From: David Turner <dturner@xxxxxxxxxxx>
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@xxxxxxxxxxx>
---
tree-walk.c | 206 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
tree-walk.h | 18 ++++++
2 files changed, 224 insertions(+)
diff --git a/tree-walk.c b/tree-walk.c
index 5dd9a71..81d6604 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 +484,206 @@ 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.
+ *
+ * See the code for enum follow_symlink_result for a description of
+ * the return values.
+ */
+enum follow_symlinks_result get_tree_entry_follow_symlinks(unsigned char *tree_sha1, const char *name, unsigned char *result, struct strbuf *result_path, unsigned *mode)
+{
+ int retval = MISSING_OBJECT;
+ 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 = FOUND;
+ 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 = FOUND;
+ 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 = FOUND;
+ 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) {
+ goto done;
+ }
+
+ if (S_ISDIR(*mode)) {
+ if (!remainder) {
+ hashcpy(result, current_tree_sha1);
+ retval = FOUND;
+ 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 = FOUND;
+ } else {
+ retval = NOT_DIR;
+ }
+ goto done;
+ } else if (S_ISLNK(*mode)) {
+ /* Follow a symlink */
+ unsigned long link_len;
+ size_t len;
+ char *contents, *contents_start;
+ struct dir_state *parent;
+ enum object_type type;
+
+ if (follows_remaining-- == 0) {
+ /* Too many symlinks followed */
+ retval = SYMLINK_LOOP;
+ goto done;
+ }
+
+ /*
+ * At this point, we have followed at a least
+ * one symlink, so on error we need to report this.
+ */
+ retval = DANGLING_SYMLINK;
+
+ 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 = FOUND;
+ 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..3b2f7bf 100644
--- a/tree-walk.h
+++ b/tree-walk.h
@@ -40,6 +40,24 @@ 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);
+enum follow_symlinks_result {
+ FOUND = 0, /* This includes out-of-tree links */
+ MISSING_OBJECT = -1, /* The initial symlink is missing */
+ DANGLING_SYMLINK = -2, /*
+ * The initial symlink is there, but
+ * (transitively) points to a missing
+ * in-tree file
+ */
+ SYMLINK_LOOP = -3,
+ NOT_DIR = -4, /*
+ * Somewhere along the symlink chain, a path is
+ * requested which contains a file as a
+ * non-final element.
+ */
+};
+
+enum follow_symlinks_result 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
--
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