and server advertised. As a consequence of these rules, server MUST
NOT advertise capabilities it does not understand.
-The 'report-status' and 'delete-refs' capabilities are sent and
+The 'report-status', 'delete-refs', and 'quiet' 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.
+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.
thin-pack
---------
-This capability means that the server can send a 'thin' pack, a pack
-which does not contain base objects; if those base objects are available
-on client side. Client requests 'thin-pack' capability when it
-understands how to "thicken" it by adding required delta bases making
-it self-contained.
+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.
-Client MUST NOT request 'thin-pack' capability if it cannot turn a thin
-pack into a self-contained 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
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 programatically assume the presence
+or absence of particular features.
+
shallow
-------
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.