adding arch iso checker/downloader

.idea/vcs.xml

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="VcsDirectoryMappings">
+    <mapping directory="$PROJECT_DIR$" vcs="Git" />
+  </component>
+</project>

arch/relchk.py

@@ -0,0 +1,86 @@
+#!/usr/bin/env python3
+
+import configparser
+import hashlib
+import os
+import re
+from bs4 import BeautifulSoup
+from urllib.parse import urljoin, urlparse
+from urllib.request import urlopen
+try:
+    import lxml
+    htmlparser = 'lxml'
+except ImportError:
+    htmlparser = 'html.parser'
+
+cfgpath = os.path.abspath(os.path.expanduser(
+                                        '~/.config/optools/relchk/arch.ini'))
+
+cfg = configparser.ConfigParser()
+cfg['arch'] = {'url': 'https://arch.mirror.square-r00t.net/iso/latest/',
+               'path': '/boot/iso/arch.iso',
+               'hashtype': 'sha1',
+               'hashurl': (
+                'https://arch.mirror.square-r00t.net/iso/latest/sha1sums.txt')
+                }
+
+if not os.path.isfile(cfgpath):
+    os.makedirs(os.path.dirname(cfgpath), exist_ok = True)
+    with open(cfgpath, 'w') as f:
+        cfg.write(f)
+else:
+    cfg.read(cfgpath)
+
+cfg['arch']['path'] = os.path.abspath(os.path.expanduser(cfg['arch']['path']))
+
+# We need the hashes first. We'll pop them into memory,
+# no need to save locally.
+# Must be in GNU checksum format (i.e. "<HASH>  <FILENAME>\n").
+hashes = {}
+if 'hashurl' in cfg['arch']:
+    with urlopen(cfg['arch']['hashurl']) as h:
+        for i in h.read().decode('utf-8').splitlines():
+            line = [x.strip() for x in i.split()]
+            hashes[os.path.basename(line[1])] = line[0]
+chksum = hashlib.new(cfg['arch']['hashtype'])
+
+# Now we (try to) get a list of files available for download. We're looking
+# for .iso or .img files. Compressed images not currently supported; TODO.
+exts = re.compile('.*\.(iso|img)$', re.IGNORECASE)
+imgfiles = []
+with urlopen(cfg['arch']['url']) as u:
+    dlsoup = BeautifulSoup(u.read().decode('utf-8'), htmlparser)
+for a in dlsoup.find_all('a'):
+    if a['href']:
+        if exts.search(a['href']):
+            if not urlparse(a['href']).netloc:
+                imgfiles.append(urljoin(cfg['arch']['url'], a['href']))
+            else:
+                imgfiles.append(a['href'])
+if not imgfiles:
+    raise RuntimeError('Could not find any ISO or IMG files at {0}'.format(
+            cfg['arch']['url']))
+# Not foolproof, but will handle standard Arch ISO mirrors just fine.
+imgfiles.sort()
+iso = imgfiles[0]
+
+# Now we get the existing file (if it exists) and grab the hash (if we have
+# one fetched).
+up2date = False
+if os.path.isfile(cfg['arch']['path']):
+    _fname = os.path.basename(iso)
+    if _fname in hashes:
+        with open(cfg['arch']['path'], 'rb') as f:
+            chksum.update(f.read())
+        if chksum.hexdigest().lower() == hashes[_fname].lower():
+            up2date = True
+
+if not up2date:
+    print('Downloading...')
+    os.makedirs(os.path.dirname(cfg['arch']['path']), exist_ok = True)
+    with open(cfg['arch']['path'], 'wb') as f, urlopen(iso) as u:
+        f.write(u.read())
+else:
+    print('No need to download; we are up to date')
+
+print('Done')