// Package capability defines the server and client capabilities.
package capability
import (
"fmt"
"os"
)
// Capability describes a server or client capability.
type Capability string
func (n Capability) String() string {
return string(n)
}
const (
// MultiACK 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.
MultiACK Capability = "multi_ack"
// MultiACKDetailed is an extension of multi_ack that permits client to
// better understand the server's in-memory state.
MultiACKDetailed Capability = "multi_ack_detailed"
// NoDone 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.
NoDone Capability = "no-done"
// ThinPack 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.
ThinPack Capability = "thin-pack"
// Sideband 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 Sideband64k.
//
// 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.
Sideband Capability = "side-band"
Sideband64k Capability = "side-band-64k"
// OFSDelta 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.
OFSDelta Capability = "ofs-delta"
// Agent the server may optionally send this capability 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.
Agent Capability = "agent"
// Shallow capability adds "deepen", "shallow" and "unshallow" commands to
// the fetch-pack/upload-pack protocol so clients can request shallow
// clones.
Shallow Capability = "shallow"
// DeepenSince adds "deepen-since" command to fetch-pack/upload-pack
// protocol so the client can request shallow clones that are cut at a
// specific time, instead of depth. Internally it's equivalent of doing
// "rev-list --max-age=<timestamp>" on the server side. "deepen-since"
// cannot be used with "deepen".
DeepenSince Capability = "deepen-since"
// DeepenNot adds "deepen-not" command to fetch-pack/upload-pack
// protocol so the client can request shallow clones that are cut at a
// specific revision, instead of depth. Internally it's equivalent of
// doing "rev-list --not <rev>" on the server side. "deepen-not"
// cannot be used with "deepen", but can be used with "deepen-since".
DeepenNot Capability = "deepen-not"
// DeepenRelative if this capability is requested by the client, the
// semantics of "deepen" command is changed. The "depth" argument is the
// depth from the current shallow boundary, instead of the depth from
// remote refs.
DeepenRelative Capability = "deepen-relative"
// NoProgress 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.
NoProgress Capability = "no-progress"
// IncludeTag 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.
IncludeTag Capability = "include-tag"
// ReportStatus 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.
ReportStatus Capability = "report-status"
// DeleteRefs If the server sends back this 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
DeleteRefs Capability = "delete-refs"
// Quiet If the receive-pack server advertises this 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).
Quiet Capability = "quiet"
// Atomic If the server sends this capability it is capable of accepting
// atomic pushes. If the pushing client requests this capability, the server
// will update the refs in one atomic transaction. Either all refs are
// updated or none.
Atomic Capability = "atomic"
// PushOptions If the server sends this capability it is able to accept
// push options after the update commands have been sent, but before the
// packfile is streamed. If the pushing client requests this capability,
// the server will pass the options to the pre- and post- receive hooks
// that process this push request.
PushOptions Capability = "push-options"
// AllowTipSHA1InWant 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.
AllowTipSHA1InWant Capability = "allow-tip-sha1-in-want"
// AllowReachableSHA1InWant 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.
AllowReachableSHA1InWant Capability = "allow-reachable-sha1-in-want"
// PushCert 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.
PushCert Capability = "push-cert"
// SymRef symbolic reference support for better negotiation.
SymRef Capability = "symref"
// ObjectFormat takes a hash algorithm as an argument, indicates that the
// server supports the given hash algorithms.
ObjectFormat Capability = "object-format"
// Filter if present, fetch-pack may send "filter" commands to request a
// partial clone or partial fetch and request that the server omit various objects from the packfile
Filter Capability = "filter"
)
const userAgent = "go-git/5.x"
// DefaultAgent provides the user agent string.
func DefaultAgent() string {
if envUserAgent, ok := os.LookupEnv("GO_GIT_USER_AGENT_EXTRA"); ok {
return fmt.Sprintf("%s %s", userAgent, envUserAgent)
}
return userAgent
}
var known = map[Capability]bool{
MultiACK: true, MultiACKDetailed: true, NoDone: true, ThinPack: true,
Sideband: true, Sideband64k: true, OFSDelta: true, Agent: true,
Shallow: true, DeepenSince: true, DeepenNot: true, DeepenRelative: true,
NoProgress: true, IncludeTag: true, ReportStatus: true, DeleteRefs: true,
Quiet: true, Atomic: true, PushOptions: true, AllowTipSHA1InWant: true,
AllowReachableSHA1InWant: true, PushCert: true, SymRef: true,
ObjectFormat: true, Filter: true,
}
var requiresArgument = map[Capability]bool{
Agent: true, PushCert: true, SymRef: true, ObjectFormat: true,
}
var multipleArgument = map[Capability]bool{
SymRef: true,
}
