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Diffstat (limited to 'Documentation/technical')
| -rw-r--r-- | Documentation/technical/http-protocol.txt | 503 |
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diff --git a/Documentation/technical/http-protocol.txt b/Documentation/technical/http-protocol.txt new file mode 100644 index 0000000000..a1173ee266 --- /dev/null +++ b/Documentation/technical/http-protocol.txt @@ -0,0 +1,503 @@ +HTTP transfer protocols +======================= + +Git supports two HTTP based transfer protocols. A "dumb" protocol +which requires only a standard HTTP server on the server end of the +connection, and a "smart" protocol which requires a Git aware CGI +(or server module). This document describes both protocols. + +As a design feature smart clients can automatically upgrade "dumb" +protocol URLs to smart URLs. This permits all users to have the +same published URL, and the peers automatically select the most +efficient transport available to them. + + +URL Format +---------- + +URLs for Git repositories accessed by HTTP use the standard HTTP +URL syntax documented by RFC 1738, so they are of the form: + + http://<host>:<port>/<path>?<searchpart> + +Within this documentation the placeholder $GIT_URL will stand for +the http:// repository URL entered by the end-user. + +Servers SHOULD handle all requests to locations matching $GIT_URL, as +both the "smart" and "dumb" HTTP protocols used by Git operate +by appending additional path components onto the end of the user +supplied $GIT_URL string. + +An example of a dumb client requesting for a loose object: + + $GIT_URL: http://example.com:8080/git/repo.git + URL request: http://example.com:8080/git/repo.git/objects/d0/49f6c27a2244e12041955e262a404c7faba355 + +An example of a smart request to a catch-all gateway: + + $GIT_URL: http://example.com/daemon.cgi?svc=git&q= + URL request: http://example.com/daemon.cgi?svc=git&q=/info/refs&service=git-receive-pack + +An example of a request to a submodule: + + $GIT_URL: http://example.com/git/repo.git/path/submodule.git + URL request: http://example.com/git/repo.git/path/submodule.git/info/refs + +Clients MUST strip a trailing '/', if present, from the user supplied +$GIT_URL string to prevent empty path tokens ('//') from appearing +in any URL sent to a server. Compatible clients MUST expand +'$GIT_URL/info/refs' as 'foo/info/refs' and not 'foo//info/refs'. + + +Authentication +-------------- + +Standard HTTP authentication is used if authentication is required +to access a repository, and MAY be configured and enforced by the +HTTP server software. + +Because Git repositories are accessed by standard path components +server administrators MAY use directory based permissions within +their HTTP server to control repository access. + +Clients SHOULD support Basic authentication as described by RFC 2616. +Servers SHOULD support Basic authentication by relying upon the +HTTP server placed in front of the Git server software. + +Servers SHOULD NOT require HTTP cookies for the purposes of +authentication or access control. + +Clients and servers MAY support other common forms of HTTP based +authentication, such as Digest authentication. + + +SSL +--- + +Clients and servers SHOULD support SSL, particularly to protect +passwords when relying on Basic HTTP authentication. + + +Session State +------------- + +The Git over HTTP protocol (much like HTTP itself) is stateless +from the perspective of the HTTP server side. All state MUST be +retained and managed by the client process. This permits simple +round-robin load-balancing on the server side, without needing to +worry about state management. + +Clients MUST NOT require state management on the server side in +order to function correctly. + +Servers MUST NOT require HTTP cookies in order to function correctly. +Clients MAY store and forward HTTP cookies during request processing +as described by RFC 2616 (HTTP/1.1). Servers SHOULD ignore any +cookies sent by a client. + + +General Request Processing +-------------------------- + +Except where noted, all standard HTTP behavior SHOULD be assumed +by both client and server. This includes (but is not necessarily +limited to): + +If there is no repository at $GIT_URL, or the resource pointed to by a +location matching $GIT_URL does not exist, the server MUST NOT respond +with '200 OK' response. A server SHOULD respond with +'404 Not Found', '410 Gone', or any other suitable HTTP status code +which does not imply the resource exists as requested. + +If there is a repository at $GIT_URL, but access is not currently +permitted, the server MUST respond with the '403 Forbidden' HTTP +status code. + +Servers SHOULD support both HTTP 1.0 and HTTP 1.1. +Servers SHOULD support chunked encoding for both request and response +bodies. + +Clients SHOULD support both HTTP 1.0 and HTTP 1.1. +Clients SHOULD support chunked encoding for both request and response +bodies. + +Servers MAY return ETag and/or Last-Modified headers. + +Clients MAY revalidate cached entities by including If-Modified-Since +and/or If-None-Match request headers. + +Servers MAY return '304 Not Modified' if the relevant headers appear +in the request and the entity has not changed. Clients MUST treat +'304 Not Modified' identical to '200 OK' by reusing the cached entity. + +Clients MAY reuse a cached entity without revalidation if the +Cache-Control and/or Expires header permits caching. Clients and +servers MUST follow RFC 2616 for cache controls. + + +Discovering References +---------------------- + +All HTTP clients MUST begin either a fetch or a push exchange by +discovering the references available on the remote repository. + +Dumb Clients +~~~~~~~~~~~~ + +HTTP clients that only support the "dumb" protocol MUST discover +references by making a request for the special info/refs file of +the repository. + +Dumb HTTP clients MUST make a GET request to $GIT_URL/info/refs, +without any search/query parameters. + + C: GET $GIT_URL/info/refs HTTP/1.0 + + S: 200 OK + S: + S: 95dcfa3633004da0049d3d0fa03f80589cbcaf31 refs/heads/maint + S: d049f6c27a2244e12041955e262a404c7faba355 refs/heads/master + S: 2cb58b79488a98d2721cea644875a8dd0026b115 refs/tags/v1.0 + S: a3c2e2402b99163d1d59756e5f207ae21cccba4c refs/tags/v1.0^{} + +The Content-Type of the returned info/refs entity SHOULD be +"text/plain; charset=utf-8", but MAY be any content type. +Clients MUST NOT attempt to validate the returned Content-Type. +Dumb servers MUST NOT return a return type starting with +"application/x-git-". + +Cache-Control headers MAY be returned to disable caching of the +returned entity. + +When examining the response clients SHOULD only examine the HTTP +status code. Valid responses are '200 OK', or '304 Not Modified'. + +The returned content is a UNIX formatted text file describing +each ref and its known value. The file SHOULD be sorted by name +according to the C locale ordering. The file SHOULD NOT include +the default ref named 'HEAD'. + + info_refs = *( ref_record ) + ref_record = any_ref / peeled_ref + + any_ref = obj-id HTAB refname LF + peeled_ref = obj-id HTAB refname LF + obj-id HTAB refname "^{}" LF + +Smart Clients +~~~~~~~~~~~~~ + +HTTP clients that support the "smart" protocol (or both the +"smart" and "dumb" protocols) MUST discover references by making +a parameterized request for the info/refs file of the repository. + +The request MUST contain exactly one query parameter, +'service=$servicename', where $servicename MUST be the service +name the client wishes to contact to complete the operation. +The request MUST NOT contain additional query parameters. + + C: GET $GIT_URL/info/refs?service=git-upload-pack HTTP/1.0 + + dumb server reply: + S: 200 OK + S: + S: 95dcfa3633004da0049d3d0fa03f80589cbcaf31 refs/heads/maint + S: d049f6c27a2244e12041955e262a404c7faba355 refs/heads/master + S: 2cb58b79488a98d2721cea644875a8dd0026b115 refs/tags/v1.0 + S: a3c2e2402b99163d1d59756e5f207ae21cccba4c refs/tags/v1.0^{} + + smart server reply: + S: 200 OK + S: Content-Type: application/x-git-upload-pack-advertisement + S: Cache-Control: no-cache + S: + S: 001e# service=git-upload-pack\n + S: 004895dcfa3633004da0049d3d0fa03f80589cbcaf31 refs/heads/maint\0multi_ack\n + S: 0042d049f6c27a2244e12041955e262a404c7faba355 refs/heads/master\n + S: 003c2cb58b79488a98d2721cea644875a8dd0026b115 refs/tags/v1.0\n + S: 003fa3c2e2402b99163d1d59756e5f207ae21cccba4c refs/tags/v1.0^{}\n + +Dumb Server Response +^^^^^^^^^^^^^^^^^^^^ +Dumb servers MUST respond with the dumb server reply format. + +See the prior section under dumb clients for a more detailed +description of the dumb server response. + +Smart Server Response +^^^^^^^^^^^^^^^^^^^^^ +If the server does not recognize the requested service name, or the +requested service name has been disabled by the server administrator, +the server MUST respond with the '403 Forbidden' HTTP status code. + +Otherwise, smart servers MUST respond with the smart server reply +format for the requested service name. + +Cache-Control headers SHOULD be used to disable caching of the +returned entity. + +The Content-Type MUST be 'application/x-$servicename-advertisement'. +Clients SHOULD fall back to the dumb protocol if another content +type is returned. When falling back to the dumb protocol clients +SHOULD NOT make an additional request to $GIT_URL/info/refs, but +instead SHOULD use the response already in hand. Clients MUST NOT +continue if they do not support the dumb protocol. + +Clients MUST validate the status code is either '200 OK' or +'304 Not Modified'. + +Clients MUST validate the first five bytes of the response entity +matches the regex "^[0-9a-f]{4}#". If this test fails, clients +MUST NOT continue. + +Clients MUST parse the entire response as a sequence of pkt-line +records. + +Clients MUST verify the first pkt-line is "# service=$servicename". +Servers MUST set $servicename to be the request parameter value. +Servers SHOULD include an LF at the end of this line. +Clients MUST ignore an LF at the end of the line. + +Servers MUST terminate the response with the magic "0000" end +pkt-line marker. + +The returned response is a pkt-line stream describing each ref and +its known value. The stream SHOULD be sorted by name according to +the C locale ordering. The stream SHOULD include the default ref +named 'HEAD' as the first ref. The stream MUST include capability +declarations behind a NUL on the first ref. + + smart_reply = PKT-LINE("# service=$servicename" LF) + ref_list + "0000" + ref_list = empty_list / non_empty_list + + empty_list = PKT-LINE(zero-id SP "capabilities^{}" NUL cap-list LF) + + non_empty_list = PKT-LINE(obj-id SP name NUL cap_list LF) + *ref_record + + cap-list = capability *(SP capability) + capability = 1*(LC_ALPHA / DIGIT / "-" / "_") + LC_ALPHA = %x61-7A + + ref_record = any_ref / peeled_ref + any_ref = PKT-LINE(obj-id SP name LF) + peeled_ref = PKT-LINE(obj-id SP name LF) + PKT-LINE(obj-id SP name "^{}" LF + +Smart Service git-upload-pack +------------------------------ +This service reads from the repository pointed to by $GIT_URL. + +Clients MUST first perform ref discovery with +'$GIT_URL/info/refs?service=git-upload-pack'. + + C: POST $GIT_URL/git-upload-pack HTTP/1.0 + C: Content-Type: application/x-git-upload-pack-request + C: + C: 0032want 0a53e9ddeaddad63ad106860237bbf53411d11a7\n + C: 0032have 441b40d833fdfa93eb2908e52742248faf0ee993\n + C: 0000 + + S: 200 OK + S: Content-Type: application/x-git-upload-pack-result + S: Cache-Control: no-cache + S: + S: ....ACK %s, continue + S: ....NAK + +Clients MUST NOT reuse or revalidate a cached reponse. +Servers MUST include sufficient Cache-Control headers +to prevent caching of the response. + +Servers SHOULD support all capabilities defined here. + +Clients MUST send at least one 'want' command in the request body. +Clients MUST NOT reference an id in a 'want' command which did not +appear in the response obtained through ref discovery unless the +server advertises capability "allow-tip-sha1-in-want". + + compute_request = want_list + have_list + request_end + request_end = "0000" / "done" + + want_list = PKT-LINE(want NUL cap_list LF) + *(want_pkt) + want_pkt = PKT-LINE(want LF) + want = "want" SP id + cap_list = *(SP capability) SP + + have_list = *PKT-LINE("have" SP id LF) + +TODO: Document this further. +TODO: Don't use uppercase for variable names below. + +The Negotiation Algorithm +~~~~~~~~~~~~~~~~~~~~~~~~~ +The computation to select the minimal pack proceeds as follows +(c = client, s = server): + + init step: + (c) Use ref discovery to obtain the advertised refs. + (c) Place any object seen into set ADVERTISED. + + (c) Build an empty set, COMMON, to hold the objects that are later + determined to be on both ends. + (c) Build a set, WANT, of the objects from ADVERTISED the client + wants to fetch, based on what it saw during ref discovery. + + (c) Start a queue, C_PENDING, ordered by commit time (popping newest + first). Add all client refs. When a commit is popped from + the queue its parents SHOULD be automatically inserted back. + Commits MUST only enter the queue once. + + one compute step: + (c) Send one $GIT_URL/git-upload-pack request: + + C: 0032want <WANT #1>............................... + C: 0032want <WANT #2>............................... + .... + C: 0032have <COMMON #1>............................. + C: 0032have <COMMON #2>............................. + .... + C: 0032have <HAVE #1>............................... + C: 0032have <HAVE #2>............................... + .... + C: 0000 + + The stream is organized into "commands", with each command + appearing by itself in a pkt-line. Within a command line + the text leading up to the first space is the command name, + and the remainder of the line to the first LF is the value. + Command lines are terminated with an LF as the last byte of + the pkt-line value. + + Commands MUST appear in the following order, if they appear + at all in the request stream: + + * want + * have + + The stream is terminated by a pkt-line flush ("0000"). + + A single "want" or "have" command MUST have one hex formatted + SHA-1 as its value. Multiple SHA-1s MUST be sent by sending + multiple commands. + + The HAVE list is created by popping the first 32 commits + from C_PENDING. Less can be supplied if C_PENDING empties. + + If the client has sent 256 HAVE commits and has not yet + received one of those back from S_COMMON, or the client has + emptied C_PENDING it SHOULD include a "done" command to let + the server know it won't proceed: + + C: 0009done + + (s) Parse the git-upload-pack request: + + Verify all objects in WANT are directly reachable from refs. + + The server MAY walk backwards through history or through + the reflog to permit slightly stale requests. + + If no WANT objects are received, send an error: + +TODO: Define error if no want lines are requested. + + If any WANT object is not reachable, send an error: + +TODO: Define error if an invalid want is requested. + + Create an empty list, S_COMMON. + + If 'have' was sent: + + Loop through the objects in the order supplied by the client. + For each object, if the server has the object reachable from + a ref, add it to S_COMMON. If a commit is added to S_COMMON, + do not add any ancestors, even if they also appear in HAVE. + + (s) Send the git-upload-pack response: + + If the server has found a closed set of objects to pack or the + request ends with "done", it replies with the pack. + +TODO: Document the pack based response + S: PACK... + + The returned stream is the side-band-64k protocol supported + by the git-upload-pack service, and the pack is embedded into + stream 1. Progress messages from the server side MAY appear + in stream 2. + + Here a "closed set of objects" is defined to have at least + one path from every WANT to at least one COMMON object. + + If the server needs more information, it replies with a + status continue response: + +TODO: Document the non-pack response + + (c) Parse the upload-pack response: + +TODO: Document parsing response + + Do another compute step. + + +Smart Service git-receive-pack +------------------------------ +This service reads from the repository pointed to by $GIT_URL. + +Clients MUST first perform ref discovery with +'$GIT_URL/info/refs?service=git-receive-pack'. + + C: POST $GIT_URL/git-receive-pack HTTP/1.0 + C: Content-Type: application/x-git-receive-pack-request + C: + C: ....0a53e9ddeaddad63ad106860237bbf53411d11a7 441b40d833fdfa93eb2908e52742248faf0ee993 refs/heads/maint\0 report-status + C: 0000 + C: PACK.... + + S: 200 OK + S: Content-Type: application/x-git-receive-pack-result + S: Cache-Control: no-cache + S: + S: .... + +Clients MUST NOT reuse or revalidate a cached reponse. +Servers MUST include sufficient Cache-Control headers +to prevent caching of the response. + +Servers SHOULD support all capabilities defined here. + +Clients MUST send at least one command in the request body. +Within the command portion of the request body clients SHOULD send +the id obtained through ref discovery as old_id. + + update_request = command_list + "PACK" <binary data> + + command_list = PKT-LINE(command NUL cap_list LF) + *(command_pkt) + command_pkt = PKT-LINE(command LF) + cap_list = *(SP capability) SP + + command = create / delete / update + create = zero-id SP new_id SP name + delete = old_id SP zero-id SP name + update = old_id SP new_id SP name + +TODO: Document this further. + + +References +---------- + +link:http://www.ietf.org/rfc/rfc1738.txt[RFC 1738: Uniform Resource Locators (URL)] +link:http://www.ietf.org/rfc/rfc2616.txt[RFC 2616: Hypertext Transfer Protocol -- HTTP/1.1] +link:technical/pack-protocol.txt +link:technical/protocol-capabilities.txt |