(unknown),

(unknown),

[dturner]

This version includes style fixups suggested by Junio Hamano.  As
suggested, I moved the addition of the new object_context field to the
patch where it is used.

In addition, I moved a few variables into smaller scopes.

I also (hopefully) fixed the tests on Windows thanks to some
suggestions from Johannes Sixt

[PATCH v4 1/3] tree-walk: learn get_tree_entry_follow_symlinks

[dturner]

From: David Turner <dturner@twitter.com>

Add a new function, get_tree_entry_follow_symlinks, to tree-walk.[ch].
The function is not yet used.  It will be used to implement git
cat-file --batch --follow-symlinks.

The function locates an object by path, following symlinks in the
repository.  If the symlinks lead outside the repository, the function
reports this to the caller.

Signed-off-by: David Turner <dturner@twitter.com>
---
 tree-walk.c | 193 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 tree-walk.h |   2 +
 2 files changed, 195 insertions(+)

diff --git a/tree-walk.c b/tree-walk.c
index 5dd9a71..3d088b6 100644
--- a/tree-walk.c
+++ b/tree-walk.c
@@ -415,6 +415,12 @@ int traverse_trees(int n, struct tree_desc *t, struct traverse_info *info)
 	return error;
 }
 
+struct dir_state {
+	void *tree;
+	unsigned long size;
+	unsigned char sha1[20];
+};
+
 static int find_tree_entry(struct tree_desc *t, const char *name, unsigned char *result, unsigned *mode)
 {
 	int namelen = strlen(name);
@@ -478,6 +484,193 @@ int get_tree_entry(const unsigned char *tree_sha1, const char *name, unsigned ch
 	return retval;
 }
 
+/*
+ * This is Linux's built-in max for the number of symlinks to follow.
+ * That limit, of course, does not affect git, but it's a reasonable
+ * choice.
+ */
+#define GET_TREE_ENTRY_FOLLOW_SYMLINKS_MAX_LINKS 40
+
+/**
+ * Find a tree entry by following symlinks in tree_sha (which is
+ * assumed to be the root of the repository).  In the event that a
+ * symlink points outside the repository (e.g. a link to /foo or a
+ * root-level link to ../foo), the portion of the link which is
+ * outside the repository will be returned in result_path, and *mode
+ * will be set to 0.  It is assumed that result_path is uninitialized.
+ * If there are no symlinks, or the end result of the symlink chain
+ * points to an object inside the repository, result will be filled in
+ * with the sha1 of the found object, and *mode will hold the mode of
+ * the object.  If there is a symlink loop, -1 will be returned.
+ */
+int get_tree_entry_follow_symlinks(unsigned char *tree_sha1, const char *name, unsigned char *result, struct strbuf *result_path, unsigned *mode)
+{
+	int retval = -1;
+	struct dir_state *parents = NULL;
+	size_t parents_alloc = 0;
+	ssize_t parents_nr = 0;
+	unsigned char current_tree_sha1[20];
+	struct strbuf namebuf = STRBUF_INIT;
+	struct tree_desc t = {0};
+	int follows_remaining = GET_TREE_ENTRY_FOLLOW_SYMLINKS_MAX_LINKS;
+	int i;
+
+	result_path->buf = 0;
+	result_path->alloc = 0;
+	result_path->len = 0;
+	strbuf_addstr(&namebuf, name);
+	hashcpy(current_tree_sha1, tree_sha1);
+
+	while (1) {
+		int find_result;
+		char *first_slash;
+		char *remainder = NULL;
+
+		if (!t.buffer) {
+			void *tree;
+			unsigned char root[20];
+			unsigned long size;
+			tree = read_object_with_reference(current_tree_sha1,
+							  tree_type, &size,
+							  root);
+			if (!tree)
+				goto done;
+
+			ALLOC_GROW(parents, parents_nr + 1, parents_alloc);
+			parents[parents_nr].tree = tree;
+			parents[parents_nr].size = size;
+			hashcpy(parents[parents_nr].sha1, root);
+			parents_nr++;
+
+			if (namebuf.buf[0] == '\0') {
+				hashcpy(result, root);
+				retval = 0;
+				goto done;
+			}
+
+			if (!size)
+				goto done;
+
+			/* descend */
+			init_tree_desc(&t, tree, size);
+		}
+
+		/* Handle symlinks to e.g. a//b by removing leading slashes */
+		while (namebuf.buf[0] == '/') {
+			strbuf_remove(&namebuf, 0, 1);
+		}
+
+		/* Split namebuf into a first component and a remainder */
+		if ((first_slash = strchr(namebuf.buf, '/'))) {
+			*first_slash = 0;
+			remainder = first_slash + 1;
+		}
+
+		if (!strcmp(namebuf.buf, "..")) {
+			struct dir_state *parent;
+			/*
+			 * We could end up with .. in the namebuf if it
+			 * appears in a symlink.
+			 */
+
+			if (parents_nr == 1) {
+				if (remainder)
+					*first_slash = '/';
+				strbuf_add(result_path, namebuf.buf,
+					   namebuf.len);
+				*mode = 0;
+				retval = 0;
+				goto done;
+			}
+			parent = &parents[parents_nr - 1];
+			free(parent->tree);
+			parents_nr--;
+			parent = &parents[parents_nr - 1];
+			init_tree_desc(&t, parent->tree, parent->size);
+			strbuf_remove(&namebuf, 0, remainder ? 3 : 2);
+			continue;
+		}
+
+		/* We could end up here via a symlink to dir/.. */
+		if (namebuf.buf[0] == '\0') {
+			hashcpy(result, parents[parents_nr - 1].sha1);
+			retval = 0;
+			goto done;
+		}
+
+		/* Look up the first (or only) path component in the tree. */
+		find_result = find_tree_entry(&t, namebuf.buf,
+					      current_tree_sha1, mode);
+		if (find_result) {
+			retval = find_result;
+			goto done;
+		}
+
+		if (S_ISDIR(*mode)) {
+			if (!remainder) {
+				hashcpy(result, current_tree_sha1);
+				retval = 0;
+				goto done;
+			}
+			/* Descend the tree */
+			t.buffer = NULL;
+			strbuf_remove(&namebuf, 0,
+				      1 + first_slash - namebuf.buf);
+		} else if (S_ISREG(*mode)) {
+			if (!remainder) {
+				hashcpy(result, current_tree_sha1);
+				retval = 0;
+			}
+			goto done;
+		} else if (S_ISLNK(*mode)) {
+			/* Follow a symlink */
+			size_t link_len, len;
+			char *contents, *contents_start;
+			struct dir_state *parent;
+			enum object_type type;
+
+			if (follows_remaining-- == 0)
+				/* Too many symlinks followed */
+				goto done;
+
+			contents = read_sha1_file(current_tree_sha1, &type,
+						  &link_len);
+
+			if (!contents)
+				goto done;
+
+			if (contents[0] == '/') {
+				strbuf_addstr(result_path, contents);
+				*mode = 0;
+				retval = 0;
+				goto done;
+			}
+
+			if (remainder)
+				len = first_slash - namebuf.buf;
+			else
+				len = namebuf.len;
+
+			contents_start = contents;
+
+			parent = &parents[parents_nr - 1];
+			init_tree_desc(&t, parent->tree, parent->size);
+			strbuf_splice(&namebuf, 0, len,
+				      contents_start, link_len);
+			if (remainder)
+				namebuf.buf[link_len] = '/';
+			free(contents);
+		}
+	}
+done:
+	for (i = 0; i < parents_nr; i++)
+		free(parents[i].tree);
+	free(parents);
+
+	strbuf_release(&namebuf);
+	return retval;
+}
+
 static int match_entry(const struct pathspec_item *item,
 		       const struct name_entry *entry, int pathlen,
 		       const char *match, int matchlen,
diff --git a/tree-walk.h b/tree-walk.h
index ae7fb3a..d1670c6 100644
--- a/tree-walk.h
+++ b/tree-walk.h
@@ -40,6 +40,8 @@ struct traverse_info;
 typedef int (*traverse_callback_t)(int n, unsigned long mask, unsigned long dirmask, struct name_entry *entry, struct traverse_info *);
 int traverse_trees(int n, struct tree_desc *t, struct traverse_info *info);
 
+int get_tree_entry_follow_symlinks(unsigned char *tree_sha1, const char *name, unsigned char *result, struct strbuf *result_path, unsigned *mode);
+
 struct traverse_info {
 	struct traverse_info *prev;
 	struct name_entry name;
-- 
2.0.4.315.gad8727a-twtrsrc

[PATCH v4 2/3] sha1_name: get_sha1_with_context learns to follow symlinks

[dturner]

From: David Turner <dturner@twitter.com>

Wire up get_sha1_with_context to call get_tree_entry_follow_symlinks
when GET_SHA1_FOLLOW_SYMLINKS is passed in flags. G_S_FOLLOW_SYMLINKS
is incompatible with G_S_ONLY_TO_DIE because the diagnosis
that ONLY_TO_DIE triggers does not at present consider symlinks, and
it would be a significant amount of additional code to allow it to
do so.

Signed-off-by: David Turner <dturner@twitter.com>
---
 cache.h     | 20 +++++++++++++-------
 sha1_name.c | 20 +++++++++++++++-----
 2 files changed, 28 insertions(+), 12 deletions(-)

diff --git a/cache.h b/cache.h
index 3d3244b..65505d1 100644
--- a/cache.h
+++ b/cache.h
@@ -922,15 +922,21 @@ struct object_context {
 	unsigned char tree[20];
 	char path[PATH_MAX];
 	unsigned mode;
+	/*
+	 * symlink_path is only used by get_tree_entry_follow_symlinks,
+	 * and only for symlinks that point outside the repository.
+	 */
+	struct strbuf symlink_path;
 };
 
-#define GET_SHA1_QUIETLY        01
-#define GET_SHA1_COMMIT         02
-#define GET_SHA1_COMMITTISH     04
-#define GET_SHA1_TREE          010
-#define GET_SHA1_TREEISH       020
-#define GET_SHA1_BLOB	       040
-#define GET_SHA1_ONLY_TO_DIE 04000
+#define GET_SHA1_QUIETLY           01
+#define GET_SHA1_COMMIT            02
+#define GET_SHA1_COMMITTISH        04
+#define GET_SHA1_TREE             010
+#define GET_SHA1_TREEISH          020
+#define GET_SHA1_BLOB             040
+#define GET_SHA1_FOLLOW_SYMLINKS 0100
+#define GET_SHA1_ONLY_TO_DIE    04000
 
 extern int get_sha1(const char *str, unsigned char *sha1);
 extern int get_sha1_commit(const char *str, unsigned char *sha1);
diff --git a/sha1_name.c b/sha1_name.c
index 6d10f05..0c26515 100644
--- a/sha1_name.c
+++ b/sha1_name.c
@@ -1434,11 +1434,19 @@ static int get_sha1_with_context_1(const char *name,
 			new_filename = resolve_relative_path(filename);
 			if (new_filename)
 				filename = new_filename;
-			ret = get_tree_entry(tree_sha1, filename, sha1, &oc->mode);
-			if (ret && only_to_die) {
-				diagnose_invalid_sha1_path(prefix, filename,
-							   tree_sha1,
-							   name, len);
+			if (flags & GET_SHA1_FOLLOW_SYMLINKS) {
+				ret = get_tree_entry_follow_symlinks(tree_sha1,
+					filename, sha1, &oc->symlink_path,
+					&oc->mode);
+			} else {
+				ret = get_tree_entry(tree_sha1, filename,
+						     sha1, &oc->mode);
+				if (ret && only_to_die) {
+					diagnose_invalid_sha1_path(prefix,
+								   filename,
+								   tree_sha1,
+								   name, len);
+				}
 			}
 			hashcpy(oc->tree, tree_sha1);
 			strlcpy(oc->path, filename, sizeof(oc->path));
@@ -1469,5 +1477,7 @@ void maybe_die_on_misspelt_object_name(const char *name, const char *prefix)
 
 int get_sha1_with_context(const char *str, unsigned flags, unsigned char *sha1, struct object_context *orc)
 {
+	if (flags & GET_SHA1_FOLLOW_SYMLINKS && flags & GET_SHA1_ONLY_TO_DIE)
+		die("BUG: incompatible flags for get_sha1_with_context");
 	return get_sha1_with_context_1(str, flags, NULL, sha1, orc);
 }
-- 
2.0.4.315.gad8727a-twtrsrc

[PATCH v4 3/3] cat-file: add --follow-symlinks to --batch

[dturner]

From: David Turner <dturner@twitter.com>

This wires the in-repo-symlink following code through to the cat-file
builtin.  In the event of an out-of-repo link, cat-file will print
the link in a new format.

Signed-off-by: David Turner <dturner@twitter.com>
---
 Documentation/git-cat-file.txt |  28 +++++-
 builtin/cat-file.c             |  24 +++++-
 t/t1006-cat-file.sh            | 189 +++++++++++++++++++++++++++++++++++++++++
 3 files changed, 236 insertions(+), 5 deletions(-)

diff --git a/Documentation/git-cat-file.txt b/Documentation/git-cat-file.txt
index f6a16f4..18b67a3 100644
--- a/Documentation/git-cat-file.txt
+++ b/Documentation/git-cat-file.txt
@@ -10,7 +10,7 @@ SYNOPSIS
 --------
 [verse]
 'git cat-file' (-t | -s | -e | -p | <type> | --textconv ) <object>
-'git cat-file' (--batch | --batch-check) < <list-of-objects>
+'git cat-file' (--batch | --batch-check) [--follow-symlinks] < <list-of-objects>
 
 DESCRIPTION
 -----------
@@ -69,6 +69,19 @@ OPTIONS
 	not be combined with any other options or arguments.  See the
 	section `BATCH OUTPUT` below for details.
 
+--follow-symlinks::
+	Follow symlinks inside the repository.  Instead of providing
+	output about the link itself, provide output about the linked-to
+	object.  This option requires --batch or --batch-check.  In the
+	event of a symlink loop (or more than 40 symlinks in a symlink
+	resolution chain), the file will be treated as missing.  If a
+	symlink points outside the repository (e.g. a link to /foo or a
+	root-level link to ../foo), the portion of the link which is
+	outside the repository will be printed.  Follow-symlinks will
+	be silently turned off if <object> specifies an object in the
+	index rather than one in the object database.
+
+
 OUTPUT
 ------
 If '-t' is specified, one of the <type>.
@@ -148,6 +161,19 @@ the repository, then `cat-file` will ignore any custom format and print:
 <object> SP missing LF
 ------------
 
+If --follow-symlinks is used, and a symlink in the repository points
+outside the repository, then `cat-file` will ignore any custom format
+and print:
+
+------------
+symlink SP <size> LF <symlink> LF
+------------
+
+The symlink will either be absolute (beginning with a /), or relative
+to the repository root.  For instance, if dir/link points to ../../foo,
+then <symlink> will be ../foo.  <size> is the size of the symlink in
+bytes.
+
 
 CAVEATS
 -------
diff --git a/builtin/cat-file.c b/builtin/cat-file.c
index df99df4..6bcf9a0 100644
--- a/builtin/cat-file.c
+++ b/builtin/cat-file.c
@@ -224,6 +224,7 @@ static void print_object_or_die(int fd, struct expand_data *data)
 
 struct batch_options {
 	int enabled;
+	int follow_symlinks;
 	int print_contents;
 	const char *format;
 };
@@ -232,16 +233,25 @@ static int batch_one_object(const char *obj_name, struct batch_options *opt,
 			    struct expand_data *data)
 {
 	struct strbuf buf = STRBUF_INIT;
+	struct object_context ctx;
+	int flags = opt->follow_symlinks ? GET_SHA1_FOLLOW_SYMLINKS : 0;
 
 	if (!obj_name)
 	   return 1;
 
-	if (get_sha1(obj_name, data->sha1)) {
+	if (get_sha1_with_context(obj_name, flags, data->sha1, &ctx)) {
 		printf("%s missing\n", obj_name);
 		fflush(stdout);
 		return 0;
 	}
 
+	if (ctx.mode == 0) {
+		printf("symlink %"PRIuMAX"\n%s\n",
+		       (uintmax_t)ctx.symlink_path.len,
+		       ctx.symlink_path.buf);
+		return 0;
+	}
+
 	if (sha1_object_info_extended(data->sha1, &data->info, LOOKUP_REPLACE_OBJECT) < 0) {
 		printf("%s missing\n", obj_name);
 		fflush(stdout);
@@ -342,9 +352,8 @@ static int batch_option_callback(const struct option *opt,
 {
 	struct batch_options *bo = opt->value;
 
-	if (unset) {
-		memset(bo, 0, sizeof(*bo));
-		return 0;
+	if (bo->enabled) {
+		return 1;
 	}
 
 	bo->enabled = 1;
@@ -369,6 +378,9 @@ int cmd_cat_file(int argc, const char **argv, const char *prefix)
 		OPT_SET_INT('p', NULL, &opt, N_("pretty-print object's content"), 'p'),
 		OPT_SET_INT(0, "textconv", &opt,
 			    N_("for blob objects, run textconv on object's content"), 'c'),
+		OPT_SET_INT(0, "follow-symlinks", &batch.follow_symlinks,
+			N_("follow in-repo symlinks; report out-of-repo symlinks (requires --batch or --batch-check)"),
+			    1),
 		{ OPTION_CALLBACK, 0, "batch", &batch, "format",
 			N_("show info and content of objects fed from the standard input"),
 			PARSE_OPT_OPTARG, batch_option_callback },
@@ -402,6 +414,10 @@ int cmd_cat_file(int argc, const char **argv, const char *prefix)
 		usage_with_options(cat_file_usage, options);
 	}
 
+	if (batch.follow_symlinks && !batch.enabled) {
+		usage_with_options(cat_file_usage, options);
+	}
+
 	if (batch.enabled)
 		return batch_objects(&batch);
 
diff --git a/t/t1006-cat-file.sh b/t/t1006-cat-file.sh
index ab36b1e..500cfa9 100755
--- a/t/t1006-cat-file.sh
+++ b/t/t1006-cat-file.sh
@@ -189,6 +189,13 @@ do
     '
 done
 
+for opt in t s e p
+do
+    test_expect_success "Passing -$opt with --follow-symlinks fails" '
+	    test_must_fail git cat-file --follow-symlinks -$opt $hello_sha1
+	'
+done
+
 test_expect_success "--batch-check for a non-existent named object" '
     test "foobar42 missing
 foobar84 missing" = \
@@ -296,4 +303,186 @@ test_expect_success '%(deltabase) reports packed delta bases' '
 	}
 '
 
+# Tests for git cat-file --follow-symlinks
+test_expect_success 'prep for symlink tests' '
+	echo_without_newline "$hello_content" >morx &&
+	test_ln_s_add morx same-dir-link &&
+	test_ln_s_add ../fleem out-of-repo-link &&
+	test_ln_s_add .. out-of-repo-link-dir &&
+	test_ln_s_add same-dir-link link-to-link &&
+	test_ln_s_add nope broken-same-dir-link &&
+	mkdir dir &&
+	test_ln_s_add ../morx dir/parent-dir-link &&
+	test_ln_s_add .. dir/link-dir &&
+	test_ln_s_add ../../escape dir/out-of-repo-link &&
+	test_ln_s_add ../.. dir/out-of-repo-link-dir &&
+	test_ln_s_add nope dir/broken-link-in-dir &&
+	mkdir dir/subdir &&
+	test_ln_s_add ../../morx dir/subdir/grandparent-dir-link &&
+	test_ln_s_add ../../../great-escape dir/subdir/out-of-repo-link &&
+	test_ln_s_add ../../.. dir/subdir/out-of-repo-link-dir &&
+	test_ln_s_add ../../../ dir/subdir/out-of-repo-link-dir-trailing &&
+	test_ln_s_add ../parent-dir-link dir/subdir/parent-dir-link-to-link &&
+	echo_without_newline "$hello_content" >dir/subdir/ind2 &&
+	echo_without_newline "$hello_content" >dir/ind1 &&
+	test_ln_s_add dir dirlink &&
+	test_ln_s_add dir/subdir subdirlink &&
+	test_ln_s_add subdir/ind2 dir/link-to-child &&
+	test_ln_s_add dir/link-to-child link-to-down-link &&
+	test_ln_s_add dir/.. up-down &&
+	test_ln_s_add dir/../ up-down-trailing &&
+	test_ln_s_add dir/../morx up-down-file &&
+	test_ln_s_add dir/../../morx up-up-down-file &&
+	test_ln_s_add subdirlink/../../morx up-two-down-file &&
+	test_ln_s_add loop1 loop2 &&
+	test_ln_s_add loop2 loop1 &&
+	git add morx dir/subdir/ind2 dir/ind1 &&
+	git commit -am "test"
+	echo $hello_sha1 blob $hello_size >found
+'
+
+test_expect_success 'git cat-file --batch-check --follow-symlinks works for non-links' '
+	echo HEAD:morx | git cat-file --batch-check --follow-symlinks >actual &&
+	test_cmp found actual &&
+	echo HEAD:nope missing >expect &&
+	echo HEAD:nope | git cat-file --batch-check --follow-symlinks >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'git cat-file --batch-check --follow-symlinks works for in-repo, same-dir links' '
+	echo HEAD:same-dir-link | git cat-file --batch-check --follow-symlinks >actual &&
+	test_cmp found actual
+'
+
+test_expect_success 'git cat-file --batch-check --follow-symlinks works for broken in-repo, same-dir links' '
+	echo HEAD:broken-same-dir-link missing >expect &&
+	echo HEAD:broken-same-dir-link | git cat-file --batch-check --follow-symlinks >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'git cat-file --batch-check --follow-symlinks works for same-dir links-to-links' '
+	echo HEAD:link-to-link | git cat-file --batch-check --follow-symlinks >actual &&
+	test_cmp found actual
+'
+
+test_expect_success 'git cat-file --batch-check --follow-symlinks works for parent-dir links' '
+	echo HEAD:dir/parent-dir-link | git cat-file --batch-check --follow-symlinks >actual &&
+	test_cmp found actual &&
+	echo HEAD:dir/parent-dir-link/nope missing >expect &&
+	echo HEAD:dir/parent-dir-link/nope | git cat-file --batch-check --follow-symlinks >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'git cat-file --batch-check --follow-symlinks works for .. links' '
+	echo HEAD:dir/link-dir/nope missing >expect &&
+	echo HEAD:dir/link-dir/nope | git cat-file --batch-check --follow-symlinks >actual &&
+	test_cmp expect actual &&
+	echo HEAD:dir/link-dir/morx | git cat-file --batch-check --follow-symlinks >actual &&
+	test_cmp found actual &&
+	echo HEAD:dir/broken-link-in-dir missing >expect &&
+	echo HEAD:dir/broken-link-in-dir | git cat-file --batch-check --follow-symlinks >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'git cat-file --batch-check --follow-symlinks works for ../.. links' '
+	echo HEAD:dir/subdir/grandparent-dir-link/nope missing >expect &&
+	echo HEAD:dir/subdir/grandparent-dir-link/nope | git cat-file --batch-check --follow-symlinks >actual &&
+	test_cmp expect actual &&
+	echo HEAD:dir/subdir/grandparent-dir-link | git cat-file --batch-check --follow-symlinks >actual &&
+	test_cmp found actual &&
+	echo HEAD:dir/subdir/parent-dir-link-to-link | git cat-file --batch-check --follow-symlinks >actual &&
+	test_cmp found actual
+'
+
+test_expect_success 'git cat-file --batch-check --follow-symlinks works for dir/ links' '
+	echo HEAD:dirlink/morx missing >expect &&
+	echo HEAD:dirlink/morx | git cat-file --batch-check --follow-symlinks >actual &&
+	test_cmp expect actual &&
+	echo $hello_sha1 blob $hello_size >expect &&
+	echo HEAD:dirlink/ind1 | git cat-file --batch-check --follow-symlinks >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'git cat-file --batch-check --follow-symlinks works for dir/subdir links' '
+	echo HEAD:subdirlink/morx missing >expect &&
+	echo HEAD:subdirlink/morx | git cat-file --batch-check --follow-symlinks >actual &&
+	test_cmp expect actual &&
+	echo HEAD:subdirlink/ind2 | git cat-file --batch-check --follow-symlinks >actual &&
+	test_cmp found actual
+'
+
+test_expect_success 'git cat-file --batch-check --follow-symlinks works for dir ->subdir links' '
+	echo HEAD:dir/link-to-child/morx missing >expect &&
+	echo HEAD:dir/link-to-child/morx | git cat-file --batch-check --follow-symlinks >actual &&
+	test_cmp expect actual &&
+	echo HEAD:dir/link-to-child | git cat-file --batch-check --follow-symlinks >actual &&
+	test_cmp found actual &&
+	echo HEAD:link-to-down-link | git cat-file --batch-check --follow-symlinks >actual &&
+	test_cmp found actual
+'
+
+test_expect_success 'git cat-file --batch-check --follow-symlinks works for out-of-repo symlinks' '
+	echo symlink 8 >expect &&
+	echo ../fleem >>expect &&
+	echo HEAD:out-of-repo-link | git cat-file --batch-check --follow-symlinks >actual &&
+	test_cmp expect actual &&
+	echo symlink 2 >expect &&
+	echo .. >>expect &&
+	echo HEAD:out-of-repo-link-dir | git cat-file --batch-check --follow-symlinks >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'git cat-file --batch-check --follow-symlinks works for out-of-repo symlinks in dirs' '
+	echo symlink 9 >expect &&
+	echo ../escape >>expect &&
+	echo HEAD:dir/out-of-repo-link | git cat-file --batch-check --follow-symlinks >actual &&
+	test_cmp expect actual &&
+	echo symlink 2 >expect &&
+	echo .. >>expect &&
+	echo HEAD:dir/out-of-repo-link-dir | git cat-file --batch-check --follow-symlinks >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'git cat-file --batch-check --follow-symlinks works for out-of-repo symlinks in subdirs' '
+	echo symlink 15 >expect &&
+	echo ../great-escape >>expect &&
+	echo HEAD:dir/subdir/out-of-repo-link | git cat-file --batch-check --follow-symlinks >actual &&
+	test_cmp expect actual &&
+	echo symlink 2 >expect &&
+	echo .. >>expect &&
+	echo HEAD:dir/subdir/out-of-repo-link-dir | git cat-file --batch-check --follow-symlinks >actual &&
+	test_cmp expect actual &&
+	echo symlink 3 >expect &&
+	echo ../ >>expect &&
+	echo HEAD:dir/subdir/out-of-repo-link-dir-trailing | git cat-file --batch-check --follow-symlinks >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'git cat-file --batch-check --follow-symlinks works for symlinks with internal ..' '
+	echo HEAD: | git cat-file --batch-check >expect &&
+	echo HEAD:up-down | git cat-file --batch-check --follow-symlinks >actual &&
+	test_cmp expect actual &&
+	echo HEAD:up-down-trailing | git cat-file --batch-check --follow-symlinks >actual &&
+	test_cmp expect actual &&
+	echo HEAD:up-down-file | git cat-file --batch-check --follow-symlinks >actual &&
+	test_cmp found actual &&
+	echo symlink 7 >expect &&
+	echo ../morx >>expect &&
+	echo HEAD:up-up-down-file | git cat-file --batch-check --follow-symlinks >actual &&
+	test_cmp expect actual &&
+	echo HEAD:up-two-down-file | git cat-file --batch-check --follow-symlinks >actual &&
+	test_cmp found actual
+'
+
+test_expect_success 'git cat-file --batch-check --follow-symlink breaks loops' '
+	echo HEAD:loop1 missing >expect &&
+	echo HEAD:loop1 | git cat-file --batch-check --follow-symlinks >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'git cat-file --batch --follow-symlink returns correct sha and mode' '
+	echo HEAD:morx | git cat-file --batch >expect &&
+	echo HEAD:morx | git cat-file --batch --follow-symlinks >actual &&
+	test_cmp expect actual
+'
 test_done
-- 
2.0.4.315.gad8727a-twtrsrc

Re: [PATCH v4 2/3] sha1_name: get_sha1_with_context learns to follow symlinks

[Junio C Hamano]

dturner@twopensource.com writes:

> From: David Turner <dturner@twitter.com>
>
> Wire up get_sha1_with_context to call get_tree_entry_follow_symlinks
> when GET_SHA1_FOLLOW_SYMLINKS is passed in flags. G_S_FOLLOW_SYMLINKS
> is incompatible with G_S_ONLY_TO_DIE because the diagnosis
> that ONLY_TO_DIE triggers does not at present consider symlinks, and
> it would be a significant amount of additional code to allow it to
> do so.
>
> Signed-off-by: David Turner <dturner@twitter.com>
> ---
>  cache.h     | 20 +++++++++++++-------
>  sha1_name.c | 20 +++++++++++++++-----
>  2 files changed, 28 insertions(+), 12 deletions(-)
>
> diff --git a/cache.h b/cache.h
> index 3d3244b..65505d1 100644
> --- a/cache.h
> +++ b/cache.h
> @@ -922,15 +922,21 @@ struct object_context {
>  	unsigned char tree[20];
>  	char path[PATH_MAX];
>  	unsigned mode;
> +	/*
> +	 * symlink_path is only used by get_tree_entry_follow_symlinks,
> +	 * and only for symlinks that point outside the repository.
> +	 */
> +	struct strbuf symlink_path;
>  };
>...
> @@ -1469,5 +1477,7 @@ void maybe_die_on_misspelt_object_name(const char *name, const char *prefix)
>  
>  int get_sha1_with_context(const char *str, unsigned flags, unsigned char *sha1, struct object_context *orc)
>  {
> +	if (flags & GET_SHA1_FOLLOW_SYMLINKS && flags & GET_SHA1_ONLY_TO_DIE)
> +		die("BUG: incompatible flags for get_sha1_with_context");
>  	return get_sha1_with_context_1(str, flags, NULL, sha1, orc);
>  }

Looks good; thanks.

Re: [PATCH v4 3/3] cat-file: add --follow-symlinks to --batch

[Junio C Hamano]

dturner@twopensource.com writes:

> +--follow-symlinks::
> +	Follow symlinks inside the repository.  Instead of providing
> +	output about the link itself, provide output about the linked-to
> +	object.  This option requires --batch or --batch-check.  In the
> +	event of a symlink loop (or more than 40 symlinks in a symlink
> +	resolution chain), the file will be treated as missing.  If a
> +	symlink points outside the repository (e.g. a link to /foo or a
> +	root-level link to ../foo), the portion of the link which is
> +	outside the repository will be printed.  Follow-symlinks will
> +	be silently turned off if <object> specifies an object in the
> +	index rather than one in the object database.

One thing that I found is missing from the above and other places in
the documents updated by this patch, when I pretend that I am an
end-user who never saw the discussion for the problem definition and
design of the solution on the list, is what "symlink" this refers
to and how I am expected to use this feature.

Such an end-user in me without inside knowledge naively expects that
the command invocation would be like this:

	$ git cat-file --batch-check --follow-symlinks <<\EOF
	e156455ea49124c140a67623f22a393db62d5d98
	55aeb4d32091e0e6062759958c30d316f77a570e
        e50885caa1043665dfe2d995e0a2f7a7a7bb51ca
	EOF

where the last one is output from "git rev-parse v2.0.0:RelNotes"
(the second one is v2.0.0^{tree}).

As somebody who is familiar with how the implementation works, I
_know_ that such an expectation is wrong.  At least the command
would need a hint that lets it realize that the blob sits inside a
tree with mode bits that says it is a symlink, e.g.

	$ git cat-file --batch-check --follow-symlinks <<\EOF
	55aeb4d32091e0e6062759958c30d316f77a570e:RelNotes
	EOF

But that requirement is not hinted in the documentation, so there is
no way for a new user to discover how useful this feature is and how
to use it.

The above description mentions "points outside the repository", but
that also may need some clarification to such an end-user in me
without inside knowledge.

For example, if I had a tree T that records a subtree T:sub, in
which a symbolic link sub/link that points at "../target", i.e. with
this setup (8fb753 is T):

    $ git rev-parse 8fb7535cc62fd9a0a804f21389667f9505299fb4:sub
    13056eb35d037f4af8be37e6a1ba983235bd7613
    $ git ls-tree 13056eb35d037f4af8be37e6a1ba983235bd7613 link
    120000 blob 78bc33729bacb569b76aaef40fec807af2ec1274    link
    $ git cat-file blob 78bc33729ba
    ../target
    $ git ls-tree 8fb7535cc62 target
    100644 blob e69de29bb2d1d6434b8b29ae775ad8c2e48c5391    target

These behave differently

    $ git cat-file --batch-check --follow-symlinks <<\EOF
    8fb7535cc62f:sub/link
    13056eb35d03:link
    EOF

and that is correct for obvious reasons, but is the reason obvious
enough to an end-user in me without inside knowledge?  The symlink
points inside the repository, but it is outside the starting object
of the extended SHA-1 expression that was used to name the object.

So in short, the description above should mention that this feature
is about asking for the object with extended SHA-1 expression that
begins with a tree-ish, colon and a path to in the tree.  And it
needs to rephrase "outside the repository" with something like
"outside the tree-ish on the left hand side of the colon in the
extended SHA-1 expression" or something.

Others better at phrasing may be able to offer a better wording than
my clumsy attempt above, though ;-)

> +If --follow-symlinks is used, and a symlink in the repository points
> +outside the repository, then `cat-file` will ignore any custom format
> +and print:
> +
> +------------
> +symlink SP <size> LF <symlink> LF
> +------------

A symlink contain LF, obviously, and we should use some quoting
convention.  Perhaps quote_c_style() on a string that needs it is
sufficient---most sane people do not put LF or literally '\' 'n' or
'"' in their symbolic links, so the ugly output is not visible for
them, and it is far better to be able to say "If you have funny
characters in your symlinks, they will be quoted" than "If you have
funny characters in your symlinks, you are SOL".

Thanks.

Re: [PATCH v4 3/3] cat-file: add --follow-symlinks to --batch

[David Turner]

On Mon, 2015-05-11 at 13:21 -0700, Junio C Hamano wrote:
dturner@twopensource.com writes:
> 
> > +--follow-symlinks::
> > +	Follow symlinks inside the repository.  Instead of providing
> > +	output about the link itself, provide output about the linked-to
> > +	object.  This option requires --batch or --batch-check.  In the
> > +	event of a symlink loop (or more than 40 symlinks in a symlink
> > +	resolution chain), the file will be treated as missing.  If a
> > +	symlink points outside the repository (e.g. a link to /foo or a
> > +	root-level link to ../foo), the portion of the link which is
> > +	outside the repository will be printed.  Follow-symlinks will
> > +	be silently turned off if <object> specifies an object in the
> > +	index rather than one in the object database.
> 
> One thing that I found is missing from the above and other places in
> the documents updated by this patch, when I pretend that I am an
> end-user who never saw the discussion for the problem definition and
> design of the solution on the list, is what "symlink" this refers
> to and how I am expected to use this feature.
> 
I'll send something like this when I re-roll:

Follow symlinks inside the repository when requesting objects with
extended SHA-1 expressions of the form tree-ish:path-in-tree. Instead of
providing output about the link itself, provide output about the
linked-to object.  This option requires --batch or	--batch-check.  In
the event of a symlink loop (or more than 40 symlinks in a symlink
resolution chain), the file will be treated as missing.  If a symlink
points outside the tree-ish (e.g. a link to /foo or a root-level link
to ../foo), the portion of the link which is outside the tree will be
printed. Follow-symlinks will be silently turned off if <object>
specifies an object in the index rather than one in the object database.

I could also provide some examples, if you think this would be useful.

> +If --follow-symlinks is used, and a symlink in the repository points
> > +outside the repository, then `cat-file` will ignore any custom
format
> > +and print:
> > +
> > +------------
> > +symlink SP <size> LF <symlink> LF
> > +------------
> 
> A symlink contain LF, obviously, and we should use some quoting
> convention.  Perhaps quote_c_style() on a string that needs it is
> sufficient---most sane people do not put LF or literally '\' 'n' or
> '"' in their symbolic links, so the ugly output is not visible for
> them, and it is far better to be able to say "If you have funny
> characters in your symlinks, they will be quoted" than "If you have
> funny characters in your symlinks, you are SOL".
> 
There is no need for quoting because <size> is sufficient to
disambiguate the parsing (just as is the case for blobs, which might
contain arbitrary characters).

Re: [PATCH v4 3/3] cat-file: add --follow-symlinks to --batch

[Junio C Hamano]

David Turner <dturner@twopensource.com> writes:

> I'll send something like this when I re-roll:
>
> Follow symlinks inside the repository when requesting objects with
> extended SHA-1 expressions of the form tree-ish:path-in-tree. Instead of
> providing output about the link itself, provide output about the
> linked-to object.  This option requires --batch or	--batch-check.  In
> the event of a symlink loop (or more than 40 symlinks in a symlink
> resolution chain), the file will be treated as missing.  If a symlink
> points outside the tree-ish (e.g. a link to /foo or a root-level link
> to ../foo), the portion of the link which is outside the tree will be
> printed. Follow-symlinks will be silently turned off if <object>
> specifies an object in the index rather than one in the object database.

Very understandable. I like it.

>
> I could also provide some examples, if you think this would be useful.

That may not be a bad idea.

>> > +symlink SP <size> LF <symlink> LF
>> > +------------
>> 
>> A symlink contain LF, obviously, and we should use some quoting
>> convention.  Perhaps quote_c_style() on a string that needs it is
>> sufficient---most sane people do not put LF or literally '\' 'n' or
>> '"' in their symbolic links, so the ugly output is not visible for
>> them, and it is far better to be able to say "If you have funny
>> characters in your symlinks, they will be quoted" than "If you have
>> funny characters in your symlinks, you are SOL".
>> 
> There is no need for quoting because <size> is sufficient to
> disambiguate the parsing (just as is the case for blobs, which might
> contain arbitrary characters).

OK.  That is a very sensible way to think about it.

I briefly wondered if trailing LF is a healthy thing, but blob
output also gives an extra LF after <contents> (i.e. the reader of
"<name> SP blob SP <size> LF <contents> LF" must skip (size + 1)
bytes to get to the next record), so it is consistent.

Thanks.