git-pack-objects: create a packed object representation.

This is kind of like a tar-ball for a set of objects, ready to be
shipped off to another end.  Alternatively, you could use is as a packed
representation of the object database directly, if you changed
"read_sha1_file()" to read these kinds of packs.

The latter is partiularly useful to generate a "packed history", ie you
could pack up your old history efficiently, but still have it available
(at a performance hit, of course).

I haven't actually written an unpacker yet, so the end result has not
been verified in any way yet.  I obviously always write bug-free code,
so it just has to work, no?

diff --git a/Makefile b/Makefile
index fd5c80f753fd696f251bc18150d6cd34d4faa161..37fdbb04efbb53e6e4112b56114845206940219b 100644 (file)
--- a/Makefile
+++ b/Makefile
@@ -35,7 +35,8 @@ PROG=   git-update-cache git-diff-files git-init-db git-write-tree \
        git-http-pull git-ssh-push git-ssh-pull git-rev-list git-mktag \
        git-diff-helper git-tar-tree git-local-pull git-write-blob \
        git-get-tar-commit-id git-mkdelta git-apply git-stripspace \
-       git-cvs2git git-diff-stages git-rev-parse git-patch-id
+       git-cvs2git git-diff-stages git-rev-parse git-patch-id \
+       git-pack-objects
 
 all: $(PROG)
 
@@ -122,6 +123,7 @@ git-cvs2git: cvs2git.c
 git-diff-stages: diff-stages.c
 git-rev-parse: rev-parse.c
 git-patch-id: patch-id.c
+git-pack-objects: pack-objects.c
 
 git-http-pull: LIBS += -lcurl
 git-rev-list: LIBS += -lssl

diff --git a/pack-objects.c b/pack-objects.c
new file mode 100644 (file)
index 0000000..322c4bc
--- /dev/null
+++ b/pack-objects.c
@@ -0,0 +1,403 @@
+#include "cache.h"
+#include "object.h"
+#include "delta.h"
+
+static const char pack_usage[] = "git-pack-objects [--window=N] base-name < object-list";
+
+enum object_type {
+       OBJ_NONE,
+       OBJ_COMMIT,
+       OBJ_TREE,
+       OBJ_BLOB,
+       OBJ_DELTA       // NOTE! This is _not_ the same as a "delta" object in the filesystem
+};
+
+struct object_entry {
+       unsigned char sha1[20];
+       unsigned long size;
+       unsigned long offset;
+       unsigned int depth;
+       unsigned int flags;
+       enum object_type type;
+       unsigned long delta_size;
+       struct object_entry *delta;
+};
+
+static struct object_entry **sorted_by_sha, **sorted_by_type;
+static struct object_entry *objects = NULL;
+static int nr_objects = 0, nr_alloc = 0;
+static int delta_window = 10;
+static const char *base_name;
+
+struct myfile {
+       int fd;
+       unsigned long chars;
+       unsigned char buffer[8192];
+};
+
+static FILE *create_file(const char *suffix)
+{
+       static char filename[PATH_MAX];
+       unsigned len;
+
+       len = snprintf(filename, PATH_MAX, "%s.%s", base_name, suffix);
+       if (len >= PATH_MAX)
+               die("you wascally wabbit, you");
+       return fopen(filename, "w");
+}
+
+static unsigned long fwrite_compressed(void *in, unsigned long size, FILE *f)
+{
+       z_stream stream;
+       unsigned long maxsize;
+       void *out;
+
+       memset(&stream, 0, sizeof(stream));
+       deflateInit(&stream, Z_DEFAULT_COMPRESSION);
+       maxsize = deflateBound(&stream, size);
+       out = xmalloc(maxsize);
+
+       /* Compress it */
+       stream.next_in = in;
+       stream.avail_in = size;
+
+       stream.next_out = out;
+       stream.avail_out = maxsize;
+
+       while (deflate(&stream, Z_FINISH) == Z_OK)
+               /* nothing */;
+       deflateEnd(&stream);
+
+       size = stream.total_out;
+       fwrite(out, size, 1, f);
+       free(out);
+       return size;
+}
+
+static void *delta_against(void *buf, unsigned long size, struct object_entry *entry)
+{
+       unsigned long othersize, delta_size;
+       char type[10];
+       void *otherbuf = read_sha1_file(entry->delta->sha1, type, &othersize);
+       void *delta_buf;
+
+       if (!otherbuf)
+               die("unable to read %s", sha1_to_hex(entry->delta->sha1));
+        delta_buf = diff_delta(buf, size, otherbuf, othersize, &delta_size);
+        if (delta_size != entry->delta_size)
+               die("delta size changed");
+        free(buf);
+        free(otherbuf);
+       return delta_buf;
+}
+
+static unsigned long write_object(FILE *f, struct object_entry *entry)
+{
+       unsigned long size;
+       char type[10];
+       void *buf = read_sha1_file(entry->sha1, type, &size);
+       char header[21];
+       unsigned hdrlen, datalen;
+
+       if (!buf)
+               die("unable to read %s", sha1_to_hex(entry->sha1));
+       if (size != entry->size)
+               die("object %s size inconsistency (%lu vs %lu)", sha1_to_hex(entry->sha1), size, entry->size);
+
+       /*
+        * The object header is a byte of 'type' followed by four bytes of
+        * length, except for deltas that has the 20 bytes of delta sha
+        * instead.
+        */
+       header[0] = ".CTB"[entry->type];
+       datalen = htonl(size);
+       memcpy(header+1, &datalen, 4);
+       hdrlen = 5;
+       if (entry->delta) {
+               memcpy(header+1, entry->delta, 20);
+               buf = delta_against(buf, size, entry);
+               size = entry->delta_size;
+               hdrlen = 21;
+       }
+       fwrite(header, hdrlen, 1, f);
+       datalen = fwrite_compressed(buf, size, f);
+       free(buf);
+       return hdrlen + datalen;
+}
+
+static void write_pack_file(void)
+{
+       int i;
+       FILE *f = create_file("pack");
+       unsigned long offset = 0;
+       unsigned long mb;
+
+       for (i = 0; i < nr_objects; i++) {
+               struct object_entry *entry = objects + i;
+               entry->offset = offset;
+               offset += write_object(f, entry);
+       }
+       fclose(f);
+       mb = offset >> 20;
+       offset &= 0xfffff;
+}
+
+static void write_index_file(void)
+{
+       int i;
+       FILE *f = create_file("idx");
+       struct object_entry **list = sorted_by_sha;
+       struct object_entry **last = list + nr_objects;
+       unsigned int array[256];
+
+       /*
+        * Write the first-level table (the list is sorted,
+        * but we use a 256-entry lookup to be able to avoid
+        * having to do eight extra binary search iterations)
+        */
+       for (i = 0; i < 256; i++) {
+               struct object_entry **next = list;
+               while (next < last) {
+                       struct object_entry *entry = *next;
+                       if (entry->sha1[0] != i)
+                               break;
+                       next++;
+               }
+               array[i] = htonl(next - sorted_by_sha);
+               list = next;
+       }
+       fwrite(array, 256, sizeof(int), f);
+
+       /*
+        * Write the actual SHA1 entries..
+        */
+       list = sorted_by_sha;
+       for (i < 0; i < nr_objects; i++) {
+               struct object_entry *entry = *list++;
+               unsigned int offset = htonl(entry->offset);
+               fwrite(&offset, 4, 1, f);
+               fwrite(entry->sha1, 20, 1, f);
+       }
+       fclose(f);
+}
+
+static void add_object_entry(unsigned char *sha1)
+{
+       unsigned int idx = nr_objects;
+       struct object_entry *entry;
+
+       if (idx >= nr_alloc) {
+               unsigned int needed = (idx + 1024) * 3 / 2;
+               objects = xrealloc(objects, needed * sizeof(*entry));
+               nr_alloc = needed;
+       }
+       entry = objects + idx;
+       memset(entry, 0, sizeof(*entry));
+       memcpy(entry->sha1, sha1, 20);
+       nr_objects = idx+1;
+}
+
+static void check_object(struct object_entry *entry)
+{
+       char buffer[128];
+       char type[10];
+       unsigned long mapsize;
+       z_stream stream;
+       void *map;
+
+       map = map_sha1_file(entry->sha1, &mapsize);
+       if (!map)
+               die("unable to map %s", sha1_to_hex(entry->sha1));
+       if (unpack_sha1_header(&stream, map, mapsize, buffer, sizeof(buffer)) < 0)
+               die("unable to unpack %s header", sha1_to_hex(entry->sha1));
+       munmap(map, mapsize);
+       if (parse_sha1_header(buffer, type, &entry->size) < 0)
+               die("unable to parse %s header", sha1_to_hex(entry->sha1));
+       if (!strcmp(type, "commit")) {
+               entry->type = OBJ_COMMIT;
+       } else if (!strcmp(type, "tree")) {
+               entry->type = OBJ_TREE;
+       } else if (!strcmp(type, "blob")) {
+               entry->type = OBJ_BLOB;
+       } else
+               die("unable to pack object %s of type %s", sha1_to_hex(entry->sha1), type);
+}
+
+static void get_object_details(void)
+{
+       int i;
+       struct object_entry *entry = objects;
+
+       for (i = 0; i < nr_objects; i++)
+               check_object(entry++);
+}
+
+typedef int (*entry_sort_t)(const struct object_entry *, const struct object_entry *);
+
+static entry_sort_t current_sort;
+
+static int sort_comparator(const void *_a, const void *_b)
+{
+       struct object_entry *a = *(struct object_entry **)_a;
+       struct object_entry *b = *(struct object_entry **)_b;
+       return current_sort(a,b);
+}
+
+static struct object_entry **create_sorted_list(entry_sort_t sort)
+{
+       struct object_entry **list = xmalloc(nr_objects * sizeof(struct object_entry *));
+       int i;
+
+       for (i = 0; i < nr_objects; i++)
+               list[i] = objects + i;
+       current_sort = sort;
+       qsort(list, nr_objects, sizeof(struct object_entry *), sort_comparator);
+       return list;
+}
+
+static int sha1_sort(const struct object_entry *a, const struct object_entry *b)
+{
+       return memcmp(a->sha1, b->sha1, 20);
+}
+
+static int type_size_sort(const struct object_entry *a, const struct object_entry *b)
+{
+       if (a->type < b->type)
+               return -1;
+       if (a->type > b->type)
+               return 1;
+       if (a->size < b->size)
+               return -1;
+       if (a->size > b->size)
+               return 1;
+       return a < b ? -1 : (a > b);
+}
+
+struct unpacked {
+       struct object_entry *entry;
+       void *data;
+};
+
+/*
+ * We search for deltas in a list sorted by type and by size, and
+ * walk the "old" chain backwards in the list, so if the type
+ * has changed or the size difference is too big, there's no point
+ * in even continuing the walk, since the other old objects are
+ * going to be even smaller or of a different type. So return -1
+ * once we determine that there's no point even trying.
+ */
+static int try_delta(struct unpacked *cur, struct unpacked *old)
+{
+       struct object_entry *cur_entry = cur->entry;
+       struct object_entry *old_entry = old->entry;
+       unsigned long size, oldsize, delta_size;
+       void *delta_buf;
+
+       /* Don't bother doing diffs between different types */
+       if (cur_entry->type != old_entry->type)
+               return -1;
+
+       /* Size is guaranteed to be larger than or equal to oldsize */
+       size = cur_entry->size;
+       oldsize = old_entry->size;
+       if (size - oldsize > oldsize / 4)
+               return -1;
+
+       /*
+        * NOTE!
+        *
+        * We always delta from the bigger to the smaller, since that's
+        * more space-efficient (deletes don't have to say _what_ they
+        * delete).
+        */
+       delta_buf = diff_delta(cur->data, size, old->data, oldsize, &delta_size);
+       if (!delta_buf)
+               die("unable to create delta");
+       if (delta_size + 20 < size / 2) {
+               if (!cur_entry->delta || cur_entry->delta_size > delta_size) {
+                       cur_entry->delta = old_entry;
+                       cur_entry->delta_size = delta_size;
+               }
+       }
+       free(delta_buf);
+}
+
+static void find_deltas(struct object_entry **list, int window)
+{
+       unsigned int i;
+       unsigned int array_size = window * sizeof(struct unpacked);
+       struct unpacked *array = xmalloc(array_size);
+
+       memset(array, 0, array_size);
+       for (i = 0; i < nr_objects; i++) {
+               unsigned int idx = i % window;
+               struct object_entry *entry = list[i];
+               struct unpacked *n = array + idx;
+               unsigned long size;
+               char type[10];
+               int j;
+
+               free(n->data);
+               n->entry = entry;
+               n->data = read_sha1_file(entry->sha1, type, &size);
+               if (size != entry->size)
+                       die("object %s inconsistent object length (%lu vs %lu)", sha1_to_hex(entry->sha1), size, entry->size);
+               for (j = 0; j < window; j++) {
+                       unsigned int other_idx = idx - 1 - j;
+                       struct unpacked *m;
+                       if (other_idx < 0)
+                               other_idx += window;
+                       m = array + other_idx;
+                       if (!m->entry)
+                               break;
+                       if (try_delta(n, m) < 0)
+                               break;
+               }
+       }
+}
+
+int main(int argc, char **argv)
+{
+       char line[128];
+       int i;
+
+       for (i = 1; i < argc; i++) {
+               const char *arg = argv[i];
+
+               if (*arg == '-') {
+                       if (!strncmp("--window=", arg, 9)) {
+                               char *end;
+                               delta_window = strtoul(arg+9, &end, 0);
+                               if (!arg[9] || *end)
+                                       usage(pack_usage);
+                               continue;
+                       }
+                       usage(pack_usage);
+               }
+               if (base_name)
+                       usage(pack_usage);
+               base_name = arg;
+       }
+
+       if (!base_name)
+               usage(pack_usage);
+
+       while (fgets(line, sizeof(line), stdin) != NULL) {
+               unsigned char sha1[20];
+               if (get_sha1_hex(line, sha1))
+                       die("expected sha1, got garbage");
+               add_object_entry(sha1);
+       }
+       get_object_details();
+
+       printf("Packing %d objects\n", nr_objects);
+
+       sorted_by_sha = create_sorted_list(sha1_sort);
+       sorted_by_type = create_sorted_list(type_size_sort);
+       if (delta_window)
+               find_deltas(sorted_by_type, delta_window);
+
+       write_pack_file();
+       write_index_file();
+       return 0;
+}