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

> 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 <bmwill@google.com>
>>> ---
>>>    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
>