commit 7f8fc4ec0150a8db7769565c60168b34ce0bc907
from: Stefan Sperling <stsp@stsp.name>
date: Sun Dec 03 16:43:45 2017 UTC

add a header file for pack files

commit - 9b1d51628a0607649aa115d28b74ffe730fb9c78
commit + 7f8fc4ec0150a8db7769565c60168b34ce0bc907
blob - /dev/null
blob + f19f0a407da1cd971837ccc4b575836d81fd45b9 (mode 644)
--- /dev/null
+++ lib/pack.h
@@ -0,0 +1,122 @@
+
+/*
+ * Copyright (c) 2017 Stefan Sperling <stsp@openbsd.org>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+/* See Documentation/technical/pack-format.txt in Git. */
+
+struct got_pack_obj_id {
+	u_int8_t sha1[SHA1_DIGEST_LENGTH];
+} __attribute__((__packed__));
+
+struct got_pack_idx_trailer {
+	u_int8_t	pack_file_sha1[SHA1_DIGEST_LENGTH];
+	u_int8_t	pack_idx_sha1[SHA1_DIGEST_LENGTH];
+} __attribute__((__packed__));
+
+/* Ignore pack index version 1 which is no longer written by Git. */
+#define GOT_PACKIDX_VERSION 2
+
+struct got_packidx_v2_hdr {
+	uint32_t	magic;		/* big endian */
+#define GOT_PACKIDX_V2_MAGIC 0xff744f63	/* "\377t0c" */
+	uint32_t	version;
+
+	/* 
+	 * Each entry N in the fanout table contains the number of objects in
+	 * the packfile whose SHA1 begins with a byte less than or equal to N.
+	 * The last entry (index 255) contains the number of objects in the
+	 * pack file whose first SHA1 byte is <= 0xff, and thus records the
+	 * total number of objects in the pack file. All pointer variables
+	 * below point to tables with a corresponding number of entries.
+	 */
+	uint32_t	fanout_table[0xff];	/* values are big endian */
+
+	/* Sorted SHA1 checksums for each object in the pack file. */
+	struct got_pack_obj_id *sorted_ids;
+
+	/* Offset into the pack file for each object. */
+	uint32_t	*offsets;		/* values are big endian */
+#define GOT_PACKIDX_OFFSET_VAL_MASK		0x7fffffff
+#define GOT_PACKIDX_OFFSET_VAL_IS_LARGE_IDX	0x80000000
+
+	/* CRC32 of the packed representation of each object. */
+	uint32_t	*crc32;
+
+	/* Large offsets table is empty for pack files < 2 GB. */
+	uint64_t	*large_offsets;		/* values are big endian */
+
+	struct got_pack_idx_trailer trailer;
+};
+
+struct got_packfile_hdr {
+	uint32_t	signature;
+#define GOT_PACKFILE_SIGNATURE	0x4041434b	/* 'P' 'A' 'C' 'K' */
+	uint32_t	version;	/* big endian */
+#define GOT_PACKFILE_VERSION 2
+	uint32_t	nobjects;	/* big endian */
+};
+
+struct got_packfile_obj_hdr {
+	/* 
+	 * The object size field uses a variable length encoding:
+	 * size0...sizeN form a 4+7+7+...+7 bit integer, where size0 is the
+	 * least significant part and sizeN is the most significant part.
+	 * If the MSB of a size byte is set, an additional size byte follows.
+	 * Of the 7 remaining bits of size0, the first 3 bits indicate the
+	 * object's type, and the remaining 4 bits contribute to the size.
+	 */
+	uint8_t *size;		/* variable length */
+#define GOT_PACK_OBJ_SIZE_MORE		0x80
+#define GOT_PACK_OBJ_SIZE0_TYPE_MASK	0x70 /* See struct got_object->type */
+#define GOT_PACK_OBJ_SIZE0_VAL_MASK	0x0f
+#define GOT_PACK_OBJ_SIZEN_VAL_MASK	0x7f
+};
+
+/* If object is not a DELTA type. */
+struct got_packfile_object_data {
+	uint8_t *data;	/* compressed */
+};
+
+/* If object is of type	GOT_OBJ_TYPE_REF_DELTA. */
+struct got_packfile_object_data_ref_delta {
+	struct got_pack_obj_id id;
+	uint8_t *delta_data;		/* compressed */
+};
+
+/* If object is of type GOT_OBJ_TYPE_OFFSET_DELTA. */
+struct got_packfile_object_data_offset_delta {
+	/* 
+	 * This offset is interpreted as a negative offset from
+	 * the got_packfile_obj_hdr corresponding to this object.
+	 * The size provided in the header specifies the amount
+	 * of compressed delta data that follows.
+	 *
+	 * This field uses a variable length encoding of N bytes,
+	 * where the MSB is always set except for the last byte.
+	 * The value is encoded as a series of N 7 bit integers,
+	 * which are concatenated, and if N > 1 the value 2^7 +
+	 * 2^14 + ... + 2^(7 * (n-1)) is added to the result.
+	 */
+	uint8_t *offset;	/* variable length */
+};
+
+struct got_packfile_obj_data {
+	union {
+		struct got_packfile_object_data;
+		struct got_packfile_object_data_ref_delta;
+		struct got_packfile_object_data_offset_delta;
+	} __attribute__((__packed__));
+} __attribute__((__packed__));