thodg/libgit2

diff --git a/include/git2.h b/include/git2.h
index 805044a..d555439 100644
--- a/include/git2.h
+++ b/include/git2.h
@@ -51,5 +51,6 @@
 #include "git2/notes.h"
 #include "git2/reset.h"
 #include "git2/message.h"
+#include "git2/pack.h"
 
 #endif
diff --git a/include/git2/errors.h b/include/git2/errors.h
index f6d9bf2..1c4e910 100644
--- a/include/git2/errors.h
+++ b/include/git2/errors.h
@@ -56,6 +56,7 @@ typedef enum {
 	GITERR_INDEXER,
 	GITERR_SSL,
 	GITERR_SUBMODULE,
+	GITERR_THREAD,
 } git_error_t;
 
 /**
diff --git a/include/git2/pack.h b/include/git2/pack.h
new file mode 100644
index 0000000..748ad2e
--- /dev/null
+++ b/include/git2/pack.h
@@ -0,0 +1,89 @@
+/*
+ * Copyright (C) 2009-2012 the libgit2 contributors
+ *
+ * This file is part of libgit2, distributed under the GNU GPL v2 with
+ * a Linking Exception. For full terms see the included COPYING file.
+ */
+#ifndef INCLUDE_git_pack_h__
+#define INCLUDE_git_pack_h__
+
+#include "common.h"
+#include "oid.h"
+
+/**
+ * @file git2/pack.h
+ * @brief Git pack management routines
+ * @defgroup git_pack Git pack management routines
+ * @ingroup Git
+ * @{
+ */
+GIT_BEGIN_DECL
+
+/**
+ * Initialize a new packbuilder
+ *
+ * @param out The new packbuilder object
+ * @param repo The repository
+ *
+ * @return 0 or an error code
+ */
+GIT_EXTERN(int) git_packbuilder_new(git_packbuilder **out, git_repository *repo);
+
+/**
+ * Set number of threads to spawn
+ *
+ * By default, libgit2 won't spawn any threads at all;
+ * when set to 0, libgit2 will autodetect the number of
+ * CPUs.
+ *
+ * @param pb The packbuilder
+ * @param n Number of threads to spawn
+ */
+GIT_EXTERN(void) git_packbuilder_set_threads(git_packbuilder *pb, unsigned int n);
+
+/**
+ * Insert a single object
+ *
+ * For an optimal pack it's mandatory to insert objects in recency order,
+ * commits followed by trees and blobs.
+ *
+ * @param pb The packbuilder
+ * @param oid The oid of the commit
+ * @param oid The name; might be NULL
+ *
+ * @return 0 or an error code
+ */
+GIT_EXTERN(int) git_packbuilder_insert(git_packbuilder *pb, const git_oid *oid,	const char *name);
+
+/**
+ * Insert a root tree object
+ *
+ * This will add the tree as well as all referenced trees and blobs.
+ *
+ * @param pb The packbuilder
+ * @param oid The oid of the root tree
+ *
+ * @return 0 or an error code
+ */
+GIT_EXTERN(int) git_packbuilder_insert_tree(git_packbuilder *pb, const git_oid *oid);
+
+/**
+ * Write the new pack and the corresponding index to path
+ *
+ * @param pb The packbuilder
+ * @param path Directory to store the new pack and index
+ *
+ * @return 0 or an error code
+ */
+GIT_EXTERN(int) git_packbuilder_write(git_packbuilder *pb, const char *file);
+
+/**
+ * Free the packbuilder and all associated data
+ *
+ * @param pb The packbuilder
+ */
+GIT_EXTERN(void) git_packbuilder_free(git_packbuilder *pb);
+
+/** @} */
+GIT_END_DECL
+#endif
diff --git a/include/git2/types.h b/include/git2/types.h
index 26e9c57..01ddbf3 100644
--- a/include/git2/types.h
+++ b/include/git2/types.h
@@ -137,6 +137,9 @@ typedef struct git_reflog git_reflog;
 /** Representation of a git note */
 typedef struct git_note git_note;
 
+/** Representation of a git packbuilder */
+typedef struct git_packbuilder git_packbuilder;
+
 /** Time in a signature */
 typedef struct git_time {
 	git_time_t time; /** time in seconds from epoch */
diff --git a/src/pack-objects.c b/src/pack-objects.c
new file mode 100644
index 0000000..bb0dfb6
--- /dev/null
+++ b/src/pack-objects.c
@@ -0,0 +1,1339 @@
+/*
+ * Copyright (C) 2009-2012 the libgit2 contributors
+ *
+ * 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 "pack-objects.h"
+
+#include "compress.h"
+#include "delta.h"
+#include "iterator.h"
+#include "netops.h"
+#include "pack.h"
+#include "thread-utils.h"
+#include "tree.h"
+
+#include "git2/pack.h"
+#include "git2/commit.h"
+#include "git2/tag.h"
+#include "git2/indexer.h"
+#include "git2/config.h"
+
+struct unpacked {
+	git_pobject *object;
+	void *data;
+	struct git_delta_index *index;
+	unsigned int depth;
+};
+
+static int locate_object_entry_hash(git_packbuilder *pb, const git_oid *oid)
+{
+	int i;
+	unsigned int ui;
+	memcpy(&ui, oid->id, sizeof(unsigned int));
+	i = ui % pb->object_ix_hashsz;
+	while (0 < pb->object_ix[i]) {
+		if (!git_oid_cmp(oid, &pb->object_list[pb->object_ix[i]-1].id))
+			return i;
+		if (++i == pb->object_ix_hashsz)
+			i = 0;
+	}
+	return -1 - i;
+}
+
+static git_pobject *locate_object_entry(git_packbuilder *pb, const git_oid *oid)
+{
+	int i;
+
+	if (!pb->object_ix_hashsz)
+		return NULL;
+
+	i = locate_object_entry_hash(pb, oid);
+	if (0 <= i)
+		return &pb->object_list[pb->object_ix[i]-1];
+	return NULL;
+}
+
+static void rehash_objects(git_packbuilder *pb)
+{
+	git_pobject *po;
+	uint32_t i;
+
+	pb->object_ix_hashsz = pb->nr_objects * 3;
+	if (pb->object_ix_hashsz < 1024)
+		pb->object_ix_hashsz = 1024;
+	pb->object_ix = git__realloc(pb->object_ix, sizeof(int) * pb->object_ix_hashsz);
+	memset(pb->object_ix, 0, sizeof(int) * pb->object_ix_hashsz);
+	for (i = 0, po = pb->object_list; i < pb->nr_objects; i++, po++) {
+		int ix = locate_object_entry_hash(pb, &po->id);
+		if (0 <= ix)
+			continue;
+		ix = -1 - ix;
+		pb->object_ix[ix] = i + 1;
+	}
+}
+
+static unsigned name_hash(const char *name)
+{
+	unsigned c, hash = 0;
+
+	if (!name)
+		return 0;
+
+	/*
+	 * This effectively just creates a sortable number from the
+	 * last sixteen non-whitespace characters. Last characters
+	 * count "most", so things that end in ".c" sort together.
+	 */
+	while ((c = *name++) != 0) {
+		if (git__isspace(c))
+			continue;
+		hash = (hash >> 2) + (c << 24);
+	}
+	return hash;
+}
+
+static int packbuilder_config(git_packbuilder *pb)
+{
+	git_config *config;
+	int ret;
+
+	if (git_repository_config__weakptr(&config, pb->repo) < 0)
+		return -1;
+
+#define config_get(key, dst, default) \
+	ret = git_config_get_int64((int64_t *)&dst, config, key); \
+	if (ret == GIT_ENOTFOUND) \
+		dst = default; \
+	else if (ret < 0) \
+		return -1;
+
+	config_get("pack.deltaCacheSize", pb->max_delta_cache_size,
+		   GIT_PACK_DELTA_CACHE_SIZE);
+	config_get("pack.deltaCacheLimit", pb->cache_max_small_delta_size,
+		   GIT_PACK_DELTA_CACHE_LIMIT);
+	config_get("pack.deltaCacheSize", pb->big_file_threshold,
+		   GIT_PACK_BIG_FILE_THRESHOLD);
+	config_get("pack.windowMemory", pb->window_memory_limit, 0);
+
+#undef config_get
+
+	return 0;
+}
+
+int git_packbuilder_new(git_packbuilder **out, git_repository *repo)
+{
+	git_packbuilder *pb;
+
+	*out = NULL;
+
+	pb = git__malloc(sizeof(*pb));
+	GITERR_CHECK_ALLOC(pb);
+
+	memset(pb, 0x0, sizeof(*pb));
+
+	pb->repo = repo;
+	pb->nr_threads = 1; /* do not spawn any thread by default */
+	pb->ctx = git_hash_new_ctx();
+
+	if (git_repository_odb(&pb->odb, repo) < 0)
+		goto on_error;
+
+	if (packbuilder_config(pb) < 0)
+		goto on_error;
+
+	*out = pb;
+	return 0;
+
+on_error:
+	git__free(pb);
+	return -1;
+}
+
+void git_packbuilder_set_threads(git_packbuilder *pb, unsigned int n)
+{
+	assert(pb);
+	pb->nr_threads = n;
+}
+
+int git_packbuilder_insert(git_packbuilder *pb, const git_oid *oid,
+			   const char *name)
+{
+	git_pobject *po;
+	git_odb_object *obj;
+	int ix;
+
+	assert(pb && oid);
+
+	ix = pb->nr_objects ? locate_object_entry_hash(pb, oid) : -1;
+	if (ix >=0)
+		return 0;
+
+	if (pb->nr_objects >= pb->nr_alloc) {
+		pb->nr_alloc = (pb->nr_alloc + 1024) * 3 / 2;
+		pb->object_list = git__realloc(pb->object_list,
+					       pb->nr_alloc * sizeof(*po));
+		GITERR_CHECK_ALLOC(pb->object_list);
+	}
+
+	if (git_odb_read(&obj, pb->odb, oid) < 0)
+		return -1;
+
+	po = pb->object_list + pb->nr_objects++;
+	memset(po, 0x0, sizeof(*po));
+
+	git_oid_cpy(&po->id, oid);
+	po->type = git_odb_object_type(obj);
+	po->size = git_odb_object_size(obj);
+	po->hash = name_hash(name);
+
+	git_odb_object_free(obj);
+
+	if ((uint32_t)pb->object_ix_hashsz * 3 <= pb->nr_objects * 4)
+		rehash_objects(pb);
+	else
+		pb->object_ix[-1 - ix] = pb->nr_objects;
+
+	pb->done = false;
+	return 0;
+}
+
+/*
+ * The per-object header is a pretty dense thing, which is
+ *  - first byte: low four bits are "size",
+ *    then three bits of "type",
+ *    with the high bit being "size continues".
+ *  - each byte afterwards: low seven bits are size continuation,
+ *    with the high bit being "size continues"
+ */
+static int gen_pack_object_header(
+		unsigned char *hdr,
+		unsigned long size,
+		git_otype type)
+{
+	unsigned char *hdr_base;
+	unsigned char c;
+
+	assert(type >= GIT_OBJ_COMMIT && type <= GIT_OBJ_REF_DELTA);
+
+	/* TODO: add support for chunked objects; see git.git 6c0d19b1 */
+
+	c = (unsigned char)((type << 4) | (size & 15));
+	size >>= 4;
+	hdr_base = hdr;
+
+	while (size) {
+		*hdr++ = c | 0x80;
+		c = size & 0x7f;
+		size >>= 7;
+	}
+	*hdr++ = c;
+
+	return hdr - hdr_base;
+}
+
+static int get_delta(void **out, git_odb *odb, git_pobject *po)
+{
+	git_odb_object *src = NULL, *trg = NULL;
+	unsigned long delta_size;
+	void *delta_buf;
+
+	*out = NULL;
+
+	if (git_odb_read(&src, odb, &po->delta->id) < 0 ||
+	    git_odb_read(&trg, odb, &po->id) < 0)
+		goto on_error;
+
+	delta_buf = git_delta(git_odb_object_data(src), git_odb_object_size(src),
+			      git_odb_object_data(trg), git_odb_object_size(trg),
+			      &delta_size, 0);
+
+	if (!delta_buf || delta_size != po->delta_size) {
+		giterr_set(GITERR_INVALID, "Delta size changed");
+		goto on_error;
+	}
+
+	*out = delta_buf;
+
+	git_odb_object_free(src);
+	git_odb_object_free(trg);
+	return 0;
+
+on_error:
+	git_odb_object_free(src);
+	git_odb_object_free(trg);
+	return -1;
+}
+
+static int write_object(git_buf *buf, git_packbuilder *pb, git_pobject *po)
+{
+	git_odb_object *obj = NULL;
+	git_buf zbuf = GIT_BUF_INIT;
+	git_otype type;
+	unsigned char hdr[10];
+	unsigned int hdr_len;
+	unsigned long size;
+	void *data;
+
+	if (po->delta) {
+		if (po->delta_data)
+			data = po->delta_data;
+		else if (get_delta(&data, pb->odb, po) < 0)
+				goto on_error;
+		size = po->delta_size;
+		type = GIT_OBJ_REF_DELTA;
+	} else {
+		if (git_odb_read(&obj, pb->odb, &po->id))
+			goto on_error;
+
+		data = (void *)git_odb_object_data(obj);
+		size = git_odb_object_size(obj);
+		type = git_odb_object_type(obj);
+	}
+
+	/* Write header */
+	hdr_len = gen_pack_object_header(hdr, size, type);
+
+	if (git_buf_put(buf, (char *)hdr, hdr_len) < 0)
+		goto on_error;
+
+	git_hash_update(pb->ctx, hdr, hdr_len);
+
+	if (type == GIT_OBJ_REF_DELTA) {
+		if (git_buf_put(buf, (char *)po->delta->id.id,
+				GIT_OID_RAWSZ) < 0)
+			goto on_error;
+
+		git_hash_update(pb->ctx, po->delta->id.id, GIT_OID_RAWSZ);
+	}
+
+	/* Write data */
+	if (po->z_delta_size)
+		size = po->z_delta_size;
+	else if (git__compress(&zbuf, data, size) < 0)
+		goto on_error;
+	else {
+		if (po->delta)
+			git__free(data);
+		data = zbuf.ptr;
+		size = zbuf.size;
+	}
+
+	if (git_buf_put(buf, data, size) < 0)
+		goto on_error;
+
+	git_hash_update(pb->ctx, data, size);
+
+	if (po->delta_data)
+		git__free(po->delta_data);
+
+	git_odb_object_free(obj);
+	git_buf_free(&zbuf);
+
+	pb->nr_written++;
+	return 0;
+
+on_error:
+	git_odb_object_free(obj);
+	git_buf_free(&zbuf);
+	return -1;
+}
+
+enum write_one_status {
+	WRITE_ONE_SKIP = -1, /* already written */
+	WRITE_ONE_BREAK = 0, /* writing this will bust the limit; not written */
+	WRITE_ONE_WRITTEN = 1, /* normal */
+	WRITE_ONE_RECURSIVE = 2 /* already scheduled to be written */
+};
+
+static int write_one(git_buf *buf, git_packbuilder *pb, git_pobject *po,
+		     enum write_one_status *status)
+{
+	if (po->recursing) {
+		*status = WRITE_ONE_RECURSIVE;
+		return 0;
+	} else if (po->written) {
+		*status = WRITE_ONE_SKIP;
+		return 0;
+	}
+
+	if (po->delta) {
+		po->recursing = 1;
+		if (write_one(buf, pb, po->delta, status) < 0)
+			return -1;
+		switch (*status) {
+		case WRITE_ONE_RECURSIVE:
+			/* we cannot depend on this one */
+			po->delta = NULL;
+			break;
+		default:
+			break;
+		}
+	}
+
+	po->written = 1;
+	po->recursing = 0;
+	return write_object(buf, pb, po);
+}
+
+GIT_INLINE(void) add_to_write_order(git_pobject **wo, unsigned int *endp,
+				    git_pobject *po)
+{
+	if (po->filled)
+		return;
+	wo[(*endp)++] = po;
+	po->filled = 1;
+}
+
+static void add_descendants_to_write_order(git_pobject **wo, unsigned int *endp,
+					   git_pobject *po)
+{
+	int add_to_order = 1;
+	while (po) {
+		if (add_to_order) {
+			git_pobject *s;
+			/* add this node... */
+			add_to_write_order(wo, endp, po);
+			/* all its siblings... */
+			for (s = po->delta_sibling; s; s = s->delta_sibling) {
+				add_to_write_order(wo, endp, s);
+			}
+		}
+		/* drop down a level to add left subtree nodes if possible */
+		if (po->delta_child) {
+			add_to_order = 1;
+			po = po->delta_child;
+		} else {
+			add_to_order = 0;
+			/* our sibling might have some children, it is next */
+			if (po->delta_sibling) {
+				po = po->delta_sibling;
+				continue;
+			}
+			/* go back to our parent node */
+			po = po->delta;
+			while (po && !po->delta_sibling) {
+				/* we're on the right side of a subtree, keep
+				 * going up until we can go right again */
+				po = po->delta;
+			}
+			if (!po) {
+				/* done- we hit our original root node */
+				return;
+			}
+			/* pass it off to sibling at this level */
+			po = po->delta_sibling;
+		}
+	};
+}
+
+static void add_family_to_write_order(git_pobject **wo, unsigned int *endp,
+				      git_pobject *po)
+{
+	git_pobject *root;
+
+	for (root = po; root->delta; root = root->delta)
+		; /* nothing */
+	add_descendants_to_write_order(wo, endp, root);
+}
+
+static int cb_tag_foreach(const char *name, git_oid *oid, void *data)
+{
+	git_packbuilder *pb = data;
+	git_pobject *po = locate_object_entry(pb, oid);
+
+	GIT_UNUSED(name);
+
+	if (po)
+		po->tagged = 1;
+	/* TODO: peel objects */
+	return 0;
+}
+
+static git_pobject **compute_write_order(git_packbuilder *pb)
+{
+	unsigned int i, wo_end, last_untagged;
+
+	git_pobject **wo = git__malloc(sizeof(*wo) * pb->nr_objects);
+
+	for (i = 0; i < pb->nr_objects; i++) {
+		git_pobject *po = pb->object_list + i;
+		po->tagged = 0;
+		po->filled = 0;
+		po->delta_child = NULL;
+		po->delta_sibling = NULL;
+	}
+
+	/*
+	 * Fully connect delta_child/delta_sibling network.
+	 * Make sure delta_sibling is sorted in the original
+	 * recency order.
+	 */
+	for (i = pb->nr_objects; i > 0;) {
+		git_pobject *po = &pb->object_list[--i];
+		if (!po->delta)
+			continue;
+		/* Mark me as the first child */
+		po->delta_sibling = po->delta->delta_child;
+		po->delta->delta_child = po;
+	}
+
+	/*
+	 * Mark objects that are at the tip of tags.
+	 */
+	if (git_tag_foreach(pb->repo, &cb_tag_foreach, pb) < 0)
+		return NULL;
+
+	/*
+	 * Give the objects in the original recency order until
+	 * we see a tagged tip.
+	 */
+	for (i = wo_end = 0; i < pb->nr_objects; i++) {
+		git_pobject *po = pb->object_list + i;
+		if (po->tagged)
+			break;
+		add_to_write_order(wo, &wo_end, po);
+	}
+	last_untagged = i;
+
+	/*
+	 * Then fill all the tagged tips.
+	 */
+	for (; i < pb->nr_objects; i++) {
+		git_pobject *po = pb->object_list + i;
+		if (po->tagged)
+			add_to_write_order(wo, &wo_end, po);
+	}
+
+	/*
+	 * And then all remaining commits and tags.
+	 */
+	for (i = last_untagged; i < pb->nr_objects; i++) {
+		git_pobject *po = pb->object_list + i;
+		if (po->type != GIT_OBJ_COMMIT &&
+		    po->type != GIT_OBJ_TAG)
+			continue;
+		add_to_write_order(wo, &wo_end, po);
+	}
+
+	/*
+	 * And then all the trees.
+	 */
+	for (i = last_untagged; i < pb->nr_objects; i++) {
+		git_pobject *po = pb->object_list + i;
+		if (po->type != GIT_OBJ_TREE)
+			continue;
+		add_to_write_order(wo, &wo_end, po);
+	}
+
+	/*
+	 * Finally all the rest in really tight order
+	 */
+	for (i = last_untagged; i < pb->nr_objects; i++) {
+		git_pobject *po = pb->object_list + i;
+		if (!po->filled)
+			add_family_to_write_order(wo, &wo_end, po);
+	}
+
+	if (wo_end != pb->nr_objects) {
+		giterr_set(GITERR_INVALID, "invalid write order");
+		return NULL;
+	}
+
+	return wo;
+}
+
+static int write_pack(git_packbuilder *pb,
+		      int (*cb)(void *buf, size_t size, void *data),
+		      void *data)
+{
+	git_pobject **write_order;
+	git_pobject *po;
+	git_buf buf = GIT_BUF_INIT;
+	enum write_one_status status;
+	struct git_pack_header ph;
+	unsigned int i = 0;
+
+	write_order = compute_write_order(pb);
+	if (write_order == NULL)
+		goto on_error;
+
+	/* Write pack header */
+	ph.hdr_signature = htonl(PACK_SIGNATURE);
+	ph.hdr_version = htonl(PACK_VERSION);
+	ph.hdr_entries = htonl(pb->nr_objects);
+
+	if (cb(&ph, sizeof(ph), data) < 0)
+		goto on_error;
+
+	git_hash_update(pb->ctx, &ph, sizeof(ph));
+
+	pb->nr_remaining = pb->nr_objects;
+	do {
+		pb->nr_written = 0;
+		for ( ; i < pb->nr_objects; ++i) {
+			po = write_order[i];
+			if (write_one(&buf, pb, po, &status) < 0)
+				goto on_error;
+			if (cb(buf.ptr, buf.size, data) < 0)
+				goto on_error;
+			git_buf_clear(&buf);
+		}
+
+		pb->nr_remaining -= pb->nr_written;
+	} while (pb->nr_remaining && i < pb->nr_objects);
+
+	git__free(write_order);
+	git_buf_free(&buf);
+	git_hash_final(&pb->pack_oid, pb->ctx);
+
+	return cb(pb->pack_oid.id, GIT_OID_RAWSZ, data);
+
+on_error:
+	git__free(write_order);
+	git_buf_free(&buf);
+	return -1;
+}
+
+static int send_pack_file(void *buf, size_t size, void *data)
+{
+	git_transport *t = (git_transport *)data;
+	return gitno_send(t, buf, size, 0);
+}
+
+static int write_pack_buf(void *buf, size_t size, void *data)
+{
+	git_buf *b = (git_buf *)data;
+	return git_buf_put(b, buf, size);
+}
+
+static int write_pack_to_file(void *buf, size_t size, void *data)
+{
+	git_filebuf *file = (git_filebuf *)data;
+	return git_filebuf_write(file, buf, size);
+}
+
+static int write_pack_file(git_packbuilder *pb, const char *path)
+{
+	git_filebuf file = GIT_FILEBUF_INIT;
+
+	if (git_filebuf_open(&file, path, 0) < 0 ||
+	    write_pack(pb, &write_pack_to_file, &file) < 0 ||
+	    git_filebuf_commit(&file, GIT_PACK_FILE_MODE) < 0) {
+		git_filebuf_cleanup(&file);
+		return -1;
+	}
+
+	return 0;
+}
+
+static int type_size_sort(const void *_a, const void *_b)
+{
+	const git_pobject *a = (git_pobject *)_a;
+	const git_pobject *b = (git_pobject *)_b;
+
+	if (a->type > b->type)
+		return -1;
+	if (a->type < b->type)
+		return 1;
+	if (a->hash > b->hash)
+		return -1;
+	if (a->hash < b->hash)
+		return 1;
+	/*
+	 * TODO
+	 *
+	if (a->preferred_base > b->preferred_base)
+		return -1;
+	if (a->preferred_base < b->preferred_base)
+		return 1;
+	*/
+	if (a->size > b->size)
+		return -1;
+	if (a->size < b->size)
+		return 1;
+	return a < b ? -1 : (a > b); /* newest first */
+}
+
+static int delta_cacheable(git_packbuilder *pb, unsigned long src_size,
+			   unsigned long trg_size, unsigned long delta_size)
+{
+	if (pb->max_delta_cache_size &&
+		pb->delta_cache_size + delta_size > pb->max_delta_cache_size)
+		return 0;
+
+	if (delta_size < pb->cache_max_small_delta_size)
+		return 1;
+
+	/* cache delta, if objects are large enough compared to delta size */
+	if ((src_size >> 20) + (trg_size >> 21) > (delta_size >> 10))
+		return 1;
+
+	return 0;
+}
+
+#ifdef GIT_THREADS
+static git_mutex cache_mutex;
+#define cache_lock()		git_mutex_lock(&cache_mutex);
+#define cache_unlock()		git_mutex_unlock(&cache_mutex);
+
+static git_mutex progress_mutex;
+#define progress_lock()		git_mutex_lock(&progress_mutex);
+#define progress_unlock()	git_mutex_unlock(&progress_mutex);
+
+static git_cond progress_cond;
+#else
+
+#define cache_lock()		(void)0;
+#define cache_unlock()		(void)0;
+#define progress_lock()		(void)0;
+#define progress_unlock()	(void)0;
+#endif
+
+static int try_delta(git_packbuilder *pb, struct unpacked *trg,
+		     struct unpacked *src, unsigned int max_depth,
+		     unsigned long *mem_usage, int *ret)
+{
+	git_pobject *trg_object = trg->object;
+	git_pobject *src_object = src->object;
+	git_odb_object *obj;
+	unsigned long trg_size, src_size, delta_size,
+		      sizediff, max_size, sz;
+	unsigned int ref_depth;
+	void *delta_buf;
+
+	/* Don't bother doing diffs between different types */
+	if (trg_object->type != src_object->type) {
+		*ret = -1;
+		return 0;
+	}
+
+	*ret = 0;
+
+	/* TODO: support reuse-delta */
+
+	/* Let's not bust the allowed depth. */
+	if (src->depth >= max_depth)
+		return 0;
+
+	/* Now some size filtering heuristics. */
+	trg_size = trg_object->size;
+	if (!trg_object->delta) {
+		max_size = trg_size/2 - 20;
+		ref_depth = 1;
+	} else {
+		max_size = trg_object->delta_size;
+		ref_depth = trg->depth;
+	}
+
+	max_size = (uint64_t)max_size * (max_depth - src->depth) /
+					(max_depth - ref_depth + 1);
+	if (max_size == 0)
+		return 0;
+
+	src_size = src_object->size;
+	sizediff = src_size < trg_size ? trg_size - src_size : 0;
+	if (sizediff >= max_size)
+		return 0;
+	if (trg_size < src_size / 32)
+		return 0;
+
+	/* Load data if not already done */
+	if (!trg->data) {
+		if (git_odb_read(&obj, pb->odb, &trg_object->id) < 0)
+			return -1;
+
+		sz = git_odb_object_size(obj);
+		trg->data = git__malloc(sz);
+		GITERR_CHECK_ALLOC(trg->data);
+		memcpy(trg->data, git_odb_object_data(obj), sz);
+
+		git_odb_object_free(obj);
+
+		if (sz != trg_size) {
+			giterr_set(GITERR_INVALID,
+				   "Inconsistent target object length");
+			return -1;
+		}
+
+		*mem_usage += sz;
+	}
+	if (!src->data) {
+		if (git_odb_read(&obj, pb->odb, &src_object->id) < 0)
+			return -1;
+
+		sz = git_odb_object_size(obj);
+		src->data = git__malloc(sz);
+		GITERR_CHECK_ALLOC(src->data);
+		memcpy(src->data, git_odb_object_data(obj), sz);
+
+		git_odb_object_free(obj);
+
+		if (sz != src_size) {
+			giterr_set(GITERR_INVALID,
+				   "Inconsistent source object length");
+			return -1;
+		}
+
+		*mem_usage += sz;
+	}
+	if (!src->index) {
+		src->index = git_delta_create_index(src->data, src_size);
+		if (!src->index)
+			return 0; /* suboptimal pack - out of memory */
+
+		*mem_usage += git_delta_sizeof_index(src->index);
+	}
+
+	delta_buf = git_delta_create(src->index, trg->data, trg_size,
+				     &delta_size, max_size);
+	if (!delta_buf)
+		return 0;
+
+	if (trg_object->delta) {
+		/* Prefer only shallower same-sized deltas. */
+		if (delta_size == trg_object->delta_size &&
+		    src->depth + 1 >= trg->depth) {
+			git__free(delta_buf);
+			return 0;
+		}
+	}
+
+	cache_lock();
+	if (trg_object->delta_data) {
+		git__free(trg_object->delta_data);
+		pb->delta_cache_size -= trg_object->delta_size;
+		trg_object->delta_data = NULL;
+	}
+	if (delta_cacheable(pb, src_size, trg_size, delta_size)) {
+		pb->delta_cache_size += delta_size;
+		cache_unlock();
+
+		trg_object->delta_data = git__realloc(delta_buf, delta_size);
+		GITERR_CHECK_ALLOC(trg_object->delta_data);
+	} else {
+		/* create delta when writing the pack */
+		cache_unlock();
+		git__free(delta_buf);
+	}
+
+	trg_object->delta = src_object;
+	trg_object->delta_size = delta_size;
+	trg->depth = src->depth + 1;
+
+	*ret = 1;
+	return 0;
+}
+
+static unsigned int check_delta_limit(git_pobject *me, unsigned int n)
+{
+	git_pobject *child = me->delta_child;
+	unsigned int m = n;
+
+	while (child) {
+		unsigned int c = check_delta_limit(child, n + 1);
+		if (m < c)
+			m = c;
+		child = child->delta_sibling;
+	}
+	return m;
+}
+
+static unsigned long free_unpacked(struct unpacked *n)
+{
+	unsigned long freed_mem = git_delta_sizeof_index(n->index);
+	git_delta_free_index(n->index);
+	n->index = NULL;
+	if (n->data) {
+		freed_mem += n->object->size;
+		git__free(n->data);
+		n->data = NULL;
+	}
+	n->object = NULL;
+	n->depth = 0;
+	return freed_mem;
+}
+
+static int find_deltas(git_packbuilder *pb, git_pobject **list,
+		       unsigned int *list_size, unsigned int window,
+		       unsigned int depth)
+{
+	git_pobject *po;
+	git_buf zbuf = GIT_BUF_INIT;
+	struct unpacked *array;
+	uint32_t idx = 0, count = 0;
+	unsigned long mem_usage = 0;
+	unsigned int i;
+	int error = -1;
+
+	array = git__calloc(window, sizeof(struct unpacked));
+	GITERR_CHECK_ALLOC(array);
+
+	for (;;) {
+		struct unpacked *n = array + idx;
+		unsigned int max_depth;
+		int j, best_base = -1;
+
+		progress_lock();
+		if (!*list_size) {
+			progress_unlock();
+			break;
+		}
+
+		po = *list++;
+		(*list_size)--;
+		progress_unlock();
+
+		mem_usage -= free_unpacked(n);
+		n->object = po;
+
+		while (pb->window_memory_limit &&
+		       mem_usage > pb->window_memory_limit &&
+		       count > 1) {
+			uint32_t tail = (idx + window - count) % window;
+			mem_usage -= free_unpacked(array + tail);
+			count--;
+		}
+
+		/*
+		 * If the current object is at pack edge, take the depth the
+		 * objects that depend on the current object into account
+		 * otherwise they would become too deep.
+		 */
+		max_depth = depth;
+		if (po->delta_child) {
+			max_depth -= check_delta_limit(po, 0);
+			if (max_depth <= 0)
+				goto next;
+		}
+
+		j = window;
+		while (--j > 0) {
+			int ret;
+			uint32_t other_idx = idx + j;
+			struct unpacked *m;
+
+			if (other_idx >= window)
+				other_idx -= window;
+
+			m = array + other_idx;
+			if (!m->object)
+				break;
+
+			if (try_delta(pb, n, m, max_depth, &mem_usage, &ret) < 0)
+				goto on_error;
+			if (ret < 0)
+				break;
+			else if (ret > 0)
+				best_base = other_idx;
+		}
+
+		/*
+		 * If we decided to cache the delta data, then it is best
+		 * to compress it right away.  First because we have to do
+		 * it anyway, and doing it here while we're threaded will
+		 * save a lot of time in the non threaded write phase,
+		 * as well as allow for caching more deltas within
+		 * the same cache size limit.
+		 * ...
+		 * But only if not writing to stdout, since in that case
+		 * the network is most likely throttling writes anyway,
+		 * and therefore it is best to go to the write phase ASAP
+		 * instead, as we can afford spending more time compressing
+		 * between writes at that moment.
+		 */
+		if (po->delta_data) {
+			if (git__compress(&zbuf, po->delta_data, po->delta_size) < 0)
+				goto on_error;
+
+			git__free(po->delta_data);
+			po->delta_data = git__malloc(zbuf.size);
+			GITERR_CHECK_ALLOC(po->delta_data);
+
+			memcpy(po->delta_data, zbuf.ptr, zbuf.size);
+			po->z_delta_size = zbuf.size;
+			git_buf_clear(&zbuf);
+
+			cache_lock();
+			pb->delta_cache_size -= po->delta_size;
+			pb->delta_cache_size += po->z_delta_size;
+			cache_unlock();
+		}
+
+		/*
+		 * If we made n a delta, and if n is already at max
+		 * depth, leaving it in the window is pointless.  we
+		 * should evict it first.
+		 */
+		if (po->delta && max_depth <= n->depth)
+			continue;
+
+		/*
+		 * Move the best delta base up in the window, after the
+		 * currently deltified object, to keep it longer.  It will
+		 * be the first base object to be attempted next.
+		 */
+		if (po->delta) {
+			struct unpacked swap = array[best_base];
+			int dist = (window + idx - best_base) % window;
+			int dst = best_base;
+			while (dist--) {
+				int src = (dst + 1) % window;
+				array[dst] = array[src];
+				dst = src;
+			}
+			array[dst] = swap;
+		}
+
+		next:
+		idx++;
+		if (count + 1 < window)
+			count++;
+		if (idx >= window)
+			idx = 0;
+	}
+	error = 0;
+
+on_error:
+	for (i = 0; i < window; ++i) {
+		git__free(array[i].index);
+		git__free(array[i].data);
+	}
+	git__free(array);
+	git_buf_free(&zbuf);
+
+	return error;
+}
+
+#ifdef GIT_THREADS
+
+struct thread_params {
+	git_thread thread;
+	git_packbuilder *pb;
+
+	git_pobject **list;
+
+	git_cond cond;
+	git_mutex mutex;
+
+	unsigned int list_size;
+	unsigned int remaining;
+
+	int window;
+	int depth;
+	int working;
+	int data_ready;
+};
+
+static void init_threaded_search(void)
+{
+	git_mutex_init(&cache_mutex);
+	git_mutex_init(&progress_mutex);
+
+	git_cond_init(&progress_cond);
+}
+
+static void cleanup_threaded_search(void)
+{
+	git_cond_free(&progress_cond);
+
+	git_mutex_free(&cache_mutex);
+	git_mutex_free(&progress_mutex);
+}
+
+static void *threaded_find_deltas(void *arg)
+{
+	struct thread_params *me = arg;
+
+	while (me->remaining) {
+		if (find_deltas(me->pb, me->list, &me->remaining,
+				me->window, me->depth) < 0) {
+			; /* TODO */
+		}
+
+		progress_lock();
+		me->working = 0;
+		git_cond_signal(&progress_cond);
+		progress_unlock();
+
+		/*
+		 * We must not set ->data_ready before we wait on the
+		 * condition because the main thread may have set it to 1
+		 * before we get here. In order to be sure that new
+		 * work is available if we see 1 in ->data_ready, it
+		 * was initialized to 0 before this thread was spawned
+		 * and we reset it to 0 right away.
+		 */
+		git_mutex_lock(&me->mutex);
+		while (!me->data_ready)
+			git_cond_wait(&me->cond, &me->mutex);
+		me->data_ready = 0;
+		git_mutex_unlock(&me->mutex);
+	}
+	/* leave ->working 1 so that this doesn't get more work assigned */
+	return NULL;
+}
+
+static int ll_find_deltas(git_packbuilder *pb, git_pobject **list,
+			  unsigned int list_size, unsigned int window,
+			  unsigned int depth)
+{
+	struct thread_params *p;
+	int i, ret, active_threads = 0;
+
+	init_threaded_search();
+
+	if (!pb->nr_threads)
+		pb->nr_threads = git_online_cpus();
+	if (pb->nr_threads <= 1) {
+		find_deltas(pb, list, &list_size, window, depth);
+		cleanup_threaded_search();
+		return 0;
+	}
+
+	p = git__malloc(pb->nr_threads * sizeof(*p));
+	GITERR_CHECK_ALLOC(p);
+
+	/* Partition the work among the threads */
+	for (i = 0; i < pb->nr_threads; ++i) {
+		unsigned sub_size = list_size / (pb->nr_threads - i);
+
+		/* don't use too small segments or no deltas will be found */
+		if (sub_size < 2*window && i+1 < pb->nr_threads)
+			sub_size = 0;
+
+		p[i].pb = pb;
+		p[i].window = window;
+		p[i].depth = depth;
+		p[i].working = 1;
+		p[i].data_ready = 0;
+
+		/* try to split chunks on "path" boundaries */
+		while (sub_size && sub_size < list_size &&
+		       list[sub_size]->hash &&
+		       list[sub_size]->hash == list[sub_size-1]->hash)
+			sub_size++;
+
+		p[i].list = list;
+		p[i].list_size = sub_size;
+		p[i].remaining = sub_size;
+
+		list += sub_size;
+		list_size -= sub_size;
+	}
+
+	/* Start work threads */
+	for (i = 0; i < pb->nr_threads; ++i) {
+		if (!p[i].list_size)
+			continue;
+
+		git_mutex_init(&p[i].mutex);
+		git_cond_init(&p[i].cond);
+
+		ret = git_thread_create(&p[i].thread, NULL,
+					threaded_find_deltas, &p[i]);
+		if (ret) {
+			giterr_set(GITERR_THREAD, "unable to create thread");
+			return -1;
+		}
+		active_threads++;
+	}
+
+	/*
+	 * Now let's wait for work completion.  Each time a thread is done
+	 * with its work, we steal half of the remaining work from the
+	 * thread with the largest number of unprocessed objects and give
+	 * it to that newly idle thread.  This ensure good load balancing
+	 * until the remaining object list segments are simply too short
+	 * to be worth splitting anymore.
+	 */
+	while (active_threads) {
+		struct thread_params *target = NULL;
+		struct thread_params *victim = NULL;
+		unsigned sub_size = 0;
+
+		progress_lock();
+		for (;;) {
+			for (i = 0; !target && i < pb->nr_threads; i++)
+				if (!p[i].working)
+					target = &p[i];
+			if (target)
+				break;
+			git_cond_wait(&progress_cond, &progress_mutex);
+		}
+
+		for (i = 0; i < pb->nr_threads; i++)
+			if (p[i].remaining > 2*window &&
+			    (!victim || victim->remaining < p[i].remaining))
+				victim = &p[i];
+		if (victim) {
+			sub_size = victim->remaining / 2;
+			list = victim->list + victim->list_size - sub_size;
+			while (sub_size && list[0]->hash &&
+			       list[0]->hash == list[-1]->hash) {
+				list++;
+				sub_size--;
+			}
+			if (!sub_size) {
+				/*
+				 * It is possible for some "paths" to have
+				 * so many objects that no hash boundary
+				 * might be found.  Let's just steal the
+				 * exact half in that case.
+				 */
+				sub_size = victim->remaining / 2;
+				list -= sub_size;
+			}
+			target->list = list;
+			victim->list_size -= sub_size;
+			victim->remaining -= sub_size;
+		}
+		target->list_size = sub_size;
+		target->remaining = sub_size;
+		target->working = 1;
+		progress_unlock();
+
+		git_mutex_lock(&target->mutex);
+		target->data_ready = 1;
+		git_cond_signal(&target->cond);
+		git_mutex_unlock(&target->mutex);
+
+		if (!sub_size) {
+			git_thread_join(target->thread, NULL);
+			git_cond_free(&target->cond);
+			git_mutex_free(&target->mutex);
+			active_threads--;
+		}
+	}
+
+	cleanup_threaded_search();
+	git__free(p);
+	return 0;
+}
+
+#else
+#define ll_find_deltas(pb, l, ls, w, d) find_deltas(pb, l, &ls, w, d)
+#endif
+
+static void get_object_details(git_packbuilder *pb)
+{
+	git_pobject *po;
+	unsigned int i;
+
+	for (i = 0; i < pb->nr_objects; ++i) {
+		po = &pb->object_list[i];
+		if (pb->big_file_threshold < po->size)
+			po->no_try_delta = 1;
+	}
+}
+
+static int prepare_pack(git_packbuilder *pb)
+{
+	git_pobject **delta_list;
+	unsigned int i, n = 0;
+
+	if (pb->nr_objects == 0 || pb->done)
+		return 0; /* nothing to do */
+
+	get_object_details(pb);
+
+	delta_list = git__malloc(pb->nr_objects * sizeof(*delta_list));
+	GITERR_CHECK_ALLOC(delta_list);
+
+	for (i = 0; i < pb->nr_objects; ++i) {
+		git_pobject *po = pb->object_list + i;
+
+		if (po->size < 50)
+			continue;
+
+		if (po->no_try_delta)
+			continue;
+
+		delta_list[n++] = po;
+	}
+
+	if (n > 1) {
+		git__tsort((void **)delta_list, n, type_size_sort);
+		if (ll_find_deltas(pb, delta_list, n,
+				   GIT_PACK_WINDOW + 1,
+				   GIT_PACK_DEPTH) < 0) {
+			git__free(delta_list);
+			return -1;
+		}
+	}
+
+	pb->done = true;
+	git__free(delta_list);
+	return 0;
+}
+
+#define PREPARE_PACK if (prepare_pack(pb) < 0) { return -1; }
+
+int git_packbuilder_send(git_packbuilder *pb, git_transport *t)
+{
+	PREPARE_PACK;
+	return write_pack(pb, &send_pack_file, t);
+}
+
+int git_packbuilder_write_buf(git_buf *buf, git_packbuilder *pb)
+{
+	PREPARE_PACK;
+	return write_pack(pb, &write_pack_buf, buf);
+}
+
+int git_packbuilder_write(git_packbuilder *pb, const char *path)
+{
+	PREPARE_PACK;
+	return write_pack_file(pb, path);
+}
+
+#undef PREPARE_PACK
+
+static int cb_tree_walk(const char *root, const git_tree_entry *entry, void *payload)
+{
+	git_packbuilder *pb = payload;
+	git_buf buf = GIT_BUF_INIT;
+
+	git_buf_puts(&buf, root);
+	git_buf_puts(&buf, git_tree_entry_name(entry));
+
+	if (git_packbuilder_insert(pb, git_tree_entry_id(entry),
+				   git_buf_cstr(&buf)) < 0) {
+		git_buf_free(&buf);
+		return -1;
+	}
+
+	git_buf_free(&buf);
+	return 0;
+}
+
+int git_packbuilder_insert_tree(git_packbuilder *pb, const git_oid *oid)
+{
+	git_tree *tree;
+
+	if (git_tree_lookup(&tree, pb->repo, oid) < 0 ||
+	    git_packbuilder_insert(pb, oid, NULL) < 0)
+		return -1;
+
+	if (git_tree_walk(tree, cb_tree_walk, GIT_TREEWALK_PRE, pb) < 0) {
+		git_tree_free(tree);
+		return -1;
+	}
+
+	git_tree_free(tree);
+	return 0;
+}
+
+void git_packbuilder_free(git_packbuilder *pb)
+{
+	if (pb == NULL)
+		return;
+
+	git_odb_free(pb->odb);
+	git_hash_free_ctx(pb->ctx);
+	git__free(pb->object_ix);
+	git__free(pb->object_list);
+	git__free(pb);
+}
diff --git a/src/pack-objects.h b/src/pack-objects.h
new file mode 100644
index 0000000..971b302
--- /dev/null
+++ b/src/pack-objects.h
@@ -0,0 +1,85 @@
+/*
+ * Copyright (C) 2009-2012 the libgit2 contributors
+ *
+ * This file is part of libgit2, distributed under the GNU GPL v2 with
+ * a Linking Exception. For full terms see the included COPYING file.
+ */
+
+#ifndef INCLUDE_pack_objects_h__
+#define INCLUDE_pack_objects_h__
+
+#include "common.h"
+
+#include "buffer.h"
+#include "hash.h"
+
+#include "git2/oid.h"
+
+#define GIT_PACK_WINDOW 10 /* number of objects to possibly delta against */
+#define GIT_PACK_DEPTH 50 /* max delta depth */
+#define GIT_PACK_DELTA_CACHE_SIZE (256 * 1024 * 1024)
+#define GIT_PACK_DELTA_CACHE_LIMIT 1000
+#define GIT_PACK_BIG_FILE_THRESHOLD (512 * 1024 * 1024)
+
+typedef struct git_pobject {
+	git_oid id;
+	git_otype type;
+	git_off_t offset;
+
+	size_t size;
+
+	unsigned int hash; /* name hint hash */
+
+	struct git_pobject *delta; /* delta base object */
+	struct git_pobject *delta_child; /* deltified objects who bases me */
+	struct git_pobject *delta_sibling; /* other deltified objects
+					    * who uses the same base as
+					    * me */
+
+	void *delta_data;
+	unsigned long delta_size;
+	unsigned long z_delta_size;
+
+	int written:1,
+	    recursing:1,
+	    no_try_delta:1,
+	    tagged:1,
+	    filled:1;
+} git_pobject;
+
+struct git_packbuilder {
+	git_repository *repo; /* associated repository */
+	git_odb *odb; /* associated object database */
+
+	git_hash_ctx *ctx;
+
+	uint32_t nr_objects,
+		 nr_alloc,
+		 nr_written,
+		 nr_remaining;
+
+	git_pobject *object_list;
+
+	int *object_ix;
+	int object_ix_hashsz;
+
+
+	git_oid pack_oid; /* hash of written pack */
+
+	/* configs */
+	unsigned long delta_cache_size;
+	unsigned long max_delta_cache_size;
+	unsigned long cache_max_small_delta_size;
+	unsigned long big_file_threshold;
+	unsigned long window_memory_limit;
+
+	int nr_threads; /* nr of threads to use */
+
+	bool done;
+};
+
+
+int git_packbuilder_send(git_packbuilder *pb, git_transport *t);
+int git_packbuilder_write_buf(git_buf *buf, git_packbuilder *pb);
+
+#endif
diff --git a/tests-clar/pack/packbuilder.c b/tests-clar/pack/packbuilder.c
new file mode 100644
index 0000000..fa7bec1
--- /dev/null
+++ b/tests-clar/pack/packbuilder.c
@@ -0,0 +1,67 @@
+#include "clar_libgit2.h"
+#include "iterator.h"
+#include "vector.h"
+
+static git_repository *_repo;
+static git_revwalk *_revwalker;
+static git_packbuilder *_packbuilder;
+static git_indexer *_indexer;
+static git_vector _commits;
+
+void test_pack_packbuilder__initialize(void)
+{
+	cl_git_pass(git_repository_open(&_repo, cl_fixture("testrepo.git")));
+	cl_git_pass(git_revwalk_new(&_revwalker, _repo));
+	cl_git_pass(git_packbuilder_new(&_packbuilder, _repo));
+	cl_git_pass(git_vector_init(&_commits, 0, NULL));
+}
+
+void test_pack_packbuilder__cleanup(void)
+{
+	git_oid *o;
+	unsigned int i;
+
+	git_vector_foreach(&_commits, i, o) {
+		git__free(o);
+	}
+	git_vector_free(&_commits);
+	git_packbuilder_free(_packbuilder);
+	git_revwalk_free(_revwalker);
+	git_indexer_free(_indexer);
+	git_repository_free(_repo);
+}
+
+void test_pack_packbuilder__create_pack(void)
+{
+	git_indexer_stats stats;
+	git_oid oid, *o;
+	unsigned int i;
+
+	git_revwalk_sorting(_revwalker, GIT_SORT_TIME);
+	cl_git_pass(git_revwalk_push_ref(_revwalker, "HEAD"));
+
+	while (git_revwalk_next(&oid, _revwalker) == 0) {
+		o = git__malloc(GIT_OID_RAWSZ);
+		cl_assert(o != NULL);
+		git_oid_cpy(o, &oid);
+		cl_git_pass(git_vector_insert(&_commits, o));
+	}
+
+	git_vector_foreach(&_commits, i, o) {
+		cl_git_pass(git_packbuilder_insert(_packbuilder, o, NULL));
+	}
+
+	git_vector_foreach(&_commits, i, o) {
+		git_object *obj;
+		cl_git_pass(git_object_lookup(&obj, _repo, o, GIT_OBJ_COMMIT));
+		cl_git_pass(git_packbuilder_insert_tree(_packbuilder,
+					git_commit_tree_oid((git_commit *)obj)));
+		git_object_free(obj);
+	}
+
+	cl_git_pass(git_packbuilder_write(_packbuilder, "testpack.pack"));
+
+	cl_git_pass(git_indexer_new(&_indexer, "testpack.pack"));
+	cl_git_pass(git_indexer_run(_indexer, &stats));
+	cl_git_pass(git_indexer_write(_indexer));
+}