1 Git Protocol Capabilities
2 =========================
4 Servers SHOULD support all capabilities defined in this document.
6 On the very first line of the initial server response of either
7 receive-pack and upload-pack the first reference is followed by
8 a NUL byte and then a list of space delimited server capabilities.
9 These allow the server to declare what it can and cannot support
12 Client will then send a space separated list of capabilities it wants
13 to be in effect. The client MUST NOT ask for capabilities the server
14 did not say it supports.
16 Server MUST diagnose and abort if capabilities it does not understand
17 was sent. Server MUST NOT ignore capabilities that client requested
18 and server advertised. As a consequence of these rules, server MUST
19 NOT advertise capabilities it does not understand.
21 The 'report-status', 'delete-refs', 'quiet', and 'push-cert' capabilities
22 are sent and recognized by the receive-pack (push to server) process.
24 The 'ofs-delta' and 'side-band-64k' capabilities are sent and recognized
25 by both upload-pack and receive-pack protocols. The 'agent' capability
26 may optionally be sent in both protocols.
28 All other capabilities are only recognized by the upload-pack (fetch
34 The 'multi_ack' capability allows the server to return "ACK obj-id
35 continue" as soon as it finds a commit that it can use as a common
36 base, between the client's wants and the client's have set.
38 By sending this early, the server can potentially head off the client
39 from walking any further down that particular branch of the client's
40 repository history. The client may still need to walk down other
41 branches, sending have lines for those, until the server has a
42 complete cut across the DAG, or the client has said "done".
44 Without multi_ack, a client sends have lines in --date-order until
45 the server has found a common base. That means the client will send
46 have lines that are already known by the server to be common, because
47 they overlap in time with another branch that the server hasn't found
50 For example suppose the client has commits in caps that the server
51 doesn't and the server has commits in lower case that the client
52 doesn't, as in the following diagram:
54 +---- u ---------------------- x
57 a -- b -- c -- d -- E -- F
61 If the client wants x,y and starts out by saying have F,S, the server
62 doesn't know what F,S is. Eventually the client says "have d" and
63 the server sends "ACK d continue" to let the client know to stop
64 walking down that line (so don't send c-b-a), but it's not done yet,
65 it needs a base for x. The client keeps going with S-R-Q, until a
66 gets reached, at which point the server has a clear base and it all
69 Without multi_ack the client would have sent that c-b-a chain anyway,
70 interleaved with S-R-Q.
74 This is an extension of multi_ack that permits client to better
75 understand the server's in-memory state. See pack-protocol.txt,
76 section "Packfile Negotiation" for more information.
80 This capability should only be used with the smart HTTP protocol. If
81 multi_ack_detailed and no-done are both present, then the sender is
82 free to immediately send a pack following its first "ACK obj-id ready"
85 Without no-done in the smart HTTP protocol, the server session would
86 end and the client has to make another trip to send "done" before
87 the server can send the pack. no-done removes the last round and
88 thus slightly reduces latency.
93 A thin pack is one with deltas which reference base objects not
94 contained within the pack (but are known to exist at the receiving
95 end). This can reduce the network traffic significantly, but it
96 requires the receiving end to know how to "thicken" these packs by
97 adding the missing bases to the pack.
99 The upload-pack server advertises 'thin-pack' when it can generate
100 and send a thin pack. A client requests the 'thin-pack' capability
101 when it understands how to "thicken" it, notifying the server that
102 it can receive such a pack. A client MUST NOT request the
103 'thin-pack' capability if it cannot turn a thin pack into a
106 Receive-pack, on the other hand, is assumed by default to be able to
107 handle thin packs, but can ask the client not to use the feature by
108 advertising the 'no-thin' capability. A client MUST NOT send a thin
109 pack if the server advertises the 'no-thin' capability.
111 The reasons for this asymmetry are historical. The receive-pack
112 program did not exist until after the invention of thin packs, so
113 historically the reference implementation of receive-pack always
114 understood thin packs. Adding 'no-thin' later allowed receive-pack
115 to disable the feature in a backwards-compatible manner.
118 side-band, side-band-64k
119 ------------------------
121 This capability means that server can send, and client understand multiplexed
122 progress reports and error info interleaved with the packfile itself.
124 These two options are mutually exclusive. A modern client always
125 favors 'side-band-64k'.
127 Either mode indicates that the packfile data will be streamed broken
128 up into packets of up to either 1000 bytes in the case of 'side_band',
129 or 65520 bytes in the case of 'side_band_64k'. Each packet is made up
130 of a leading 4-byte pkt-line length of how much data is in the packet,
131 followed by a 1-byte stream code, followed by the actual data.
133 The stream code can be one of:
136 2 - progress messages
137 3 - fatal error message just before stream aborts
139 The "side-band-64k" capability came about as a way for newer clients
140 that can handle much larger packets to request packets that are
141 actually crammed nearly full, while maintaining backward compatibility
142 for the older clients.
144 Further, with side-band and its up to 1000-byte messages, it's actually
145 999 bytes of payload and 1 byte for the stream code. With side-band-64k,
146 same deal, you have up to 65519 bytes of data and 1 byte for the stream
149 The client MUST send only maximum of one of "side-band" and "side-
150 band-64k". Server MUST diagnose it as an error if client requests
156 Server can send, and client understand PACKv2 with delta referring to
157 its base by position in pack rather than by an obj-id. That is, they can
158 send/read OBJ_OFS_DELTA (aka type 6) in a packfile.
163 The server may optionally send a capability of the form `agent=X` to
164 notify the client that the server is running version `X`. The client may
165 optionally return its own agent string by responding with an `agent=Y`
166 capability (but it MUST NOT do so if the server did not mention the
167 agent capability). The `X` and `Y` strings may contain any printable
168 ASCII characters except space (i.e., the byte range 32 < x < 127), and
169 are typically of the form "package/version" (e.g., "git/1.8.3.1"). The
170 agent strings are purely informative for statistics and debugging
171 purposes, and MUST NOT be used to programmatically assume the presence
172 or absence of particular features.
177 This capability adds "deepen", "shallow" and "unshallow" commands to
178 the fetch-pack/upload-pack protocol so clients can request shallow
184 The client was started with "git clone -q" or something, and doesn't
185 want that side band 2. Basically the client just says "I do not
186 wish to receive stream 2 on sideband, so do not send it to me, and if
187 you did, I will drop it on the floor anyway". However, the sideband
188 channel 3 is still used for error responses.
193 The 'include-tag' capability is about sending annotated tags if we are
194 sending objects they point to. If we pack an object to the client, and
195 a tag object points exactly at that object, we pack the tag object too.
196 In general this allows a client to get all new annotated tags when it
197 fetches a branch, in a single network connection.
199 Clients MAY always send include-tag, hardcoding it into a request when
200 the server advertises this capability. The decision for a client to
201 request include-tag only has to do with the client's desires for tag
202 data, whether or not a server had advertised objects in the
203 refs/tags/* namespace.
205 Servers MUST pack the tags if their referrant is packed and the client
206 has requested include-tags.
208 Clients MUST be prepared for the case where a server has ignored
209 include-tag and has not actually sent tags in the pack. In such
210 cases the client SHOULD issue a subsequent fetch to acquire the tags
211 that include-tag would have otherwise given the client.
213 The server SHOULD send include-tag, if it supports it, regardless
214 of whether or not there are tags available.
219 The receive-pack process can receive a 'report-status' capability,
220 which tells it that the client wants a report of what happened after
221 a packfile upload and reference update. If the pushing client requests
222 this capability, after unpacking and updating references the server
223 will respond with whether the packfile unpacked successfully and if
224 each reference was updated successfully. If any of those were not
225 successful, it will send back an error message. See pack-protocol.txt
226 for example messages.
231 If the server sends back the 'delete-refs' capability, it means that
232 it is capable of accepting a zero-id value as the target
233 value of a reference update. It is not sent back by the client, it
234 simply informs the client that it can be sent zero-id values
235 to delete references.
240 If the receive-pack server advertises the 'quiet' capability, it is
241 capable of silencing human-readable progress output which otherwise may
242 be shown when processing the received pack. A send-pack client should
243 respond with the 'quiet' capability to suppress server-side progress
244 reporting if the local progress reporting is also being suppressed
245 (e.g., via `push -q`, or if stderr does not go to a tty).
247 allow-tip-sha1-in-want
248 ----------------------
250 If the upload-pack server advertises this capability, fetch-pack may
251 send "want" lines with SHA-1s that exist at the server but are not
252 advertised by upload-pack.
257 The receive-pack server that advertises this capability is willing
258 to accept a signed push certificate, and asks the <nonce> to be
259 included in the push certificate. A send-pack client MUST NOT
260 send a push-cert packet unless the receive-pack server advertises
projects / git / blob