// Package capability defines the server and client capabilities. package capability // 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=" 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 " 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 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" ) const DefaultAgent = "go-git/4.x" 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, } var requiresArgument = map[Capability]bool{ Agent: true, PushCert: true, SymRef: true, } var multipleArgument = map[Capability]bool{ SymRef: true, }