Merge pull request #345 from carlosmn/gsoc2011/indexer

Implement a pack indexer

include/git2.h

@@ -60,5 +60,6 @@
 #include "git2/net.h"
 #include "git2/transport.h"
 #include "git2/status.h"
+#include "git2/indexer.h"
 
 #endif

include/git2/indexer.h

@@ -0,0 +1,67 @@
+#ifndef _INCLUDE_git_indexer_h__
+#define _INCLUDE_git_indexer_h__
+
+#include "git2/common.h"
+#include "git2/oid.h"
+
+/**
+ * This is passed as the first argument to the callback to allow the
+ * user to see the progress.
+ */
+typedef struct git_indexer_stats {
+	unsigned int total;
+	unsigned int processed;
+} git_indexer_stats;
+
+
+typedef struct git_indexer git_indexer;
+
+/**
+ * Create a new indexer instance
+ *
+ * @param out where to store the indexer instance
+ * @param packname the absolute filename of the packfile to index
+ */
+GIT_EXTERN(int) git_indexer_new(git_indexer **out, const char *packname);
+
+/**
+ * Iterate over the objects in the packfile and extract the information
+ *
+ * Indexing a packfile can be very expensive so this function is
+ * expected to be run in a worker thread and the stats used to provide
+ * feedback the user.
+ *
+ * @param idx the indexer instance
+ * @param stats storage for the running state
+ */
+GIT_EXTERN(int) git_indexer_run(git_indexer *idx, git_indexer_stats *stats);
+
+/**
+ * Write the index file to disk.
+ *
+ * The file will be stored as pack-$hash.idx in the same directory as
+ * the packfile.
+ *
+ * @param idx the indexer instance
+ */
+GIT_EXTERN(int) git_indexer_write(git_indexer *idx);
+
+/**
+ * Get the packfile's hash
+ *
+ * A packfile's name is derived from the sorted hashing of all object
+ * names. This is only correct after the index has been written to disk.
+ *
+ * @param idx the indexer instance
+ */
+GIT_EXTERN(const git_oid *) git_indexer_hash(git_indexer *idx);
+
+/**
+ * Free the indexer and its resources
+ *
+ * @param idx the indexer to free
+ */
+GIT_EXTERN(void) git_indexer_free(git_indexer *idx);
+
+
+#endif

src/indexer.c

@@ -0,0 +1,380 @@
+/*
+ * This file is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License, version 2,
+ * as published by the Free Software Foundation.
+ *
+ * In addition to the permissions in the GNU General Public License,
+ * the authors give you unlimited permission to link the compiled
+ * version of this file into combinations with other programs,
+ * and to distribute those combinations without any restriction
+ * coming from the use of this file.  (The General Public License
+ * restrictions do apply in other respects; for example, they cover
+ * modification of the file, and distribution when not linked into
+ * a combined executable.)
+ *
+ * This file is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; see the file COPYING.  If not, write to
+ * the Free Software Foundation, 51 Franklin Street, Fifth Floor,
+ * Boston, MA 02110-1301, USA.
+ */
+
+#include "git2/indexer.h"
+#include "git2/object.h"
+#include "git2/zlib.h"
+#include "git2/oid.h"
+
+#include "common.h"
+#include "pack.h"
+#include "mwindow.h"
+#include "posix.h"
+#include "pack.h"
+#include "filebuf.h"
+#include "sha1.h"
+
+#define UINT31_MAX (0x7FFFFFFF)
+
+struct entry {
+	git_oid oid;
+	uint32_t crc;
+	uint32_t offset;
+	uint64_t offset_long;
+};
+
+typedef struct git_indexer {
+	struct git_pack_file *pack;
+	struct stat st;
+	struct git_pack_header hdr;
+	size_t nr_objects;
+	git_vector objects;
+	git_filebuf file;
+	unsigned int fanout[256];
+	git_oid hash;
+} git_indexer;
+
+const git_oid *git_indexer_hash(git_indexer *idx)
+{
+	return &idx->hash;
+}
+
+static int parse_header(git_indexer *idx)
+{
+	int error;
+
+	/* Verify we recognize this pack file format. */
+	if ((error = p_read(idx->pack->mwf.fd, &idx->hdr, sizeof(idx->hdr))) < GIT_SUCCESS)
+		return git__rethrow(error, "Failed to read in pack header");
+
+	if (idx->hdr.hdr_signature != ntohl(PACK_SIGNATURE))
+		return git__throw(GIT_EOBJCORRUPTED, "Wrong pack signature");
+
+	if (!pack_version_ok(idx->hdr.hdr_version))
+		return git__throw(GIT_EOBJCORRUPTED, "Wrong pack version");
+
+
+	return GIT_SUCCESS;
+}
+
+int objects_cmp(const void *a, const void *b)
+{
+	const struct entry *entrya = a;
+	const struct entry *entryb = b;
+
+	return git_oid_cmp(&entrya->oid, &entryb->oid);
+}
+
+int git_indexer_new(git_indexer **out, const char *packname)
+{
+	git_indexer *idx;
+	unsigned int namelen;
+	int ret, error;
+
+	if (git_path_root(packname) < 0)
+		return git__throw(GIT_EINVALIDPATH, "Path is not absolute");
+
+	idx = git__malloc(sizeof(git_indexer));
+	if (idx == NULL)
+		return GIT_ENOMEM;
+
+	memset(idx, 0x0, sizeof(*idx));
+
+	namelen = strlen(packname);
+	idx->pack = git__malloc(sizeof(struct git_pack_file) + namelen + 1);
+	if (idx->pack == NULL)
+		goto cleanup;
+
+	memset(idx->pack, 0x0, sizeof(struct git_pack_file));
+	memcpy(idx->pack->pack_name, packname, namelen + 1);
+
+	ret = p_stat(packname, &idx->st);
+	if (ret < 0) {
+		if (errno == ENOENT)
+			error = git__throw(GIT_ENOTFOUND, "Failed to stat packfile. File not found");
+		else
+			error = git__throw(GIT_EOSERR, "Failed to stat packfile.");
+
+		goto cleanup;
+	}
+
+	ret = p_open(idx->pack->pack_name, O_RDONLY);
+	if (ret < 0) {
+		error = git__throw(GIT_EOSERR, "Failed to open packfile");
+		goto cleanup;
+	}
+
+	idx->pack->mwf.fd = ret;
+	idx->pack->mwf.size = idx->st.st_size;
+
+	error = parse_header(idx);
+	if (error < GIT_SUCCESS) {
+		error = git__rethrow(error, "Failed to parse packfile header");
+		goto cleanup;
+	}
+
+	idx->nr_objects = ntohl(idx->hdr.hdr_entries);
+
+	error = git_vector_init(&idx->objects, idx->nr_objects, objects_cmp);
+	if (error < GIT_SUCCESS) {
+		goto cleanup;
+	}
+
+	*out = idx;
+
+	return GIT_SUCCESS;
+
+cleanup:
+	git_indexer_free(idx);
+
+	return error;
+}
+
+static void index_path(char *path, git_indexer *idx)
+{
+	char *ptr;
+	const char prefix[] = "pack-", suffix[] = ".idx\0";
+
+	ptr = strrchr(path, '/') + 1;
+
+	memcpy(ptr, prefix, STRLEN(prefix));
+	ptr += STRLEN(prefix);
+	git_oid_fmt(ptr, &idx->hash);
+	ptr += GIT_OID_HEXSZ;
+	memcpy(ptr, suffix, STRLEN(suffix));
+}
+
+int git_indexer_write(git_indexer *idx)
+{
+	git_mwindow *w = NULL;
+	int error, namelen;
+	unsigned int i, long_offsets, left;
+	struct git_pack_idx_header hdr;
+	char filename[GIT_PATH_MAX];
+	struct entry *entry;
+	void *packfile_hash;
+	git_oid file_hash;
+	SHA_CTX ctx;
+
+	git_vector_sort(&idx->objects);
+
+	namelen = strlen(idx->pack->pack_name);
+	memcpy(filename, idx->pack->pack_name, namelen);
+	memcpy(filename + namelen - STRLEN("pack"), "idx\0", STRLEN("idx\0"));
+
+	error = git_filebuf_open(&idx->file, filename, GIT_FILEBUF_HASH_CONTENTS);
+
+	/* Write out the header */
+	hdr.idx_signature = htonl(PACK_IDX_SIGNATURE);
+	hdr.idx_version = htonl(2);
+	error = git_filebuf_write(&idx->file, &hdr, sizeof(hdr));
+
+	/* Write out the fanout table */
+	for (i = 0; i < 256; ++i) {
+		uint32_t n = htonl(idx->fanout[i]);
+		error = git_filebuf_write(&idx->file, &n, sizeof(n));
+		if (error < GIT_SUCCESS)
+			goto cleanup;
+	}
+
+	/* Write out the object names (SHA-1 hashes) */
+	SHA1_Init(&ctx);
+	git_vector_foreach(&idx->objects, i, entry) {
+		error = git_filebuf_write(&idx->file, &entry->oid, sizeof(git_oid));
+		SHA1_Update(&ctx, &entry->oid, GIT_OID_RAWSZ);
+		if (error < GIT_SUCCESS)
+			goto cleanup;
+	}
+	SHA1_Final(idx->hash.id, &ctx);
+
+	/* Write out the CRC32 values */
+	git_vector_foreach(&idx->objects, i, entry) {
+		error = git_filebuf_write(&idx->file, &entry->crc, sizeof(uint32_t));
+		if (error < GIT_SUCCESS)
+			goto cleanup;
+	}
+
+	/* Write out the offsets */
+	git_vector_foreach(&idx->objects, i, entry) {
+		uint32_t n;
+
+		if (entry->offset == UINT32_MAX)
+			n = htonl(0x80000000 | long_offsets++);
+		else
+			n = htonl(entry->offset);
+
+		error = git_filebuf_write(&idx->file, &n, sizeof(uint32_t));
+		if (error < GIT_SUCCESS)
+			goto cleanup;
+	}
+
+	/* Write out the long offsets */
+	git_vector_foreach(&idx->objects, i, entry) {
+		uint32_t split[2];
+
+		if (entry->offset != UINT32_MAX)
+			continue;
+
+		split[0] = htonl(entry->offset_long >> 32);
+		split[1] = htonl(entry->offset_long & 0xffffffff);
+
+		error = git_filebuf_write(&idx->file, &split, sizeof(uint32_t) * 2);
+		if (error < GIT_SUCCESS)
+			goto cleanup;
+	}
+
+	/* Write out the packfile trailer */
+
+	packfile_hash = git_mwindow_open(&idx->pack->mwf, &w, idx->st.st_size - GIT_OID_RAWSZ, GIT_OID_RAWSZ, &left);
+	if (packfile_hash == NULL) {
+		error = git__rethrow(GIT_ENOMEM, "Failed to open window to packfile hash");
+		goto cleanup;
+	}
+
+	memcpy(&file_hash, packfile_hash, GIT_OID_RAWSZ);
+
+	git_mwindow_close(&w);
+
+	error = git_filebuf_write(&idx->file, &file_hash, sizeof(git_oid));
+
+	/* Write out the index sha */
+	error = git_filebuf_hash(&file_hash, &idx->file);
+	if (error < GIT_SUCCESS)
+		goto cleanup;
+
+	error = git_filebuf_write(&idx->file, &file_hash, sizeof(git_oid));
+	if (error < GIT_SUCCESS)
+		goto cleanup;
+
+	/* Figure out what the final name should be */
+	index_path(filename, idx);
+	/* Commit file */
+	error = git_filebuf_commit_at(&idx->file, filename);
+
+cleanup:
+	if (error < GIT_SUCCESS)
+		git_filebuf_cleanup(&idx->file);
+
+	return error;
+}
+
+int git_indexer_run(git_indexer *idx, git_indexer_stats *stats)
+{
+	git_mwindow_file *mwf;
+	off_t off = sizeof(struct git_pack_header);
+	int error;
+	struct entry *entry;
+	unsigned int left, processed;
+
+	assert(idx && stats);
+
+	mwf = &idx->pack->mwf;
+	error = git_mwindow_file_register(mwf);
+	if (error < GIT_SUCCESS)
+		return git__rethrow(error, "Failed to register mwindow file");
+
+	stats->total = idx->nr_objects;
+	stats->processed = processed = 0;
+
+	while (processed < idx->nr_objects) {
+		git_rawobj obj;
+		git_oid oid;
+		git_mwindow *w = NULL;
+		char hdr[512] = {0}; /* FIXME: How long should this be? */
+		int i, hdr_len;
+		off_t entry_start = off;
+		void *packed;
+		size_t entry_size;
+
+		entry = git__malloc(sizeof(struct entry));
+		memset(entry, 0x0, sizeof(struct entry));
+
+		if (off > UINT31_MAX) {
+			entry->offset = UINT32_MAX;
+			entry->offset_long = off;
+		} else {
+			entry->offset = off;
+		}
+
+		error = git_packfile_unpack(&obj, idx->pack, &off);
+		if (error < GIT_SUCCESS) {
+			error = git__rethrow(error, "Failed to unpack object");
+			goto cleanup;
+		}
+
+		error = git_odb__hash_obj(&oid, hdr, sizeof(hdr), &hdr_len, &obj);
+		if (error < GIT_SUCCESS) {
+			error = git__rethrow(error, "Failed to hash object");
+			goto cleanup;
+		}
+
+		git_oid_cpy(&entry->oid, &oid);
+		entry->crc = crc32(0L, Z_NULL, 0);
+
+		entry_size = off - entry_start;
+		packed = git_mwindow_open(mwf, &w, entry_start, entry_size, &left);
+		if (packed == NULL) {
+			error = git__rethrow(error, "Failed to open window to read packed data");
+			goto cleanup;
+		}
+		entry->crc = htonl(crc32(entry->crc, packed, entry_size));
+		git_mwindow_close(&w);
+
+		/* Add the object to the list */
+		error = git_vector_insert(&idx->objects, entry);
+		if (error < GIT_SUCCESS) {
+			error = git__rethrow(error, "Failed to add entry to list");
+			goto cleanup;
+		}
+
+		for (i = oid.id[0]; i < 256; ++i) {
+			idx->fanout[i]++;
+		}
+
+		free(obj.data);
+
+		stats->processed = ++processed;
+	}
+
+cleanup:
+	git_mwindow_free_all(mwf);
+
+	return error;
+
+}
+
+void git_indexer_free(git_indexer *idx)
+{
+	unsigned int i;
+	struct entry *e;
+
+	p_close(idx->pack->mwf.fd);
+	git_vector_foreach(&idx->objects, i, e)
+		free(e);
+	git_vector_free(&idx->objects);
+	free(idx->pack);
+	free(idx);
+}
+

src/mwindow.c

@@ -0,0 +1,271 @@
+/*
+ * This file is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License, version 2,
+ * as published by the Free Software Foundation.
+ *
+ * In addition to the permissions in the GNU General Public License,
+ * the authors give you unlimited permission to link the compiled
+ * version of this file into combinations with other programs,
+ * and to distribute those combinations without any restriction
+ * coming from the use of this file.  (The General Public License
+ * restrictions do apply in other respects; for example, they cover
+ * modification of the file, and distribution when not linked into
+ * a combined executable.)
+ *
+ * This file is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; see the file COPYING.  If not, write to
+ * the Free Software Foundation, 51 Franklin Street, Fifth Floor,
+ * Boston, MA 02110-1301, USA.
+ */
+
+#include "common.h"
+#include "mwindow.h"
+#include "vector.h"
+#include "fileops.h"
+#include "map.h"
+
+#define DEFAULT_WINDOW_SIZE \
+	(sizeof(void*) >= 8 \
+		?  1 * 1024 * 1024 * 1024 \
+		: 32 * 1024 * 1024)
+
+#define DEFAULT_MAPPED_LIMIT \
+	((1024L * 1024L) * (sizeof(void*) >= 8 ? 8192 : 256))
+
+/*
+ * We need this because each process is only allowed a specific amount
+ * of memory. Making it writable should generate one instance per
+ * process, but we still need to set a couple of variables.
+ */
+
+static git_mwindow_ctl ctl = {
+	.window_size = DEFAULT_WINDOW_SIZE,
+	.mapped_limit = DEFAULT_MAPPED_LIMIT
+};
+
+/*
+ * Free all the windows in a sequence, typically because we're done
+ * with the file
+ */
+void git_mwindow_free_all(git_mwindow_file *mwf)
+{
+	unsigned int i;
+	/*
+	 * Remove these windows from the global list
+	 */
+	for (i = 0; i < ctl.windowfiles.length; ++i){
+		if (git_vector_get(&ctl.windowfiles, i) == mwf) {
+			git_vector_remove(&ctl.windowfiles, i);
+			break;
+		}
+	}
+
+	if (ctl.windowfiles.length == 0) {
+		git_vector_free(&ctl.windowfiles);
+		ctl.windowfiles.contents = NULL;
+	}
+
+	while (mwf->windows) {
+		git_mwindow *w = mwf->windows;
+		assert(w->inuse_cnt == 0);
+
+		ctl.mapped -= w->window_map.len;
+		ctl.open_windows--;
+
+		git_futils_mmap_free(&w->window_map);
+
+		mwf->windows = w->next;
+		free(w);
+	}
+}
+
+/*
+ * Check if a window 'win' contains the address 'offset'
+ */
+int git_mwindow_contains(git_mwindow *win, off_t offset)
+{
+	off_t win_off = win->offset;
+	return win_off <= offset
+		&& offset <= (off_t)(win_off + win->window_map.len);
+}
+
+/*
+ * Find the least-recently-used window in a file
+ */
+void git_mwindow_scan_lru(
+	git_mwindow_file *mwf,
+	git_mwindow **lru_w,
+	git_mwindow **lru_l)
+{
+	git_mwindow *w, *w_l;
+
+	for (w_l = NULL, w = mwf->windows; w; w = w->next) {
+		if (!w->inuse_cnt) {
+			/*
+			 * If the current one is more recent than the last one,
+			 * store it in the output parameter. If lru_w is NULL,
+			 * it's the first loop, so store it as well.
+			 */
+			if (!*lru_w || w->last_used < (*lru_w)->last_used) {
+				*lru_w = w;
+				*lru_l = w_l;
+			}
+		}
+		w_l = w;
+	}
+}
+
+/*
+ * Close the least recently used window. You should check to see if
+ * the file descriptors need closing from time to time.
+ */
+int git_mwindow_close_lru(git_mwindow_file *mwf)
+{
+	unsigned int i;
+	git_mwindow *lru_w = NULL, *lru_l = NULL;
+
+	/* FIMXE: Does this give us any advantage? */
+	if(mwf->windows)
+		git_mwindow_scan_lru(mwf, &lru_w, &lru_l);
+
+	for (i = 0; i < ctl.windowfiles.length; ++i) {
+		git_mwindow_scan_lru(git_vector_get(&ctl.windowfiles, i), &lru_w, &lru_l);
+	}
+
+	if (lru_w) {
+		git_mwindow_close(&lru_w);
+		ctl.mapped -= lru_w->window_map.len;
+		git_futils_mmap_free(&lru_w->window_map);
+
+		if (lru_l)
+			lru_l->next = lru_w->next;
+		else
+			mwf->windows = lru_w->next;
+
+		free(lru_w);
+		ctl.open_windows--;
+
+		return GIT_SUCCESS;
+	}
+
+	return git__throw(GIT_ERROR, "Failed to close memory window. Couln't find LRU");
+}
+
+static git_mwindow *new_window(git_mwindow_file *mwf, git_file fd, size_t size, off_t offset)
+{
+	size_t walign = ctl.window_size / 2;
+	size_t len;
+	git_mwindow *w;
+
+	w = git__malloc(sizeof(*w));
+	if (w == NULL)
+		return w;
+
+	memset(w, 0x0, sizeof(*w));
+	w->offset = (offset / walign) * walign;
+
+	len = size - w->offset;
+	if (len > ctl.window_size)
+		len = ctl.window_size;
+
+	ctl.mapped += len;
+
+	while(ctl.mapped_limit < ctl.mapped &&
+	      git_mwindow_close_lru(mwf) == GIT_SUCCESS) {}
+
+	/* FIXME: Shouldn't we error out if there's an error in closing lru? */
+
+	if (git_futils_mmap_ro(&w->window_map, fd, w->offset, len) < GIT_SUCCESS)
+		goto cleanup;
+
+	ctl.mmap_calls++;
+	ctl.open_windows++;
+
+	if (ctl.mapped > ctl.peak_mapped)
+		ctl.peak_mapped = ctl.mapped;
+
+	if (ctl.open_windows > ctl.peak_open_windows)
+		ctl.peak_open_windows = ctl.open_windows;
+
+	return w;
+
+cleanup:
+	free(w);
+	return NULL;
+}
+
+/*
+ * Open a new window, closing the least recenty used until we have
+ * enough space. Don't forget to add it to your list
+ */
+unsigned char *git_mwindow_open(git_mwindow_file *mwf, git_mwindow **cursor,
+                                off_t offset, int extra, unsigned int *left)
+{
+	git_mwindow *w = *cursor;
+
+	if (!w || !git_mwindow_contains(w, offset + extra)) {
+		if (w) {
+			w->inuse_cnt--;
+		}
+
+		for (w = mwf->windows; w; w = w->next) {
+			if (git_mwindow_contains(w, offset + extra))
+				break;
+		}
+
+		/*
+		 * If there isn't a suitable window, we need to create a new
+		 * one.
+		 */
+		if (!w) {
+			w = new_window(mwf, mwf->fd, mwf->size, offset);
+			if (w == NULL)
+				return NULL;
+			w->next = mwf->windows;
+			mwf->windows = w;
+		}
+	}
+
+	/* If we changed w, store it in the cursor */
+	if (w != *cursor) {
+		w->last_used = ctl.used_ctr++;
+		w->inuse_cnt++;
+		*cursor = w;
+	}
+
+	offset -= w->offset;
+	assert(git__is_sizet(offset));
+
+	if (left)
+		*left = w->window_map.len - offset;
+
+	return (unsigned char *) w->window_map.data + offset;
+
+	free(w);
+	return NULL;
+}
+
+int git_mwindow_file_register(git_mwindow_file *mwf)
+{
+	int error;
+
+	if (ctl.windowfiles.length == 0 &&
+	    (error = git_vector_init(&ctl.windowfiles, 8, NULL)) < GIT_SUCCESS)
+		return error;
+
+	return git_vector_insert(&ctl.windowfiles, mwf);
+}
+
+void git_mwindow_close(git_mwindow **window)
+{
+	git_mwindow *w = *window;
+	if (w) {
+		w->inuse_cnt--;
+		*window = NULL;
+	}
+}

src/mwindow.h

@@ -0,0 +1,66 @@
+/*
+ * This file is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License, version 2,
+ * as published by the Free Software Foundation.
+ *
+ * In addition to the permissions in the GNU General Public License,
+ * the authors give you unlimited permission to link the compiled
+ * version of this file into combinations with other programs,
+ * and to distribute those combinations without any restriction
+ * coming from the use of this file.  (The General Public License
+ * restrictions do apply in other respects; for example, they cover
+ * modification of the file, and distribution when not linked into
+ * a combined executable.)
+ *
+ * This file is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; see the file COPYING.  If not, write to
+ * the Free Software Foundation, 51 Franklin Street, Fifth Floor,
+ * Boston, MA 02110-1301, USA.
+ */
+
+#ifndef INCLUDE_mwindow__
+#define INCLUDE_mwindow__
+
+#include "map.h"
+#include "vector.h"
+#include "fileops.h"
+
+typedef struct git_mwindow {
+	struct git_mwindow *next;
+	git_map window_map;
+	off_t offset;
+	unsigned int last_used;
+	unsigned int inuse_cnt;
+} git_mwindow;
+
+typedef struct git_mwindow_file {
+	git_mwindow *windows;
+	int fd;
+	off_t size;
+} git_mwindow_file;
+
+typedef struct git_mwindow_ctl {
+	size_t mapped;
+	unsigned int open_windows;
+	size_t window_size; /* needs default value */
+	size_t mapped_limit; /* needs default value */
+	unsigned int mmap_calls;
+	unsigned int peak_open_windows;
+	size_t peak_mapped;
+	size_t used_ctr;
+	git_vector windowfiles;
+} git_mwindow_ctl;
+
+int git_mwindow_contains(git_mwindow *win, off_t offset);
+void git_mwindow_free_all(git_mwindow_file *mwf);
+unsigned char *git_mwindow_open(git_mwindow_file *mwf, git_mwindow **cursor, off_t offset, int extra, unsigned int *left);
+void git_mwindow_scan_lru(git_mwindow_file *mwf, git_mwindow **lru_w, git_mwindow **lru_l);
+int git_mwindow_file_register(git_mwindow_file *mwf);
+void git_mwindow_close(git_mwindow **w_cursor);
+
+#endif

src/pack.c

@@ -0,0 +1,790 @@
+/*
+ * This file is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License, version 2,
+ * as published by the Free Software Foundation.
+ *
+ * In addition to the permissions in the GNU General Public License,
+ * the authors give you unlimited permission to link the compiled
+ * version of this file into combinations with other programs,
+ * and to distribute those combinations without any restriction
+ * coming from the use of this file.  (The General Public License
+ * restrictions do apply in other respects; for example, they cover
+ * modification of the file, and distribution when not linked into
+ * a combined executable.)
+ *
+ * This file is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; see the file COPYING.  If not, write to
+ * the Free Software Foundation, 51 Franklin Street, Fifth Floor,
+ * Boston, MA 02110-1301, USA.
+ */
+
+#include "mwindow.h"
+#include "odb.h"
+#include "pack.h"
+#include "delta-apply.h"
+#include "sha1_lookup.h"
+
+#include "git2/oid.h"
+#include "git2/zlib.h"
+
+static int packfile_open(struct git_pack_file *p);
+static off_t nth_packed_object_offset(const struct git_pack_file *p, uint32_t n);
+int packfile_unpack_compressed(
+		git_rawobj *obj,
+		struct git_pack_file *p,
+		git_mwindow **w_curs,
+		off_t *curpos,
+		size_t size,
+		git_otype type);
+
+/* Can find the offset of an object given
+ * a prefix of an identifier.
+ * Throws GIT_EAMBIGUOUSOIDPREFIX if short oid
+ * is ambiguous within the pack.
+ * This method assumes that len is between
+ * GIT_OID_MINPREFIXLEN and GIT_OID_HEXSZ.
+ */
+static int pack_entry_find_offset(
+		off_t *offset_out,
+		git_oid *found_oid,
+		struct git_pack_file *p,
+		const git_oid *short_oid,
+		unsigned int len);
+
+/***********************************************************
+ *
+ * PACK INDEX METHODS
+ *
+ ***********************************************************/
+
+static void pack_index_free(struct git_pack_file *p)
+{
+	if (p->index_map.data) {
+		git_futils_mmap_free(&p->index_map);
+		p->index_map.data = NULL;
+	}
+}
+
+static int pack_index_check(const char *path,  struct git_pack_file *p)
+{
+	struct git_pack_idx_header *hdr;
+	uint32_t version, nr, i, *index;
+
+	void *idx_map;
+	size_t idx_size;
+
+	struct stat st;
+
+	/* TODO: properly open the file without access time */
+	git_file fd = p_open(path, O_RDONLY /*| O_NOATIME */);
+
+	int error;
+
+	if (fd < 0)
+		return git__throw(GIT_EOSERR, "Failed to check index. File missing or corrupted");
+
+	if (p_fstat(fd, &st) < GIT_SUCCESS) {
+		p_close(fd);
+		return git__throw(GIT_EOSERR, "Failed to check index. File appears to be corrupted");
+	}
+
+	if (!git__is_sizet(st.st_size))
+		return GIT_ENOMEM;
+
+	idx_size = (size_t)st.st_size;
+
+	if (idx_size < 4 * 256 + 20 + 20) {
+		p_close(fd);
+		return git__throw(GIT_EOBJCORRUPTED, "Failed to check index. Object is corrupted");
+	}
+
+	error = git_futils_mmap_ro(&p->index_map, fd, 0, idx_size);
+	p_close(fd);
+
+	if (error < GIT_SUCCESS)
+		return git__rethrow(error, "Failed to check index");
+
+	hdr = idx_map = p->index_map.data;
+
+	if (hdr->idx_signature == htonl(PACK_IDX_SIGNATURE)) {
+		version = ntohl(hdr->idx_version);
+
+		if (version < 2 || version > 2) {
+			git_futils_mmap_free(&p->index_map);
+			return git__throw(GIT_EOBJCORRUPTED, "Failed to check index. Unsupported index version");
+		}
+
+	} else
+		version = 1;
+
+	nr = 0;
+	index = idx_map;
+
+	if (version > 1)
+		index += 2;  /* skip index header */
+
+	for (i = 0; i < 256; i++) {
+		uint32_t n = ntohl(index[i]);
+		if (n < nr) {
+			git_futils_mmap_free(&p->index_map);
+			return git__throw(GIT_EOBJCORRUPTED, "Failed to check index. Index is non-monotonic");
+		}
+		nr = n;
+	}
+
+	if (version == 1) {
+		/*
+		 * Total size:
+		 *  - 256 index entries 4 bytes each
+		 *  - 24-byte entries * nr (20-byte sha1 + 4-byte offset)
+		 *  - 20-byte SHA1 of the packfile
+		 *  - 20-byte SHA1 file checksum
+		 */
+		if (idx_size != 4*256 + nr * 24 + 20 + 20) {
+			git_futils_mmap_free(&p->index_map);
+			return git__throw(GIT_EOBJCORRUPTED, "Failed to check index. Object is corrupted");
+		}
+	} else if (version == 2) {
+		/*
+		 * Minimum size:
+		 *  - 8 bytes of header
+		 *  - 256 index entries 4 bytes each
+		 *  - 20-byte sha1 entry * nr
+		 *  - 4-byte crc entry * nr
+		 *  - 4-byte offset entry * nr
+		 *  - 20-byte SHA1 of the packfile
+		 *  - 20-byte SHA1 file checksum
+		 * And after the 4-byte offset table might be a
+		 * variable sized table containing 8-byte entries
+		 * for offsets larger than 2^31.
+		 */
+		unsigned long min_size = 8 + 4*256 + nr*(20 + 4 + 4) + 20 + 20;
+		unsigned long max_size = min_size;
+
+		if (nr)
+			max_size += (nr - 1)*8;
+
+		if (idx_size < min_size || idx_size > max_size) {
+			git_futils_mmap_free(&p->index_map);
+			return git__throw(GIT_EOBJCORRUPTED, "Failed to check index. Wrong index size");
+		}
+
+		/* Make sure that off_t is big enough to access the whole pack...
+		 * Is this an issue in libgit2? It shouldn't. */
+		if (idx_size != min_size && (sizeof(off_t) <= 4)) {
+			git_futils_mmap_free(&p->index_map);
+			return git__throw(GIT_EOSERR, "Failed to check index. off_t not big enough to access the whole pack");
+		}
+	}
+
+	p->index_version = version;
+	p->num_objects = nr;
+	return GIT_SUCCESS;
+}
+
+static int pack_index_open(struct git_pack_file *p)
+{
+	char *idx_name;
+	int error;
+
+	if (p->index_map.data)
+		return GIT_SUCCESS;
+
+	idx_name = git__strdup(p->pack_name);
+	strcpy(idx_name + strlen(idx_name) - STRLEN(".pack"), ".idx");
+
+	error = pack_index_check(idx_name, p);
+	free(idx_name);
+
+	return error == GIT_SUCCESS ? GIT_SUCCESS : git__rethrow(error, "Failed to open index");
+}
+
+static unsigned char *pack_window_open(
+		struct git_pack_file *p,
+		git_mwindow **w_cursor,
+		off_t offset,
+		unsigned int *left)
+{
+	if (p->mwf.fd == -1 && packfile_open(p) < GIT_SUCCESS)
+		return NULL;
+
+	/* Since packfiles end in a hash of their content and it's
+	 * pointless to ask for an offset into the middle of that
+	 * hash, and the pack_window_contains function above wouldn't match
+	 * don't allow an offset too close to the end of the file.
+	 */
+	if (offset > (p->mwf.size - 20))
+		return NULL;
+
+	return git_mwindow_open(&p->mwf, w_cursor, offset, 20, left);
+ }
+
+static unsigned long packfile_unpack_header1(
+		size_t *sizep,
+		git_otype *type,
+		const unsigned char *buf,
+		unsigned long len)
+{
+	unsigned shift;
+	unsigned long size, c;
+	unsigned long used = 0;
+
+	c = buf[used++];
+	*type = (c >> 4) & 7;
+	size = c & 15;
+	shift = 4;
+	while (c & 0x80) {
+		if (len <= used || bitsizeof(long) <= shift)
+			return 0;
+
+		c = buf[used++];
+		size += (c & 0x7f) << shift;
+		shift += 7;
+	}
+
+	*sizep = (size_t)size;
+	return used;
+}
+
+int git_packfile_unpack_header(
+		size_t *size_p,
+		git_otype *type_p,
+		git_mwindow_file *mwf,
+		git_mwindow **w_curs,
+		off_t *curpos)
+{
+	unsigned char *base;
+	unsigned int left;
+	unsigned long used;
+
+	/* pack_window_open() assures us we have [base, base + 20) available
+	 * as a range that we can look at at.  (Its actually the hash
+	 * size that is assured.)  With our object header encoding
+	 * the maximum deflated object size is 2^137, which is just
+	 * insane, so we know won't exceed what we have been given.
+	 */
+//	base = pack_window_open(p, w_curs, *curpos, &left);
+	base = git_mwindow_open(mwf, w_curs, *curpos, 20, &left);
+	if (base == NULL)
+		return GIT_ENOMEM;
+
+	used = packfile_unpack_header1(size_p, type_p, base, left);
+
+	if (used == 0)
+		return git__throw(GIT_EOBJCORRUPTED, "Header length is zero");
+
+	*curpos += used;
+	return GIT_SUCCESS;
+}
+
+static int packfile_unpack_delta(
+		git_rawobj *obj,
+		struct git_pack_file *p,
+		git_mwindow **w_curs,
+		off_t *curpos,
+		size_t delta_size,
+		git_otype delta_type,
+		off_t obj_offset)
+{
+	off_t base_offset;
+	git_rawobj base, delta;
+	int error;
+
+	base_offset = get_delta_base(p, w_curs, curpos, delta_type, obj_offset);
+	if (base_offset == 0)
+		return git__throw(GIT_EOBJCORRUPTED, "Delta offset is zero");
+
+	git_mwindow_close(w_curs);
+	error = git_packfile_unpack(&base, p, &base_offset);
+
+	/*
+	 * TODO: git.git tries to load the base from other packfiles
+	 * or loose objects.
+	 *
+	 * We'll need to do this in order to support thin packs.
+	 */
+	if (error < GIT_SUCCESS)
+		return git__rethrow(error, "Corrupted delta");
+
+	error = packfile_unpack_compressed(&delta, p, w_curs, curpos, delta_size, delta_type);
+	if (error < GIT_SUCCESS) {
+		free(base.data);
+		return git__rethrow(error, "Corrupted delta");
+	}
+
+	obj->type = base.type;
+	error = git__delta_apply(obj,
+			base.data, base.len,
+			delta.data, delta.len);
+
+	free(base.data);
+	free(delta.data);
+
+	/* TODO: we might want to cache this shit. eventually */
+	//add_delta_base_cache(p, base_offset, base, base_size, *type);
+	return error; /* error set by git__delta_apply */
+}
+
+int git_packfile_unpack(
+		git_rawobj *obj,
+		struct git_pack_file *p,
+		off_t *obj_offset)
+{
+	git_mwindow *w_curs = NULL;
+	off_t curpos = *obj_offset;
+	int error;
+
+	size_t size = 0;
+	git_otype type;
+
+	/*
+	 * TODO: optionally check the CRC on the packfile
+	 */
+
+	obj->data = NULL;
+	obj->len = 0;
+	obj->type = GIT_OBJ_BAD;
+
+	error = git_packfile_unpack_header(&size, &type, &p->mwf, &w_curs, &curpos);
+	if (error < GIT_SUCCESS)
+		return git__rethrow(error, "Failed to unpack packfile");
+
+	switch (type) {
+	case GIT_OBJ_OFS_DELTA:
+	case GIT_OBJ_REF_DELTA:
+		error = packfile_unpack_delta(
+				obj, p, &w_curs, &curpos,
+				size, type, *obj_offset);
+		break;
+
+	case GIT_OBJ_COMMIT:
+	case GIT_OBJ_TREE:
+	case GIT_OBJ_BLOB:
+	case GIT_OBJ_TAG:
+		error = packfile_unpack_compressed(
+				obj, p, &w_curs, &curpos,
+				size, type);
+		break;
+
+	default:
+		error = GIT_EOBJCORRUPTED;
+		break;
+	}
+
+	git_mwindow_close(&w_curs);
+
+	if (error < GIT_SUCCESS)
+		return git__rethrow(error, "Failed to unpack object");
+
+	*obj_offset = curpos;
+	return GIT_SUCCESS;
+}
+
+int packfile_unpack_compressed(
+		git_rawobj *obj,
+		struct git_pack_file *p,
+		git_mwindow **w_curs,
+		off_t *curpos,
+		size_t size,
+		git_otype type)
+{
+	int st;
+	z_stream stream;
+	unsigned char *buffer, *in;
+
+	buffer = git__malloc(size + 1);
+	memset(buffer, 0x0, size + 1);
+
+	memset(&stream, 0, sizeof(stream));
+	stream.next_out = buffer;
+	stream.avail_out = size + 1;
+
+	st = inflateInit(&stream);
+	if (st != Z_OK) {
+		free(buffer);
+		return git__throw(GIT_EZLIB, "Error in zlib");
+	}
+
+	do {
+		in = pack_window_open(p, w_curs, *curpos, &stream.avail_in);
+		stream.next_in = in;
+		st = inflate(&stream, Z_FINISH);
+
+		if (!stream.avail_out)
+			break; /* the payload is larger than it should be */
+
+		*curpos += stream.next_in - in;
+	} while (st == Z_OK || st == Z_BUF_ERROR);
+
+	inflateEnd(&stream);
+
+	if ((st != Z_STREAM_END) || stream.total_out != size) {
+		free(buffer);
+		return git__throw(GIT_EZLIB, "Error in zlib");
+	}
+
+	obj->type = type;
+	obj->len = size;
+	obj->data = buffer;
+	return GIT_SUCCESS;
+}
+
+/*
+ * curpos is where the data starts, delta_obj_offset is the where the
+ * header starts
+ */
+off_t get_delta_base(
+		struct git_pack_file *p,
+		git_mwindow **w_curs,
+		off_t *curpos,
+		git_otype type,
+		off_t delta_obj_offset)
+{
+	unsigned char *base_info = pack_window_open(p, w_curs, *curpos, NULL);
+	off_t base_offset;
+	git_oid unused;
+
+	/* pack_window_open() assured us we have [base_info, base_info + 20)
+	 * as a range that we can look at without walking off the
+	 * end of the mapped window.  Its actually the hash size
+	 * that is assured.  An OFS_DELTA longer than the hash size
+	 * is stupid, as then a REF_DELTA would be smaller to store.
+	 */
+	if (type == GIT_OBJ_OFS_DELTA) {
+		unsigned used = 0;
+		unsigned char c = base_info[used++];
+		base_offset = c & 127;
+		while (c & 128) {
+			base_offset += 1;
+			if (!base_offset || MSB(base_offset, 7))
+				return 0;  /* overflow */
+			c = base_info[used++];
+			base_offset = (base_offset << 7) + (c & 127);
+		}
+		base_offset = delta_obj_offset - base_offset;
+		if (base_offset <= 0 || base_offset >= delta_obj_offset)
+			return 0;  /* out of bound */
+		*curpos += used;
+	} else if (type == GIT_OBJ_REF_DELTA) {
+		/* The base entry _must_ be in the same pack */
+		if (pack_entry_find_offset(&base_offset, &unused, p, (git_oid *)base_info, GIT_OID_HEXSZ) < GIT_SUCCESS)
+			return git__throw(GIT_EPACKCORRUPTED, "Base entry delta is not in the same pack");
+		*curpos += 20;
+	} else
+		return 0;
+
+	return base_offset;
+}
+
+/***********************************************************
+ *
+ * PACKFILE METHODS
+ *
+ ***********************************************************/
+
+static struct git_pack_file *packfile_alloc(int extra)
+{
+	struct git_pack_file *p = git__malloc(sizeof(*p) + extra);
+	memset(p, 0, sizeof(*p));
+	p->mwf.fd = -1;
+	return p;
+}
+
+
+void packfile_free(struct git_pack_file *p)
+{
+	assert(p);
+
+	/* clear_delta_base_cache(); */
+	git_mwindow_free_all(&p->mwf);
+
+	if (p->mwf.fd != -1)
+		p_close(p->mwf.fd);
+
+	pack_index_free(p);
+
+	free(p->bad_object_sha1);
+	free(p);
+}
+
+static int packfile_open(struct git_pack_file *p)
+{
+	struct stat st;
+	struct git_pack_header hdr;
+	git_oid sha1;
+	unsigned char *idx_sha1;
+
+	if (!p->index_map.data && pack_index_open(p) < GIT_SUCCESS)
+		return git__throw(GIT_ENOTFOUND, "Failed to open packfile. File not found");
+
+	/* TODO: open with noatime */
+	p->mwf.fd = p_open(p->pack_name, O_RDONLY);
+	if (p->mwf.fd < 0 || p_fstat(p->mwf.fd, &st) < GIT_SUCCESS)
+		return git__throw(GIT_EOSERR, "Failed to open packfile. File appears to be corrupted");
+
+	if (git_mwindow_file_register(&p->mwf) < GIT_SUCCESS) {
+		p_close(p->mwf.fd);
+		return git__throw(GIT_ERROR, "Failed to register packfile windows");
+	}
+
+	/* If we created the struct before we had the pack we lack size. */
+	if (!p->mwf.size) {
+		if (!S_ISREG(st.st_mode))
+			goto cleanup;
+		p->mwf.size = (off_t)st.st_size;
+	} else if (p->mwf.size != st.st_size)
+		goto cleanup;
+
+#if 0
+	/* We leave these file descriptors open with sliding mmap;
+	 * there is no point keeping them open across exec(), though.
+	 */
+	fd_flag = fcntl(p->mwf.fd, F_GETFD, 0);
+	if (fd_flag < 0)
+		return error("cannot determine file descriptor flags");
+
+	fd_flag |= FD_CLOEXEC;
+	if (fcntl(p->pack_fd, F_SETFD, fd_flag) == -1)
+		return GIT_EOSERR;
+#endif
+
+	/* Verify we recognize this pack file format. */
+	if (p_read(p->mwf.fd, &hdr, sizeof(hdr)) < GIT_SUCCESS)
+		goto cleanup;
+
+	if (hdr.hdr_signature != htonl(PACK_SIGNATURE))
+		goto cleanup;
+
+	if (!pack_version_ok(hdr.hdr_version))
+		goto cleanup;
+
+	/* Verify the pack matches its index. */
+	if (p->num_objects != ntohl(hdr.hdr_entries))
+		goto cleanup;
+
+	if (p_lseek(p->mwf.fd, p->mwf.size - GIT_OID_RAWSZ, SEEK_SET) == -1)
+		goto cleanup;
+
+	if (p_read(p->mwf.fd, sha1.id, GIT_OID_RAWSZ) < GIT_SUCCESS)
+		goto cleanup;
+
+	idx_sha1 = ((unsigned char *)p->index_map.data) + p->index_map.len - 40;
+
+	if (git_oid_cmp(&sha1, (git_oid *)idx_sha1) != 0)
+		goto cleanup;
+
+	return GIT_SUCCESS;
+
+cleanup:
+	p_close(p->mwf.fd);
+	p->mwf.fd = -1;
+	return git__throw(GIT_EPACKCORRUPTED, "Failed to open packfile. Pack is corrupted");
+}
+
+int git_packfile_check(struct git_pack_file **pack_out, const char *path)
+{
+	struct stat st;
+	struct git_pack_file *p;
+	size_t path_len;
+
+	*pack_out = NULL;
+	path_len = strlen(path);
+	p = packfile_alloc(path_len + 2);
+
+	/*
+	 * Make sure a corresponding .pack file exists and that
+	 * the index looks sane.
+	 */
+	path_len -= STRLEN(".idx");
+	if (path_len < 1) {
+		free(p);
+		return git__throw(GIT_ENOTFOUND, "Failed to check packfile. Wrong path name");
+	}
+
+	memcpy(p->pack_name, path, path_len);
+
+	strcpy(p->pack_name + path_len, ".keep");
+	if (git_futils_exists(p->pack_name) == GIT_SUCCESS)
+		p->pack_keep = 1;
+
+	strcpy(p->pack_name + path_len, ".pack");
+	if (p_stat(p->pack_name, &st) < GIT_SUCCESS || !S_ISREG(st.st_mode)) {
+		free(p);
+		return git__throw(GIT_ENOTFOUND, "Failed to check packfile. File not found");
+	}
+
+	/* ok, it looks sane as far as we can check without
+	 * actually mapping the pack file.
+	 */
+	p->mwf.size = (off_t)st.st_size;
+	p->pack_local = 1;
+	p->mtime = (git_time_t)st.st_mtime;
+
+	/* see if we can parse the sha1 oid in the packfile name */
+	if (path_len < 40 ||
+		git_oid_fromstr(&p->sha1, path + path_len - GIT_OID_HEXSZ) < GIT_SUCCESS)
+		memset(&p->sha1, 0x0, GIT_OID_RAWSZ);
+
+	*pack_out = p;
+	return GIT_SUCCESS;
+}
+
+/***********************************************************
+ *
+ * PACKFILE ENTRY SEARCH INTERNALS
+ *
+ ***********************************************************/
+
+static off_t nth_packed_object_offset(const struct git_pack_file *p, uint32_t n)
+{
+	const unsigned char *index = p->index_map.data;
+	index += 4 * 256;
+	if (p->index_version == 1) {
+		return ntohl(*((uint32_t *)(index + 24 * n)));
+	} else {
+		uint32_t off;
+		index += 8 + p->num_objects * (20 + 4);
+		off = ntohl(*((uint32_t *)(index + 4 * n)));
+		if (!(off & 0x80000000))
+			return off;
+		index += p->num_objects * 4 + (off & 0x7fffffff) * 8;
+		return (((uint64_t)ntohl(*((uint32_t *)(index + 0)))) << 32) |
+				   ntohl(*((uint32_t *)(index + 4)));
+	}
+}
+
+static int pack_entry_find_offset(
+		off_t *offset_out,
+		git_oid *found_oid,
+		struct git_pack_file *p,
+		const git_oid *short_oid,
+		unsigned int len)
+{
+	const uint32_t *level1_ofs = p->index_map.data;
+	const unsigned char *index = p->index_map.data;
+	unsigned hi, lo, stride;
+	int pos, found = 0;
+	const unsigned char *current = 0;
+
+	*offset_out = 0;
+
+	if (index == NULL) {
+		int error;
+
+		if ((error = pack_index_open(p)) < GIT_SUCCESS)
+			return git__rethrow(error, "Failed to find offset for pack entry");
+
+		assert(p->index_map.data);
+
+		index = p->index_map.data;
+		level1_ofs = p->index_map.data;
+	}
+
+	if (p->index_version > 1) {
+		level1_ofs += 2;
+		index += 8;
+	}
+
+	index += 4 * 256;
+	hi = ntohl(level1_ofs[(int)short_oid->id[0]]);
+	lo = ((short_oid->id[0] == 0x0) ? 0 : ntohl(level1_ofs[(int)short_oid->id[0] - 1]));
+
+	if (p->index_version > 1) {
+		stride = 20;
+	} else {
+		stride = 24;
+		index += 4;
+	}
+
+#ifdef INDEX_DEBUG_LOOKUP
+	printf("%02x%02x%02x... lo %u hi %u nr %d\n",
+		short_oid->id[0], short_oid->id[1], short_oid->id[2], lo, hi, p->num_objects);
+#endif
+
+	/* Use git.git lookup code */
+	pos =  sha1_entry_pos(index, stride, 0, lo, hi, p->num_objects, short_oid->id);
+
+	if (pos >= 0) {
+		/* An object matching exactly the oid was found */
+		found = 1;
+		current = index + pos * stride;
+	} else {
+		/* No object was found */
+		/* pos refers to the object with the "closest" oid to short_oid */
+		pos = - 1 - pos;
+		if (pos < (int)p->num_objects) {
+			current = index + pos * stride;
+
+			if (!git_oid_ncmp(short_oid, (const git_oid *)current, len)) {
+				found = 1;
+			}
+		}
+	}
+
+	if (found && pos + 1 < (int)p->num_objects) {
+		/* Check for ambiguousity */
+		const unsigned char *next = current + stride;
+
+		if (!git_oid_ncmp(short_oid, (const git_oid *)next, len)) {
+			found = 2;
+		}
+	}
+
+	if (!found) {
+		return git__throw(GIT_ENOTFOUND, "Failed to find offset for pack entry. Entry not found");
+	} else if (found > 1) {
+		return git__throw(GIT_EAMBIGUOUSOIDPREFIX, "Failed to find offset for pack entry. Ambiguous sha1 prefix within pack");
+	} else {
+		*offset_out = nth_packed_object_offset(p, pos);
+		git_oid_fromraw(found_oid, current);
+
+#ifdef INDEX_DEBUG_LOOKUP
+		unsigned char hex_sha1[GIT_OID_HEXSZ + 1];
+		git_oid_fmt(hex_sha1, found_oid);
+		hex_sha1[GIT_OID_HEXSZ] = '\0';
+		printf("found lo=%d %s\n", lo, hex_sha1);
+#endif
+		return GIT_SUCCESS;
+	}
+}
+
+int git_pack_entry_find(
+		struct git_pack_entry *e,
+		struct git_pack_file *p,
+		const git_oid *short_oid,
+		unsigned int len)
+{
+	off_t offset;
+	git_oid found_oid;
+	int error;
+
+	assert(p);
+
+	if (len == GIT_OID_HEXSZ && p->num_bad_objects) {
+		unsigned i;
+		for (i = 0; i < p->num_bad_objects; i++)
+			if (git_oid_cmp(short_oid, &p->bad_object_sha1[i]) == 0)
+				return git__throw(GIT_ERROR, "Failed to find pack entry. Bad object found");
+	}
+
+	error = pack_entry_find_offset(&offset, &found_oid, p, short_oid, len);
+	if (error < GIT_SUCCESS)
+		return git__rethrow(error, "Failed to find pack entry. Couldn't find offset");
+
+	/* we found a unique entry in the index;
+	 * make sure the packfile backing the index
+	 * still exists on disk */
+	if (p->mwf.fd == -1 && packfile_open(p) < GIT_SUCCESS)
+		return git__throw(GIT_EOSERR, "Failed to find pack entry. Packfile doesn't exist on disk");
+
+	e->offset = offset;
+	e->p = p;
+
+	git_oid_cpy(&e->sha1, &found_oid);
+	return GIT_SUCCESS;
+}

src/pack.h

@@ -0,0 +1,114 @@
+/*
+ * This file is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License, version 2,
+ * as published by the Free Software Foundation.
+ *
+ * In addition to the permissions in the GNU General Public License,
+ * the authors give you unlimited permission to link the compiled
+ * version of this file into combinations with other programs,
+ * and to distribute those combinations without any restriction
+ * coming from the use of this file.  (The General Public License
+ * restrictions do apply in other respects; for example, they cover
+ * modification of the file, and distribution when not linked into
+ * a combined executable.)
+ *
+ * This file is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; see the file COPYING.  If not, write to
+ * the Free Software Foundation, 51 Franklin Street, Fifth Floor,
+ * Boston, MA 02110-1301, USA.
+ */
+
+#ifndef INCLUDE_pack_h__
+#define INCLUDE_pack_h__
+
+#include "git2/oid.h"
+
+#include "common.h"
+#include "map.h"
+#include "mwindow.h"
+#include "odb.h"
+
+#define PACK_SIGNATURE 0x5041434b	/* "PACK" */
+#define PACK_VERSION 2
+#define pack_version_ok(v) ((v) == htonl(2) || (v) == htonl(3))
+struct git_pack_header {
+	uint32_t hdr_signature;
+	uint32_t hdr_version;
+	uint32_t hdr_entries;
+};
+
+/*
+ * The first four bytes of index formats later than version 1 should
+ * start with this signature, as all older git binaries would find this
+ * value illegal and abort reading the file.
+ *
+ * This is the case because the number of objects in a packfile
+ * cannot exceed 1,431,660,000 as every object would need at least
+ * 3 bytes of data and the overall packfile cannot exceed 4 GiB with
+ * version 1 of the index file due to the offsets limited to 32 bits.
+ * Clearly the signature exceeds this maximum.
+ *
+ * Very old git binaries will also compare the first 4 bytes to the
+ * next 4 bytes in the index and abort with a "non-monotonic index"
+ * error if the second 4 byte word is smaller than the first 4
+ * byte word.  This would be true in the proposed future index
+ * format as idx_signature would be greater than idx_version.
+ */
+
+#define PACK_IDX_SIGNATURE 0xff744f63	/* "\377tOc" */
+
+struct git_pack_idx_header {
+	uint32_t idx_signature;
+	uint32_t idx_version;
+};
+
+struct git_pack_file {
+	git_mwindow_file mwf;
+	git_map index_map;
+
+	uint32_t num_objects;
+	uint32_t num_bad_objects;
+	git_oid *bad_object_sha1; /* array of git_oid */
+
+	int index_version;
+	git_time_t mtime;
+	unsigned pack_local:1, pack_keep:1;
+	git_oid sha1;
+
+	/* something like ".git/objects/pack/xxxxx.pack" */
+	char pack_name[GIT_FLEX_ARRAY]; /* more */
+};
+
+struct git_pack_entry {
+	off_t offset;
+	git_oid sha1;
+	struct git_pack_file *p;
+};
+
+int git_packfile_unpack_header(
+		size_t *size_p,
+		git_otype *type_p,
+		git_mwindow_file *mwf,
+		git_mwindow **w_curs,
+		off_t *curpos);
+
+int git_packfile_unpack(git_rawobj *obj, struct git_pack_file *p, off_t *obj_offset);
+
+off_t get_delta_base(struct git_pack_file *p, git_mwindow **w_curs,
+		off_t *curpos, git_otype type,
+		off_t delta_obj_offset);
+
+void packfile_free(struct git_pack_file *p);
+int git_packfile_check(struct git_pack_file **pack_out, const char *path);
+int git_pack_entry_find(
+		struct git_pack_entry *e,
+		struct git_pack_file *p,
+		const git_oid *short_oid,
+		unsigned int len);
+
+#endif

src/vector.h

@@ -30,6 +30,9 @@ GIT_INLINE(void *) git_vector_get(git_vector *v, unsigned int position)
 	return (position < v->length) ? v->contents[position] : NULL;
 }
 
+#define git_vector_foreach(v, iter, elem)	\
+	for ((iter) = 0; (iter) < (v)->length && ((elem) = (v)->contents[(iter)], 1); (iter)++ )
+
 int git_vector_insert(git_vector *v, void *element);
 int git_vector_remove(git_vector *v, unsigned int idx);
 void git_vector_uniq(git_vector *v);