Merge branch 'pr/3809'

[libgit2.git] / src / tree.c

/*
 * Copyright (C) the libgit2 contributors. All rights reserved.
 *
 * This file is part of libgit2, distributed under the GNU GPL v2 with
 * a Linking Exception. For full terms see the included COPYING file.
 */

#include "common.h"
#include "commit.h"
#include "tree.h"
#include "git2/repository.h"
#include "git2/object.h"
#include "fileops.h"
#include "tree-cache.h"
#include "index.h"

#define DEFAULT_TREE_SIZE 16
#define MAX_FILEMODE_BYTES 6

#define TREE_ENTRY_CHECK_NAMELEN(n) \
        if (n > UINT16_MAX) { giterr_set(GITERR_INVALID, "tree entry path too long"); }

GIT__USE_STRMAP

static bool valid_filemode(const int filemode)
{
        return (filemode == GIT_FILEMODE_TREE
                || filemode == GIT_FILEMODE_BLOB
                || filemode == GIT_FILEMODE_BLOB_EXECUTABLE
                || filemode == GIT_FILEMODE_LINK
                || filemode == GIT_FILEMODE_COMMIT);
}

GIT_INLINE(git_filemode_t) normalize_filemode(git_filemode_t filemode)
{
        /* Tree bits set, but it's not a commit */
        if (GIT_MODE_TYPE(filemode) == GIT_FILEMODE_TREE)
                return GIT_FILEMODE_TREE;

        /* If any of the x bits are set */
        if (GIT_PERMS_IS_EXEC(filemode))
                return GIT_FILEMODE_BLOB_EXECUTABLE;

        /* 16XXXX means commit */
        if (GIT_MODE_TYPE(filemode) == GIT_FILEMODE_COMMIT)
                return GIT_FILEMODE_COMMIT;

        /* 12XXXX means symlink */
        if (GIT_MODE_TYPE(filemode) == GIT_FILEMODE_LINK)
                return GIT_FILEMODE_LINK;

        /* Otherwise, return a blob */
        return GIT_FILEMODE_BLOB;
}

static int valid_entry_name(git_repository *repo, const char *filename)
{
        return *filename != '\0' &&
                git_path_isvalid(repo, filename,
                GIT_PATH_REJECT_TRAVERSAL | GIT_PATH_REJECT_DOT_GIT | GIT_PATH_REJECT_SLASH);
}

static int entry_sort_cmp(const void *a, const void *b)
{
        const git_tree_entry *e1 = (const git_tree_entry *)a;
        const git_tree_entry *e2 = (const git_tree_entry *)b;

        return git_path_cmp(
                e1->filename, e1->filename_len, git_tree_entry__is_tree(e1),
                e2->filename, e2->filename_len, git_tree_entry__is_tree(e2),
                git__strncmp);
}

int git_tree_entry_cmp(const git_tree_entry *e1, const git_tree_entry *e2)
{
        return entry_sort_cmp(e1, e2);
}

int git_tree_entry_icmp(const git_tree_entry *e1, const git_tree_entry *e2)
{
        return git_path_cmp(
                e1->filename, e1->filename_len, git_tree_entry__is_tree(e1),
                e2->filename, e2->filename_len, git_tree_entry__is_tree(e2),
                git__strncasecmp);
}

/**
 * Allocate a new self-contained entry, with enough space after it to
 * store the filename and the id.
 */
static git_tree_entry *alloc_entry(const char *filename, size_t filename_len, const git_oid *id)
{
        git_tree_entry *entry = NULL;
        size_t tree_len;

        TREE_ENTRY_CHECK_NAMELEN(filename_len);

        if (GIT_ADD_SIZET_OVERFLOW(&tree_len, sizeof(git_tree_entry), filename_len) ||
            GIT_ADD_SIZET_OVERFLOW(&tree_len, tree_len, 1) ||
            GIT_ADD_SIZET_OVERFLOW(&tree_len, tree_len, GIT_OID_RAWSZ))
                return NULL;

        entry = git__calloc(1, tree_len);
        if (!entry)
                return NULL;

        {
                char *filename_ptr;
                void *id_ptr;

                filename_ptr = ((char *) entry) + sizeof(git_tree_entry);
                memcpy(filename_ptr, filename, filename_len);
                entry->filename = filename_ptr;

                id_ptr = filename_ptr + filename_len + 1;
                git_oid_cpy(id_ptr, id);
                entry->oid = id_ptr;
        }

        entry->filename_len = (uint16_t)filename_len;

        return entry;
}

struct tree_key_search {
        const char *filename;
        uint16_t filename_len;
};

static int homing_search_cmp(const void *key, const void *array_member)
{
        const struct tree_key_search *ksearch = key;
        const git_tree_entry *entry = array_member;

        const uint16_t len1 = ksearch->filename_len;
        const uint16_t len2 = entry->filename_len;

        return memcmp(
                ksearch->filename,
                entry->filename,
                len1 < len2 ? len1 : len2
        );
}

/*
 * Search for an entry in a given tree.
 *
 * Note that this search is performed in two steps because
 * of the way tree entries are sorted internally in git:
 *
 * Entries in a tree are not sorted alphabetically; two entries
 * with the same root prefix will have different positions
 * depending on whether they are folders (subtrees) or normal files.
 *
 * Consequently, it is not possible to find an entry on the tree
 * with a binary search if you don't know whether the filename
 * you're looking for is a folder or a normal file.
 *
 * To work around this, we first perform a homing binary search
 * on the tree, using the minimal length root prefix of our filename.
 * Once the comparisons for this homing search start becoming
 * ambiguous because of folder vs file sorting, we look linearly
 * around the area for our target file.
 */
static int tree_key_search(
        size_t *at_pos,
        const git_tree *tree,
        const char *filename,
        size_t filename_len)
{
        struct tree_key_search ksearch;
        const git_tree_entry *entry;
        size_t homing, i;

        TREE_ENTRY_CHECK_NAMELEN(filename_len);

        ksearch.filename = filename;
        ksearch.filename_len = (uint16_t)filename_len;

        /* Initial homing search; find an entry on the tree with
         * the same prefix as the filename we're looking for */

        if (git_array_search(&homing,
                tree->entries, &homing_search_cmp, &ksearch) < 0)
                return GIT_ENOTFOUND; /* just a signal error; not passed back to user */

        /* We found a common prefix. Look forward as long as
         * there are entries that share the common prefix */
        for (i = homing; i < tree->entries.size; ++i) {
                entry = git_array_get(tree->entries, i);

                if (homing_search_cmp(&ksearch, entry) < 0)
                        break;

                if (entry->filename_len == filename_len &&
                        memcmp(filename, entry->filename, filename_len) == 0) {
                        if (at_pos)
                                *at_pos = i;

                        return 0;
                }
        }

        /* If we haven't found our filename yet, look backwards
         * too as long as we have entries with the same prefix */
        if (homing > 0) {
                i = homing - 1;

                do {
                        entry = git_array_get(tree->entries, i);

                        if (homing_search_cmp(&ksearch, entry) > 0)
                                break;

                        if (entry->filename_len == filename_len &&
                                memcmp(filename, entry->filename, filename_len) == 0) {
                                if (at_pos)
                                        *at_pos = i;

                                return 0;
                        }
                } while (i-- > 0);
        }

        /* The filename doesn't exist at all */
        return GIT_ENOTFOUND;
}

void git_tree_entry_free(git_tree_entry *entry)
{
        if (entry == NULL)
                return;

        git__free(entry);
}

int git_tree_entry_dup(git_tree_entry **dest, const git_tree_entry *source)
{
        git_tree_entry *cpy;

        assert(source);

        cpy = alloc_entry(source->filename, source->filename_len, source->oid);
        if (cpy == NULL)
                return -1;

        cpy->attr = source->attr;

        *dest = cpy;
        return 0;
}

void git_tree__free(void *_tree)
{
        git_tree *tree = _tree;

        git_odb_object_free(tree->odb_obj);
        git_array_clear(tree->entries);
        git__free(tree);
}

git_filemode_t git_tree_entry_filemode(const git_tree_entry *entry)
{
        return normalize_filemode(entry->attr);
}

git_filemode_t git_tree_entry_filemode_raw(const git_tree_entry *entry)
{
        return entry->attr;
}

const char *git_tree_entry_name(const git_tree_entry *entry)
{
        assert(entry);
        return entry->filename;
}

const git_oid *git_tree_entry_id(const git_tree_entry *entry)
{
        assert(entry);
        return entry->oid;
}

git_otype git_tree_entry_type(const git_tree_entry *entry)
{
        assert(entry);

        if (S_ISGITLINK(entry->attr))
                return GIT_OBJ_COMMIT;
        else if (S_ISDIR(entry->attr))
                return GIT_OBJ_TREE;
        else
                return GIT_OBJ_BLOB;
}

int git_tree_entry_to_object(
        git_object **object_out,
        git_repository *repo,
        const git_tree_entry *entry)
{
        assert(entry && object_out);
        return git_object_lookup(object_out, repo, entry->oid, GIT_OBJ_ANY);
}

static const git_tree_entry *entry_fromname(
        const git_tree *tree, const char *name, size_t name_len)
{
        size_t idx;

        if (tree_key_search(&idx, tree, name, name_len) < 0)
                return NULL;

        return git_array_get(tree->entries, idx);
}

const git_tree_entry *git_tree_entry_byname(
        const git_tree *tree, const char *filename)
{
        assert(tree && filename);

        return entry_fromname(tree, filename, strlen(filename));
}

const git_tree_entry *git_tree_entry_byindex(
        const git_tree *tree, size_t idx)
{
        assert(tree);
        return git_array_get(tree->entries, idx);
}

const git_tree_entry *git_tree_entry_byid(
        const git_tree *tree, const git_oid *id)
{
        size_t i;
        const git_tree_entry *e;

        assert(tree);

        git_array_foreach(tree->entries, i, e) {
                if (memcmp(&e->oid->id, &id->id, sizeof(id->id)) == 0)
                        return e;
        }

        return NULL;
}

int git_tree__prefix_position(const git_tree *tree, const char *path)
{
        struct tree_key_search ksearch;
        size_t at_pos, path_len;

        if (!path)
                return 0;

        path_len = strlen(path);
        TREE_ENTRY_CHECK_NAMELEN(path_len);

        ksearch.filename = path;
        ksearch.filename_len = (uint16_t)path_len;

        /* Find tree entry with appropriate prefix */
        git_array_search(
                &at_pos, tree->entries, &homing_search_cmp, &ksearch);

        for (; at_pos < tree->entries.size; ++at_pos) {
                const git_tree_entry *entry = git_array_get(tree->entries, at_pos);
                if (homing_search_cmp(&ksearch, entry) < 0)
                        break;
        }

        for (; at_pos > 0; --at_pos) {
                const git_tree_entry *entry =
                        git_array_get(tree->entries, at_pos - 1);

                if (homing_search_cmp(&ksearch, entry) > 0)
                        break;
        }

        return (int)at_pos;
}

size_t git_tree_entrycount(const git_tree *tree)
{
        assert(tree);
        return tree->entries.size;
}

unsigned int git_treebuilder_entrycount(git_treebuilder *bld)
{
        assert(bld);

        return git_strmap_num_entries(bld->map);
}

static int tree_error(const char *str, const char *path)
{
        if (path)
                giterr_set(GITERR_TREE, "%s - %s", str, path);
        else
                giterr_set(GITERR_TREE, "%s", str);
        return -1;
}

static int parse_mode(unsigned int *modep, const char *buffer, const char **buffer_out)
{
        unsigned char c;
        unsigned int mode = 0;

        if (*buffer == ' ')
                return -1;

        while ((c = *buffer++) != ' ') {
                if (c < '0' || c > '7')
                        return -1;
                mode = (mode << 3) + (c - '0');
        }
        *modep = mode;
        *buffer_out = buffer;

        return 0;
}

int git_tree__parse(void *_tree, git_odb_object *odb_obj)
{
        git_tree *tree = _tree;
        const char *buffer;
        const char *buffer_end;

        if (git_odb_object_dup(&tree->odb_obj, odb_obj) < 0)
                return -1;

        buffer = git_odb_object_data(tree->odb_obj);
        buffer_end = buffer + git_odb_object_size(tree->odb_obj);

        git_array_init_to_size(tree->entries, DEFAULT_TREE_SIZE);
        GITERR_CHECK_ARRAY(tree->entries);

        while (buffer < buffer_end) {
                git_tree_entry *entry;
                size_t filename_len;
                const char *nul;
                unsigned int attr;

                if (parse_mode(&attr, buffer, &buffer) < 0 || !buffer)
                        return tree_error("Failed to parse tree. Can't parse filemode", NULL);

                if ((nul = memchr(buffer, 0, buffer_end - buffer)) == NULL)
                        return tree_error("Failed to parse tree. Object is corrupted", NULL);

                if ((filename_len = nul - buffer) == 0)
                        return tree_error("Failed to parse tree. Can't parse filename", NULL);

                if ((buffer_end - (nul + 1)) < GIT_OID_RAWSZ)
                        return tree_error("Failed to parse tree. Can't parse OID", NULL);

                /* Allocate the entry */
                {
                        entry = git_array_alloc(tree->entries);
                        GITERR_CHECK_ALLOC(entry);

                        entry->attr = attr;
                        entry->filename_len = filename_len;
                        entry->filename = buffer;
                        entry->oid = (git_oid *) ((char *) buffer + filename_len + 1);
                }

                buffer += filename_len + 1;
                buffer += GIT_OID_RAWSZ;
        }

        return 0;
}

static size_t find_next_dir(const char *dirname, git_index *index, size_t start)
{
        size_t dirlen, i, entries = git_index_entrycount(index);

        dirlen = strlen(dirname);
        for (i = start; i < entries; ++i) {
                const git_index_entry *entry = git_index_get_byindex(index, i);
                if (strlen(entry->path) < dirlen ||
                    memcmp(entry->path, dirname, dirlen) ||
                        (dirlen > 0 && entry->path[dirlen] != '/')) {
                        break;
                }
        }

        return i;
}

static int append_entry(
        git_treebuilder *bld,
        const char *filename,
        const git_oid *id,
        git_filemode_t filemode)
{
        git_tree_entry *entry;
        int error = 0;

        if (!valid_entry_name(bld->repo, filename))
                return tree_error("Failed to insert entry. Invalid name for a tree entry", filename);

        entry = alloc_entry(filename, strlen(filename), id);
        GITERR_CHECK_ALLOC(entry);

        entry->attr = (uint16_t)filemode;

        git_strmap_insert(bld->map, entry->filename, entry, error);
        if (error < 0) {
                git_tree_entry_free(entry);
                giterr_set(GITERR_TREE, "failed to append entry %s to the tree builder", filename);
                return -1;
        }

        return 0;
}

static int write_tree(
        git_oid *oid,
        git_repository *repo,
        git_index *index,
        const char *dirname,
        size_t start)
{
        git_treebuilder *bld = NULL;
        size_t i, entries = git_index_entrycount(index);
        int error;
        size_t dirname_len = strlen(dirname);
        const git_tree_cache *cache;

        cache = git_tree_cache_get(index->tree, dirname);
        if (cache != NULL && cache->entry_count >= 0){
                git_oid_cpy(oid, &cache->oid);
                return (int)find_next_dir(dirname, index, start);
        }

        if ((error = git_treebuilder_new(&bld, repo, NULL)) < 0 || bld == NULL)
                return -1;

        /*
         * This loop is unfortunate, but necessary. The index doesn't have
         * any directores, so we need to handle that manually, and we
         * need to keep track of the current position.
         */
        for (i = start; i < entries; ++i) {
                const git_index_entry *entry = git_index_get_byindex(index, i);
                const char *filename, *next_slash;

        /*
         * If we've left our (sub)tree, exit the loop and return. The
         * first check is an early out (and security for the
         * third). The second check is a simple prefix comparison. The
         * third check catches situations where there is a directory
         * win32/sys and a file win32mmap.c. Without it, the following
         * code believes there is a file win32/mmap.c
         */
                if (strlen(entry->path) < dirname_len ||
                    memcmp(entry->path, dirname, dirname_len) ||
                    (dirname_len > 0 && entry->path[dirname_len] != '/')) {
                        break;
                }

                filename = entry->path + dirname_len;
                if (*filename == '/')
                        filename++;
                next_slash = strchr(filename, '/');
                if (next_slash) {
                        git_oid sub_oid;
                        int written;
                        char *subdir, *last_comp;

                        subdir = git__strndup(entry->path, next_slash - entry->path);
                        GITERR_CHECK_ALLOC(subdir);

                        /* Write out the subtree */
                        written = write_tree(&sub_oid, repo, index, subdir, i);
                        if (written < 0) {
                                git__free(subdir);
                                goto on_error;
                        } else {
                                i = written - 1; /* -1 because of the loop increment */
                        }

                        /*
                         * We need to figure out what we want toinsert
                         * into this tree. If we're traversing
                         * deps/zlib/, then we only want to write
                         * 'zlib' into the tree.
                         */
                        last_comp = strrchr(subdir, '/');
                        if (last_comp) {
                                last_comp++; /* Get rid of the '/' */
                        } else {
                                last_comp = subdir;
                        }

                        error = append_entry(bld, last_comp, &sub_oid, S_IFDIR);
                        git__free(subdir);
                        if (error < 0)
                                goto on_error;
                } else {
                        error = append_entry(bld, filename, &entry->id, entry->mode);
                        if (error < 0)
                                goto on_error;
                }
        }

        if (git_treebuilder_write(oid, bld) < 0)
                goto on_error;

        git_treebuilder_free(bld);
        return (int)i;

on_error:
        git_treebuilder_free(bld);
        return -1;
}

int git_tree__write_index(
        git_oid *oid, git_index *index, git_repository *repo)
{
        int ret;
        git_tree *tree;
        bool old_ignore_case = false;

        assert(oid && index && repo);

        if (git_index_has_conflicts(index)) {
                giterr_set(GITERR_INDEX,
                        "Cannot create a tree from a not fully merged index.");
                return GIT_EUNMERGED;
        }

        if (index->tree != NULL && index->tree->entry_count >= 0) {
                git_oid_cpy(oid, &index->tree->oid);
                return 0;
        }

        /* The tree cache didn't help us; we'll have to write
         * out a tree. If the index is ignore_case, we must
         * make it case-sensitive for the duration of the tree-write
         * operation. */

        if (index->ignore_case) {
                old_ignore_case = true;
                git_index__set_ignore_case(index, false);
        }

        ret = write_tree(oid, repo, index, "", 0);

        if (old_ignore_case)
                git_index__set_ignore_case(index, true);

        index->tree = NULL;

        if (ret < 0)
                return ret;

        git_pool_clear(&index->tree_pool);

        if ((ret = git_tree_lookup(&tree, repo, oid)) < 0)
                return ret;

        /* Read the tree cache into the index */
        ret = git_tree_cache_read_tree(&index->tree, tree, &index->tree_pool);
        git_tree_free(tree);

        return ret;
}

int git_treebuilder_new(
        git_treebuilder **builder_p,
        git_repository *repo,
        const git_tree *source)
{
        git_treebuilder *bld;
        size_t i;

        assert(builder_p && repo);

        bld = git__calloc(1, sizeof(git_treebuilder));
        GITERR_CHECK_ALLOC(bld);

        bld->repo = repo;

        if (git_strmap_alloc(&bld->map) < 0) {
                git__free(bld);
                return -1;
        }

        if (source != NULL) {
                git_tree_entry *entry_src;

                git_array_foreach(source->entries, i, entry_src) {
                        if (append_entry(
                                bld, entry_src->filename,
                                entry_src->oid,
                                entry_src->attr) < 0)
                                goto on_error;
                }
        }

        *builder_p = bld;
        return 0;

on_error:
        git_treebuilder_free(bld);
        return -1;
}

static git_otype otype_from_mode(git_filemode_t filemode)
{
        switch (filemode) {
        case GIT_FILEMODE_TREE:
                return GIT_OBJ_TREE;
        case GIT_FILEMODE_COMMIT:
                return GIT_OBJ_COMMIT;
        default:
                return GIT_OBJ_BLOB;
        }
}

int git_treebuilder_insert(
        const git_tree_entry **entry_out,
        git_treebuilder *bld,
        const char *filename,
        const git_oid *id,
        git_filemode_t filemode)
{
        git_tree_entry *entry;
        int error;
        git_strmap_iter pos;

        assert(bld && id && filename);

        if (!valid_filemode(filemode))
                return tree_error("Failed to insert entry. Invalid filemode for file", filename);

        if (!valid_entry_name(bld->repo, filename))
                return tree_error("Failed to insert entry. Invalid name for a tree entry", filename);

        if (filemode != GIT_FILEMODE_COMMIT &&
            !git_object__is_valid(bld->repo, id, otype_from_mode(filemode)))
                return tree_error("Failed to insert entry; invalid object specified", filename);

        pos = git_strmap_lookup_index(bld->map, filename);
        if (git_strmap_valid_index(bld->map, pos)) {
                entry = git_strmap_value_at(bld->map, pos);
                git_oid_cpy((git_oid *) entry->oid, id);
        } else {
                entry = alloc_entry(filename, strlen(filename), id);
                GITERR_CHECK_ALLOC(entry);

                git_strmap_insert(bld->map, entry->filename, entry, error);

                if (error < 0) {
                        git_tree_entry_free(entry);
                        giterr_set(GITERR_TREE, "failed to insert %s", filename);
                        return -1;
                }
        }

        entry->attr = filemode;

        if (entry_out)
                *entry_out = entry;

        return 0;
}

static git_tree_entry *treebuilder_get(git_treebuilder *bld, const char *filename)
{
        git_tree_entry *entry = NULL;
        git_strmap_iter pos;

        assert(bld && filename);

        pos = git_strmap_lookup_index(bld->map, filename);
        if (git_strmap_valid_index(bld->map, pos))
                entry = git_strmap_value_at(bld->map, pos);

        return entry;
}

const git_tree_entry *git_treebuilder_get(git_treebuilder *bld, const char *filename)
{
        return treebuilder_get(bld, filename);
}

int git_treebuilder_remove(git_treebuilder *bld, const char *filename)
{
        git_tree_entry *entry = treebuilder_get(bld, filename);

        if (entry == NULL)
                return tree_error("Failed to remove entry. File isn't in the tree", filename);

        git_strmap_delete(bld->map, filename);
        git_tree_entry_free(entry);

        return 0;
}

int git_treebuilder_write(git_oid *oid, git_treebuilder *bld)
{
        int error = 0;
        size_t i, entrycount;
        git_buf tree = GIT_BUF_INIT;
        git_odb *odb;
        git_tree_entry *entry;
        git_vector entries;

        assert(bld);

        entrycount = git_strmap_num_entries(bld->map);
        if (git_vector_init(&entries, entrycount, entry_sort_cmp) < 0)
                return -1;

        git_strmap_foreach_value(bld->map, entry, {
                if (git_vector_insert(&entries, entry) < 0)
                        return -1;
        });

        git_vector_sort(&entries);

        /* Grow the buffer beforehand to an estimated size */
        error = git_buf_grow(&tree, entrycount * 72);

        for (i = 0; i < entries.length && !error; ++i) {
                git_tree_entry *entry = git_vector_get(&entries, i);

                git_buf_printf(&tree, "%o ", entry->attr);
                git_buf_put(&tree, entry->filename, entry->filename_len + 1);
                git_buf_put(&tree, (char *)entry->oid->id, GIT_OID_RAWSZ);

                if (git_buf_oom(&tree))
                        error = -1;
        }


        if (!error &&
                !(error = git_repository_odb__weakptr(&odb, bld->repo)))
                error = git_odb_write(oid, odb, tree.ptr, tree.size, GIT_OBJ_TREE);

        git_buf_free(&tree);
        git_vector_free(&entries);

        return error;
}

void git_treebuilder_filter(
        git_treebuilder *bld,
        git_treebuilder_filter_cb filter,
        void *payload)
{
        const char *filename;
        git_tree_entry *entry;

        assert(bld && filter);

        git_strmap_foreach(bld->map, filename, entry, {
                        if (filter(entry, payload)) {
                                git_strmap_delete(bld->map, filename);
                                git_tree_entry_free(entry);
                        }
        });
}

void git_treebuilder_clear(git_treebuilder *bld)
{
        git_tree_entry *e;

        assert(bld);

        git_strmap_foreach_value(bld->map, e, git_tree_entry_free(e));
        git_strmap_clear(bld->map);
}

void git_treebuilder_free(git_treebuilder *bld)
{
        if (bld == NULL)
                return;

        git_treebuilder_clear(bld);
        git_strmap_free(bld->map);
        git__free(bld);
}

static size_t subpath_len(const char *path)
{
        const char *slash_pos = strchr(path, '/');
        if (slash_pos == NULL)
                return strlen(path);

        return slash_pos - path;
}

int git_tree_entry_bypath(
        git_tree_entry **entry_out,
        const git_tree *root,
        const char *path)
{
        int error = 0;
        git_tree *subtree;
        const git_tree_entry *entry;
        size_t filename_len;

        /* Find how long is the current path component (i.e.
         * the filename between two slashes */
        filename_len = subpath_len(path);

        if (filename_len == 0) {
                giterr_set(GITERR_TREE, "Invalid tree path given");
                return GIT_ENOTFOUND;
        }

        entry = entry_fromname(root, path, filename_len);

        if (entry == NULL) {
                giterr_set(GITERR_TREE,
                           "the path '%.*s' does not exist in the given tree", filename_len, path);
                return GIT_ENOTFOUND;
        }

        switch (path[filename_len]) {
        case '/':
                /* If there are more components in the path...
                 * then this entry *must* be a tree */
                if (!git_tree_entry__is_tree(entry)) {
                        giterr_set(GITERR_TREE,
                                   "the path '%.*s' exists but is not a tree", filename_len, path);
                        return GIT_ENOTFOUND;
                }

                /* If there's only a slash left in the path, we 
                 * return the current entry; otherwise, we keep
                 * walking down the path */
                if (path[filename_len + 1] != '\0')
                        break;

        case '\0':
                /* If there are no more components in the path, return
                 * this entry */
                return git_tree_entry_dup(entry_out, entry);
        }

        if (git_tree_lookup(&subtree, root->object.repo, entry->oid) < 0)
                return -1;

        error = git_tree_entry_bypath(
                entry_out,
                subtree,
                path + filename_len + 1
        );

        git_tree_free(subtree);
        return error;
}

static int tree_walk(
        const git_tree *tree,
        git_treewalk_cb callback,
        git_buf *path,
        void *payload,
        bool preorder)
{
        int error = 0;
        size_t i;
        const git_tree_entry *entry;

        git_array_foreach(tree->entries, i, entry) {
                if (preorder) {
                        error = callback(path->ptr, entry, payload);
                        if (error < 0) { /* negative value stops iteration */
                                giterr_set_after_callback_function(error, "git_tree_walk");
                                break;
                        }
                        if (error > 0) { /* positive value skips this entry */
                                error = 0;
                                continue;
                        }
                }

                if (git_tree_entry__is_tree(entry)) {
                        git_tree *subtree;
                        size_t path_len = git_buf_len(path);

                        error = git_tree_lookup(&subtree, tree->object.repo, entry->oid);
                        if (error < 0)
                                break;

                        /* append the next entry to the path */
                        git_buf_puts(path, entry->filename);
                        git_buf_putc(path, '/');

                        if (git_buf_oom(path))
                                error = -1;
                        else
                                error = tree_walk(subtree, callback, path, payload, preorder);

                        git_tree_free(subtree);
                        if (error != 0)
                                break;

                        git_buf_truncate(path, path_len);
                }

                if (!preorder) {
                        error = callback(path->ptr, entry, payload);
                        if (error < 0) { /* negative value stops iteration */
                                giterr_set_after_callback_function(error, "git_tree_walk");
                                break;
                        }
                        error = 0;
                }
        }

        return error;
}

int git_tree_walk(
        const git_tree *tree,
        git_treewalk_mode mode,
        git_treewalk_cb callback,
        void *payload)
{
        int error = 0;
        git_buf root_path = GIT_BUF_INIT;

        if (mode != GIT_TREEWALK_POST && mode != GIT_TREEWALK_PRE) {
                giterr_set(GITERR_INVALID, "Invalid walking mode for tree walk");
                return -1;
        }

        error = tree_walk(
                tree, callback, &root_path, payload, (mode == GIT_TREEWALK_PRE));

        git_buf_free(&root_path);

        return error;
}

static int compare_entries(const void *_a, const void *_b)
{
        const git_tree_update *a = (git_tree_update *) _a;
        const git_tree_update *b = (git_tree_update *) _b;

        return strcmp(a->path, b->path);
}

static int on_dup_entry(void **old, void *new)
{
        GIT_UNUSED(old); GIT_UNUSED(new);

        giterr_set(GITERR_TREE, "duplicate entries given for update");
        return -1;
}

/*
 * We keep the previous tree and the new one at each level of the
 * stack. When we leave a level we're done with that tree and we can
 * write it out to the odb.
 */
typedef struct {
        git_treebuilder *bld;
        git_tree *tree;
        char *name;
} tree_stack_entry;

/** Count how many slashes (i.e. path components) there are in this string */
GIT_INLINE(size_t) count_slashes(const char *path)
{
        size_t count = 0;
        const char *slash;

        while ((slash = strchr(path, '/')) != NULL) {
                count++;
                path = slash + 1;
        }

        return count;
}

static bool next_component(git_buf *out, const char *in)
{
        const char *slash = strchr(in, '/');

        git_buf_clear(out);

        if (slash)
                git_buf_put(out, in, slash - in);

        return !!slash;
}

static int create_popped_tree(tree_stack_entry *current, tree_stack_entry *popped, git_buf *component)
{
        int error;
        git_oid new_tree;

        git_tree_free(popped->tree);

        /* If the tree would be empty, remove it from the one higher up */
        if (git_treebuilder_entrycount(popped->bld) == 0) {
                git_treebuilder_free(popped->bld);
                error = git_treebuilder_remove(current->bld, popped->name);
                git__free(popped->name);
                return error;
        }

        error = git_treebuilder_write(&new_tree, popped->bld);
        git_treebuilder_free(popped->bld);

        if (error < 0) {
                git__free(popped->name);
                return error;
        }

        /* We've written out the tree, now we have to put the new value into its parent */
        git_buf_clear(component);
        git_buf_puts(component, popped->name);
        git__free(popped->name);

        GITERR_CHECK_ALLOC(component->ptr);

        /* Error out if this would create a D/F conflict in this update */
        if (current->tree) {
                const git_tree_entry *to_replace;
                to_replace = git_tree_entry_byname(current->tree, component->ptr);
                if (to_replace && git_tree_entry_type(to_replace) != GIT_OBJ_TREE) {
                        giterr_set(GITERR_TREE, "D/F conflict when updating tree");
                        return -1;
                }
        }

        return git_treebuilder_insert(NULL, current->bld, component->ptr, &new_tree, GIT_FILEMODE_TREE);
}

int git_tree_create_updated(git_oid *out, git_repository *repo, git_tree *baseline, size_t nupdates, const git_tree_update *updates)
{
        git_array_t(tree_stack_entry) stack = GIT_ARRAY_INIT;
        tree_stack_entry *root_elem;
        git_vector entries;
        int error;
        size_t i;
        git_buf component = GIT_BUF_INIT;

        if ((error = git_vector_init(&entries, nupdates, compare_entries)) < 0)
                return error;

        /* Sort the entries for treversal */
        for (i = 0 ; i < nupdates; i++) {
                if ((error = git_vector_insert_sorted(&entries, (void *) &updates[i], on_dup_entry)) < 0)
                        goto cleanup;
        }

        root_elem = git_array_alloc(stack);
        GITERR_CHECK_ALLOC(root_elem);
        memset(root_elem, 0, sizeof(*root_elem));

        if (baseline && (error = git_tree_dup(&root_elem->tree, baseline)) < 0)
                goto cleanup;

        if ((error = git_treebuilder_new(&root_elem->bld, repo, root_elem->tree)) < 0)
                goto cleanup;

        for (i = 0; i < nupdates; i++) {
                const git_tree_update *last_update = i == 0 ? NULL : &updates[i-1];
                const git_tree_update *update = &updates[i];
                size_t common_prefix = 0, steps_up, j;
                const char *path;

                /* Figure out how much we need to change from the previous tree */
                if (last_update)
                        common_prefix = git_path_common_dirlen(last_update->path, update->path);

                /*
                 * The entries are sorted, so when we find we're no
                 * longer in the same directory, we need to abandon
                 * the old tree (steps up) and dive down to the next
                 * one.
                 */
                steps_up = last_update == NULL ? 0 : count_slashes(&last_update->path[common_prefix]);

                for (j = 0; j < steps_up; j++) {
                        tree_stack_entry *current, *popped = git_array_pop(stack);
                        assert(popped);

                        current = git_array_last(stack);
                        assert(current);

                        if ((error = create_popped_tree(current, popped, &component)) < 0)
                                goto cleanup;
                }

                /* Now that we've created the trees we popped from the stack, let's go back down */
                path = &update->path[common_prefix];
                while (next_component(&component, path)) {
                        tree_stack_entry *last, *new_entry;
                        const git_tree_entry *entry;

                        last = git_array_last(stack);
                        entry = last->tree ? git_tree_entry_byname(last->tree, component.ptr) : NULL;
                        if (entry && git_tree_entry_type(entry) != GIT_OBJ_TREE) {
                                giterr_set(GITERR_TREE, "D/F conflict when updating tree");
                                error = -1;
                                goto cleanup;
                        }

                        new_entry = git_array_alloc(stack);
                        GITERR_CHECK_ALLOC(new_entry);
                        memset(new_entry, 0, sizeof(*new_entry));

                        new_entry->tree = NULL;
                        if (entry && (error = git_tree_lookup(&new_entry->tree, repo, git_tree_entry_id(entry))) < 0)
                                goto cleanup;

                        if ((error = git_treebuilder_new(&new_entry->bld, repo, new_entry->tree)) < 0)
                                goto cleanup;

                        new_entry->name = git__strdup(component.ptr);
                        GITERR_CHECK_ALLOC(new_entry->name);

                        /* Get to the start of the next component */
                        path += component.size + 1;
                }

                /* After all that, we're finally at the place where we want to perform the update */
                switch (update->action) {
                        case GIT_TREE_UPDATE_UPSERT:
                        {
                                /* Make sure we're replacing something of the same type */
                                tree_stack_entry *last = git_array_last(stack);
                                char *basename = git_path_basename(update->path);
                                const git_tree_entry *e = git_treebuilder_get(last->bld, basename);
                                if (e && git_tree_entry_type(e) != git_object__type_from_filemode(update->filemode)) {
                                        git__free(basename);
                                        giterr_set(GITERR_TREE, "Cannot replace '%s' with '%s' at '%s'",
                                                   git_object_type2string(git_tree_entry_type(e)),
                                                   git_object_type2string(git_object__type_from_filemode(update->filemode)),
                                                   update->path);
                                        error = -1;
                                        goto cleanup;
                                }

                                error = git_treebuilder_insert(NULL, last->bld, basename, &update->id, update->filemode);
                                git__free(basename);
                                break;
                        }
                        case GIT_TREE_UPDATE_REMOVE:
                        {
                                char *basename = git_path_basename(update->path);
                                error = git_treebuilder_remove(git_array_last(stack)->bld, basename);
                                git__free(basename);
                                break;
                        }
                        default:
                                giterr_set(GITERR_TREE, "unkown action for update");
                                error = -1;
                                goto cleanup;
                }

                if (error < 0)
                        goto cleanup;
        }

        /* We're done, go up the stack again and write out the tree */
        {
                tree_stack_entry *current = NULL, *popped = NULL;
                while ((popped = git_array_pop(stack)) != NULL) {
                        current = git_array_last(stack);
                        /* We've reached the top, current is the root tree */
                        if (!current)
                                break;

                        if ((error = create_popped_tree(current, popped, &component)) < 0)
                                goto cleanup;
                }

                /* Write out the root tree */
                git__free(popped->name);
                git_tree_free(popped->tree);

                error = git_treebuilder_write(out, popped->bld);
                git_treebuilder_free(popped->bld);
                if (error < 0)
                        goto cleanup;
        }

cleanup:
        {
                tree_stack_entry *e;
                while ((e = git_array_pop(stack)) != NULL) {
                        git_treebuilder_free(e->bld);
                        git_tree_free(e->tree);
                        git__free(e->name);
                }
        }

        git_buf_free(&component);
        git_array_clear(stack);
        git_vector_free(&entries);
        return error;
}