add a httpheader source

see #175 for use cases.

docs/usage.rst

@@ -235,6 +235,34 @@ regex
 
 This source supports :ref:`list options`.
 
+Search in an HTTP header
+~~~~~~~~~~~~~~~~~~~~~~~~
+::
+
+  source = "httpheader"
+
+Send an HTTP request and search through a specific header.
+
+url
+  The URL of the HTTP request.
+
+header
+  (*Optional*) The header to look at. Default is ``Location``. Another useful header is ``Content-Disposition``.
+
+regex
+  A regular expression used to find the version string.
+
+  It can have zero or one capture group. The capture group or the whole match is the version string.
+
+  When multiple version strings are found, the maximum of those is chosen.
+
+method
+  (*Optional*) The HTTP method to use. Default is ``HEAD``.
+
+follow_redirects
+  (*Optional*) Whether to follow 3xx HTTP redirects. Default is ``false``. If you are looking at a ``Location`` header, you shouldn't change this.
+
+
 Find with a Command
 ~~~~~~~~~~~~~~~~~~~
 ::

nvchecker_source/httpheader.py

@@ -0,0 +1,39 @@
+# MIT licensed
+# Copyright (c) 2021 lilydjwg <lilydjwg@gmail.com>, et al.
+
+import re
+import sre_constants
+
+from nvchecker.api import session, GetVersionError
+
+async def get_version(name, conf, *, cache, **kwargs):
+  key = tuple(sorted(conf.items()))
+  return await cache.get(key, get_version_impl)
+
+async def get_version_impl(info):
+  conf = dict(info)
+  url = conf['url']
+  header = conf.get('header', 'Location')
+  follow_redirects = conf.get('follow_redirects', False)
+  method = conf.get('method', 'HEAD')
+
+  try:
+    regex = re.compile(conf['regex'])
+  except sre_constants.error as e:
+    raise GetVersionError('bad regex', exc_info=e)
+
+  res = await session.request(
+    url,
+    method = method,
+    follow_redirects = follow_redirects,
+  )
+
+  header_value = res.headers.get(header)
+  if not header_value:
+    raise GetVersionError('header %s not found or is empty' % header)
+
+  try:
+    version = regex.findall(header_value)
+  except ValueError:
+    raise GetVersionError('version string not found.')
+  return version

nvchecker_source/regex.py

@@ -25,7 +25,6 @@ async def get_version_impl(info):
   try:
     version = regex.findall(body)
   except ValueError:
-    version = None
     if not conf.get('missing_ok', False):
       raise GetVersionError('version string not found.')
   return version

tests/test_httpheader.py

@@ -0,0 +1,14 @@
+# MIT licensed
+# Copyright (c) 2021 lilydjwg <lilydjwg@gmail.com>, et al.
+
+import pytest
+
+pytestmark = pytest.mark.asyncio
+
+async def test_redirection(get_version):
+    assert await get_version("jmeter-plugins-manager", {
+        "source": "httpheader",
+        "url": "https://jmeter-plugins.org/get/",
+        "regex": r'/([\d.]+)/',
+    }) == "1.6"
+