From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on dcvr.yhbt.net X-Spam-Level: X-Spam-ASN: AS31976 209.132.180.0/23 X-Spam-Status: No, score=-11.7 required=3.0 tests=AWL,BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI,USER_IN_DEF_DKIM_WL shortcircuit=no autolearn=ham autolearn_force=no version=3.4.2 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by dcvr.yhbt.net (Postfix) with ESMTP id B805720248 for ; Fri, 8 Mar 2019 21:55:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726427AbfCHVzt (ORCPT ); Fri, 8 Mar 2019 16:55:49 -0500 Received: from mail-pg1-f201.google.com ([209.85.215.201]:53630 "EHLO mail-pg1-f201.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726267AbfCHVzt (ORCPT ); Fri, 8 Mar 2019 16:55:49 -0500 Received: by mail-pg1-f201.google.com with SMTP id k198so21696366pgc.20 for ; Fri, 08 Mar 2019 13:55:48 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:in-reply-to:message-id:mime-version:references:subject:from:to :cc; bh=l60cNizw3k+R6216CyLcKW576KmjfOXpd+EXhbatOVg=; b=DFfgYn2v2cgz8mfw31cwxrMJ0ZNtlBr7+lp7cPTw7vxbCqRq32LSZ02ZVMqogR2XIO LyKrL7Ivq72nOuUddD5ncyH3qUk46wgevmKlolb4RlNQeT8VY3aSBUubyXQSgIkITaN/ gZYoEbiJ+0ApgjkxpSqdCedIRkckeLYXJ3bGlNPucXVcba30gXG8nNPLN0JdbmVwSg9O fI9faoCcjM4aKx+78E6bWN3TIwcQFhMb5C88QfZ0pKmntHS6aY0ayGyw32ARln5/fmiP nNZ2/pn41R4D7NaUgwFA/8zZo0WE4AjcujtMTa9K/es22yAWV82gT+KT7MfBDC1BgDzw bvzw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:in-reply-to:message-id:mime-version :references:subject:from:to:cc; bh=l60cNizw3k+R6216CyLcKW576KmjfOXpd+EXhbatOVg=; b=DUwPtztvdN0BxP+Hxvbt7YYqwQxBbX8mZngzU2pjX2dkldGluhInjv0Kvn6opNJjrE SogXdLMTPfwGCoPVsFWh8VQxt+69eYwWM6uiReuUPCC/0nkYhOOkYKsKImvy/0w69w0C V97BJ5SWqCass96IkA+Gpm2sC/i4tZBI6nwplWpFtmOW5VUpuZ1OJpw9xddFA6hDSJAS mb6mnsfVbPA3cf8yO+b8pPeKF7Fz7NIcq2yJK7WdLdOSmN7dCNtscCF3upwhrD10WXow myTo4iVnQ/Xs9als8z3FuRw+PX3pYarHnBVXtqfQ3mgBCVqxMbDky5wbZz0PTeTOqtE8 oAmA== X-Gm-Message-State: APjAAAWHKqonKp1i+fcyVy0st/FtUFS4TU4MuyVWZ2yIS7ZEajxgOP4i ARNyGd3L2jMeNgRxOH/YIu/wgDRF0dDstgrZRk/F X-Google-Smtp-Source: APXvYqw2w7ERBUNcAbL//4uLGQ2RoQY3Qf7wHHtOfXuYdGPQ23twJnqxujU90vQ5YmlH68gRnMnYr4F4+AlIiipuB38H X-Received: by 2002:a17:902:8643:: with SMTP id y3mr6328474plt.125.1552082148512; Fri, 08 Mar 2019 13:55:48 -0800 (PST) Date: Fri, 8 Mar 2019 13:55:17 -0800 In-Reply-To: Message-Id: <5ce56844d3fb740e29d2f3d4be2ade0b2ad5f7fd.1552073690.git.jonathantanmy@google.com> Mime-Version: 1.0 References: X-Mailer: git-send-email 2.19.0.271.gfe8321ec05.dirty Subject: [PATCH v2 5/8] Documentation: add Packfile URIs design doc From: Jonathan Tan To: avarab@gmail.com, git@vger.kernel.org Cc: Jonathan Tan , Junio C Hamano Content-Type: text/plain; charset="UTF-8" Sender: git-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org Signed-off-by: Jonathan Tan Signed-off-by: Junio C Hamano --- Documentation/technical/packfile-uri.txt | 78 ++++++++++++++++++++++++ Documentation/technical/protocol-v2.txt | 28 ++++++++- 2 files changed, 105 insertions(+), 1 deletion(-) create mode 100644 Documentation/technical/packfile-uri.txt diff --git a/Documentation/technical/packfile-uri.txt b/Documentation/technical/packfile-uri.txt new file mode 100644 index 0000000000..6a5a6440d5 --- /dev/null +++ b/Documentation/technical/packfile-uri.txt @@ -0,0 +1,78 @@ +Packfile URIs +============= + +This feature allows servers to serve part of their packfile response as URIs. +This allows server designs that improve scalability in bandwidth and CPU usage +(for example, by serving some data through a CDN), and (in the future) provides +some measure of resumability to clients. + +This feature is available only in protocol version 2. + +Protocol +-------- + +The server advertises `packfile-uris`. + +If the client then communicates which protocols (HTTPS, etc.) it supports with +a `packfile-uris` argument, the server MAY send a `packfile-uris` section +directly before the `packfile` section (right after `wanted-refs` if it is +sent) containing URIs of any of the given protocols. The URIs point to +packfiles that use only features that the client has declared that it supports +(e.g. ofs-delta and thin-pack). See protocol-v2.txt for the documentation of +this section. + +Clients then should understand that the returned packfile could be incomplete, +and that it needs to download all the given URIs before the fetch or clone is +complete. + +Server design +------------- + +The server can be trivially made compatible with the proposed protocol by +having it advertise `packfile-uris`, tolerating the client sending +`packfile-uris`, and never sending any `packfile-uris` section. But we should +include some sort of non-trivial implementation in the Minimum Viable Product, +at least so that we can test the client. + +This is the implementation: a feature, marked experimental, that allows the +server to be configured by one or more `uploadpack.blobPackfileUri= +` entries. Whenever the list of objects to be sent is assembled, a blob +with the given sha1 can be replaced by the given URI. This allows, for example, +servers to delegate serving of large blobs to CDNs. + +Client design +------------- + +While fetching, the client needs to remember the list of URIs and cannot +declare that the fetch is complete until all URIs have been downloaded as +packfiles. + +The division of work (initial fetch + additional URIs) introduces convenient +points for resumption of an interrupted clone - such resumption can be done +after the Minimum Viable Product (see "Future work"). + +The client can inhibit this feature (i.e. refrain from sending the +`packfile-uris` parameter) by passing --no-packfile-uris to `git fetch`. + +Future work +----------- + +The protocol design allows some evolution of the server and client without any +need for protocol changes, so only a small-scoped design is included here to +form the MVP. For example, the following can be done: + + * On the server, a long-running process that takes in entire requests and + outputs a list of URIs and the corresponding inclusion and exclusion sets of + objects. This allows, e.g., signed URIs to be used and packfiles for common + requests to be cached. + * On the client, resumption of clone. If a clone is interrupted, information + could be recorded in the repository's config and a "clone-resume" command + can resume the clone in progress. (Resumption of subsequent fetches is more + difficult because that must deal with the user wanting to use the repository + even after the fetch was interrupted.) + +There are some possible features that will require a change in protocol: + + * Additional HTTP headers (e.g. authentication) + * Byte range support + * Different file formats referenced by URIs (e.g. raw object) diff --git a/Documentation/technical/protocol-v2.txt b/Documentation/technical/protocol-v2.txt index 36239ec7e9..7b63c26ecd 100644 --- a/Documentation/technical/protocol-v2.txt +++ b/Documentation/technical/protocol-v2.txt @@ -323,13 +323,26 @@ included in the client's request: indicating its sideband (1, 2, or 3), and the server may send "0005\2" (a PKT-LINE of sideband 2 with no payload) as a keepalive packet. +If the 'packfile-uris' feature is advertised, the following argument +can be included in the client's request as well as the potential +addition of the 'packfile-uris' section in the server's response as +explained below. + + packfile-uris + Indicates to the server that the client is willing to receive + URIs of any of the given protocols in place of objects in the + sent packfile. Before performing the connectivity check, the + client should download from all given URIs. Currently, the + protocols supported are "http" and "https". + The response of `fetch` is broken into a number of sections separated by delimiter packets (0001), with each section beginning with its section header. Most sections are sent only when the packfile is sent. output = acknowledgements flush-pkt | [acknowledgments delim-pkt] [shallow-info delim-pkt] - [wanted-refs delim-pkt] packfile flush-pkt + [wanted-refs delim-pkt] [packfile-uris delim-pkt] + packfile flush-pkt acknowledgments = PKT-LINE("acknowledgments" LF) (nak | *ack) @@ -347,6 +360,9 @@ header. Most sections are sent only when the packfile is sent. *PKT-LINE(wanted-ref LF) wanted-ref = obj-id SP refname + packfile-uris = PKT-LINE("packfile-uris" LF) *packfile-uri + packfile-uri = PKT-LINE(40*(HEXDIGIT) SP *%x20-ff LF) + packfile = PKT-LINE("packfile" LF) *PKT-LINE(%x01-03 *%x00-ff) @@ -418,6 +434,16 @@ header. Most sections are sent only when the packfile is sent. * The server MUST NOT send any refs which were not requested using 'want-ref' lines. + packfile-uris section + * This section is only included if the client sent + 'packfile-uris' and the server has at least one such URI to + send. + + * Always begins with the section header "packfile-uris". + + * For each URI the server sends, it sends a hash of the pack's + contents (as output by git index-pack) followed by the URI. + packfile section * This section is only included if the client has sent 'want' lines in its request and either requested that no more -- 2.19.0.271.gfe8321ec05.dirty