import: Add github-updater.

* guix/import/github.scm: New file.
* guix/scripts/refresh.scm (%updaters): Add %GITHUB-UPDATER.
* doc/guix.texi (Invoking guix refresh): Mention it.
* Makefile.am (MODULES): Add gnu/import/github.scm.

4 files changed, 216 insertions, 1 deletions

diff --git a/Makefile.am b/Makefile.am
index 01d7fbecb7..4c53779aaa 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -109,6 +109,7 @@ MODULES =					\
   guix/import/cran.scm				\
   guix/import/hackage.scm			\
   guix/import/elpa.scm   			\
+  guix/import/github.scm   			\
   guix/scripts.scm				\
   guix/scripts/download.scm			\
   guix/scripts/build.scm			\
diff --git a/doc/guix.texi b/doc/guix.texi
index c111b0ffbf..4c9a91b399 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -17,6 +17,7 @@ Copyright @copyright{} 2015 Mathieu Lirzin@*
 Copyright @copyright{} 2014 Pierre-Antoine Rault@*
 Copyright @copyright{} 2015 Taylan Ulrich Bayırlı/Kammer@*
 Copyright @copyright{} 2015, 2016 Leo Famulari
+Copyright @copyright{} 2016 Ben Woodcroft
 
 Permission is granted to copy, distribute and/or modify this document
 under the terms of the GNU Free Documentation License, Version 1.3 or
@@ -4660,6 +4661,8 @@ the updater for @uref{http://www.bioconductor.org/, Bioconductor} R packages;
 the updater for @uref{https://pypi.python.org, PyPI} packages.
 @item gem
 the updater for @uref{https://rubygems.org, RubyGems} packages.
+@item github
+the updater for @uref{https://github.com, GitHub} packages.
 @end table
 
 For instance, the following command only checks for updates of Emacs
@@ -4746,6 +4749,18 @@ Use @var{host} as the OpenPGP key server when importing a public key.
 
 @end table
 
+The @code{github} updater uses the
+@uref{https://developer.github.com/v3/, GitHub API} to query for new
+releases.  When used repeatedly e.g. when refreshing all packages,
+GitHub will eventually refuse to answer any further API requests.  By
+default 60 API requests per hour are allowed, and a full refresh on all
+GitHub packages in Guix requires more than this.  Authentication with
+GitHub through the use of an API token alleviates these limits.  To use
+an API token, set the environment variable @code{GUIX_GITHUB_TOKEN} to a
+token procured from @uref{https://github.com/settings/tokens} or
+otherwise.
+
+
 @node Invoking guix lint
 @section Invoking @command{guix lint}
 The @command{guix lint} command is meant to help package developers avoid
diff --git a/guix/import/github.scm b/guix/import/github.scm
new file mode 100644
index 0000000000..c696dcb363
--- /dev/null
+++ b/guix/import/github.scm
@@ -0,0 +1,198 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2016 Ben Woodcroft <donttrustben@gmail.com>
+;;;
+;;; This file is part of GNU Guix.
+;;;
+;;; GNU Guix is free software; you can redistribute it and/or modify it
+;;; under the terms of the GNU General Public License as published by
+;;; the Free Software Foundation; either version 3 of the License, or (at
+;;; your option) any later version.
+;;;
+;;; GNU Guix is distributed in the hope that it will be useful, but
+;;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;;; GNU General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.
+
+(define-module (guix import github)
+  #:use-module (ice-9 match)
+  #:use-module (srfi srfi-1)
+  #:use-module (json)
+  #:use-module (guix utils)
+  #:use-module ((guix download) #:prefix download:)
+  #:use-module (guix import utils)
+  #:use-module (guix packages)
+  #:use-module (guix upstream)
+  #:use-module (gnu packages)
+  #:use-module (web uri)
+  #:export (%github-updater))
+
+(define (json-fetch* url)
+  "Return a list/hash representation of the JSON resource URL, or #f on
+failure."
+  (call-with-output-file "/dev/null"
+    (lambda (null)
+      (with-error-to-port null
+        (lambda ()
+          (call-with-temporary-output-file
+           (lambda (temp port)
+             (and (url-fetch url temp)
+                  (call-with-input-file temp json->scm)))))))))
+
+(define (find-extension url)
+  "Return the extension of the archive e.g. '.tar.gz' given a URL, or
+false if none is recognized"
+  (find (lambda x (string-suffix? (first x) url))
+        (list ".tar.gz" ".tar.bz2" ".tar.xz" ".zip" ".tar")))
+
+(define (updated-github-url old-package new-version)
+  ;; Return a url for the OLD-PACKAGE with NEW-VERSION.  If no source url in
+  ;; the OLD-PACKAGE is a GitHub url, then return false.
+
+  (define (updated-url url)
+    (if (string-prefix? "https://github.com/" url)
+        (let ((ext     (find-extension url))
+              (name    (package-name old-package))
+              (version (package-version old-package))
+              (prefix  (string-append "https://github.com/"
+                                      (github-user-slash-repository url)))
+              (repo    (github-repository url)))
+          (cond
+           ((string-suffix? (string-append "/tarball/v" version) url)
+            (string-append prefix "/tarball/v" new-version))
+           ((string-suffix? (string-append "/tarball/" version) url)
+            (string-append prefix "/tarball/" new-version))
+           ((string-suffix? (string-append "/archive/v" version ext) url)
+            (string-append prefix "/archive/v" new-version ext))
+           ((string-suffix? (string-append "/archive/" version ext) url)
+            (string-append prefix "/archive/" new-version ext))
+           ((string-suffix? (string-append "/archive/" name "-" version ext)
+                            url)
+            (string-append prefix "/archive/" name "-" new-version ext))
+           ((string-suffix? (string-append "/releases/download/v" version "/"
+                                           name "-" version ext)
+                            url)
+            (string-append prefix "/releases/download/v" new-version "/" name
+                           "-" new-version ext))
+           ((string-suffix? (string-append "/releases/download/" version "/"
+                                           name "-" version ext)
+                            url)
+            (string-append prefix "/releases/download/" new-version "/" name
+                           "-" new-version ext))
+           ((string-suffix? (string-append "/releases/download/" version "/"
+                                           repo "-" version ext)
+                            url)
+            (string-append prefix "/releases/download/" new-version "/" repo
+                           "-" new-version ext))
+           ((string-suffix? (string-append "/releases/download/" repo "-"
+                                           version "/" repo "-" version ext)
+                            url)
+            (string-append "/releases/download/" repo "-" version "/" repo "-"
+                           version ext))
+           (#t #f))) ; Some URLs are not recognised.
+        #f))
+
+  (let ((source-url (and=> (package-source old-package) origin-uri))
+        (fetch-method (and=> (package-source old-package) origin-method)))
+    (if (eq? fetch-method download:url-fetch)
+        (match source-url
+          ((? string?)
+           (updated-url source-url))
+          ((source-url ...)
+           (find updated-url source-url)))
+        #f)))
+
+(define (github-package? package)
+  "Return true if PACKAGE is a package from GitHub, else false."
+  (not (eq? #f (updated-github-url package "dummy"))))
+
+(define (github-repository url)
+  "Return a string e.g. bedtools2 of the name of the repository, from a string
+URL of the form 'https://github.com/arq5x/bedtools2/archive/v2.24.0.tar.gz'"
+  (match (string-split (uri-path (string->uri url)) #\/)
+    ((_ owner project . rest)
+     (string-append project))))
+
+(define (github-user-slash-repository url)
+  "Return a string e.g. arq5x/bedtools2 of the owner and the name of the
+repository separated by a forward slash, from a string URL of the form
+'https://github.com/arq5x/bedtools2/archive/v2.24.0.tar.gz'"
+  (match (string-split (uri-path (string->uri url)) #\/)
+    ((_ owner project . rest)
+     (string-append owner "/" project))))
+
+(define %github-token
+  ;; Token to be passed to Github.com to avoid the 60-request per hour
+  ;; limit, or #f.
+  (make-parameter (getenv "GUIX_GITHUB_TOKEN")))
+
+(define (latest-released-version url package-name)
+  "Return a string of the newest released version name given a string URL like
+'https://github.com/arq5x/bedtools2/archive/v2.24.0.tar.gz' and the name of
+the package e.g. 'bedtools2'.  Return #f if there is no releases"
+  (let* ((token (%github-token))
+         (api-url (string-append
+                   "https://api.github.com/repos/"
+                   (github-user-slash-repository url)
+                   "/releases"))
+         (json (json-fetch*
+                (if token
+                    (string-append api-url "?access_token=" token)
+                    api-url))))
+    (if (eq? json #f)
+        (if token
+            (error "Error downloading release information through the GitHub
+API when using a GitHub token")
+            (error "Error downloading release information through the GitHub
+API. This may be fixed by using an access token and setting the environment
+variable GUIX_GITHUB_TOKEN, for instance one procured from
+https://github.com/settings/tokens"))
+        (let ((proper-releases
+               (filter
+                (lambda (x)
+                  ;; example pre-release:
+                  ;; https://github.com/wwood/OrfM/releases/tag/v0.5.1
+                  ;; or an all-prerelease set
+                  ;; https://github.com/powertab/powertabeditor/releases
+                  (not (hash-ref x "prerelease")))
+                json)))
+          (match proper-releases
+            (()                       ;empty release list
+             #f)
+            ((release . rest)         ;one or more releases
+             (let ((tag (hash-ref release "tag_name"))
+                   (name-length (string-length package-name)))
+               ;; some tags include the name of the package e.g. "fdupes-1.51"
+               ;; so remove these
+               (if (and (< name-length (string-length tag))
+                        (string=? (string-append package-name "-")
+                                  (substring tag 0 (+ name-length 1))))
+                   (substring tag (+ name-length 1))
+                   ;; some tags start with a "v" e.g. "v0.25.0"
+                   ;; where some are just the version number
+                   (if (eq? (string-ref tag 0) #\v)
+                       (substring tag 1) tag)))))))))
+
+(define (latest-release guix-package)
+  "Return an <upstream-source> for the latest release of GUIX-PACKAGE."
+  (let* ((pkg (specification->package guix-package))
+         (source-uri (origin-uri (package-source pkg)))
+         (name (package-name pkg))
+         (newest-version (latest-released-version source-uri name)))
+    (if newest-version
+        (upstream-source
+         (package pkg)
+         (version newest-version)
+         (urls (list (updated-github-url pkg newest-version))))
+        #f))) ; On GitHub but no proper releases
+
+(define %github-updater
+  (upstream-updater
+   (name 'github)
+   (description "Updater for GitHub packages")
+   (pred github-package?)
+   (latest latest-release)))
+
+
diff --git a/guix/scripts/refresh.scm b/guix/scripts/refresh.scm
index bbc3521f11..e541138682 100644
--- a/guix/scripts/refresh.scm
+++ b/guix/scripts/refresh.scm
@@ -199,7 +199,8 @@ unavailable optional dependencies such as Guile-JSON."
                  %cran-updater
                  %bioconductor-updater
                  ((guix import pypi) => %pypi-updater)
-                 ((guix import gem) => %gem-updater)))
+                 ((guix import gem) => %gem-updater)
+                 ((guix import github) => %github-updater)))
 
 (define (lookup-updater name)
   "Return the updater called NAME."