Add `webmap-download` script.

1 files changed, 235 insertions, 0 deletions

diff --git a/webmap-download b/webmap-download
new file mode 100755
index 0000000..39c48c2
--- /dev/null
+++ b/webmap-download
@@ -0,0 +1,235 @@
+#!/usr/bin/python3
+
+from os import O_RDONLY, O_WRONLY, O_CREAT, O_TRUNC, O_CLOEXEC, O_PATH, O_DIRECTORY, O_TMPFILE
+import os, sys
+from fcntl import flock, LOCK_EX
+import logging
+from time import time, monotonic as time_monotonic
+import argparse
+import itertools
+from pathlib import Path
+from email.utils import parsedate_to_datetime, formatdate
+from hashlib import sha1
+from math import modf
+import requests
+
+import common
+
+def download_trystream(url, **kwargs):
+    max_tries = 10
+    f = kwargs.pop('session', requests)
+    for i in itertools.count(1):
+        try:
+            r = f.get(url, **kwargs, stream=True)
+        except (requests.Timeout, requests.ConnectionError):
+            if i < max_tries:
+                logging.error('timeout')
+                continue
+            raise
+        else:
+            r.raise_for_status()
+            return r
+
+def download(url, dest, dir_fd=None, headers={}, max_size=None, session=requests):
+    logging.info('Downloading %s…', url)
+    destPath = Path(dest)
+    dest_tmp = destPath.with_stem(f'.{destPath.stem}.new').as_posix()
+    try:
+        # delete any leftover
+        os.unlink(dest_tmp, dir_fd=dir_fd)
+    except FileNotFoundError:
+        pass
+
+    start = time_monotonic()
+    r = download_trystream(url, headers=headers, session=session, timeout=30)
+    if r.status_code == requests.codes.not_modified:
+        # XXX shouldn't we call os.utime(dest) to bump its ctime here?
+        # otherwise we'll make several queries and get multiple 304
+        # replies if the file is used by multiple layers
+        logging.info('%s: %d Not Modified', dest, r.status_code)
+        return
+
+    last_modified = r.headers.get('Last-Modified', None)
+    if last_modified is not None:
+        try:
+            last_modified = parsedate_to_datetime(last_modified)
+            last_modified = last_modified.timestamp()
+        except ValueError:
+            logging.exception('Could not parse Last-Modified value')
+            last_modified = None
+
+    # XXX we can't use TemporaryFile as it uses O_EXCL, cf.
+    # https://discuss.python.org/t/temporaryfile-contextmanager-that-allows-creating-a-directory-entry-on-success/19094/2
+    fd = os.open(os.path.dirname(dest), O_WRONLY|O_CLOEXEC|O_TMPFILE, mode=0o644, dir_fd=dir_fd)
+    with os.fdopen(fd, mode='wb') as fp:
+        size = 0
+        for chunk in r.iter_content(chunk_size=2**16):
+            size = size + len(chunk)
+            if max_size is not None and size > max_size:
+                raise Exception(f'Payload exceeds max-size ({max_size})')
+            fp.write(chunk)
+        r = None
+        end = time_monotonic()
+
+        # XXX unfortunately there is no way for linkat() to clobber the destination,
+        # so we use a temporary file; it's racy, but thanks to O_TMPFILE better
+        # (shorter race) than if we were dumping chunks in a named file descriptor
+        os.link(f'/proc/self/fd/{fp.fileno()}', dest_tmp,
+            dst_dir_fd=dir_fd, follow_symlinks=True)
+
+    # no need to close fd here, it was taken care of by the context manager above
+
+    try:
+        if last_modified is not None:
+            # XXX os.utime() doesn't work on file descriptors so we set mtime
+            # after linkat() instead
+            os.utime(dest_tmp, times=(last_modified, last_modified),
+                dir_fd=dir_fd, follow_symlinks=False)
+        os.rename(dest_tmp, dest, src_dir_fd=dir_fd, dst_dir_fd=dir_fd)
+
+        elapsed = end - start
+        logging.info("%s: Downloaded %s in %s (%s/s)", dest, format_bytes(size),
+            format_time(elapsed), format_bytes(int(size/elapsed)))
+    except Exception as e:
+        try:
+            os.unlink(dest_tmp, dir_fd=dir_fd)
+        except Exception:
+            pass
+        raise e
+
+def format_bytes(n):
+    if n < 768:
+        return f'{n}B'
+    elif n < 786432:
+        return f'{n/1024:.2f}kiB'
+    elif n < 805306368:
+        return f'{n/1048576:.2f}MiB'
+    else:
+        return f'{n/1073741824:.2f}GiB'
+
+def format_time(s):
+    fs, s = modf(s)
+    m, s = divmod(int(s), 60)
+    h, m = divmod(m, 60)
+    return f'{h:02d}:{m:02d}:{s + fs:06.3f}'
+
+if __name__ == '__main__':
+    logging.basicConfig(format='%(levelname)s: %(message)s', level=logging.INFO)
+
+    parser = argparse.ArgumentParser(description='Download or update GIS layers.')
+    parser.add_argument('--cachedir', default=None,
+        help='destination directory for downloaded files (default: .)')
+    parser.add_argument('--lockdir', default=None,
+        help='directory for lock files (default: value of --cachedir option)')
+    parser.add_argument('--debug', action='store_true', help=argparse.SUPPRESS)
+    parser.add_argument('--exit-code', action=argparse.BooleanOptionalAction,
+        help='whether to exit with status 1 in case of download failures')
+    parser.add_argument('groupname', nargs='*', help='Group(s) to process')
+    args = parser.parse_args()
+
+    if args.debug:
+        from http.client import HTTPConnection
+        HTTPConnection.debuglevel = 1
+        logging.getLogger().setLevel(logging.DEBUG)
+        requests_log = logging.getLogger("urllib3")
+        requests_log.setLevel(logging.DEBUG)
+        requests_log.propagate = True
+
+    common.load_config(groupnames=None if args.groupname == [] else args.groupname)
+
+    sources = []
+    for name, layerdefs in common.config.get('layers', {}).items():
+        for layerdef in layerdefs:
+            sourcedef = layerdef.get('source', {})
+            sourcedef['layername'] = name
+            sources.append(sourcedef)
+
+    # intentionally leave the dirfd open until the program terminates
+    opendir_args = O_RDONLY|O_CLOEXEC|O_PATH|O_DIRECTORY
+    destdir_fd = None       if args.cachedir is None else os.open(args.cachedir, opendir_args)
+    lockdir_fd = destdir_fd if args.lockdir  is None else os.open(args.lockdir, opendir_args)
+
+    if ((destdir_fd is None and lockdir_fd is None) or
+            (destdir_fd is not None and lockdir_fd is not None and destdir_fd == lockdir_fd)):
+        lockdir_is_destdir = True
+    else:
+        destdir_st = os.fstat(destdir_fd)
+        lockdir_st = os.fstat(lockdir_fd)
+        lockdir_is_destdir = destdir_st.st_ino == lockdir_st.st_ino
+
+    sessionRequests = requests.Session()
+
+    rv = 0
+    downloads = set()
+    for source in sources:
+        dl = source.get('download', None)
+        script = None if dl is None else dl.get('script', None)
+        if script is not None and script != os.path.basename(__file__):
+            logging.info('Layer "%s" is not for us (%s != %s), skipping',
+                source['layername'],
+                script, os.path.basename(__file__))
+            continue
+
+        url = None if dl is None else dl.get('url', None)
+        if url is None:
+            logging.error('Layer "%s" has no source URL, ignoring',
+                source['layername'])
+            continue
+
+        cache = source.get('cache', None)
+        dest = None if cache is None else cache.get('path', None)
+        if dest is None:
+            raise Exception('Impossible')
+        elif url in downloads:
+            logging.info('%s was already downloaded, skipping', dest)
+            continue
+
+        headers = {}
+        user_agent = common.config.get('User-Agent', None)
+        if user_agent is not None:
+            headers['User-Agent'] = user_agent
+        dest = str(dest) # convert from Path()
+
+        try:
+            # create parent directories
+            destdir = os.path.dirname(dest)
+            common.makedirs(destdir, mode=0o755, dir_fd=destdir_fd, exist_ok=True, logging=logging)
+
+            # place an exclusive lock on a lockfile as the destination can be used by other layers
+            # hence might be updated in parallel
+            if lockdir_is_destdir:
+                lockfile = dest + '.lck'
+            else:
+                # use a flat hierarchy when lockdir != destdir as this avoids leaving empty directories
+                # behind when removing left overs with tmpfiles.d(5)
+                lockfile = sha1(dest.encode('utf-8')).hexdigest() + '.lck'
+            # use O_TRUNC to bump lockfile's mtime
+            lock_fd = os.open(lockfile, O_WRONLY|O_CREAT|O_TRUNC|O_CLOEXEC, mode=0o644, dir_fd=lockdir_fd)
+            try:
+                logging.debug('flock("%s", LOCK_EX)', lockfile)
+                flock(lock_fd, LOCK_EX)
+                try:
+                    st = os.stat(dest, dir_fd=destdir_fd)
+                except (OSError, ValueError):
+                    # the file doesn't exist, or stat() failed for some reason
+                    pass
+                else:
+                    max_age = cache.get('max-age', 6*3600) # 6h
+                    if max_age is not None:
+                        s = max_age + max(st.st_ctime, st.st_mtime) - time()
+                        if s > 0:
+                            logging.info('%s: Too young, try again in %s',
+                                dest, format_time(s))
+                            continue
+                    headers['If-Modified-Since'] = formatdate(timeval=st.st_mtime, localtime=False, usegmt=True)
+                max_size = dl.get('max-size', 2**26) # 64MiB
+                download(url, dest, dir_fd=destdir_fd, max_size=max_size,
+                    headers=headers, session=sessionRequests)
+                downloads.add(url)
+            finally:
+                os.close(lock_fd)
+        except Exception:
+            logging.exception('Could not download %s as %s', url, dest)
+            if args.exit_code:
+                rv = 1
+    exit(rv)