Re: [PATCH v4 20/35] upload-pack: introduce fetch server command

> +    output = *section
> +    section = (acknowledgments | packfile)
> +	      (flush-pkt | delim-pkt)
> +
> +    acknowledgments = PKT-LINE("acknowledgments" LF)
> +		      (nak | *ack)
> +		      (ready)
> +    ready = PKT-LINE("ready" LF)
> +    nak = PKT-LINE("NAK" LF)
> +    ack = PKT-LINE("ACK" SP obj-id LF)
> +
> +    packfile = PKT-LINE("packfile" LF)
> +	       [PACKFILE]

> +    acknowledgments section
> +	* Always begins with the section header "acknowledgments"
> +
> +	* The server will respond with "NAK" if none of the object ids sent
> +	  as have lines were common.
> +
> +	* The server will respond with "ACK obj-id" for all of the
> +	  object ids sent as have lines which are common.
> +
> +	* A response cannot have both "ACK" lines as well as a "NAK"
> +	  line.
> +
> +	* The server will respond with a "ready" line indicating that
> +	  the server has found an acceptable common base and is ready to
> +	  make and send a packfile (which will be found in the packfile
> +	  section of the same response)
> +
> +	* If the client determines that it is finished with negotiations
> +	  by sending a "done" line, the acknowledgments sections MUST be
> +	  omitted from the server's response.
> +
> +	* If the server has found a suitable cut point and has decided
> +	  to send a "ready" line, then the server can decide to (as an
> +	  optimization) omit any "ACK" lines it would have sent during
> +	  its response.  This is because the server will have already
> +	  determined the objects it plans to send to the client and no
> +	  further negotiation is needed.
> +
> +----
> +    packfile section
> +	* Always begins with the section header "packfile"
> +
> +	* The transmission of the packfile begins immediately after the
> +	  section header
> +
> +	* The data transfer of the packfile is always multiplexed, using
> +	  the same semantics of the 'side-band-64k' capability from
> +	  protocol version 1.  This means that each packet, during the
> +	  packfile data stream, is made up of a leading 4-byte pkt-line
> +	  length (typical of the pkt-line format), followed by a 1-byte
> +	  stream code, followed by the actual data.
> +
> +	  The stream code can be one of:
> +		1 - pack data
> +		2 - progress messages
> +		3 - fatal error message just before stream aborts
> +
> +	* This section is only included if the client has sent 'want'
> +	  lines in its request and either requested that no more
> +	  negotiation be done by sending 'done' or if the server has
> +	  decided it has found a sufficient cut point to produce a
> +	  packfile.

> +static void upload_pack_data_init(struct upload_pack_data *data)
> +{
> +	struct object_array wants = OBJECT_ARRAY_INIT;
> +	struct oid_array haves = OID_ARRAY_INIT;
> +
> +	memset(data, 0, sizeof(*data));
> +	data->wants = wants;
> +	data->haves = haves;
> +}