Re: [PATCH] strbuf: add strbuf_add_real_path()
- From
Jeff King <peff@peff.net>
- Date
- Feb 25, 2017, 20:11 UTC
- Message-ID
- <20170225201123.ozrrfgim2rdctczv@sigill.intra.peff.net>
- In-Reply-To
- <4d191b86-d36c-e3ec-99c6-d15baa6b659a@web.de>
On Sat, Feb 25, 2017 at 05:00:33PM +0100, René Scharfe wrote:
Show 9 quoted lines
> Add a function for appending the canonized absolute pathname of a given > path to a strbuf. It keeps the existing contents intact, as expected of > a function of the strbuf_add() family, while avoiding copying the result > if the given strbuf is empty. It's more consistent with the rest of the > strbuf API than strbuf_realpath(), which it's wrapping. > > Also add a semantic patch demonstrating its intended usage and apply it > to the current tree. Using strbuf_add_real_path() instead of calling > strbuf_addstr() and real_path() avoids an extra copy to a static buffer.
It's also re-entrant, which real_path() is not.
Show 10 quoted lines
> +void strbuf_add_real_path(struct strbuf *sb, const char *path)
> +{
> + if (sb->len) {
> + struct strbuf resolved = STRBUF_INIT;
> + strbuf_realpath(&resolved, path, 1);
> + strbuf_addbuf(sb, &resolved);
> + strbuf_release(&resolved);
> + } else
> + strbuf_realpath(sb, path, 1);
> +}The wrapping here seems a little backwards. If strbuf_add_real_path() were the inner one, then we would not need this extra allocation. I know that the reasons are historical, but I don't think it would be impossible to teach the realpath code to do it.
OTOH, it may not be worth the effort. It's not like strbuf_realpath() doesn't allocate secondary strbufs for its work already, so dropping one more is probably not that exciting. And certainly think your patch is an incremental improvement.
Out of curiosity, I took a stab at the patch, which is below. Only lightly tested by me, and it does make the logic a bit more complicated to read, as you have to adjust for the original "base" in several places.
diff --git a/abspath.c b/abspath.c index 2f0c26e0e..286072f48 100644 --- a/abspath.c +++ b/abspath.c @@ -12,9 +12,9 @@ int is_directory(const char *path) } /* removes the last path component from 'path' except if 'path' is root */ -static void strip_last_component(struct strbuf *path) +static void strip_last_component(struct strbuf *path, size_t base) { - size_t offset = offset_1st_component(path->buf); + size_t offset = base + offset_1st_component(path->buf + base); size_t len = path->len; /* Find start of the last component */ @@ -49,14 +49,15 @@ static void get_next_component(struct strbuf *next, struct strbuf *remaining) } /* copies root part from remaining to resolved, canonicalizing it on the way */ -static void get_root_part(struct strbuf *resolved, struct strbuf *remaining) +static void get_root_part(struct strbuf *resolved, struct strbuf *remaining, + size_t base) { int offset = offset_1st_component(remaining->buf); - strbuf_reset(resolved); + strbuf_setlen(resolved, base); strbuf_add(resolved, remaining->buf, offset); #ifdef GIT_WINDOWS_NATIVE - convert_slashes(resolved->buf); + convert_slashes(resolved->buf + base); #endif strbuf_remove(remaining, 0, offset); } @@ -78,8 +79,8 @@ static void get_root_part(struct strbuf *resolved, struct strbuf *remaining) * informative error message if there is a problem. Otherwise, return * NULL on errors (without generating any output). */ -char *strbuf_realpath(struct strbuf *resolved, const char *path, - int die_on_error) +char *strbuf_add_real_path(struct strbuf *resolved, const char *path, + int die_on_error) { struct strbuf remaining = STRBUF_INIT; struct strbuf next = STRBUF_INIT; @@ -87,6 +88,7 @@ char *strbuf_realpath(struct strbuf *resolved, const char *path, char *retval = NULL; int num_symlinks = 0; struct stat st; + size_t base = resolved->len; if (!*path) { if (die_on_error) @@ -96,9 +98,9 @@ char *strbuf_realpath(struct strbuf *resolved, const char *path, } strbuf_addstr(&remaining, path); - get_root_part(resolved, &remaining); + get_root_part(resolved, &remaining, base); - if (!resolved->len) { + if (resolved->len == base) { /* relative path; can use CWD as the initial resolved path */ if (strbuf_getcwd(resolved)) { if (die_on_error) @@ -118,7 +120,7 @@ char *strbuf_realpath(struct strbuf *resolved, const char *path, continue; /* '.' component */ } else if (next.len == 2 && !strcmp(next.buf, "..")) { /* '..' component; strip the last path component */ - strip_last_component(resolved); + strip_last_component(resolved, base); continue; } @@ -127,12 +129,12 @@ char *strbuf_realpath(struct strbuf *resolved, const char *path, strbuf_addch(resolved, '/'); strbuf_addbuf(resolved, &next); - if (lstat(resolved->buf, &st)) { + if (lstat(resolved->buf + base, &st)) { /* error out unless this was the last component */ if (errno != ENOENT || remaining.len) { if (die_on_error) die_errno("Invalid path '%s'", - resolved->buf); + resolved->buf + base); else goto error_out; } @@ -150,7 +152,7 @@ char *strbuf_realpath(struct strbuf *resolved, const char *path, goto error_out; } - len = strbuf_readlink(&symlink, resolved->buf, + len = strbuf_readlink(&symlink, resolved->buf + base, st.st_size); if (len < 0) { if (die_on_error) @@ -162,14 +164,14 @@ char *strbuf_realpath(struct strbuf *resolved, const char *path, if (is_absolute_path(symlink.buf)) { /* absolute symlink; set resolved to root */ - get_root_part(resolved, &symlink); + get_root_part(resolved, &symlink, base); } else { /* * relative symlink * strip off the last component since it will * be replaced with the contents of the symlink */ - strip_last_component(resolved); + strip_last_component(resolved, base); } /* @@ -202,6 +204,12 @@ char *strbuf_realpath(struct strbuf *resolved, const char *path, return retval; } +char *strbuf_realpath(struct strbuf *sb, const char *path, int die_on_error) +{ + strbuf_reset(sb); + return strbuf_add_real_path(sb, path, die_on_error); +} + const char *real_path(const char *path) { static struct strbuf realpath = STRBUF_INIT;