server: Stub out a WSGI server

This still needs source-fetching and Content-Range support, but it
should handle serving from the cache well enough.

diff --git a/package_cache/server.py b/package_cache/server.py
new file mode 100644 (file)
index 0000000..9fea4a5
--- /dev/null
+++ b/package_cache/server.py
@@ -0,0 +1,95 @@
+# Copyright
+
+import email.utils as _email_utils
+import mimetypes as _mimetypes
+import os as _os
+import urllib.parse as _urllib_parse
+
+
+class InvalidFile (ValueError):
+    def __init__(self, url):
+        super(InvalidFile, self).__init__('invalid file {!r}'.format(url))
+        self.url = url
+
+
+class Server (object):
+    def __init__(self, sources, cache):
+        self.sources = sources
+        self.cache = cache
+
+    def __call__(self, environ, start_response):
+        try:
+            return self._serve_request(
+                environ=environ, start_response=start_response)
+        except InvalidFile:
+            start_response(status='404 Not Found', response_headers=[])
+
+    def _serve_request(self, environ, start_response):
+        method = environ['REQUEST_METHOD']
+        url = environ.get('PATH_INFO', None)
+        if url is None:
+            raise InvalidFile(url=url)
+        parsed_url = _urllib_parse.urlparse(urlstring=url)
+        relative_path = parsed_url.path.lstrip('/').replace('/', _os.path.sep)
+        cache_path = _os.path.join(self.cache, relative_path)
+        if not _os.path.exists(path=cache_path):
+            self._get_file(url=url, path=cache_path)
+        if not _os.path.isfile(path=cache_path):
+            raise InvalidFile(url=url)
+        return self._serve_file(
+            path=cache_path, environ=environ, start_response=start_response)
+
+    def _get_file(self, url, path):
+        raise NotImplementedError()
+
+    def _serve_file(self, path, environ, start_response):
+        headers = {
+            'Content-Length': self._get_content_length(path=path),
+            'Content-Type': self._get_content_type(path=path),
+            'Last-Modified': self._get_last_modified(path=path),
+            }
+        f = open(path, 'rb')
+        if 'wsgi.file_wrapper' in environ:
+            file_iterator = environ['wsgi.file_wrapper'](f)
+        else:
+            file_iterator = iter(lambda: f.read(block_size), '')
+        start_response(
+            status='200 OK',
+            response_headers=list(headers.items()))
+        return file_iterator
+
+    def _get_content_length(self, path):
+        """Content-Length value per RFC 2616
+
+        Content-Length:
+          https://tools.ietf.org/html/rfc2616#section-14.13
+        """
+        return str(_os.path.getsize(path=path))
+
+    def _get_content_type(self, path):
+        """Content-Type value per RFC 2616
+
+        Content-Type:
+          https://tools.ietf.org/html/rfc2616#section-14.17
+        Media types:
+          https://tools.ietf.org/html/rfc2616#section-3.7
+        """
+        mimetype, charset = _mimetypes.guess_type(url=path)
+        if charset:
+            return '{}; charset={}'.format(mimetype, charset)
+        else:
+            return mimetype
+
+    def _get_last_modified(self, path):
+        """Last-Modified value per RFC 2616
+
+        Last-Modified:
+          https://tools.ietf.org/html/rfc2616#section-14.29
+        Date formats:
+          https://tools.ietf.org/html/rfc2616#section-3.3.1
+          https://tools.ietf.org/html/rfc1123#page-55
+          https://tools.ietf.org/html/rfc822#section-5
+        """
+        mtime = _os.path.getmtime(path=path)
+        return _email_utils.formatdate(
+            timeval=mtime, localtime=False, usegmt=True)