Subject: Re: [PATCH v2 10/27] protocol: introduce enum protocol_version value protocol_v2

From: Brandon Williams <[email-masked]>
Date: Fri, 2 Feb 2018 14:44:54 -0800

On 01/31, Derrick Stolee wrote:
> On 1/25/2018 6:58 PM, Brandon Williams wrote:
> > Introduce protocol_v2, a new value for 'enum protocol_version'.
> > Subsequent patches will fill in the implementation of protocol_v2.
> > 
> > Signed-off-by: Brandon Williams <[email-masked]>
> > ---
> >   builtin/fetch-pack.c   | 3 +++
> >   builtin/receive-pack.c | 6 ++++++
> >   builtin/send-pack.c    | 3 +++
> >   builtin/upload-pack.c  | 7 +++++++
> >   connect.c              | 3 +++
> >   protocol.c             | 2 ++
> >   protocol.h             | 1 +
> >   remote-curl.c          | 3 +++
> >   transport.c            | 9 +++++++++
> >   9 files changed, 37 insertions(+)
> > 
> > diff --git a/builtin/fetch-pack.c b/builtin/fetch-pack.c
> > index 85d4faf76..f492e8abd 100644
> > --- a/builtin/fetch-pack.c
> > +++ b/builtin/fetch-pack.c
> > @@ -201,6 +201,9 @@ int cmd_fetch_pack(int argc, const char **argv, const char *prefix)
> >   			   PACKET_READ_GENTLE_ON_EOF);
> >   	switch (discover_version(&reader)) {
> > +	case protocol_v2:
> > +		die("support for protocol v2 not implemented yet");
> > +		break;
> >   	case protocol_v1:
> >   	case protocol_v0:
> >   		get_remote_heads(&reader, &ref, 0, NULL, &shallow);
> > diff --git a/builtin/receive-pack.c b/builtin/receive-pack.c
> > index b7ce7c7f5..3656e94fd 100644
> > --- a/builtin/receive-pack.c
> > +++ b/builtin/receive-pack.c
> > @@ -1963,6 +1963,12 @@ int cmd_receive_pack(int argc, const char **argv, const char *prefix)
> >   		unpack_limit = receive_unpack_limit;
> >   	switch (determine_protocol_version_server()) {
> > +	case protocol_v2:
> > +		/*
> > +		 * push support for protocol v2 has not been implemented yet,
> > +		 * so ignore the request to use v2 and fallback to using v0.
> > +		 */
> > +		break;
> >   	case protocol_v1:
> >   		/*
> >   		 * v1 is just the original protocol with a version string,
> > diff --git a/builtin/send-pack.c b/builtin/send-pack.c
> > index 83cb125a6..b5427f75e 100644
> > --- a/builtin/send-pack.c
> > +++ b/builtin/send-pack.c
> > @@ -263,6 +263,9 @@ int cmd_send_pack(int argc, const char **argv, const char *prefix)
> >   			   PACKET_READ_GENTLE_ON_EOF);
> >   	switch (discover_version(&reader)) {
> > +	case protocol_v2:
> > +		die("support for protocol v2 not implemented yet");
> > +		break;
> >   	case protocol_v1:
> >   	case protocol_v0:
> >   		get_remote_heads(&reader, &remote_refs, REF_NORMAL,
> > diff --git a/builtin/upload-pack.c b/builtin/upload-pack.c
> > index 2cb5cb35b..8d53e9794 100644
> > --- a/builtin/upload-pack.c
> > +++ b/builtin/upload-pack.c
> > @@ -47,6 +47,13 @@ int cmd_upload_pack(int argc, const char **argv, const char *prefix)
> >   		die("'%s' does not appear to be a git repository", dir);
> >   	switch (determine_protocol_version_server()) {
> > +	case protocol_v2:
> > +		/*
> > +		 * fetch support for protocol v2 has not been implemented yet,
> > +		 * so ignore the request to use v2 and fallback to using v0.
> > +		 */
> > +		upload_pack(&opts);
> > +		break;
> >   	case protocol_v1:
> >   		/*
> >   		 * v1 is just the original protocol with a version string,
> > diff --git a/connect.c b/connect.c
> > index db3c9d24c..f2157a821 100644
> > --- a/connect.c
> > +++ b/connect.c
> > @@ -84,6 +84,9 @@ enum protocol_version discover_version(struct packet_reader *reader)
> >   	/* Maybe process capabilities here, at least for v2 */
> >   	switch (version) {
> > +	case protocol_v2:
> > +		die("support for protocol v2 not implemented yet");
> > +		break;
> >   	case protocol_v1:
> >   		/* Read the peeked version line */
> >   		packet_reader_read(reader);
> > diff --git a/protocol.c b/protocol.c
> > index 43012b7eb..5e636785d 100644
> > --- a/protocol.c
> > +++ b/protocol.c
> > @@ -8,6 +8,8 @@ static enum protocol_version parse_protocol_version(const char *value)
> >   		return protocol_v0;
> >   	else if (!strcmp(value, "1"))
> >   		return protocol_v1;
> > +	else if (!strcmp(value, "2"))
> > +		return protocol_v2;
> >   	else
> >   		return protocol_unknown_version;
> >   }
> > diff --git a/protocol.h b/protocol.h
> > index 1b2bc94a8..2ad35e433 100644
> > --- a/protocol.h
> > +++ b/protocol.h
> > @@ -5,6 +5,7 @@ enum protocol_version {
> >   	protocol_unknown_version = -1,
> >   	protocol_v0 = 0,
> >   	protocol_v1 = 1,
> > +	protocol_v2 = 2,
> >   };
> >   /*
> > diff --git a/remote-curl.c b/remote-curl.c
> > index 9f6d07683..dae8a4a48 100644
> > --- a/remote-curl.c
> > +++ b/remote-curl.c
> > @@ -185,6 +185,9 @@ static struct ref *parse_git_refs(struct discovery *heads, int for_push)
> >   			   PACKET_READ_GENTLE_ON_EOF);
> >   	switch (discover_version(&reader)) {
> > +	case protocol_v2:
> > +		die("support for protocol v2 not implemented yet");
> > +		break;
> >   	case protocol_v1:
> >   	case protocol_v0:
> >   		get_remote_heads(&reader, &list, for_push ? REF_NORMAL : 0,
> > diff --git a/transport.c b/transport.c
> > index 2378dcb38..83d9dd1df 100644
> > --- a/transport.c
> > +++ b/transport.c
> > @@ -203,6 +203,9 @@ static struct ref *get_refs_via_connect(struct transport *transport, int for_pus
> >   	data->version = discover_version(&reader);
> >   	switch (data->version) {
> > +	case protocol_v2:
> > +		die("support for protocol v2 not implemented yet");
> > +		break;
> >   	case protocol_v1:
> >   	case protocol_v0:
> >   		get_remote_heads(&reader, &refs,
> > @@ -250,6 +253,9 @@ static int fetch_refs_via_pack(struct transport *transport,
> >   		refs_tmp = get_refs_via_connect(transport, 0);
> >   	switch (data->version) {
> > +	case protocol_v2:
> > +		die("support for protocol v2 not implemented yet");
> > +		break;
> >   	case protocol_v1:
> >   	case protocol_v0:
> >   		refs = fetch_pack(&args, data->fd, data->conn,
> > @@ -585,6 +591,9 @@ static int git_transport_push(struct transport *transport, struct ref *remote_re
> >   		args.push_cert = SEND_PACK_PUSH_CERT_NEVER;
> >   	switch (data->version) {
> > +	case protocol_v2:
> > +		die("support for protocol v2 not implemented yet");
> > +		break;
> >   	case protocol_v1:
> >   	case protocol_v0:
> >   		ret = send_pack(&args, data->fd, data->conn, remote_refs,
> 
> With a macro approach to version selection, this change becomes simpler in
> some ways and harder in others.
> 
> It is simpler in that we can have the macro from the previous commits just
> fall back to version 0 behavior.
> 
> It is harder in that this commit would need one of two options:
> 
> 1. A macro that performs an arbitrary statement when given v2, which would
> be the die() for these actions not in v2.
> 2. A macro that clearly states v2 is not supported and calls die() on v2.
> 
> Here is my simple, untested attempt at a union of these options:
> 
> #define ON_PROTOCOL_VERSION(version,v0,v2) switch(version) {\
> case protocol_v2:\
>     (v2);\
>     break;\
> case protocol_v1:\
> case protocol_v0:\
>     (v0);\
>     break;\
> case protocol_unknown_version:\
>     BUG("unknown protocol version");\
> }
> #define ON_PROTOCOL_VERSION_V0_FALLBACK(version,v0) switch(version) {\
> case protocol_v2:\
> case protocol_v1:\
> case protocol_v0:\
>     (v0);\
>     break;\
> case protocol_unknown_version:\
>     BUG("unknown protocol version");\
> }
> #define ON_PROTOCOL_VERSION_V0_ONLY(version,v0) \
>     ON_PROTOCOL_VERSION(version,v0,\
>                 BUG("support for protocol v2 not implemented yet"))

While I understand wanting to isolate the switch statement code, I think
that creating such a macro would make reading the code much more
difficult (and a pain to get right).  Really I don't want to try my hand
at crafting such a macro :D

-- 
Brandon Williams