mirror of
https://github.com/git/git.git
synced 2024-11-16 06:03:44 +01:00
f745acb028
In addition to fixing trivial and obvious typos, be careful about the following points: - Spell ASCII, URL and CRC in ALL CAPS; - Spell Linux as Capitalized; - Do not omit periods in "i.e." and "e.g.". Signed-off-by: Thomas Ackermann <th.acker@arcor.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>
261 lines
10 KiB
Text
261 lines
10 KiB
Text
Git Protocol Capabilities
|
|
=========================
|
|
|
|
Servers SHOULD support all capabilities defined in this document.
|
|
|
|
On the very first line of the initial server response of either
|
|
receive-pack and upload-pack the first reference is followed by
|
|
a NUL byte and then a list of space delimited server capabilities.
|
|
These allow the server to declare what it can and cannot support
|
|
to the client.
|
|
|
|
Client will then send a space separated list of capabilities it wants
|
|
to be in effect. The client MUST NOT ask for capabilities the server
|
|
did not say it supports.
|
|
|
|
Server MUST diagnose and abort if capabilities it does not understand
|
|
was sent. Server MUST NOT ignore capabilities that client requested
|
|
and server advertised. As a consequence of these rules, server MUST
|
|
NOT advertise capabilities it does not understand.
|
|
|
|
The 'report-status', 'delete-refs', 'quiet', and 'push-cert' capabilities
|
|
are sent and recognized by the receive-pack (push to server) process.
|
|
|
|
The 'ofs-delta' and 'side-band-64k' capabilities are sent and recognized
|
|
by both upload-pack and receive-pack protocols. The 'agent' capability
|
|
may optionally be sent in both protocols.
|
|
|
|
All other capabilities are only recognized by the upload-pack (fetch
|
|
from server) process.
|
|
|
|
multi_ack
|
|
---------
|
|
|
|
The 'multi_ack' capability allows the server to return "ACK obj-id
|
|
continue" as soon as it finds a commit that it can use as a common
|
|
base, between the client's wants and the client's have set.
|
|
|
|
By sending this early, the server can potentially head off the client
|
|
from walking any further down that particular branch of the client's
|
|
repository history. The client may still need to walk down other
|
|
branches, sending have lines for those, until the server has a
|
|
complete cut across the DAG, or the client has said "done".
|
|
|
|
Without multi_ack, a client sends have lines in --date-order until
|
|
the server has found a common base. That means the client will send
|
|
have lines that are already known by the server to be common, because
|
|
they overlap in time with another branch that the server hasn't found
|
|
a common base on yet.
|
|
|
|
For example suppose the client has commits in caps that the server
|
|
doesn't and the server has commits in lower case that the client
|
|
doesn't, as in the following diagram:
|
|
|
|
+---- u ---------------------- x
|
|
/ +----- y
|
|
/ /
|
|
a -- b -- c -- d -- E -- F
|
|
\
|
|
+--- Q -- R -- S
|
|
|
|
If the client wants x,y and starts out by saying have F,S, the server
|
|
doesn't know what F,S is. Eventually the client says "have d" and
|
|
the server sends "ACK d continue" to let the client know to stop
|
|
walking down that line (so don't send c-b-a), but it's not done yet,
|
|
it needs a base for x. The client keeps going with S-R-Q, until a
|
|
gets reached, at which point the server has a clear base and it all
|
|
ends.
|
|
|
|
Without multi_ack the client would have sent that c-b-a chain anyway,
|
|
interleaved with S-R-Q.
|
|
|
|
multi_ack_detailed
|
|
------------------
|
|
This is an extension of multi_ack that permits client to better
|
|
understand the server's in-memory state. See pack-protocol.txt,
|
|
section "Packfile Negotiation" for more information.
|
|
|
|
no-done
|
|
-------
|
|
This capability should only be used with the smart HTTP protocol. If
|
|
multi_ack_detailed and no-done are both present, then the sender is
|
|
free to immediately send a pack following its first "ACK obj-id ready"
|
|
message.
|
|
|
|
Without no-done in the smart HTTP protocol, the server session would
|
|
end and the client has to make another trip to send "done" before
|
|
the server can send the pack. no-done removes the last round and
|
|
thus slightly reduces latency.
|
|
|
|
thin-pack
|
|
---------
|
|
|
|
A thin pack is one with deltas which reference base objects not
|
|
contained within the pack (but are known to exist at the receiving
|
|
end). This can reduce the network traffic significantly, but it
|
|
requires the receiving end to know how to "thicken" these packs by
|
|
adding the missing bases to the pack.
|
|
|
|
The upload-pack server advertises 'thin-pack' when it can generate
|
|
and send a thin pack. A client requests the 'thin-pack' capability
|
|
when it understands how to "thicken" it, notifying the server that
|
|
it can receive such a pack. A client MUST NOT request the
|
|
'thin-pack' capability if it cannot turn a thin pack into a
|
|
self-contained pack.
|
|
|
|
Receive-pack, on the other hand, is assumed by default to be able to
|
|
handle thin packs, but can ask the client not to use the feature by
|
|
advertising the 'no-thin' capability. A client MUST NOT send a thin
|
|
pack if the server advertises the 'no-thin' capability.
|
|
|
|
The reasons for this asymmetry are historical. The receive-pack
|
|
program did not exist until after the invention of thin packs, so
|
|
historically the reference implementation of receive-pack always
|
|
understood thin packs. Adding 'no-thin' later allowed receive-pack
|
|
to disable the feature in a backwards-compatible manner.
|
|
|
|
|
|
side-band, side-band-64k
|
|
------------------------
|
|
|
|
This capability means that server can send, and client understand multiplexed
|
|
progress reports and error info interleaved with the packfile itself.
|
|
|
|
These two options are mutually exclusive. A modern client always
|
|
favors 'side-band-64k'.
|
|
|
|
Either mode indicates that the packfile data will be streamed broken
|
|
up into packets of up to either 1000 bytes in the case of 'side_band',
|
|
or 65520 bytes in the case of 'side_band_64k'. Each packet is made up
|
|
of a leading 4-byte pkt-line length of how much data is in the packet,
|
|
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
|
|
|
|
The "side-band-64k" capability came about as a way for newer clients
|
|
that can handle much larger packets to request packets that are
|
|
actually crammed nearly full, while maintaining backward compatibility
|
|
for the older clients.
|
|
|
|
Further, with side-band and its up to 1000-byte messages, it's actually
|
|
999 bytes of payload and 1 byte for the stream code. With side-band-64k,
|
|
same deal, you have up to 65519 bytes of data and 1 byte for the stream
|
|
code.
|
|
|
|
The client MUST send only maximum of one of "side-band" and "side-
|
|
band-64k". Server MUST diagnose it as an error if client requests
|
|
both.
|
|
|
|
ofs-delta
|
|
---------
|
|
|
|
Server can send, and client understand PACKv2 with delta referring to
|
|
its base by position in pack rather than by an obj-id. That is, they can
|
|
send/read OBJ_OFS_DELTA (aka type 6) in a packfile.
|
|
|
|
agent
|
|
-----
|
|
|
|
The server may optionally send a capability of the form `agent=X` to
|
|
notify the client that the server is running version `X`. The client may
|
|
optionally return its own agent string by responding with an `agent=Y`
|
|
capability (but it MUST NOT do so if the server did not mention the
|
|
agent capability). The `X` and `Y` strings may contain any printable
|
|
ASCII characters except space (i.e., the byte range 32 < x < 127), and
|
|
are typically of the form "package/version" (e.g., "git/1.8.3.1"). The
|
|
agent strings are purely informative for statistics and debugging
|
|
purposes, and MUST NOT be used to programmatically assume the presence
|
|
or absence of particular features.
|
|
|
|
shallow
|
|
-------
|
|
|
|
This capability adds "deepen", "shallow" and "unshallow" commands to
|
|
the fetch-pack/upload-pack protocol so clients can request shallow
|
|
clones.
|
|
|
|
no-progress
|
|
-----------
|
|
|
|
The client was started with "git clone -q" or something, and doesn't
|
|
want that side band 2. Basically the client just says "I do not
|
|
wish to receive stream 2 on sideband, so do not send it to me, and if
|
|
you did, I will drop it on the floor anyway". However, the sideband
|
|
channel 3 is still used for error responses.
|
|
|
|
include-tag
|
|
-----------
|
|
|
|
The 'include-tag' capability is about sending annotated tags if we are
|
|
sending objects they point to. If we pack an object to the client, and
|
|
a tag object points exactly at that object, we pack the tag object too.
|
|
In general this allows a client to get all new annotated tags when it
|
|
fetches a branch, in a single network connection.
|
|
|
|
Clients MAY always send include-tag, hardcoding it into a request when
|
|
the server advertises this capability. The decision for a client to
|
|
request include-tag only has to do with the client's desires for tag
|
|
data, whether or not a server had advertised objects in the
|
|
refs/tags/* namespace.
|
|
|
|
Servers MUST pack the tags if their referrant is packed and the client
|
|
has requested include-tags.
|
|
|
|
Clients MUST be prepared for the case where a server has ignored
|
|
include-tag and has not actually sent tags in the pack. In such
|
|
cases the client SHOULD issue a subsequent fetch to acquire the tags
|
|
that include-tag would have otherwise given the client.
|
|
|
|
The server SHOULD send include-tag, if it supports it, regardless
|
|
of whether or not there are tags available.
|
|
|
|
report-status
|
|
-------------
|
|
|
|
The receive-pack process can receive a 'report-status' capability,
|
|
which tells it that the client wants a report of what happened after
|
|
a packfile upload and reference update. If the pushing client requests
|
|
this capability, after unpacking and updating references the server
|
|
will respond with whether the packfile unpacked successfully and if
|
|
each reference was updated successfully. If any of those were not
|
|
successful, it will send back an error message. See pack-protocol.txt
|
|
for example messages.
|
|
|
|
delete-refs
|
|
-----------
|
|
|
|
If the server sends back the 'delete-refs' capability, it means that
|
|
it is capable of accepting a zero-id value as the target
|
|
value of a reference update. It is not sent back by the client, it
|
|
simply informs the client that it can be sent zero-id values
|
|
to delete references.
|
|
|
|
quiet
|
|
-----
|
|
|
|
If the receive-pack server advertises the 'quiet' capability, it is
|
|
capable of silencing human-readable progress output which otherwise may
|
|
be shown when processing the received pack. A send-pack client should
|
|
respond with the 'quiet' capability to suppress server-side progress
|
|
reporting if the local progress reporting is also being suppressed
|
|
(e.g., via `push -q`, or if stderr does not go to a tty).
|
|
|
|
allow-tip-sha1-in-want
|
|
----------------------
|
|
|
|
If the upload-pack server advertises this capability, fetch-pack may
|
|
send "want" lines with SHA-1s that exist at the server but are not
|
|
advertised by upload-pack.
|
|
|
|
push-cert=<nonce>
|
|
-----------------
|
|
|
|
The receive-pack server that advertises this capability is willing
|
|
to accept a signed push certificate, and asks the <nonce> to be
|
|
included in the push certificate. A send-pack client MUST NOT
|
|
send a push-cert packet unless the receive-pack server advertises
|
|
this capability.
|