build: download code from github using archive API

A new python script scripts/download.py is added to fetch tarballs using
GitHub archive API [1], then repack in a reproducible way same as the
current DownloadMethod/git

GitHub imposes a 60 reqs/hour rate limit on unauthenticated API
access[2].  This affects fetching commit date for feeding tar --mtime=
argument.  However, observation indicates that archive download is NOT
subject to this limit at the moment.  In the rare cases where download
fails because of this, we will falback to using DownloadMethod/git

The missing piece in the GitHub API is that it cannot provide in the
tarball dependent submodules's source code.  In that case, the
implementation will also fallback to using DownloadMethod/git

 [1] Get archive link, https://developer.github.com/v3/repos/contents/#get-archive-link
 [2] Rate limiting, https://developer.github.com/v3/#rate-limiting

v2 <- v1:

 - allow passing multiple urls with --urls argument
 - add commit ts cache.  can be helpful on retry

Signed-off-by: Yousong Zhou <yszhou4tech@gmail.com>

2 files changed, 464 insertions, 31 deletions

diff --git a/include/download.mk b/include/download.mk
index 2ba8a7bdf4..91a22c2316 100644
--- a/include/download.mk
+++ b/include/download.mk
@@ -21,23 +21,7 @@ DOWNLOAD_RDEP=$(STAMP_PREPARED) $(HOST_STAMP_PREPARED)
 
 # Try to guess the download method from the URL
 define dl_method
-$(strip \
-  $(if $(2),$(2), \
-    $(if $(filter @APACHE/% @GITHUB/% @GNOME/% @GNU/% @KERNEL/% @SF/% @SAVANNAH/% ftp://% http://% https://% file://%,$(1)),default, \
-      $(if $(filter git://%,$(1)),git, \
-        $(if $(filter svn://%,$(1)),svn, \
-          $(if $(filter cvs://%,$(1)),cvs, \
-            $(if $(filter hg://%,$(1)),hg, \
-              $(if $(filter sftp://%,$(1)),bzr, \
-                unknown \
-              ) \
-            ) \
-          ) \
-        ) \
-      ) \
-    ) \
-  ) \
-)
+$(shell $(SCRIPT_DIR)/download.py dl_method --url $(foreach url,$(1),"$(url)") --proto="$(2)")
 endef
 
 # code for creating tarballs from cvs/svn/git/bzr/hg/darcs checkouts - useful for mirror support
@@ -56,6 +40,10 @@ ifdef CHECK
 check_escape=$(subst ','\'',$(1))
 #')
 
+# $(1): suffix of the F_, C_ variables, e.g. hash_deprecated, hash_mismatch, etc.
+# $(2): filename
+# $(3): expected hash value
+# $(4): hash var name: MD5SUM, HASH
 check_warn_nofix = $(info $(shell printf "$(_R)WARNING: %s$(_N)" '$(call check_escape,$(call C_$(1),$(2),$(3),$(4)))'))
 ifndef FIXUP
   check_warn = $(check_warn_nofix)
@@ -71,6 +59,9 @@ F_hash_mismatch = $(F_hash_deprecated)
 F_hash_missing = $(SCRIPT_DIR)/fixup-makefile.pl $(CURDIR)/Makefile add-hash $(3) $(call gen_sha256sum,$(1))
 endif
 
+# $(1): filename
+# $(2): expected hash value
+# $(3): hash var name: MD5SUM, HASH
 C_download_missing = $(1) is missing, please run make download before re-running this check
 C_hash_mismatch = $(3) does not match $(1) hash $(call gen_sha256sum,$(1))
 C_hash_deprecated = $(3) uses deprecated hash, set to $(call gen_sha256sum,$(1))
@@ -116,6 +107,9 @@ define DownloadMethod/default
 	)
 endef
 
+# $(1): "check"
+# $(2): "PKG_" if <name> as in Download/<name> is "default", otherwise "Download/<name>:"
+# $(3): shell command sequence to do the download
 define wrap_mirror
 $(if $(if $(MIRROR),$(filter-out x,$(MIRROR_HASH))),$(SCRIPT_DIR)/download.pl "$(DL_DIR)" "$(FILE)" "$(MIRROR_HASH)" "" || ( $(3) ),$(3)) \
 $(if $(filter check,$(1)), \
@@ -159,23 +153,41 @@ endef
 
 define DownloadMethod/git
 	$(call wrap_mirror,$(1),$(2), \
-		echo "Checking out files from the git repository..."; \
-		mkdir -p $(TMP_DIR)/dl && \
-		cd $(TMP_DIR)/dl && \
-		rm -rf $(SUBDIR) && \
-		[ \! -d $(SUBDIR) ] && \
-		git clone $(OPTS) $(URL) $(SUBDIR) && \
-		(cd $(SUBDIR) && git checkout $(VERSION) && \
-		git submodule update --init --recursive) && \
-		echo "Packing checkout..." && \
-		export TAR_TIMESTAMP=`cd $(SUBDIR) && git log -1 --format='@%ct'` && \
-		rm -rf $(SUBDIR)/.git && \
-		$(call dl_tar_pack,$(TMP_DIR)/dl/$(FILE),$(SUBDIR)) && \
-		mv $(TMP_DIR)/dl/$(FILE) $(DL_DIR)/ && \
-		rm -rf $(SUBDIR); \
+		$(call DownloadMethod/git-raw) \
 	)
 endef
 
+define DownloadMethod/github-tarball
+	$(call wrap_mirror,$(1),$(2), \
+		$(SCRIPT_DIR)/download.py dl \
+			--dl-dir="$(DL_DIR)" \
+			--url $(foreach url,$(URL),"$(url)") \
+			--proto="$(PROTO)" \
+			--version="$(VERSION)" \
+			--subdir="$(SUBDIR)" \
+			--source="$(FILE)" \
+		|| ( $(call DownloadMethod/git-raw) ); \
+	)
+endef
+
+# Only intends to be called as a submethod from other DownloadMethod
+define DownloadMethod/git-raw
+	echo "Checking out files from the git repository..."; \
+	mkdir -p $(TMP_DIR)/dl && \
+	cd $(TMP_DIR)/dl && \
+	rm -rf $(SUBDIR) && \
+	[ \! -d $(SUBDIR) ] && \
+	git clone $(OPTS) $(URL) $(SUBDIR) && \
+	(cd $(SUBDIR) && git checkout $(VERSION) && \
+	git submodule update --init --recursive) && \
+	echo "Packing checkout..." && \
+	export TAR_TIMESTAMP=`cd $(SUBDIR) && git log -1 --format='@%ct'` && \
+	rm -rf $(SUBDIR)/.git && \
+	$(call dl_tar_pack,$(TMP_DIR)/dl/$(FILE),$(SUBDIR)) && \
+	mv $(TMP_DIR)/dl/$(FILE) $(DL_DIR)/ && \
+	rm -rf $(SUBDIR);
+endef
+
 define DownloadMethod/bzr
 	$(call wrap_mirror,$(1),$(2), \
 		echo "Checking out files from the bzr repository..."; \
diff --git a/scripts/download.py b/scripts/download.py
new file mode 100755
index 0000000000..f7fd534ea5
--- /dev/null
+++ b/scripts/download.py
@@ -0,0 +1,421 @@
+#!/usr/bin/env python
+#
+# Copyright (c) 2018 Yousong Zhou <yszhou4tech@gmail.com>
+#
+# This is free software, licensed under the GNU General Public License v2.
+# See /LICENSE for more information.
+
+import argparse
+import calendar
+import datetime
+import errno
+import fcntl
+import json
+import os
+import os.path
+import re
+import shutil
+import ssl
+import subprocess
+import sys
+import time
+import urllib2
+
+TMPDIR = os.environ.get('TMP_DIR') or '/tmp'
+TMPDIR_DL = os.path.join(TMPDIR, 'dl')
+DOWNLOAD_METHODS = []
+
+class PathException(Exception): pass
+class DownloadException(Exception): pass
+
+
+class Path(object):
+    """Context class for preparing and cleaning up directories.
+
+    If ``path`` ``isdir``, then it will be created on context enter.
+
+    If ``keep`` is True, then ``path`` will NOT be removed on context exit
+    """
+
+    def __init__(self, path, isdir=True, keep=False):
+        self.path = path
+        self.isdir = isdir
+        self.keep = keep
+
+    def __enter__(self):
+        if self.isdir:
+            self.mkdir_all(self.path)
+        return self
+
+    def __exit__(self, exc_type, exc_value, traceback):
+        if not self.keep:
+            self.rm_all(self.path)
+
+    @staticmethod
+    def mkdir_all(path):
+        """Same as mkdir -p."""
+        names = os.path.split(path)
+        p = ''
+        for name in names:
+            p = os.path.join(p, name)
+            Path._mkdir(p)
+
+    @staticmethod
+    def _rmdir_all(dir_):
+        names = Path._listdir(dir_)
+        for name in names:
+            p = os.path.join(dir_, name)
+            if os.path.isdir(p):
+                Path._rmdir_all(p)
+            else:
+                Path._remove(p)
+        Path._rmdir(dir_)
+
+    @staticmethod
+    def _mkdir(path):
+        Path._os_func(os.mkdir, path, errno.EEXIST)
+
+    @staticmethod
+    def _rmdir(path):
+        Path._os_func(os.rmdir, path, errno.ENOENT)
+
+    @staticmethod
+    def _remove(path):
+        Path._os_func(os.remove, path, errno.ENOENT)
+
+    @staticmethod
+    def _listdir(path):
+        return Path._os_func(os.listdir, path, errno.ENOENT, default=[])
+
+    @staticmethod
+    def _os_func(func, path, errno, default=None):
+        """Call func(path) in an idempotent way.
+
+        On exception ``ex``, if the type is OSError and ``ex.errno == errno``,
+        return ``default``, otherwise, re-raise
+        """
+        try:
+            return func(path)
+        except OSError as e:
+            if e.errno == errno:
+                return default
+            else:
+                raise
+
+    @staticmethod
+    def rm_all(path):
+        """Same as rm -r."""
+        if os.path.isdir(path):
+            Path._rmdir_all(path)
+        else:
+            Path._remove(path)
+
+    @staticmethod
+    def untar(path, into=None):
+        """Extract tarball at ``path`` into subdir ``into``.
+
+        return subdir name if and only if there exists one, otherwise raise PathException
+        """
+        args = ('tar', '-C', into, '-xzf', path, '--no-same-permissions')
+        subprocess.check_call(args, preexec_fn=lambda: os.umask(0o22))
+        dirs = os.listdir(into)
+        if len(dirs) == 1:
+            return dirs[0]
+        else:
+            raise PathException('untar %s: expecting a single subdir, got %s' % (path, dirs))
+
+    @staticmethod
+    def tar(path, subdir, into=None, ts=None):
+        """Pack ``path`` into tarball ``into``."""
+        # --sort=name requires a recent build of GNU tar
+        args = ['tar', '--numeric-owner', '--owner=0', '--group=0', '--sort=name']
+        args += ['-C', path, '-cf', into, subdir]
+        envs = os.environ.copy()
+        if ts is not None:
+            args.append('--mtime=@%d' % ts)
+        if into.endswith('.xz'):
+            envs['XZ_OPT'] = '-7e'
+            args.append('-J')
+        elif into.endswith('.bz2'):
+            args.append('-j')
+        elif into.endswith('.gz'):
+            args.append('-z')
+            envs['GZIP'] = '-n'
+        else:
+            raise PathException('unknown compression type %s' % into)
+        subprocess.check_call(args, env=envs)
+
+
+class GitHubCommitTsCache(object):
+    __cachef = 'github.commit.ts.cache'
+    __cachen = 2048
+
+    def __init__(self):
+        Path.mkdir_all(TMPDIR_DL)
+        self.cachef = os.path.join(TMPDIR_DL, self.__cachef)
+        self.cache = {}
+
+    def get(self, k):
+        """Get timestamp with key ``k``."""
+        fileno = os.open(self.cachef, os.O_RDONLY | os.O_CREAT)
+        with os.fdopen(fileno) as fin:
+            try:
+                fcntl.lockf(fileno, fcntl.LOCK_SH)
+                self._cache_init(fin)
+                if k in self.cache:
+                    ts = self.cache[k][0]
+                    return ts
+            finally:
+                fcntl.lockf(fileno, fcntl.LOCK_UN)
+        return None
+
+    def set(self, k, v):
+        """Update timestamp with ``k``."""
+        fileno = os.open(self.cachef, os.O_RDWR | os.O_CREAT)
+        with os.fdopen(fileno, 'wb+') as f:
+            try:
+                fcntl.lockf(fileno, fcntl.LOCK_EX)
+                self._cache_init(f)
+                self.cache[k] = (v, int(time.time()))
+                self._cache_flush(f)
+            finally:
+                fcntl.lockf(fileno, fcntl.LOCK_UN)
+
+    def _cache_init(self, fin):
+        for line in fin:
+            k, ts, updated = line.split()
+            ts = int(ts)
+            updated = int(updated)
+            self.cache[k] = (ts, updated)
+
+    def _cache_flush(self, fout):
+        cache = sorted(self.cache.iteritems(), cmp=lambda a, b: b[1][1] - a[1][1])
+        cache = cache[:self.__cachen]
+        self.cache = {}
+        os.ftruncate(fout.fileno(), 0)
+        fout.seek(0, os.SEEK_SET)
+        for k, ent in cache:
+            ts = ent[0]
+            updated = ent[1]
+            line = '{0} {1} {2}\n'.format(k, ts, updated)
+            fout.write(line)
+
+
+class DownloadMethod(object):
+    """Base class of all download method."""
+
+    def __init__(self, args):
+        self.args = args
+        self.urls = args.urls
+        self.url = self.urls[0]
+        self.dl_dir = args.dl_dir
+
+    @classmethod
+    def resolve(cls, args):
+        """Resolve download method to use.
+
+        return instance of subclass of DownloadMethod
+        """
+        for c in DOWNLOAD_METHODS:
+            if c.match(args):
+                return c(args)
+
+    @staticmethod
+    def match(args):
+        """Return True if it can do the download."""
+        return NotImplemented
+
+    def download(self):
+        """Do the download and put it into the download dir."""
+        return NotImplemented
+
+
+class DownloadMethodGitHubTarball(DownloadMethod):
+    """Download and repack archive tarabll from GitHub."""
+
+    __repo_url_regex = re.compile(r'^(?:https|git)://github.com/(?P<owner>[^/]+)/(?P<repo>[^/]+)')
+
+    def __init__(self, args):
+        super(DownloadMethodGitHubTarball, self).__init__(args)
+        self._init_owner_repo()
+        self.version = args.version
+        self.subdir = args.subdir
+        self.source = args.source
+        self.commit_ts = None           # lazy load commit timestamp
+        self.commit_ts_cache = GitHubCommitTsCache()
+        self.name = 'github-tarball'
+
+    @staticmethod
+    def match(args):
+        """Match if it's a GitHub clone url."""
+        url = args.urls[0]
+        proto = args.proto
+        if proto == 'git' and isinstance(url, basestring) \
+                and (url.startswith('https://github.com/') or url.startswith('git://github.com/')):
+            return True
+        return False
+
+    def download(self):
+        """Download and repack GitHub archive tarball."""
+        self._init_commit_ts()
+        with Path(TMPDIR_DL, keep=True) as dir_dl:
+            # fetch tarball from GitHub
+            tarball_path = os.path.join(dir_dl.path, self.subdir + '.tar.gz.dl')
+            with Path(tarball_path, isdir=False):
+                self._fetch(tarball_path)
+                # unpack
+                d = os.path.join(dir_dl.path, self.subdir + '.untar')
+                with Path(d) as dir_untar:
+                    tarball_prefix = Path.untar(tarball_path, into=dir_untar.path)
+                    dir0 = os.path.join(dir_untar.path, tarball_prefix)
+                    dir1 = os.path.join(dir_untar.path, self.subdir)
+                    # submodules check
+                    if self._has_submodule(dir0):
+                        raise DownloadException('unable to fetch submodules\' source code')
+                    # rename subdir
+                    os.rename(dir0, dir1)
+                    # repack
+                    into=os.path.join(TMPDIR_DL, self.source)
+                    Path.tar(dir_untar.path, self.subdir, into=into, ts=self.commit_ts)
+                    # move to target location
+                    file1 = os.path.join(self.dl_dir, self.source)
+                    if into != file1:
+                        shutil.move(into, file1)
+
+    def _has_submodule(self, dir_):
+        m = os.path.join(dir_, '.gitmodules')
+        try:
+            st = os.stat(m)
+            return st.st_size > 0
+        except OSError as e:
+            return e.errno != errno.ENOENT
+
+    def _init_owner_repo(self):
+        url = self.url
+        m = self.__repo_url_regex.search(url)
+        if m is None:
+            raise DownloadException('invalid github url: %s' % url)
+        owner = m.group('owner')
+        repo = m.group('repo')
+        if repo.endswith('.git'):
+            repo = repo[:-4]
+        self.owner = owner
+        self.repo = repo
+
+    def _init_commit_ts(self):
+        if self.commit_ts is not None:
+            return
+        url = self._make_repo_url_path('commits', self.version)
+        ct = self.commit_ts_cache.get(url)
+        if ct is not None:
+            self.commit_ts = ct
+            return
+        resp = self._make_request(url)
+        data = resp.read()
+        data = json.loads(data)
+        date = data['commit']['committer']['date']
+        date = datetime.datetime.strptime(date, '%Y-%m-%dT%H:%M:%SZ')
+        date = date.timetuple()
+        ct = calendar.timegm(date)
+        self.commit_ts = ct
+        self.commit_ts_cache.set(url, ct)
+
+    def _fetch(self, path):
+        """Fetch tarball of the specified version ref."""
+        ref = self.version
+        url = self._make_repo_url_path('tarball', ref)
+        resp = self._make_request(url)
+        with open(path, 'wb') as fout:
+            while True:
+                d = resp.read(4096)
+                if not d:
+                    break
+                fout.write(d)
+
+    def _make_repo_url_path(self, *args):
+        url = '/repos/{0}/{1}'.format(self.owner, self.repo)
+        if args:
+            url += '/' + '/'.join(args)
+        return url
+
+    def _make_request(self, path):
+        """Request GitHub API endpoint on ``path``."""
+        url = 'https://api.github.com' + path
+        headers = {
+            'Accept': 'application/vnd.github.v3+json',
+            'User-Agent': 'OpenWrt',
+        }
+        req = urllib2.Request(url, headers=headers)
+        sslcontext = ssl._create_unverified_context()
+        fileobj = urllib2.urlopen(req, context=sslcontext)
+        return fileobj
+
+
+class DownloadMethodCatchall(DownloadMethod):
+    """Dummy method that knows names but not ways of download."""
+
+    def __init__(self, args):
+        super(DownloadMethodCatchall, self).__init__(args)
+        self.args = args
+        self.proto = args.proto
+        self.name = self._resolve_name()
+
+    def _resolve_name(self):
+        if self.proto:
+            return self.proto
+        methods_map = (
+            ('default', ('@APACHE/', '@GITHUB/', '@GNOME/', '@GNU/',
+                         '@KERNEL/', '@SF/', '@SAVANNAH/', 'ftp://', 'http://',
+                         'https://', 'file://')),
+            ('git', ('git://', )),
+            ('svn', ('svn://', )),
+            ('cvs', ('cvs://', )),
+            ('bzr', ('sftp://', )),
+            ('bzr', ('sftp://', )),
+            ('unknown', ('', )),
+        )
+        for name, prefixes in methods_map:
+            if any(url.startswith(prefix) for prefix in prefixes for url in self.urls):
+                return name
+
+    @staticmethod
+    def match(args):
+        """Return True."""
+        return True
+
+    def download(self):
+        """Not implemented.
+
+        raise DownloadException
+        """
+        raise DownloadException('download method for %s is not yet implemented' % self.name)
+
+# order matters
+DOWNLOAD_METHODS = [
+    DownloadMethodGitHubTarball,
+    DownloadMethodCatchall,
+]
+
+
+def main():
+    parser = argparse.ArgumentParser()
+    parser.add_argument('action', choices=('dl_method', 'dl'), help='Action to take')
+    parser.add_argument('--urls', nargs='+', metavar='URL', help='Download URLs')
+    parser.add_argument('--proto', help='Download proto')
+    parser.add_argument('--subdir', help='Source code subdir name')
+    parser.add_argument('--version', help='Source code version')
+    parser.add_argument('--source', help='Source tarball filename')
+    parser.add_argument('--dl-dir', default=os.getcwd(), help='Download dir')
+    args = parser.parse_args()
+    if args.action == 'dl_method':
+        method = DownloadMethod.resolve(args)
+        sys.stdout.write(method.name + '\n')
+    elif args.action == 'dl':
+        method = DownloadMethod.resolve(args)
+        try:
+            method.download()
+        except Exception:
+            raise
+
+if __name__ == '__main__':
+    main()