Make all transports request protocol V2 when fetching. Depending on
the transport, set the GIT_PROTOCOL environment variable (file and
ssh), pass the Git-Protocol header (http), or set the hidden
"\0version=2\0" (git anon). We'll fall back to V0 if the server
doesn't reply with a version 2 answer.

A user can control which protocol the client requests via the git
config protocol.version; if not set, JGit requests protocol V2 for
fetching. Pushing always uses protocol V0 still.

In the API, there is only a new Transport.openFetch() version that
takes a collection of RefSpecs plus additional patterns to construct
the Ref prefixes for the "ls-refs" command in protocol V2. If none
are given, the server will still advertise all refs, even in protocol
V2.

BasePackConnection.readAdvertisedRefs() handles falling back to
protocol V0. It newly returns true if V0 was used and the advertised
refs were read, and false if V2 is used and an explicit "ls-refs" is
needed. (This can't be done transparently inside readAdvertisedRefs()
because a "stateless RPC" transport like TransportHttp may need to
open a new connection for writing.)

BasePackFetchConnection implements the changes needed for the protocol
V2 "fetch" command (stateless protocol, simplified ACK handling,
delimiters, section headers).

In TransportHttp, change readSmartHeaders() to also recognize the
"version 2" packet line as a valid smart server indication.

Adapt tests, and run all the HTTP tests not only with both HTTP
connection factories (JDK and Apache HttpClient) but also with both
protocol V0 and V2. The SSH tests are much slower and much more
focused on the SSH protocol and SSH key handling. Factor out two
very simple cloning and pulling tests and make those run with
protocol V2.

Bug: 553083
Change-Id: I357c7f5daa7efb2872f1c64ee6f6d54229031ae1
Signed-off-by: Thomas Wolf <thomas.wolf@paranor.ch>

This reverts commit f802f06e7f.

I had misunderstood how protocol V2 works. This implementation only
works if the negotiation during fetch is done in one round.

Fixing this is substantial work in BasePackFetchConnection. Basically
I think I'd have to change back negotiate to the V0 version, and have
a doFetch() that does

  if protocol V2
    doFetchV2()
  else
    doFetchV0()

with doFetchV0 the old code, and doFetchV2 completely new.

Plus there would need to be a HTTP test case requiring several
negotiation rounds.

This is a couple of days work at least, and I don't know when I will
have the time to revisit this. So although the rest of the code is
fine I prefer to back this out completely and not leave a only half
working implementation in the code for an indeterminate time.

Bug: 553083
Change-Id: Icbbbb09882b3b83f9897deac4a06d5f8dc99d84e
Signed-off-by: Thomas Wolf <thomas.wolf@paranor.ch>

Make all transports request protocol V2 when fetching. Depending on
the transport, set the GIT_PROTOCOL environment variable (file and
ssh), pass the Git-Protocol header (http), or set the hidden
"\0version=2\0" (git anon). We'll fall back to V0 if the server
doesn't reply with a version 2 answer.

A user can control which protocol the client requests via the git
config protocol.version; if not set, JGit requests protocol V2 for
fetching. Pushing always uses protocol V0 still.

In the API, there is only a new Transport.openFetch() version that
takes a collection of RefSpecs plus additional patterns to construct
the Ref prefixes for the "ls-refs" command in protocol V2. If none
are given, the server will still advertise all refs, even in protocol
V2.

BasePackConnection.readAdvertisedRefs() handles falling back to
protocol V0. It newly returns true if V0 was used and the advertised
refs were read, and false if V2 is used and an explicit "ls-refs" is
needed. (This can't be done transparently inside readAdvertisedRefs()
because a "stateless RPC" transport like TransportHttp may need to
open a new connection for writing.)

BasePackFetchConnection implements the changes needed for the protocol
V2 "fetch" command (simplified ACK handling, delimiters, section
headers).

In TransportHttp, change readSmartHeaders() to also recognize the
"version 2" packet line as a valid smart server indication.

Adapt tests, and run all the HTTP tests not only with both HTTP
connection factories (JDK and Apache HttpClient) but also with both
protocol V0 and V2. Do the same for the SSH transport tests.

Bug: 553083
Change-Id: Ice9866aa78020f5ca8f397cde84dc224bf5d41b4
Signed-off-by: Thomas Wolf <thomas.wolf@paranor.ch>
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>