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[libgit2.git] / src / midx.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 "midx.h"

#include "array.h"
#include "buffer.h"
#include "filebuf.h"
#include "futils.h"
#include "hash.h"
#include "odb.h"
#include "pack.h"
#include "path.h"
#include "repository.h"

#define MIDX_SIGNATURE 0x4d494458 /* "MIDX" */
#define MIDX_VERSION 1
#define MIDX_OBJECT_ID_VERSION 1
struct git_midx_header {
        uint32_t signature;
        uint8_t version;
        uint8_t object_id_version;
        uint8_t chunks;
        uint8_t base_midx_files;
        uint32_t packfiles;
};

#define MIDX_PACKFILE_NAMES_ID 0x504e414d          /* "PNAM" */
#define MIDX_OID_FANOUT_ID 0x4f494446      /* "OIDF" */
#define MIDX_OID_LOOKUP_ID 0x4f49444c      /* "OIDL" */
#define MIDX_OBJECT_OFFSETS_ID 0x4f4f4646          /* "OOFF" */
#define MIDX_OBJECT_LARGE_OFFSETS_ID 0x4c4f4646 /* "LOFF" */

struct git_midx_chunk {
        off64_t offset;
        size_t length;
};

typedef int (*midx_write_cb)(const char *buf, size_t size, void *cb_data);

static int midx_error(const char *message)
{
        git_error_set(GIT_ERROR_ODB, "invalid multi-pack-index file - %s", message);
        return -1;
}

static int midx_parse_packfile_names(
                git_midx_file *idx,
                const unsigned char *data,
                uint32_t packfiles,
                struct git_midx_chunk *chunk)
{
        int error;
        uint32_t i;
        char *packfile_name = (char *)(data + chunk->offset);
        size_t chunk_size = chunk->length, len;
        if (chunk->offset == 0)
                return midx_error("missing Packfile Names chunk");
        if (chunk->length == 0)
                return midx_error("empty Packfile Names chunk");
        if ((error = git_vector_init(&idx->packfile_names, packfiles, git__strcmp_cb)) < 0)
                return error;
        for (i = 0; i < packfiles; ++i) {
                len = p_strnlen(packfile_name, chunk_size);
                if (len == 0)
                        return midx_error("empty packfile name");
                if (len + 1 > chunk_size)
                        return midx_error("unterminated packfile name");
                git_vector_insert(&idx->packfile_names, packfile_name);
                if (i && strcmp(git_vector_get(&idx->packfile_names, i - 1), packfile_name) >= 0)
                        return midx_error("packfile names are not sorted");
                if (strlen(packfile_name) <= strlen(".idx") || git__suffixcmp(packfile_name, ".idx") != 0)
                        return midx_error("non-.idx packfile name");
                if (strchr(packfile_name, '/') != NULL || strchr(packfile_name, '\\') != NULL)
                        return midx_error("non-local packfile");
                packfile_name += len + 1;
                chunk_size -= len + 1;
        }
        return 0;
}

static int midx_parse_oid_fanout(
                git_midx_file *idx,
                const unsigned char *data,
                struct git_midx_chunk *chunk_oid_fanout)
{
        uint32_t i, nr;
        if (chunk_oid_fanout->offset == 0)
                return midx_error("missing OID Fanout chunk");
        if (chunk_oid_fanout->length == 0)
                return midx_error("empty OID Fanout chunk");
        if (chunk_oid_fanout->length != 256 * 4)
                return midx_error("OID Fanout chunk has wrong length");

        idx->oid_fanout = (const uint32_t *)(data + chunk_oid_fanout->offset);
        nr = 0;
        for (i = 0; i < 256; ++i) {
                uint32_t n = ntohl(idx->oid_fanout[i]);
                if (n < nr)
                        return midx_error("index is non-monotonic");
                nr = n;
        }
        idx->num_objects = nr;
        return 0;
}

static int midx_parse_oid_lookup(
                git_midx_file *idx,
                const unsigned char *data,
                struct git_midx_chunk *chunk_oid_lookup)
{
        uint32_t i;
        git_oid *oid, *prev_oid, zero_oid = {{0}};

        if (chunk_oid_lookup->offset == 0)
                return midx_error("missing OID Lookup chunk");
        if (chunk_oid_lookup->length == 0)
                return midx_error("empty OID Lookup chunk");
        if (chunk_oid_lookup->length != idx->num_objects * GIT_OID_RAWSZ)
                return midx_error("OID Lookup chunk has wrong length");

        idx->oid_lookup = oid = (git_oid *)(data + chunk_oid_lookup->offset);
        prev_oid = &zero_oid;
        for (i = 0; i < idx->num_objects; ++i, ++oid) {
                if (git_oid_cmp(prev_oid, oid) >= 0)
                        return midx_error("OID Lookup index is non-monotonic");
                prev_oid = oid;
        }

        return 0;
}

static int midx_parse_object_offsets(
                git_midx_file *idx,
                const unsigned char *data,
                struct git_midx_chunk *chunk_object_offsets)
{
        if (chunk_object_offsets->offset == 0)
                return midx_error("missing Object Offsets chunk");
        if (chunk_object_offsets->length == 0)
                return midx_error("empty Object Offsets chunk");
        if (chunk_object_offsets->length != idx->num_objects * 8)
                return midx_error("Object Offsets chunk has wrong length");

        idx->object_offsets = data + chunk_object_offsets->offset;

        return 0;
}

static int midx_parse_object_large_offsets(
                git_midx_file *idx,
                const unsigned char *data,
                struct git_midx_chunk *chunk_object_large_offsets)
{
        if (chunk_object_large_offsets->length == 0)
                return 0;
        if (chunk_object_large_offsets->length % 8 != 0)
                return midx_error("malformed Object Large Offsets chunk");

        idx->object_large_offsets = data + chunk_object_large_offsets->offset;
        idx->num_object_large_offsets = chunk_object_large_offsets->length / 8;

        return 0;
}

int git_midx_parse(
                git_midx_file *idx,
                const unsigned char *data,
                size_t size)
{
        struct git_midx_header *hdr;
        const unsigned char *chunk_hdr;
        struct git_midx_chunk *last_chunk;
        uint32_t i;
        off64_t last_chunk_offset, chunk_offset, trailer_offset;
        git_oid idx_checksum = {{0}};
        int error;
        struct git_midx_chunk chunk_packfile_names = {0},
                                         chunk_oid_fanout = {0},
                                         chunk_oid_lookup = {0},
                                         chunk_object_offsets = {0},
                                         chunk_object_large_offsets = {0};

        GIT_ASSERT_ARG(idx);

        if (size < sizeof(struct git_midx_header) + GIT_OID_RAWSZ)
                return midx_error("multi-pack index is too short");

        hdr = ((struct git_midx_header *)data);

        if (hdr->signature != htonl(MIDX_SIGNATURE) ||
            hdr->version != MIDX_VERSION ||
            hdr->object_id_version != MIDX_OBJECT_ID_VERSION) {
                return midx_error("unsupported multi-pack index version");
        }
        if (hdr->chunks == 0)
                return midx_error("no chunks in multi-pack index");

        /*
         * The very first chunk's offset should be after the header, all the chunk
         * headers, and a special zero chunk.
         */
        last_chunk_offset =
                        sizeof(struct git_midx_header) +
                        (1 + hdr->chunks) * 12;
        trailer_offset = size - GIT_OID_RAWSZ;
        if (trailer_offset < last_chunk_offset)
                return midx_error("wrong index size");
        git_oid_cpy(&idx->checksum, (git_oid *)(data + trailer_offset));

        if (git_hash_buf(&idx_checksum, data, (size_t)trailer_offset) < 0)
                return midx_error("could not calculate signature");
        if (!git_oid_equal(&idx_checksum, &idx->checksum))
                return midx_error("index signature mismatch");

        chunk_hdr = data + sizeof(struct git_midx_header);
        last_chunk = NULL;
        for (i = 0; i < hdr->chunks; ++i, chunk_hdr += 12) {
                chunk_offset = ((off64_t)ntohl(*((uint32_t *)(chunk_hdr + 4)))) << 32 |
                                ((off64_t)ntohl(*((uint32_t *)(chunk_hdr + 8))));
                if (chunk_offset < last_chunk_offset)
                        return midx_error("chunks are non-monotonic");
                if (chunk_offset >= trailer_offset)
                        return midx_error("chunks extend beyond the trailer");
                if (last_chunk != NULL)
                        last_chunk->length = (size_t)(chunk_offset - last_chunk_offset);
                last_chunk_offset = chunk_offset;

                switch (ntohl(*((uint32_t *)(chunk_hdr + 0)))) {
                case MIDX_PACKFILE_NAMES_ID:
                        chunk_packfile_names.offset = last_chunk_offset;
                        last_chunk = &chunk_packfile_names;
                        break;

                case MIDX_OID_FANOUT_ID:
                        chunk_oid_fanout.offset = last_chunk_offset;
                        last_chunk = &chunk_oid_fanout;
                        break;

                case MIDX_OID_LOOKUP_ID:
                        chunk_oid_lookup.offset = last_chunk_offset;
                        last_chunk = &chunk_oid_lookup;
                        break;

                case MIDX_OBJECT_OFFSETS_ID:
                        chunk_object_offsets.offset = last_chunk_offset;
                        last_chunk = &chunk_object_offsets;
                        break;

                case MIDX_OBJECT_LARGE_OFFSETS_ID:
                        chunk_object_large_offsets.offset = last_chunk_offset;
                        last_chunk = &chunk_object_large_offsets;
                        break;

                default:
                        return midx_error("unrecognized chunk ID");
                }
        }
        last_chunk->length = (size_t)(trailer_offset - last_chunk_offset);

        error = midx_parse_packfile_names(
                        idx, data, ntohl(hdr->packfiles), &chunk_packfile_names);
        if (error < 0)
                return error;
        error = midx_parse_oid_fanout(idx, data, &chunk_oid_fanout);
        if (error < 0)
                return error;
        error = midx_parse_oid_lookup(idx, data, &chunk_oid_lookup);
        if (error < 0)
                return error;
        error = midx_parse_object_offsets(idx, data, &chunk_object_offsets);
        if (error < 0)
                return error;
        error = midx_parse_object_large_offsets(idx, data, &chunk_object_large_offsets);
        if (error < 0)
                return error;

        return 0;
}

int git_midx_open(
                git_midx_file **idx_out,
                const char *path)
{
        git_midx_file *idx;
        git_file fd = -1;
        size_t idx_size;
        struct stat st;
        int error;

        /* TODO: properly open the file without access time using O_NOATIME */
        fd = git_futils_open_ro(path);
        if (fd < 0)
                return fd;

        if (p_fstat(fd, &st) < 0) {
                p_close(fd);
                git_error_set(GIT_ERROR_ODB, "multi-pack-index file not found - '%s'", path);
                return -1;
        }

        if (!S_ISREG(st.st_mode) || !git__is_sizet(st.st_size)) {
                p_close(fd);
                git_error_set(GIT_ERROR_ODB, "invalid pack index '%s'", path);
                return -1;
        }
        idx_size = (size_t)st.st_size;

        idx = git__calloc(1, sizeof(git_midx_file));
        GIT_ERROR_CHECK_ALLOC(idx);

        error = git_buf_sets(&idx->filename, path);
        if (error < 0)
                return error;

        error = git_futils_mmap_ro(&idx->index_map, fd, 0, idx_size);
        p_close(fd);
        if (error < 0) {
                git_midx_free(idx);
                return error;
        }

        if ((error = git_midx_parse(idx, idx->index_map.data, idx_size)) < 0) {
                git_midx_free(idx);
                return error;
        }

        *idx_out = idx;
        return 0;
}

bool git_midx_needs_refresh(
                const git_midx_file *idx,
                const char *path)
{
        git_file fd = -1;
        struct stat st;
        ssize_t bytes_read;
        git_oid idx_checksum = {{0}};

        /* TODO: properly open the file without access time using O_NOATIME */
        fd = git_futils_open_ro(path);
        if (fd < 0)
                return true;

        if (p_fstat(fd, &st) < 0) {
                p_close(fd);
                return true;
        }

        if (!S_ISREG(st.st_mode) ||
            !git__is_sizet(st.st_size) ||
            (size_t)st.st_size != idx->index_map.len) {
                p_close(fd);
                return true;
        }

        bytes_read = p_pread(fd, &idx_checksum, GIT_OID_RAWSZ, st.st_size - GIT_OID_RAWSZ);
        p_close(fd);

        if (bytes_read != GIT_OID_RAWSZ)
                return true;

        return !git_oid_equal(&idx_checksum, &idx->checksum);
}

int git_midx_entry_find(
                git_midx_entry *e,
                git_midx_file *idx,
                const git_oid *short_oid,
                size_t len)
{
        int pos, found = 0;
        size_t pack_index;
        uint32_t hi, lo;
        const git_oid *current = NULL;
        const unsigned char *object_offset;
        off64_t offset;

        GIT_ASSERT_ARG(idx);

        hi = ntohl(idx->oid_fanout[(int)short_oid->id[0]]);
        lo = ((short_oid->id[0] == 0x0) ? 0 : ntohl(idx->oid_fanout[(int)short_oid->id[0] - 1]));

        pos = git_pack__lookup_sha1(idx->oid_lookup, GIT_OID_RAWSZ, lo, hi, short_oid->id);

        if (pos >= 0) {
                /* An object matching exactly the oid was found */
                found = 1;
                current = idx->oid_lookup + pos;
        } else {
                /* No object was found */
                /* pos refers to the object with the "closest" oid to short_oid */
                pos = -1 - pos;
                if (pos < (int)idx->num_objects) {
                        current = idx->oid_lookup + pos;

                        if (!git_oid_ncmp(short_oid, current, len))
                                found = 1;
                }
        }

        if (found && len != GIT_OID_HEXSZ && pos + 1 < (int)idx->num_objects) {
                /* Check for ambiguousity */
                const git_oid *next = current + 1;

                if (!git_oid_ncmp(short_oid, next, len)) {
                        found = 2;
                }
        }

        if (!found)
                return git_odb__error_notfound("failed to find offset for multi-pack index entry", short_oid, len);
        if (found > 1)
                return git_odb__error_ambiguous("found multiple offsets for multi-pack index entry");

        object_offset = idx->object_offsets + pos * 8;
        offset = ntohl(*((uint32_t *)(object_offset + 4)));
        if (offset & 0x80000000) {
                uint32_t object_large_offsets_pos = offset & 0x7fffffff;
                const unsigned char *object_large_offsets_index = idx->object_large_offsets;

                /* Make sure we're not being sent out of bounds */
                if (object_large_offsets_pos >= idx->num_object_large_offsets)
                        return git_odb__error_notfound("invalid index into the object large offsets table", short_oid, len);

                object_large_offsets_index += 8 * object_large_offsets_pos;

                offset = (((uint64_t)ntohl(*((uint32_t *)(object_large_offsets_index + 0)))) << 32) |
                                ntohl(*((uint32_t *)(object_large_offsets_index + 4)));
        }
        pack_index = ntohl(*((uint32_t *)(object_offset + 0)));
        if (pack_index >= git_vector_length(&idx->packfile_names))
                return midx_error("invalid index into the packfile names table");
        e->pack_index = pack_index;
        e->offset = offset;
        git_oid_cpy(&e->sha1, current);
        return 0;
}

int git_midx_foreach_entry(
                git_midx_file *idx,
                git_odb_foreach_cb cb,
                void *data)
{
        size_t i;
        int error;

        GIT_ASSERT_ARG(idx);

        for (i = 0; i < idx->num_objects; ++i) {
                if ((error = cb(&idx->oid_lookup[i], data)) != 0)
                        return git_error_set_after_callback(error);
        }

        return error;
}

int git_midx_close(git_midx_file *idx)
{
        GIT_ASSERT_ARG(idx);

        if (idx->index_map.data)
                git_futils_mmap_free(&idx->index_map);

        git_vector_free(&idx->packfile_names);

        return 0;
}

void git_midx_free(git_midx_file *idx)
{
        if (!idx)
                return;

        git_buf_dispose(&idx->filename);
        git_midx_close(idx);
        git__free(idx);
}

static int packfile__cmp(const void *a_, const void *b_)
{
        const struct git_pack_file *a = a_;
        const struct git_pack_file *b = b_;

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

int git_midx_writer_new(
                git_midx_writer **out,
                const char *pack_dir)
{
        git_midx_writer *w = git__calloc(1, sizeof(git_midx_writer));
        GIT_ERROR_CHECK_ALLOC(w);

        if (git_buf_sets(&w->pack_dir, pack_dir) < 0) {
                git__free(w);
                return -1;
        }
        git_path_squash_slashes(&w->pack_dir);

        if (git_vector_init(&w->packs, 0, packfile__cmp) < 0) {
                git_buf_dispose(&w->pack_dir);
                git__free(w);
                return -1;
        }

        *out = w;
        return 0;
}

void git_midx_writer_free(git_midx_writer *w)
{
        struct git_pack_file *p;
        size_t i;

        if (!w)
                return;

        git_vector_foreach (&w->packs, i, p)
                git_mwindow_put_pack(p);
        git_vector_free(&w->packs);
        git_buf_dispose(&w->pack_dir);
        git__free(w);
}

int git_midx_writer_add(
                git_midx_writer *w,
                const char *idx_path)
{
        git_buf idx_path_buf = GIT_BUF_INIT;
        int error;
        struct git_pack_file *p;

        error = git_path_prettify(&idx_path_buf, idx_path, git_buf_cstr(&w->pack_dir));
        if (error < 0)
                return error;

        error = git_mwindow_get_pack(&p, git_buf_cstr(&idx_path_buf));
        git_buf_dispose(&idx_path_buf);
        if (error < 0)
                return error;

        error = git_vector_insert(&w->packs, p);
        if (error < 0) {
                git_mwindow_put_pack(p);
                return error;
        }

        return 0;
}

typedef git_array_t(git_midx_entry) object_entry_array_t;

struct object_entry_cb_state {
        uint32_t pack_index;
        object_entry_array_t *object_entries_array;
};

static int object_entry__cb(const git_oid *oid, off64_t offset, void *data)
{
        struct object_entry_cb_state *state = (struct object_entry_cb_state *)data;

        git_midx_entry *entry = git_array_alloc(*state->object_entries_array);
        GIT_ERROR_CHECK_ALLOC(entry);

        git_oid_cpy(&entry->sha1, oid);
        entry->offset = offset;
        entry->pack_index = state->pack_index;

        return 0;
}

static int object_entry__cmp(const void *a_, const void *b_)
{
        const git_midx_entry *a = (const git_midx_entry *)a_;
        const git_midx_entry *b = (const git_midx_entry *)b_;

        return git_oid_cmp(&a->sha1, &b->sha1);
}

static int write_offset(off64_t offset, midx_write_cb write_cb, void *cb_data)
{
        int error;
        uint32_t word;

        word = htonl((uint32_t)((offset >> 32) & 0xffffffffu));
        error = write_cb((const char *)&word, sizeof(word), cb_data);
        if (error < 0)
                return error;
        word = htonl((uint32_t)((offset >> 0) & 0xffffffffu));
        error = write_cb((const char *)&word, sizeof(word), cb_data);
        if (error < 0)
                return error;

        return 0;
}

static int write_chunk_header(int chunk_id, off64_t offset, midx_write_cb write_cb, void *cb_data)
{
        uint32_t word = htonl(chunk_id);
        int error = write_cb((const char *)&word, sizeof(word), cb_data);
        if (error < 0)
                return error;
        return write_offset(offset, write_cb, cb_data);

        return 0;
}

static int midx_write_buf(const char *buf, size_t size, void *data)
{
        git_buf *b = (git_buf *)data;
        return git_buf_put(b, buf, size);
}

struct midx_write_hash_context {
        midx_write_cb write_cb;
        void *cb_data;
        git_hash_ctx *ctx;
};

static int midx_write_hash(const char *buf, size_t size, void *data)
{
        struct midx_write_hash_context *ctx = (struct midx_write_hash_context *)data;
        int error;

        error = git_hash_update(ctx->ctx, buf, size);
        if (error < 0)
                return error;

        return ctx->write_cb(buf, size, ctx->cb_data);
}

static int midx_write(
                git_midx_writer *w,
                midx_write_cb write_cb,
                void *cb_data)
{
        int error = 0;
        size_t i;
        struct git_pack_file *p;
        struct git_midx_header hdr = {0};
        uint32_t oid_fanout_count;
        uint32_t object_large_offsets_count;
        uint32_t oid_fanout[256];
        off64_t offset;
        git_buf packfile_names = GIT_BUF_INIT,
                oid_lookup = GIT_BUF_INIT,
                object_offsets = GIT_BUF_INIT,
                object_large_offsets = GIT_BUF_INIT;
        git_oid idx_checksum = {{0}};
        git_midx_entry *entry;
        object_entry_array_t object_entries_array = GIT_ARRAY_INIT;
        git_vector object_entries = GIT_VECTOR_INIT;
        git_hash_ctx ctx;
        struct midx_write_hash_context hash_cb_data = {0};

        hdr.signature = htonl(MIDX_SIGNATURE);
        hdr.version = MIDX_VERSION;
        hdr.object_id_version = MIDX_OBJECT_ID_VERSION;
        hdr.base_midx_files = 0;

        hash_cb_data.write_cb = write_cb;
        hash_cb_data.cb_data = cb_data;
        hash_cb_data.ctx = &ctx;

        error = git_hash_ctx_init(&ctx);
        if (error < 0)
                return error;
        cb_data = &hash_cb_data;
        write_cb = midx_write_hash;

        git_vector_sort(&w->packs);
        git_vector_foreach (&w->packs, i, p) {
                git_buf relative_index = GIT_BUF_INIT;
                struct object_entry_cb_state state = {0};
                size_t path_len;

                state.pack_index = (uint32_t)i;
                state.object_entries_array = &object_entries_array;

                error = git_buf_sets(&relative_index, p->pack_name);
                if (error < 0)
                        goto cleanup;
                error = git_path_make_relative(&relative_index, git_buf_cstr(&w->pack_dir));
                if (error < 0) {
                        git_buf_dispose(&relative_index);
                        goto cleanup;
                }
                path_len = git_buf_len(&relative_index);
                if (path_len <= strlen(".pack") || git__suffixcmp(git_buf_cstr(&relative_index), ".pack") != 0) {
                        git_buf_dispose(&relative_index);
                        git_error_set(GIT_ERROR_INVALID, "invalid packfile name: '%s'", p->pack_name);
                        error = -1;
                        goto cleanup;
                }
                path_len -= strlen(".pack");

                git_buf_put(&packfile_names, git_buf_cstr(&relative_index), path_len);
                git_buf_puts(&packfile_names, ".idx");
                git_buf_putc(&packfile_names, '\0');
                git_buf_dispose(&relative_index);

                error = git_pack_foreach_entry_offset(p, object_entry__cb, &state);
                if (error < 0)
                        goto cleanup;
        }

        /* Sort the object entries. */
        error = git_vector_init(&object_entries, git_array_size(object_entries_array), object_entry__cmp);
        if (error < 0)
                goto cleanup;
        git_array_foreach (object_entries_array, i, entry) {
                if ((error = git_vector_set(NULL, &object_entries, i, entry)) < 0)
                        goto cleanup;
        }
        git_vector_set_sorted(&object_entries, 0);
        git_vector_sort(&object_entries);
        git_vector_uniq(&object_entries, NULL);

        /* Pad the packfile names so it is a multiple of four. */
        while (git_buf_len(&packfile_names) & 3)
                git_buf_putc(&packfile_names, '\0');

        /* Fill the OID Fanout table. */
        oid_fanout_count = 0;
        for (i = 0; i < 256; i++) {
                while (oid_fanout_count < git_vector_length(&object_entries) &&
                       ((const git_midx_entry *)git_vector_get(&object_entries, oid_fanout_count))->sha1.id[0] <= i)
                        ++oid_fanout_count;
                oid_fanout[i] = htonl(oid_fanout_count);
        }

        /* Fill the OID Lookup table. */
        git_vector_foreach (&object_entries, i, entry) {
                error = git_buf_put(&oid_lookup, (const char *)&entry->sha1, sizeof(entry->sha1));
                if (error < 0)
                        goto cleanup;
        }

        /* Fill the Object Offsets and Object Large Offsets tables. */
        object_large_offsets_count = 0;
        git_vector_foreach (&object_entries, i, entry) {
                uint32_t word;

                word = htonl((uint32_t)entry->pack_index);
                error = git_buf_put(&object_offsets, (const char *)&word, sizeof(word));
                if (error < 0)
                        goto cleanup;
                if (entry->offset >= 0x80000000l) {
                        word = htonl(0x80000000u | object_large_offsets_count++);
                        if ((error = write_offset(entry->offset, midx_write_buf, &object_large_offsets)) < 0)
                                goto cleanup;
                } else {
                        word = htonl((uint32_t)entry->offset & 0x7fffffffu);
                }

                error = git_buf_put(&object_offsets, (const char *)&word, sizeof(word));
                if (error < 0)
                        goto cleanup;
        }

        /* Write the header. */
        hdr.packfiles = htonl((uint32_t)git_vector_length(&w->packs));
        hdr.chunks = 4;
        if (git_buf_len(&object_large_offsets) > 0)
                hdr.chunks++;
        error = write_cb((const char *)&hdr, sizeof(hdr), cb_data);
        if (error < 0)
                goto cleanup;

        /* Write the chunk headers. */
        offset = sizeof(hdr) + (hdr.chunks + 1) * 12;
        error = write_chunk_header(MIDX_PACKFILE_NAMES_ID, offset, write_cb, cb_data);
        if (error < 0)
                goto cleanup;
        offset += git_buf_len(&packfile_names);
        error = write_chunk_header(MIDX_OID_FANOUT_ID, offset, write_cb, cb_data);
        if (error < 0)
                goto cleanup;
        offset += sizeof(oid_fanout);
        error = write_chunk_header(MIDX_OID_LOOKUP_ID, offset, write_cb, cb_data);
        if (error < 0)
                goto cleanup;
        offset += git_buf_len(&oid_lookup);
        error = write_chunk_header(MIDX_OBJECT_OFFSETS_ID, offset, write_cb, cb_data);
        if (error < 0)
                goto cleanup;
        offset += git_buf_len(&object_offsets);
        if (git_buf_len(&object_large_offsets) > 0) {
                error = write_chunk_header(MIDX_OBJECT_LARGE_OFFSETS_ID, offset, write_cb, cb_data);
                if (error < 0)
                        goto cleanup;
                offset += git_buf_len(&object_large_offsets);
        }
        error = write_chunk_header(0, offset, write_cb, cb_data);
        if (error < 0)
                goto cleanup;

        /* Write all the chunks. */
        error = write_cb(git_buf_cstr(&packfile_names), git_buf_len(&packfile_names), cb_data);
        if (error < 0)
                goto cleanup;
        error = write_cb((const char *)oid_fanout, sizeof(oid_fanout), cb_data);
        if (error < 0)
                goto cleanup;
        error = write_cb(git_buf_cstr(&oid_lookup), git_buf_len(&oid_lookup), cb_data);
        if (error < 0)
                goto cleanup;
        error = write_cb(git_buf_cstr(&object_offsets), git_buf_len(&object_offsets), cb_data);
        if (error < 0)
                goto cleanup;
        error = write_cb(git_buf_cstr(&object_large_offsets), git_buf_len(&object_large_offsets), cb_data);
        if (error < 0)
                goto cleanup;

        /* Finalize the checksum and write the trailer. */
        error = git_hash_final(&idx_checksum, &ctx);
        if (error < 0)
                goto cleanup;
        error = write_cb((const char *)&idx_checksum, sizeof(idx_checksum), cb_data);
        if (error < 0)
                goto cleanup;

cleanup:
        git_array_clear(object_entries_array);
        git_vector_free(&object_entries);
        git_buf_dispose(&packfile_names);
        git_buf_dispose(&oid_lookup);
        git_buf_dispose(&object_offsets);
        git_buf_dispose(&object_large_offsets);
        git_hash_ctx_cleanup(&ctx);
        return error;
}

static int midx_write_filebuf(const char *buf, size_t size, void *data)
{
        git_filebuf *f = (git_filebuf *)data;
        return git_filebuf_write(f, buf, size);
}

int git_midx_writer_commit(
                git_midx_writer *w)
{
        int error;
        int filebuf_flags = GIT_FILEBUF_DO_NOT_BUFFER;
        git_buf midx_path = GIT_BUF_INIT;
        git_filebuf output = GIT_FILEBUF_INIT;

        error = git_buf_joinpath(&midx_path, git_buf_cstr(&w->pack_dir), "multi-pack-index");
        if (error < 0)
                return error;

        if (git_repository__fsync_gitdir)
                filebuf_flags |= GIT_FILEBUF_FSYNC;
        error = git_filebuf_open(&output, git_buf_cstr(&midx_path), filebuf_flags, 0644);
        git_buf_dispose(&midx_path);
        if (error < 0)
                return error;

        error = midx_write(w, midx_write_filebuf, &output);
        if (error < 0) {
                git_filebuf_cleanup(&output);
                return error;
        }

        return git_filebuf_commit(&output);
}

int git_midx_writer_dump(
                git_buf *midx,
                git_midx_writer *w)
{
        return midx_write(w, midx_write_buf, midx);
}