Documentation/technical/http-protocol.txt - jrn/git - Git at Google

 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 2617.
 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 response.
 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` or
 `allow-reachable-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.

 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 response.
 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
 ----------

 http://www.ietf.org/rfc/rfc1738.txt[RFC 1738: Uniform Resource Locators (URL)]
 http://www.ietf.org/rfc/rfc2616.txt[RFC 2616: Hypertext Transfer Protocol -- HTTP/1.1]
 link:technical/pack-protocol.html
 link:technical/protocol-capabilities.html
	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 2617.
	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 response.
	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` or
	`allow-reachable-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.

	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 response.
	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
	----------

	http://www.ietf.org/rfc/rfc1738.txt[RFC 1738: Uniform Resource Locators (URL)]
	http://www.ietf.org/rfc/rfc2616.txt[RFC 2616: Hypertext Transfer Protocol -- HTTP/1.1]
	link:technical/pack-protocol.html
	link:technical/protocol-capabilities.html