diff mbox series

[v3,1/1] protocol: advertise multiple supported versions

Message ID b9968e3fb005a00e9f78627467b4fc86a6259977.1542059029.git.steadmon@google.com
State New, archived
Headers show
Series Advertise multiple supported proto versions | expand

Commit Message

Josh Steadmon Nov. 12, 2018, 9:49 p.m. UTC
Currently the client advertises that it supports the wire protocol
version set in the protocol.version config. However, not all services
support the same set of protocol versions. When connecting to
git-receive-pack, the client automatically downgrades to v0 if
config.protocol is set to v2, but this check is not performed for other
services.

This patch creates a protocol version registry. Individual operations
register all the protocol versions they support prior to communicating
with a server. Versions should be listed in preference order; the
version specified in protocol.version will automatically be moved to the
front of the registry.

The protocol version registry is passed to remote helpers via the
GIT_PROTOCOL environment variable.

Clients now advertise the full list of registered versions. Servers
select the first recognized version from this advertisement.

Signed-off-by: Josh Steadmon <steadmon@google.com>
---
 builtin/archive.c      |   3 ++
 builtin/clone.c        |   4 ++
 builtin/fetch-pack.c   |   4 ++
 builtin/fetch.c        |   5 ++
 builtin/ls-remote.c    |   5 ++
 builtin/pull.c         |   5 ++
 builtin/push.c         |   4 ++
 builtin/send-pack.c    |   3 ++
 connect.c              |  47 ++++++++---------
 protocol.c             | 112 ++++++++++++++++++++++++++++++++++++++---
 protocol.h             |  17 +++++++
 remote-curl.c          |  28 +++++++----
 t/t5570-git-daemon.sh  |   2 +-
 t/t5700-protocol-v1.sh |   8 +--
 t/t5702-protocol-v2.sh |  16 +++---
 transport-helper.c     |   6 +++
 16 files changed, 214 insertions(+), 55 deletions(-)

Comments

Stefan Beller Nov. 12, 2018, 10:33 p.m. UTC | #1
On Mon, Nov 12, 2018 at 1:49 PM <steadmon@google.com> wrote:
>
> Currently the client advertises that it supports the wire protocol
> version set in the protocol.version config. However, not all services
> support the same set of protocol versions. When connecting to
> git-receive-pack, the client automatically downgrades to v0 if
> config.protocol is set to v2, but this check is not performed for other
> services.
>
> This patch creates a protocol version registry. Individual operations
> register all the protocol versions they support prior to communicating
> with a server. Versions should be listed in preference order; the
> version specified in protocol.version will automatically be moved to the
> front of the registry.
>
> The protocol version registry is passed to remote helpers via the
> GIT_PROTOCOL environment variable.
>
> Clients now advertise the full list of registered versions. Servers
> select the first recognized version from this advertisement.
>
> Signed-off-by: Josh Steadmon <steadmon@google.com>

Thanks for resending this patch!

+cc Jonathan Tan, who works a lot on the protocol side of things.

> +void register_allowed_protocol_version(enum protocol_version version)
> +{
> +       if (have_advertised_versions_already)
> +               BUG(_("attempting to register an allowed protocol version after advertisement"));

If this is a real BUG (due to wrong program flow) instead of bad user input,
we would not want to burden the translators with this message.

If it is a message that the user is intended to see upon bad input
we'd rather go with die(_("translatable text here"));


> diff --git a/protocol.h b/protocol.h
> index 2ad35e433c..b67b2259de 100644
> --- a/protocol.h
> +++ b/protocol.h
> @@ -16,6 +16,23 @@ enum protocol_version {
>   */
>  extern enum protocol_version get_protocol_version_config(void);
>
> +/*
> + * Register an allowable protocol version for a given operation. Registration
> + * must occur before attempting to advertise a version to a server process.
> + */
> +extern void register_allowed_protocol_version(enum protocol_version version);

We keep extern here as to imitate the file-local style, although
Documentation/CodingGuidelines would prefer to not have the extern keywords.
Okay.

Bonus points for converting the file to omit all extern keywords in a
resend. :-)
(I think there is no other series currently in flight touching this header file,
so it is safe to convert it "while at it", `git log --grep "while at
it"` is shorter
than expected.)

All that said, it's only nits that I contributed to this code review;
the code/design
looks good to me, and if I were maintainer I'd include it as-is, as it
fixes a long(ish)
standing protocol error.

Thanks,
Stefan
Junio C Hamano Nov. 13, 2018, 4:01 a.m. UTC | #2
steadmon@google.com writes:

> Currently the client advertises that it supports the wire protocol
> version set in the protocol.version config. However, not all services
> support the same set of protocol versions. When connecting to
> git-receive-pack, the client automatically downgrades to v0 if
> config.protocol is set to v2, but this check is not performed for other
> services.

"downgrades to v0 even if ... is set to v2" you mean?  Otherwise it
is unclear why asking for v2 leads to using v0.

> This patch creates a protocol version registry. Individual operations
> register all the protocol versions they support prior to communicating
> with a server. Versions should be listed in preference order; the
> version specified in protocol.version will automatically be moved to the
> front of the registry.
>
> The protocol version registry is passed to remote helpers via the
> GIT_PROTOCOL environment variable.
>
> Clients now advertise the full list of registered versions. Servers
> select the first recognized version from this advertisement.

Makes sense.

> +void get_client_protocol_version_advertisement(struct strbuf *advert)
> +{
> +	int tmp_nr = nr_allowed_versions;
> +	enum protocol_version *tmp_allowed_versions, config_version;
> +	strbuf_reset(advert);
> +
> +	have_advertised_versions_already = 1;
> +
> +	config_version = get_protocol_version_config();
> +	if (config_version == protocol_v0) {
> +		strbuf_addstr(advert, "version=0");
> +		return;
> +	}
> +
> +	if (tmp_nr > 0) {
> +		ALLOC_ARRAY(tmp_allowed_versions, tmp_nr);
> +		copy_array(tmp_allowed_versions, allowed_versions, tmp_nr,
> +			   sizeof(enum protocol_version));
> +	} else {
> +		ALLOC_ARRAY(tmp_allowed_versions, 1);
> +		tmp_nr = 1;
> +		tmp_allowed_versions[0] = config_version;
> +	}
> +
> +	if (tmp_allowed_versions[0] != config_version)
> +		for (int i = 1; i < nr_allowed_versions; i++)
> +			if (tmp_allowed_versions[i] == config_version) {
> +				enum protocol_version swap =
> +					tmp_allowed_versions[0];
> +				tmp_allowed_versions[0] =
> +					tmp_allowed_versions[i];
> +				tmp_allowed_versions[i] = swap;
> +			}
> +
> +	strbuf_addf(advert, "version=%s",
> +		    format_protocol_version(tmp_allowed_versions[0]));
> +	for (int i = 1; i < tmp_nr; i++)
> +		strbuf_addf(advert, ":version=%s",
> +			    format_protocol_version(tmp_allowed_versions[i]));
> +}
> +

So the idea is that the protocols the other end can talk come in
advert in their preferred order, and we take an intersection of them
and our "allowed-versions", but the preference is further skewed
with the "swap" thing if we have our own preference specified via
config?

I am wondering if the code added by this patch outside this
function, with if (strcmp(client_ad.buf, "version=0") sprinkled all
over the place, works sensibly when the other side says "I prefer
version=0 but I do not mind talking version=1".

Isn't tmp_allowed_versions[] leaking when we return from this
function?
Junio C Hamano Nov. 13, 2018, 1:35 p.m. UTC | #3
steadmon@google.com writes:

> +	if (tmp_allowed_versions[0] != config_version)
> +		for (int i = 1; i < nr_allowed_versions; i++)
> +			if (tmp_allowed_versions[i] == config_version) {
> +				enum protocol_version swap =
> +					tmp_allowed_versions[0];
> +				tmp_allowed_versions[0] =
> +					tmp_allowed_versions[i];
> +				tmp_allowed_versions[i] = swap;
> +			}

Here is what coccicheck suggests.

diff -u -p a/protocol.c b/protocol.c
--- a/protocol.c
+++ b/protocol.c
@@ -111,11 +111,8 @@ void get_client_protocol_version_adverti
 	if (tmp_allowed_versions[0] != config_version)
 		for (int i = 1; i < nr_allowed_versions; i++)
 			if (tmp_allowed_versions[i] == config_version) {
-				enum protocol_version swap =
-					tmp_allowed_versions[0];
-				tmp_allowed_versions[0] =
-					tmp_allowed_versions[i];
-				tmp_allowed_versions[i] = swap;
+				SWAP(tmp_allowed_versions[0],
+				     tmp_allowed_versions[i]);
 			}
 
 	strbuf_addf(advert, "version=%s",
SZEDER Gábor Nov. 13, 2018, 6:28 p.m. UTC | #4
On Mon, Nov 12, 2018 at 01:49:05PM -0800, steadmon@google.com wrote:

> diff --git a/protocol.c b/protocol.c
> index 5e636785d1..54d2ab991b 100644
> --- a/protocol.c
> +++ b/protocol.c

> +void get_client_protocol_version_advertisement(struct strbuf *advert)
> +{
> +	int tmp_nr = nr_allowed_versions;
> +	enum protocol_version *tmp_allowed_versions, config_version;
> +	strbuf_reset(advert);
> +
> +	have_advertised_versions_already = 1;
> +
> +	config_version = get_protocol_version_config();
> +	if (config_version == protocol_v0) {
> +		strbuf_addstr(advert, "version=0");
> +		return;
> +	}
> +
> +	if (tmp_nr > 0) {
> +		ALLOC_ARRAY(tmp_allowed_versions, tmp_nr);
> +		copy_array(tmp_allowed_versions, allowed_versions, tmp_nr,
> +			   sizeof(enum protocol_version));
> +	} else {
> +		ALLOC_ARRAY(tmp_allowed_versions, 1);
> +		tmp_nr = 1;
> +		tmp_allowed_versions[0] = config_version;
> +	}
> +
> +	if (tmp_allowed_versions[0] != config_version)
> +		for (int i = 1; i < nr_allowed_versions; i++)

We don't do C99 yet, thus the declaration of a loop variable like this
is not allowed and triggers compiler errors.

> +			if (tmp_allowed_versions[i] == config_version) {
> +				enum protocol_version swap =
> +					tmp_allowed_versions[0];
> +				tmp_allowed_versions[0] =
> +					tmp_allowed_versions[i];
> +				tmp_allowed_versions[i] = swap;
> +			}
> +
> +	strbuf_addf(advert, "version=%s",
> +		    format_protocol_version(tmp_allowed_versions[0]));
> +	for (int i = 1; i < tmp_nr; i++)

Likewise.

> +		strbuf_addf(advert, ":version=%s",
> +			    format_protocol_version(tmp_allowed_versions[i]));
> +}
Josh Steadmon Nov. 13, 2018, 10:53 p.m. UTC | #5
On 2018.11.13 13:01, Junio C Hamano wrote:
> steadmon@google.com writes:
> 
> > Currently the client advertises that it supports the wire protocol
> > version set in the protocol.version config. However, not all services
> > support the same set of protocol versions. When connecting to
> > git-receive-pack, the client automatically downgrades to v0 if
> > config.protocol is set to v2, but this check is not performed for other
> > services.
> 
> "downgrades to v0 even if ... is set to v2" you mean?  Otherwise it
> is unclear why asking for v2 leads to using v0.

The downgrade on push happens only when the the configured version is
v2. If v1 is requested, no downgrade is triggered. I'll clarify the
commit message in the next version.

> > This patch creates a protocol version registry. Individual operations
> > register all the protocol versions they support prior to communicating
> > with a server. Versions should be listed in preference order; the
> > version specified in protocol.version will automatically be moved to the
> > front of the registry.
> >
> > The protocol version registry is passed to remote helpers via the
> > GIT_PROTOCOL environment variable.
> >
> > Clients now advertise the full list of registered versions. Servers
> > select the first recognized version from this advertisement.
> 
> Makes sense.
> 
> > +void get_client_protocol_version_advertisement(struct strbuf *advert)
> > +{
> > +	int tmp_nr = nr_allowed_versions;
> > +	enum protocol_version *tmp_allowed_versions, config_version;
> > +	strbuf_reset(advert);
> > +
> > +	have_advertised_versions_already = 1;
> > +
> > +	config_version = get_protocol_version_config();
> > +	if (config_version == protocol_v0) {
> > +		strbuf_addstr(advert, "version=0");
> > +		return;
> > +	}
> > +
> > +	if (tmp_nr > 0) {
> > +		ALLOC_ARRAY(tmp_allowed_versions, tmp_nr);
> > +		copy_array(tmp_allowed_versions, allowed_versions, tmp_nr,
> > +			   sizeof(enum protocol_version));
> > +	} else {
> > +		ALLOC_ARRAY(tmp_allowed_versions, 1);
> > +		tmp_nr = 1;
> > +		tmp_allowed_versions[0] = config_version;
> > +	}
> > +
> > +	if (tmp_allowed_versions[0] != config_version)
> > +		for (int i = 1; i < nr_allowed_versions; i++)
> > +			if (tmp_allowed_versions[i] == config_version) {
> > +				enum protocol_version swap =
> > +					tmp_allowed_versions[0];
> > +				tmp_allowed_versions[0] =
> > +					tmp_allowed_versions[i];
> > +				tmp_allowed_versions[i] = swap;
> > +			}
> > +
> > +	strbuf_addf(advert, "version=%s",
> > +		    format_protocol_version(tmp_allowed_versions[0]));
> > +	for (int i = 1; i < tmp_nr; i++)
> > +		strbuf_addf(advert, ":version=%s",
> > +			    format_protocol_version(tmp_allowed_versions[i]));
> > +}
> > +
> 
> So the idea is that the protocols the other end can talk come in
> advert in their preferred order, and we take an intersection of them
> and our "allowed-versions", but the preference is further skewed
> with the "swap" thing if we have our own preference specified via
> config?

We currently don't intersect with our own allowed list, we just accept
the first version that we recognize. This introduces its own version
negotiation bug; if we add v2 push in the future, a new client
talking to an old server would try to use v2 even though the server may
not have the corresponding v2 push implementation. I'll fix this in the
next version.

In any case, the ordering of the server's allowed versions won't matter;
we'll pick the the first version in the client's list which is also
allowed on the server.

> I am wondering if the code added by this patch outside this
> function, with if (strcmp(client_ad.buf, "version=0") sprinkled all
> over the place, works sensibly when the other side says "I prefer
> version=0 but I do not mind talking version=1".

Depends on what you mean by "sensibly" :). In the current case, if the
client prefers v0, it will always end up using v0. After the fixes
described above, it will always use v0 unless the server no longer
supports v0. Is that what you would expect?

> Isn't tmp_allowed_versions[] leaking when we return from this
> function?

Yes, sorry about that. Will fix.
Josh Steadmon Nov. 13, 2018, 11:03 p.m. UTC | #6
On 2018.11.13 19:28, SZEDER Gábor wrote:
> On Mon, Nov 12, 2018 at 01:49:05PM -0800, steadmon@google.com wrote:
> 
> > diff --git a/protocol.c b/protocol.c
> > index 5e636785d1..54d2ab991b 100644
> > --- a/protocol.c
> > +++ b/protocol.c
> 
> > +void get_client_protocol_version_advertisement(struct strbuf *advert)
> > +{
> > +	int tmp_nr = nr_allowed_versions;
> > +	enum protocol_version *tmp_allowed_versions, config_version;
> > +	strbuf_reset(advert);
> > +
> > +	have_advertised_versions_already = 1;
> > +
> > +	config_version = get_protocol_version_config();
> > +	if (config_version == protocol_v0) {
> > +		strbuf_addstr(advert, "version=0");
> > +		return;
> > +	}
> > +
> > +	if (tmp_nr > 0) {
> > +		ALLOC_ARRAY(tmp_allowed_versions, tmp_nr);
> > +		copy_array(tmp_allowed_versions, allowed_versions, tmp_nr,
> > +			   sizeof(enum protocol_version));
> > +	} else {
> > +		ALLOC_ARRAY(tmp_allowed_versions, 1);
> > +		tmp_nr = 1;
> > +		tmp_allowed_versions[0] = config_version;
> > +	}
> > +
> > +	if (tmp_allowed_versions[0] != config_version)
> > +		for (int i = 1; i < nr_allowed_versions; i++)
> 
> We don't do C99 yet, thus the declaration of a loop variable like this
> is not allowed and triggers compiler errors.
> 
> > +			if (tmp_allowed_versions[i] == config_version) {
> > +				enum protocol_version swap =
> > +					tmp_allowed_versions[0];
> > +				tmp_allowed_versions[0] =
> > +					tmp_allowed_versions[i];
> > +				tmp_allowed_versions[i] = swap;
> > +			}
> > +
> > +	strbuf_addf(advert, "version=%s",
> > +		    format_protocol_version(tmp_allowed_versions[0]));
> > +	for (int i = 1; i < tmp_nr; i++)
> 
> Likewise.
> 
> > +		strbuf_addf(advert, ":version=%s",
> > +			    format_protocol_version(tmp_allowed_versions[i]));
> > +}

Sorry about that. Will fix in v4. Out of curiousity, do you have a
config.mak snippet that will make these into errors? I played around
with adding combinations of -ansi, -std=c89, and -pedantic to CFLAGS,
but I couldn't get anything that detect the problem without also
breaking on other parts of the build.
SZEDER Gábor Nov. 14, 2018, 12:47 a.m. UTC | #7
On Tue, Nov 13, 2018 at 03:03:47PM -0800, Josh Steadmon wrote:
> > > +		for (int i = 1; i < nr_allowed_versions; i++)
> > 
> > We don't do C99 yet, thus the declaration of a loop variable like this
> > is not allowed and triggers compiler errors.

> Sorry about that. Will fix in v4. Out of curiousity, do you have a
> config.mak snippet that will make these into errors? I played around
> with adding combinations of -ansi, -std=c89, and -pedantic to CFLAGS,
> but I couldn't get anything that detect the problem without also
> breaking on other parts of the build.

Unfortunately, I don't have such an universal CFLAGS.

With gcc-4.8 the default CFLAGS is sufficient:

  $ make V=1 CC=gcc-4.8 protocol.o
  gcc-4.8 -o protocol.o -c -MF ./.depend/protocol.o.d -MQ protocol.o -MMD -MP  -g -O2 -Wall -I. -DHAVE_SYSINFO -DGIT_HOST_CPU="\"x86_64\"" -DHAVE_ALLOCA_H -DUSE_CURL_FOR_IMAP_SEND -DSHA1_DC -DSHA1DC_NO_STANDARD_INCLUDES -DSHA1DC_INIT_SAFE_HASH_DEFAULT=0 -DSHA1DC_CUSTOM_INCLUDE_SHA1_C="\"cache.h\"" -DSHA1DC_CUSTOM_INCLUDE_UBC_CHECK_C="\"git-compat-util.h\""  -DHAVE_PATHS_H -DHAVE_DEV_TTY -DHAVE_CLOCK_GETTIME -DHAVE_CLOCK_MONOTONIC -DHAVE_GETDELIM '-DPROCFS_EXECUTABLE_PATH="/proc/self/exe"'  -DFREAD_READS_DIRECTORIES -DNO_STRLCPY -DSHELL_PATH='"/bin/sh"' -DPAGER_ENV='"LESS=FRX LV=-c"'  protocol.c
  protocol.c: In function ‘get_client_protocol_version_advertisement’:
  protocol.c:112:3: error: ‘for’ loop initial declarations are only allowed in C99 mode
     for (int i = 1; i < nr_allowed_versions; i++)
     ^
  < ... snip ... >

I couldn't get this error with any newer GCC or Clang, and using
options like -std=c89 trigger many other errors as well, just like you
mentioned.
Junio C Hamano Nov. 14, 2018, 2:38 a.m. UTC | #8
Josh Steadmon <steadmon@google.com> writes:

> On 2018.11.13 13:01, Junio C Hamano wrote:
>> steadmon@google.com writes:
>> 
>> > Currently the client advertises that it supports the wire protocol
>> > version set in the protocol.version config. However, not all services
>> > support the same set of protocol versions. When connecting to
>> > git-receive-pack, the client automatically downgrades to v0 if
>> > config.protocol is set to v2, but this check is not performed for other
>> > services.
>> 
>> "downgrades to v0 even if ... is set to v2" you mean?  Otherwise it
>> is unclear why asking for v2 leads to using v0.
>
> The downgrade on push happens only when the the configured version is
> v2. If v1 is requested, no downgrade is triggered. I'll clarify the
> commit message in the next version.

OK, then it will still be confusing unless "we downgrade v2 to v0
because ..."gives the reason.

> In any case, the ordering of the server's allowed versions won't matter;
> we'll pick the the first version in the client's list which is also
> allowed on the server.

That sounds like a very sensible semantics.

>
>> I am wondering if the code added by this patch outside this
>> function, with if (strcmp(client_ad.buf, "version=0") sprinkled all
>> over the place, works sensibly when the other side says "I prefer
>> version=0 but I do not mind talking version=1".
>
> Depends on what you mean by "sensibly" :). In the current case, if the
> client prefers v0, it will always end up using v0. After the fixes
> described above, it will always use v0 unless the server no longer
> supports v0. Is that what you would expect?

Yes, that sounds like a sensible behaviour.

What I was alludding to was a lot simpler, though.  An advert string
"version=0:version=1" from a client that prefers version 0 won't be
!strcmp("version=0", advert) but seeing many strcmp() in the patch
made me wonder.
Junio C Hamano Nov. 14, 2018, 2:44 a.m. UTC | #9
SZEDER Gábor <szeder.dev@gmail.com> writes:

>> +	if (tmp_allowed_versions[0] != config_version)
>> +		for (int i = 1; i < nr_allowed_versions; i++)
>
> We don't do C99 yet, thus the declaration of a loop variable like this
> is not allowed and triggers compiler errors.

I thought we did a weather-balloon to see if this bothers people who
build on minority platforms but

	git grep 'for (int'

is coming up empty.

We have been trying designated initializers with weather-balloon
changes (both arrays and struct fields) and I somehow thought that
we already were trying this out, but apparently that is not the
case.  Also trailing comma in the enum definition was what we
discussed earlier but I do not know if we had weather-balloon for it
or not offhand.  

Perhaps we should write these down in CodingGuidelines.
SZEDER Gábor Nov. 14, 2018, 11:01 a.m. UTC | #10
On Wed, Nov 14, 2018 at 11:44:51AM +0900, Junio C Hamano wrote:
> SZEDER Gábor <szeder.dev@gmail.com> writes:
> 
> >> +	if (tmp_allowed_versions[0] != config_version)
> >> +		for (int i = 1; i < nr_allowed_versions; i++)
> >
> > We don't do C99 yet, thus the declaration of a loop variable like this
> > is not allowed and triggers compiler errors.
> 
> I thought we did a weather-balloon to see if this bothers people who
> build on minority platforms but
> 
> 	git grep 'for (int'
> 
> is coming up empty.
> 
> We have been trying designated initializers with weather-balloon
> changes (both arrays and struct fields) and I somehow thought that
> we already were trying this out, but apparently that is not the
> case.

I thought so as well, and I run the exact same 'git grep' command
before replying to Josh :)

There was a discussion about such a weather-balloon patch [1] (which
happened to use an unsigned loop variable, so our grep wouldn't have
found it anyway), but it wasn't picked up because it required new
options in CFLAGS and there was no standard way to do so [2].

[1] https://public-inbox.org/git/20170719181956.15845-1-sbeller@google.com/
[2] https://public-inbox.org/git/20170724170813.scceigybl5d3fvdd@sigill.intra.peff.net/
Josh Steadmon Nov. 14, 2018, 7:57 p.m. UTC | #11
On 2018.11.14 11:38, Junio C Hamano wrote:
> Josh Steadmon <steadmon@google.com> writes:
> 
> > On 2018.11.13 13:01, Junio C Hamano wrote:
> >> I am wondering if the code added by this patch outside this
> >> function, with if (strcmp(client_ad.buf, "version=0") sprinkled all
> >> over the place, works sensibly when the other side says "I prefer
> >> version=0 but I do not mind talking version=1".
> >
> > Depends on what you mean by "sensibly" :). In the current case, if the
> > client prefers v0, it will always end up using v0. After the fixes
> > described above, it will always use v0 unless the server no longer
> > supports v0. Is that what you would expect?
> 
> Yes, that sounds like a sensible behaviour.
> 
> What I was alludding to was a lot simpler, though.  An advert string
> "version=0:version=1" from a client that prefers version 0 won't be
> !strcmp("version=0", advert) but seeing many strcmp() in the patch
> made me wonder.

Ah I see. The strcmp()s against "version=0" are special cases for where
it looks like the client does not understand any sort of version
negotiation. If we see multiple versions listed in the advert, then the
rest of the selection logic should do the right thing.

However, I think that it might work to remove the special cases. In the
event that the client is so old that it doesn't understand any form of
version negotiation, it should just ignore the version fields /
environment vars. If you think it's cleaner to remove the special cases,
let me know.
Junio C Hamano Nov. 16, 2018, 2:45 a.m. UTC | #12
Josh Steadmon <steadmon@google.com> writes:

>> What I was alludding to was a lot simpler, though.  An advert string
>> "version=0:version=1" from a client that prefers version 0 won't be
>> !strcmp("version=0", advert) but seeing many strcmp() in the patch
>> made me wonder.
>
> Ah I see. The strcmp()s against "version=0" are special cases for where
> it looks like the client does not understand any sort of version
> negotiation. If we see multiple versions listed in the advert, then the
> rest of the selection logic should do the right thing.

OK, let me try to see if I understand correctly by rephrasing.

If the client does not say anything about which version it prefers
(because it only knows about version 0 without even realizing that
there is a version negotiation exchange), we substitute the lack of
proposed versions with string "version=0", and the strcmp()s I saw
and was puzzled by are all about special casing such a client.  But
we would end up behaving the same way (at least when judged only by
externally visible effects) to a client that is aware of version
negotiation and tells us it prefers version 0 (and nothing else)
with the selection logic anyway.

Did I get it right?  If so, yeah, I think it makes sense to avoid
two codepaths that ends up doing the same thing by removing the
special case.

> However, I think that it might work to remove the special cases. In the
> event that the client is so old that it doesn't understand any form of
> version negotiation, it should just ignore the version fields /
> environment vars. If you think it's cleaner to remove the special cases,
> let me know.
Josh Steadmon Nov. 16, 2018, 7:59 p.m. UTC | #13
On 2018.11.16 11:45, Junio C Hamano wrote:
> Josh Steadmon <steadmon@google.com> writes:
> 
> >> What I was alludding to was a lot simpler, though.  An advert string
> >> "version=0:version=1" from a client that prefers version 0 won't be
> >> !strcmp("version=0", advert) but seeing many strcmp() in the patch
> >> made me wonder.
> >
> > Ah I see. The strcmp()s against "version=0" are special cases for where
> > it looks like the client does not understand any sort of version
> > negotiation. If we see multiple versions listed in the advert, then the
> > rest of the selection logic should do the right thing.
> 
> OK, let me try to see if I understand correctly by rephrasing.
> 
> If the client does not say anything about which version it prefers
> (because it only knows about version 0 without even realizing that
> there is a version negotiation exchange), we substitute the lack of
> proposed versions with string "version=0", and the strcmp()s I saw
> and was puzzled by are all about special casing such a client.  But
> we would end up behaving the same way (at least when judged only by
> externally visible effects) to a client that is aware of version
> negotiation and tells us it prefers version 0 (and nothing else)
> with the selection logic anyway.
> 
> Did I get it right?  If so, yeah, I think it makes sense to avoid
> two codepaths that ends up doing the same thing by removing the
> special case.

Yes, that is correct. The next version will remove the special cases
here.

> > However, I think that it might work to remove the special cases. In the
> > event that the client is so old that it doesn't understand any form of
> > version negotiation, it should just ignore the version fields /
> > environment vars. If you think it's cleaner to remove the special cases,
> > let me know.
diff mbox series

Patch

diff --git a/builtin/archive.c b/builtin/archive.c
index e74f675390..8adb9f381b 100644
--- a/builtin/archive.c
+++ b/builtin/archive.c
@@ -8,6 +8,7 @@ 
 #include "transport.h"
 #include "parse-options.h"
 #include "pkt-line.h"
+#include "protocol.h"
 #include "sideband.h"
 
 static void create_output_file(const char *output_file)
@@ -94,6 +95,8 @@  int cmd_archive(int argc, const char **argv, const char *prefix)
 		OPT_END()
 	};
 
+	register_allowed_protocol_version(protocol_v0);
+
 	argc = parse_options(argc, argv, prefix, local_opts, NULL,
 			     PARSE_OPT_KEEP_ALL);
 
diff --git a/builtin/clone.c b/builtin/clone.c
index fd2c3ef090..1651a950b6 100644
--- a/builtin/clone.c
+++ b/builtin/clone.c
@@ -900,6 +900,10 @@  int cmd_clone(int argc, const char **argv, const char *prefix)
 	struct refspec rs = REFSPEC_INIT_FETCH;
 	struct argv_array ref_prefixes = ARGV_ARRAY_INIT;
 
+	register_allowed_protocol_version(protocol_v2);
+	register_allowed_protocol_version(protocol_v1);
+	register_allowed_protocol_version(protocol_v0);
+
 	fetch_if_missing = 0;
 
 	packet_trace_identity("clone");
diff --git a/builtin/fetch-pack.c b/builtin/fetch-pack.c
index 1a1bc63566..cba935e4d3 100644
--- a/builtin/fetch-pack.c
+++ b/builtin/fetch-pack.c
@@ -57,6 +57,10 @@  int cmd_fetch_pack(int argc, const char **argv, const char *prefix)
 
 	fetch_if_missing = 0;
 
+	register_allowed_protocol_version(protocol_v2);
+	register_allowed_protocol_version(protocol_v1);
+	register_allowed_protocol_version(protocol_v0);
+
 	packet_trace_identity("fetch-pack");
 
 	memset(&args, 0, sizeof(args));
diff --git a/builtin/fetch.c b/builtin/fetch.c
index 61bec5d213..2a20cf8bfd 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -21,6 +21,7 @@ 
 #include "argv-array.h"
 #include "utf8.h"
 #include "packfile.h"
+#include "protocol.h"
 #include "list-objects-filter-options.h"
 
 static const char * const builtin_fetch_usage[] = {
@@ -1476,6 +1477,10 @@  int cmd_fetch(int argc, const char **argv, const char *prefix)
 	int prune_tags_ok = 1;
 	struct argv_array argv_gc_auto = ARGV_ARRAY_INIT;
 
+	register_allowed_protocol_version(protocol_v2);
+	register_allowed_protocol_version(protocol_v1);
+	register_allowed_protocol_version(protocol_v0);
+
 	packet_trace_identity("fetch");
 
 	fetch_if_missing = 0;
diff --git a/builtin/ls-remote.c b/builtin/ls-remote.c
index 1a25df7ee1..ea685e8bb9 100644
--- a/builtin/ls-remote.c
+++ b/builtin/ls-remote.c
@@ -1,5 +1,6 @@ 
 #include "builtin.h"
 #include "cache.h"
+#include "protocol.h"
 #include "transport.h"
 #include "ref-filter.h"
 #include "remote.h"
@@ -80,6 +81,10 @@  int cmd_ls_remote(int argc, const char **argv, const char *prefix)
 
 	memset(&ref_array, 0, sizeof(ref_array));
 
+	register_allowed_protocol_version(protocol_v2);
+	register_allowed_protocol_version(protocol_v1);
+	register_allowed_protocol_version(protocol_v0);
+
 	argc = parse_options(argc, argv, prefix, options, ls_remote_usage,
 			     PARSE_OPT_STOP_AT_NON_OPTION);
 	dest = argv[0];
diff --git a/builtin/pull.c b/builtin/pull.c
index 681c127a07..cb64146834 100644
--- a/builtin/pull.c
+++ b/builtin/pull.c
@@ -9,6 +9,7 @@ 
 #include "config.h"
 #include "builtin.h"
 #include "parse-options.h"
+#include "protocol.h"
 #include "exec-cmd.h"
 #include "run-command.h"
 #include "sha1-array.h"
@@ -849,6 +850,10 @@  int cmd_pull(int argc, const char **argv, const char *prefix)
 	struct object_id rebase_fork_point;
 	int autostash;
 
+	register_allowed_protocol_version(protocol_v2);
+	register_allowed_protocol_version(protocol_v1);
+	register_allowed_protocol_version(protocol_v0);
+
 	if (!getenv("GIT_REFLOG_ACTION"))
 		set_reflog_message(argc, argv);
 
diff --git a/builtin/push.c b/builtin/push.c
index d09a42062c..10d8abe829 100644
--- a/builtin/push.c
+++ b/builtin/push.c
@@ -10,6 +10,7 @@ 
 #include "remote.h"
 #include "transport.h"
 #include "parse-options.h"
+#include "protocol.h"
 #include "submodule.h"
 #include "submodule-config.h"
 #include "send-pack.h"
@@ -587,6 +588,9 @@  int cmd_push(int argc, const char **argv, const char *prefix)
 		OPT_END()
 	};
 
+	register_allowed_protocol_version(protocol_v1);
+	register_allowed_protocol_version(protocol_v0);
+
 	packet_trace_identity("push");
 	git_config(git_push_config, &flags);
 	argc = parse_options(argc, argv, prefix, options, push_usage, 0);
diff --git a/builtin/send-pack.c b/builtin/send-pack.c
index 8e3c7490f7..f48bd1306b 100644
--- a/builtin/send-pack.c
+++ b/builtin/send-pack.c
@@ -184,6 +184,9 @@  int cmd_send_pack(int argc, const char **argv, const char *prefix)
 		OPT_END()
 	};
 
+	register_allowed_protocol_version(protocol_v1);
+	register_allowed_protocol_version(protocol_v0);
+
 	git_config(send_pack_config, NULL);
 	argc = parse_options(argc, argv, prefix, options, send_pack_usage, 0);
 	if (argc > 0) {
diff --git a/connect.c b/connect.c
index 94547e5056..a170ba1e90 100644
--- a/connect.c
+++ b/connect.c
@@ -1046,7 +1046,7 @@  static enum ssh_variant determine_ssh_variant(const char *ssh_command,
  */
 static struct child_process *git_connect_git(int fd[2], char *hostandport,
 					     const char *path, const char *prog,
-					     enum protocol_version version,
+					     const struct strbuf *version_advert,
 					     int flags)
 {
 	struct child_process *conn;
@@ -1085,10 +1085,9 @@  static struct child_process *git_connect_git(int fd[2], char *hostandport,
 		    target_host, 0);
 
 	/* If using a new version put that stuff here after a second null byte */
-	if (version > 0) {
+	if (strcmp(version_advert->buf, "version=0")) {
 		strbuf_addch(&request, '\0');
-		strbuf_addf(&request, "version=%d%c",
-			    version, '\0');
+		strbuf_addf(&request, "%s%c", version_advert->buf, '\0');
 	}
 
 	packet_write(fd[1], request.buf, request.len);
@@ -1104,14 +1103,14 @@  static struct child_process *git_connect_git(int fd[2], char *hostandport,
  */
 static void push_ssh_options(struct argv_array *args, struct argv_array *env,
 			     enum ssh_variant variant, const char *port,
-			     enum protocol_version version, int flags)
+			     const struct strbuf *version_advert, int flags)
 {
 	if (variant == VARIANT_SSH &&
-	    version > 0) {
+	    strcmp(version_advert->buf, "version=0")) {
 		argv_array_push(args, "-o");
 		argv_array_push(args, "SendEnv=" GIT_PROTOCOL_ENVIRONMENT);
-		argv_array_pushf(env, GIT_PROTOCOL_ENVIRONMENT "=version=%d",
-				 version);
+		argv_array_pushf(env, GIT_PROTOCOL_ENVIRONMENT "=%s",
+				 version_advert->buf);
 	}
 
 	if (flags & CONNECT_IPV4) {
@@ -1164,7 +1163,7 @@  static void push_ssh_options(struct argv_array *args, struct argv_array *env,
 
 /* Prepare a child_process for use by Git's SSH-tunneled transport. */
 static void fill_ssh_args(struct child_process *conn, const char *ssh_host,
-			  const char *port, enum protocol_version version,
+			  const char *port, const struct strbuf *version_advert,
 			  int flags)
 {
 	const char *ssh;
@@ -1198,15 +1197,16 @@  static void fill_ssh_args(struct child_process *conn, const char *ssh_host,
 
 		argv_array_push(&detect.args, ssh);
 		argv_array_push(&detect.args, "-G");
-		push_ssh_options(&detect.args, &detect.env_array,
-				 VARIANT_SSH, port, version, flags);
+		push_ssh_options(&detect.args, &detect.env_array, VARIANT_SSH,
+				 port, version_advert, flags);
 		argv_array_push(&detect.args, ssh_host);
 
 		variant = run_command(&detect) ? VARIANT_SIMPLE : VARIANT_SSH;
 	}
 
 	argv_array_push(&conn->args, ssh);
-	push_ssh_options(&conn->args, &conn->env_array, variant, port, version, flags);
+	push_ssh_options(&conn->args, &conn->env_array, variant, port,
+			 version_advert, flags);
 	argv_array_push(&conn->args, ssh_host);
 }
 
@@ -1226,16 +1226,10 @@  struct child_process *git_connect(int fd[2], const char *url,
 {
 	char *hostandport, *path;
 	struct child_process *conn;
+	struct strbuf version_advert = STRBUF_INIT;
 	enum protocol protocol;
-	enum protocol_version version = get_protocol_version_config();
 
-	/*
-	 * NEEDSWORK: If we are trying to use protocol v2 and we are planning
-	 * to perform a push, then fallback to v0 since the client doesn't know
-	 * how to push yet using v2.
-	 */
-	if (version == protocol_v2 && !strcmp("git-receive-pack", prog))
-		version = protocol_v0;
+	get_client_protocol_version_advertisement(&version_advert);
 
 	/* Without this we cannot rely on waitpid() to tell
 	 * what happened to our children.
@@ -1250,7 +1244,8 @@  struct child_process *git_connect(int fd[2], const char *url,
 		printf("Diag: path=%s\n", path ? path : "NULL");
 		conn = NULL;
 	} else if (protocol == PROTO_GIT) {
-		conn = git_connect_git(fd, hostandport, path, prog, version, flags);
+		conn = git_connect_git(fd, hostandport, path, prog,
+				       &version_advert, flags);
 	} else {
 		struct strbuf cmd = STRBUF_INIT;
 		const char *const *var;
@@ -1293,12 +1288,14 @@  struct child_process *git_connect(int fd[2], const char *url,
 				strbuf_release(&cmd);
 				return NULL;
 			}
-			fill_ssh_args(conn, ssh_host, port, version, flags);
+			fill_ssh_args(conn, ssh_host, port, &version_advert,
+				      flags);
 		} else {
 			transport_check_allowed("file");
-			if (version > 0) {
-				argv_array_pushf(&conn->env_array, GIT_PROTOCOL_ENVIRONMENT "=version=%d",
-						 version);
+			if (strcmp(version_advert.buf, "version=0")) {
+				argv_array_pushf(&conn->env_array,
+						 GIT_PROTOCOL_ENVIRONMENT "=%s",
+						 version_advert.buf);
 			}
 		}
 		argv_array_push(&conn->args, cmd.buf);
diff --git a/protocol.c b/protocol.c
index 5e636785d1..54d2ab991b 100644
--- a/protocol.c
+++ b/protocol.c
@@ -2,18 +2,43 @@ 
 #include "config.h"
 #include "protocol.h"
 
+static enum protocol_version *allowed_versions;
+static int nr_allowed_versions;
+static int alloc_allowed_versions;
+static int have_advertised_versions_already = 0;
+
+static const char protocol_v0_string[] = "0";
+static const char protocol_v1_string[] = "1";
+static const char protocol_v2_string[] = "2";
+
 static enum protocol_version parse_protocol_version(const char *value)
 {
-	if (!strcmp(value, "0"))
+	if (!strcmp(value, protocol_v0_string))
 		return protocol_v0;
-	else if (!strcmp(value, "1"))
+	else if (!strcmp(value, protocol_v1_string))
 		return protocol_v1;
-	else if (!strcmp(value, "2"))
+	else if (!strcmp(value, protocol_v2_string))
 		return protocol_v2;
 	else
 		return protocol_unknown_version;
 }
 
+/* Return the text representation of a wire protocol version. */
+static const char *format_protocol_version(enum protocol_version version)
+{
+	switch (version) {
+	case protocol_v0:
+		return protocol_v0_string;
+	case protocol_v1:
+		return protocol_v1_string;
+	case protocol_v2:
+		return protocol_v2_string;
+	case protocol_unknown_version:
+		die(_("Unrecognized protocol version"));
+	}
+	die(_("Unrecognized protocol_version"));
+}
+
 enum protocol_version get_protocol_version_config(void)
 {
 	const char *value;
@@ -30,6 +55,76 @@  enum protocol_version get_protocol_version_config(void)
 	return protocol_v0;
 }
 
+void register_allowed_protocol_version(enum protocol_version version)
+{
+	if (have_advertised_versions_already)
+		BUG(_("attempting to register an allowed protocol version after advertisement"));
+
+	ALLOC_GROW(allowed_versions, nr_allowed_versions + 1,
+		   alloc_allowed_versions);
+	allowed_versions[nr_allowed_versions++] = version;
+}
+
+void register_allowed_protocol_versions_from_env(void)
+{
+	const char *git_protocol = getenv(GIT_PROTOCOL_ENVIRONMENT);
+	const char *version_str;
+	struct string_list version_list = STRING_LIST_INIT_DUP;
+	struct string_list_item *version;
+
+	if (!git_protocol)
+		return;
+
+	string_list_split(&version_list, git_protocol, ':', -1);
+	for_each_string_list_item(version, &version_list) {
+		if (skip_prefix(version->string, "version=", &version_str))
+			register_allowed_protocol_version(
+				parse_protocol_version(version_str));
+	}
+	string_list_clear(&version_list, 0);
+}
+
+void get_client_protocol_version_advertisement(struct strbuf *advert)
+{
+	int tmp_nr = nr_allowed_versions;
+	enum protocol_version *tmp_allowed_versions, config_version;
+	strbuf_reset(advert);
+
+	have_advertised_versions_already = 1;
+
+	config_version = get_protocol_version_config();
+	if (config_version == protocol_v0) {
+		strbuf_addstr(advert, "version=0");
+		return;
+	}
+
+	if (tmp_nr > 0) {
+		ALLOC_ARRAY(tmp_allowed_versions, tmp_nr);
+		copy_array(tmp_allowed_versions, allowed_versions, tmp_nr,
+			   sizeof(enum protocol_version));
+	} else {
+		ALLOC_ARRAY(tmp_allowed_versions, 1);
+		tmp_nr = 1;
+		tmp_allowed_versions[0] = config_version;
+	}
+
+	if (tmp_allowed_versions[0] != config_version)
+		for (int i = 1; i < nr_allowed_versions; i++)
+			if (tmp_allowed_versions[i] == config_version) {
+				enum protocol_version swap =
+					tmp_allowed_versions[0];
+				tmp_allowed_versions[0] =
+					tmp_allowed_versions[i];
+				tmp_allowed_versions[i] = swap;
+			}
+
+	strbuf_addf(advert, "version=%s",
+		    format_protocol_version(tmp_allowed_versions[0]));
+	for (int i = 1; i < tmp_nr; i++)
+		strbuf_addf(advert, ":version=%s",
+			    format_protocol_version(tmp_allowed_versions[i]));
+}
+
 enum protocol_version determine_protocol_version_server(void)
 {
 	const char *git_protocol = getenv(GIT_PROTOCOL_ENVIRONMENT);
@@ -38,9 +133,10 @@  enum protocol_version determine_protocol_version_server(void)
 	/*
 	 * Determine which protocol version the client has requested.  Since
 	 * multiple 'version' keys can be sent by the client, indicating that
-	 * the client is okay to speak any of them, select the greatest version
-	 * that the client has requested.  This is due to the assumption that
-	 * the most recent protocol version will be the most state-of-the-art.
+	 * the client is okay to speak any of them, select the first
+	 * recognizable version that the client has requested.  This is due to
+	 * the assumption that the protocol versions will be listed in
+	 * preference order.
 	 */
 	if (git_protocol) {
 		struct string_list list = STRING_LIST_INIT_DUP;
@@ -53,8 +149,10 @@  enum protocol_version determine_protocol_version_server(void)
 
 			if (skip_prefix(item->string, "version=", &value)) {
 				v = parse_protocol_version(value);
-				if (v > version)
+				if (v != protocol_unknown_version) {
 					version = v;
+					break;
+				}
 			}
 		}
 
diff --git a/protocol.h b/protocol.h
index 2ad35e433c..b67b2259de 100644
--- a/protocol.h
+++ b/protocol.h
@@ -16,6 +16,23 @@  enum protocol_version {
  */
 extern enum protocol_version get_protocol_version_config(void);
 
+/*
+ * Register an allowable protocol version for a given operation. Registration
+ * must occur before attempting to advertise a version to a server process.
+ */
+extern void register_allowed_protocol_version(enum protocol_version version);
+
+/*
+ * Register allowable protocol versions from the GIT_PROTOCOL environment var.
+ */
+extern void register_allowed_protocol_versions_from_env(void);
+
+/*
+ * Fill a strbuf with a version advertisement string suitable for use in the
+ * GIT_PROTOCOL environment variable or similar version negotiation field.
+ */
+extern void get_client_protocol_version_advertisement(struct strbuf *advert);
+
 /*
  * Used by a server to determine which protocol version should be used based on
  * a client's request, communicated via the 'GIT_PROTOCOL' environment variable
diff --git a/remote-curl.c b/remote-curl.c
index fb28309e85..537f8c7aac 100644
--- a/remote-curl.c
+++ b/remote-curl.c
@@ -330,6 +330,20 @@  static int get_protocol_http_header(enum protocol_version version,
 	return 0;
 }
 
+static int get_client_protocol_http_header(const struct strbuf *version_advert,
+					   struct strbuf *header)
+{
+	if (version_advert->len > 0 &&
+	    strcmp(version_advert->buf, "version=0")) {
+		strbuf_addf(header, GIT_PROTOCOL_HEADER ": %s",
+			    version_advert->buf);
+
+		return 1;
+	}
+
+	return 0;
+}
+
 static struct discovery *discover_refs(const char *service, int for_push)
 {
 	struct strbuf exp = STRBUF_INIT;
@@ -339,11 +353,11 @@  static struct discovery *discover_refs(const char *service, int for_push)
 	struct strbuf refs_url = STRBUF_INIT;
 	struct strbuf effective_url = STRBUF_INIT;
 	struct strbuf protocol_header = STRBUF_INIT;
+	struct strbuf version_advert = STRBUF_INIT;
 	struct string_list extra_headers = STRING_LIST_INIT_DUP;
 	struct discovery *last = last_discovery;
 	int http_ret, maybe_smart = 0;
 	struct http_get_options http_options;
-	enum protocol_version version = get_protocol_version_config();
 
 	if (last && !strcmp(service, last->service))
 		return last;
@@ -360,16 +374,10 @@  static struct discovery *discover_refs(const char *service, int for_push)
 		strbuf_addf(&refs_url, "service=%s", service);
 	}
 
-	/*
-	 * NEEDSWORK: If we are trying to use protocol v2 and we are planning
-	 * to perform a push, then fallback to v0 since the client doesn't know
-	 * how to push yet using v2.
-	 */
-	if (version == protocol_v2 && !strcmp("git-receive-pack", service))
-		version = protocol_v0;
+	get_client_protocol_version_advertisement(&version_advert);
 
 	/* Add the extra Git-Protocol header */
-	if (get_protocol_http_header(version, &protocol_header))
+	if (get_client_protocol_http_header(&version_advert, &protocol_header))
 		string_list_append(&extra_headers, protocol_header.buf);
 
 	memset(&http_options, 0, sizeof(http_options));
@@ -1327,6 +1335,8 @@  int cmd_main(int argc, const char **argv)
 	struct strbuf buf = STRBUF_INIT;
 	int nongit;
 
+	register_allowed_protocol_versions_from_env();
+
 	setup_git_directory_gently(&nongit);
 	if (argc < 2) {
 		error("remote-curl: usage: git remote-curl <remote> [<url>]");
diff --git a/t/t5570-git-daemon.sh b/t/t5570-git-daemon.sh
index 7466aad111..d528e91630 100755
--- a/t/t5570-git-daemon.sh
+++ b/t/t5570-git-daemon.sh
@@ -186,7 +186,7 @@  test_expect_success 'hostname cannot break out of directory' '
 test_expect_success 'daemon log records all attributes' '
 	cat >expect <<-\EOF &&
 	Extended attribute "host": localhost
-	Extended attribute "protocol": version=1
+	Extended attribute "protocol": version=1:version=2:version=0
 	EOF
 	>daemon.log &&
 	GIT_OVERRIDE_VIRTUAL_HOST=localhost \
diff --git a/t/t5700-protocol-v1.sh b/t/t5700-protocol-v1.sh
index ba86a44eb1..2e56c79233 100755
--- a/t/t5700-protocol-v1.sh
+++ b/t/t5700-protocol-v1.sh
@@ -26,7 +26,7 @@  test_expect_success 'clone with git:// using protocol v1' '
 	test_cmp expect actual &&
 
 	# Client requested to use protocol v1
-	grep "clone> .*\\\0\\\0version=1\\\0$" log &&
+	grep "clone> .*\\\0\\\0version=1.*\\\0$" log &&
 	# Server responded using protocol v1
 	grep "clone< version 1" log
 '
@@ -42,7 +42,7 @@  test_expect_success 'fetch with git:// using protocol v1' '
 	test_cmp expect actual &&
 
 	# Client requested to use protocol v1
-	grep "fetch> .*\\\0\\\0version=1\\\0$" log &&
+	grep "fetch> .*\\\0\\\0version=1.*\\\0$" log &&
 	# Server responded using protocol v1
 	grep "fetch< version 1" log
 '
@@ -56,7 +56,7 @@  test_expect_success 'pull with git:// using protocol v1' '
 	test_cmp expect actual &&
 
 	# Client requested to use protocol v1
-	grep "fetch> .*\\\0\\\0version=1\\\0$" log &&
+	grep "fetch> .*\\\0\\\0version=1.*\\\0$" log &&
 	# Server responded using protocol v1
 	grep "fetch< version 1" log
 '
@@ -74,7 +74,7 @@  test_expect_success 'push with git:// using protocol v1' '
 	test_cmp expect actual &&
 
 	# Client requested to use protocol v1
-	grep "push> .*\\\0\\\0version=1\\\0$" log &&
+	grep "push> .*\\\0\\\0version=1.*\\\0$" log &&
 	# Server responded using protocol v1
 	grep "push< version 1" log
 '
diff --git a/t/t5702-protocol-v2.sh b/t/t5702-protocol-v2.sh
index 3beeed4546..78c17c25e4 100755
--- a/t/t5702-protocol-v2.sh
+++ b/t/t5702-protocol-v2.sh
@@ -24,7 +24,7 @@  test_expect_success 'list refs with git:// using protocol v2' '
 		ls-remote --symref "$GIT_DAEMON_URL/parent" >actual &&
 
 	# Client requested to use protocol v2
-	grep "git> .*\\\0\\\0version=2\\\0$" log &&
+	grep "git> .*\\\0\\\0version=2.*\\\0$" log &&
 	# Server responded using protocol v2
 	grep "git< version 2" log &&
 
@@ -56,7 +56,7 @@  test_expect_success 'clone with git:// using protocol v2' '
 	test_cmp expect actual &&
 
 	# Client requested to use protocol v2
-	grep "clone> .*\\\0\\\0version=2\\\0$" log &&
+	grep "clone> .*\\\0\\\0version=2.*\\\0$" log &&
 	# Server responded using protocol v2
 	grep "clone< version 2" log
 '
@@ -74,7 +74,7 @@  test_expect_success 'fetch with git:// using protocol v2' '
 	test_cmp expect actual &&
 
 	# Client requested to use protocol v2
-	grep "fetch> .*\\\0\\\0version=2\\\0$" log &&
+	grep "fetch> .*\\\0\\\0version=2.*\\\0$" log &&
 	# Server responded using protocol v2
 	grep "fetch< version 2" log
 '
@@ -90,7 +90,7 @@  test_expect_success 'pull with git:// using protocol v2' '
 	test_cmp expect actual &&
 
 	# Client requested to use protocol v2
-	grep "fetch> .*\\\0\\\0version=2\\\0$" log &&
+	grep "fetch> .*\\\0\\\0version=2.*\\\0$" log &&
 	# Server responded using protocol v2
 	grep "fetch< version 2" log
 '
@@ -476,7 +476,7 @@  test_expect_success 'push with http:// and a config of v2 does not request v2' '
 	test_when_finished "rm -f log" &&
 	# Till v2 for push is designed, make sure that if a client has
 	# protocol.version configured to use v2, that the client instead falls
-	# back and uses v0.
+	# back to previous versions.
 
 	test_commit -C http_child three &&
 
@@ -489,10 +489,8 @@  test_expect_success 'push with http:// and a config of v2 does not request v2' '
 	git -C "$HTTPD_DOCUMENT_ROOT_PATH/http_parent" log -1 --format=%s client_branch >expect &&
 	test_cmp expect actual &&
 
-	# Client didnt request to use protocol v2
-	! grep "Git-Protocol: version=2" log &&
-	# Server didnt respond using protocol v2
-	! grep "git< version 2" log
+	# Server responded with version 1
+	grep "git< version 1" log
 '
 
 
diff --git a/transport-helper.c b/transport-helper.c
index 143ca008c8..ac1937f1e1 100644
--- a/transport-helper.c
+++ b/transport-helper.c
@@ -105,6 +105,7 @@  static struct child_process *get_helper(struct transport *transport)
 {
 	struct helper_data *data = transport->data;
 	struct strbuf buf = STRBUF_INIT;
+	struct strbuf version_advert = STRBUF_INIT;
 	struct child_process *helper;
 	int duped;
 	int code;
@@ -127,6 +128,11 @@  static struct child_process *get_helper(struct transport *transport)
 		argv_array_pushf(&helper->env_array, "%s=%s",
 				 GIT_DIR_ENVIRONMENT, get_git_dir());
 
+	get_client_protocol_version_advertisement(&version_advert);
+	if (version_advert.len > 0)
+		argv_array_pushf(&helper->env_array, "%s=%s",
+				 GIT_PROTOCOL_ENVIRONMENT, version_advert.buf);
+
 	code = start_command(helper);
 	if (code < 0 && errno == ENOENT)
 		die(_("unable to find remote helper for '%s'"), data->name);