Re: [PATCH v2 3/4] pack-objects: refactor write_object()

[Junio C Hamano <gitster@pobox.com>]

Nguyễn Thái Ngọc Duy  <pclouds@gmail.com> writes:

> Move !to_reuse and to_reuse write code out into two separate functions
> and remove "goto no_reuse;" hack

I do not necessarily think goto is a harmful hack, but the original code
is sufficiently large and its flow clearly ought to be separable into
two phases (phase I: decide if we want to copy from existing pack or
build data to be sent to the pack afresh; phase II: carry out the
decision, doing one of the two things we decided to do), so I think it
makes tons of sense to separate out the second phase into two helper
functions.

Looks good from a cursory reading.

Thanks.

> Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
> ---
>  builtin/pack-objects.c |  322 ++++++++++++++++++++++++++----------------------
>  1 files changed, 172 insertions(+), 150 deletions(-)
>
> diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
> index b2e0940..ccfcbad 100644
> --- a/builtin/pack-objects.c
> +++ b/builtin/pack-objects.c
> @@ -200,22 +200,178 @@ static void copy_pack_data(struct sha1file *f,
>  }
>  
>  /* Return 0 if we will bust the pack-size limit */
> +static unsigned long write_no_reuse_object(struct sha1file *f, struct object_entry *entry,
> +					   unsigned long limit, int usable_delta)
>  {
> +	unsigned long size, datalen;
>  	unsigned char header[10], dheader[10];
>  	unsigned hdrlen;
>  	enum object_type type;
> +	void *buf;
> +
> +	if (!usable_delta) {
> +		buf = read_sha1_file(entry->idx.sha1, &type, &size);
> +		if (!buf)
> +			die("unable to read %s", sha1_to_hex(entry->idx.sha1));
> +		/*
> +		 * make sure no cached delta data remains from a
> +		 * previous attempt before a pack split occurred.
> +		 */
> +		free(entry->delta_data);
> +		entry->delta_data = NULL;
> +		entry->z_delta_size = 0;
> +	} else if (entry->delta_data) {
> +		size = entry->delta_size;
> +		buf = entry->delta_data;
> +		entry->delta_data = NULL;
> +		type = (allow_ofs_delta && entry->delta->idx.offset) ?
> +			OBJ_OFS_DELTA : OBJ_REF_DELTA;
> +	} else {
> +		buf = get_delta(entry);
> +		size = entry->delta_size;
> +		type = (allow_ofs_delta && entry->delta->idx.offset) ?
> +			OBJ_OFS_DELTA : OBJ_REF_DELTA;
> +	}
> +
> +	if (entry->z_delta_size)
> +		datalen = entry->z_delta_size;
> +	else
> +		datalen = do_compress(&buf, size);
> +
> +	/*
> +	 * The object header is a byte of 'type' followed by zero or
> +	 * more bytes of length.
> +	 */
> +	hdrlen = encode_in_pack_object_header(type, size, header);
> +
> +	if (type == OBJ_OFS_DELTA) {
> +		/*
> +		 * Deltas with relative base contain an additional
> +		 * encoding of the relative offset for the delta
> +		 * base from this object's position in the pack.
> +		 */
> +		off_t ofs = entry->idx.offset - entry->delta->idx.offset;
> +		unsigned pos = sizeof(dheader) - 1;
> +		dheader[pos] = ofs & 127;
> +		while (ofs >>= 7)
> +			dheader[--pos] = 128 | (--ofs & 127);
> +		if (limit && hdrlen + sizeof(dheader) - pos + datalen + 20 >= limit) {
> +			free(buf);
> +			return 0;
> +		}
> +		sha1write(f, header, hdrlen);
> +		sha1write(f, dheader + pos, sizeof(dheader) - pos);
> +		hdrlen += sizeof(dheader) - pos;
> +	} else if (type == OBJ_REF_DELTA) {
> +		/*
> +		 * Deltas with a base reference contain
> +		 * an additional 20 bytes for the base sha1.
> +		 */
> +		if (limit && hdrlen + 20 + datalen + 20 >= limit) {
> +			free(buf);
> +			return 0;
> +		}
> +		sha1write(f, header, hdrlen);
> +		sha1write(f, entry->delta->idx.sha1, 20);
> +		hdrlen += 20;
> +	} else {
> +		if (limit && hdrlen + datalen + 20 >= limit) {
> +			free(buf);
> +			return 0;
> +		}
> +		sha1write(f, header, hdrlen);
> +	}
> +	sha1write(f, buf, datalen);
> +	free(buf);
> +
> +	return hdrlen + datalen;
> +}
> +
> +/* Return 0 if we will bust the pack-size limit */
> +static unsigned long write_reuse_object(struct sha1file *f, struct object_entry *entry,
> +					unsigned long limit, int usable_delta)
> +{
> +	struct packed_git *p = entry->in_pack;
> +	struct pack_window *w_curs = NULL;
> +	struct revindex_entry *revidx;
> +	off_t offset;
> +	enum object_type type = entry->type;
> +	unsigned long datalen;
> +	unsigned char header[10], dheader[10];
> +	unsigned hdrlen;
> +
> +	if (entry->delta)
> +		type = (allow_ofs_delta && entry->delta->idx.offset) ?
> +			OBJ_OFS_DELTA : OBJ_REF_DELTA;
> +	hdrlen = encode_in_pack_object_header(type, entry->size, header);
> +
> +	offset = entry->in_pack_offset;
> +	revidx = find_pack_revindex(p, offset);
> +	datalen = revidx[1].offset - offset;
> +	if (!pack_to_stdout && p->index_version > 1 &&
> +	    check_pack_crc(p, &w_curs, offset, datalen, revidx->nr)) {
> +		error("bad packed object CRC for %s", sha1_to_hex(entry->idx.sha1));
> +		unuse_pack(&w_curs);
> +		return write_no_reuse_object(f, entry, limit, usable_delta);
> +	}
> +
> +	offset += entry->in_pack_header_size;
> +	datalen -= entry->in_pack_header_size;
> +
> +	if (!pack_to_stdout && p->index_version == 1 &&
> +	    check_pack_inflate(p, &w_curs, offset, datalen, entry->size)) {
> +		error("corrupt packed object for %s", sha1_to_hex(entry->idx.sha1));
> +		unuse_pack(&w_curs);
> +		return write_no_reuse_object(f, entry, limit, usable_delta);
> +	}
> +
> +	if (type == OBJ_OFS_DELTA) {
> +		off_t ofs = entry->idx.offset - entry->delta->idx.offset;
> +		unsigned pos = sizeof(dheader) - 1;
> +		dheader[pos] = ofs & 127;
> +		while (ofs >>= 7)
> +			dheader[--pos] = 128 | (--ofs & 127);
> +		if (limit && hdrlen + sizeof(dheader) - pos + datalen + 20 >= limit) {
> +			unuse_pack(&w_curs);
> +			return 0;
> +		}
> +		sha1write(f, header, hdrlen);
> +		sha1write(f, dheader + pos, sizeof(dheader) - pos);
> +		hdrlen += sizeof(dheader) - pos;
> +		reused_delta++;
> +	} else if (type == OBJ_REF_DELTA) {
> +		if (limit && hdrlen + 20 + datalen + 20 >= limit) {
> +			unuse_pack(&w_curs);
> +			return 0;
> +		}
> +		sha1write(f, header, hdrlen);
> +		sha1write(f, entry->delta->idx.sha1, 20);
> +		hdrlen += 20;
> +		reused_delta++;
> +	} else {
> +		if (limit && hdrlen + datalen + 20 >= limit) {
> +			unuse_pack(&w_curs);
> +			return 0;
> +		}
> +		sha1write(f, header, hdrlen);
> +	}
> +	copy_pack_data(f, p, &w_curs, offset, datalen);
> +	unuse_pack(&w_curs);
> +	reused++;
> +	return hdrlen + datalen;
> +}
> +
> +/* Return 0 if we will bust the pack-size limit */
> +static unsigned long write_object(struct sha1file *f,
> +				  struct object_entry *entry,
> +				  off_t write_offset)
> +{
> +	unsigned long limit, len;
>  	int usable_delta, to_reuse;
>  
>  	if (!pack_to_stdout)
>  		crc32_begin(f);
>  
>  	/* apply size limit if limited packsize and not first object */
>  	if (!pack_size_limit || !nr_written)
>  		limit = 0;
> @@ -243,11 +399,11 @@ static unsigned long write_object(struct sha1file *f,
>  		to_reuse = 0;	/* explicit */
>  	else if (!entry->in_pack)
>  		to_reuse = 0;	/* can't reuse what we don't have */
> +	else if (entry->type == OBJ_REF_DELTA || entry->type == OBJ_OFS_DELTA)
>  				/* check_object() decided it for us ... */
>  		to_reuse = usable_delta;
>  				/* ... but pack split may override that */
> +	else if (entry->type != entry->in_pack_type)
>  		to_reuse = 0;	/* pack has delta which is unusable */
>  	else if (entry->delta)
>  		to_reuse = 0;	/* we want to pack afresh */
> @@ -256,153 +412,19 @@ static unsigned long write_object(struct sha1file *f,
>  				 * and we do not need to deltify it.
>  				 */
>  
> +	if (!to_reuse)
> +		len = write_no_reuse_object(f, entry, limit, usable_delta);
> +	else
> +		len = write_reuse_object(f, entry, limit, usable_delta);
> +	if (!len)
> +		return 0;
>  
>  	if (usable_delta)
>  		written_delta++;
>  	written++;
>  	if (!pack_to_stdout)
>  		entry->idx.crc32 = crc32_end(f);
> -	return hdrlen + datalen;
> +	return len;
>  }
>  
>  enum write_one_status {