cwd);
+		if (sb->len > orig_len && !is_dir_sep(sb->buf[sb->len - 1]))
+			strbuf_addch(sb, '/');
+		free(cwd);
+	}
+	strbuf_addstr(sb, path);
+}
+
 int printf_ln(const char *fmt, ...)
 {
 	int ret;

strbuf.h

@@ -179,6 +179,8 @@ extern void strbuf_addstr_urlencode(struct strbuf *, const char *,
 				    int reserved);
 extern void strbuf_humanise_bytes(struct strbuf *buf, off_t bytes);
 
+extern void strbuf_add_absolute_path(struct strbuf *sb, const char *path);
+
 __attribute__((format (printf,1,2)))
 extern int printf_ln(const char *fmt, ...);
 __attribute__((format (printf,2,3)))