Break up `server.py` into multiple modules

[Mr0grog]

web_monitoring_diff/server/server.py is a pretty big and messy file. In this package, we’ve created a web_monitoring_diff.server subpackage so we can split that file up into multiple modules.

Things we should break out:

• The MockRequest/MockResponse functionality for loading files.

  web-monitoring-diff/web_monitoring_diff/server/server.py

  Lines 171 to 204 in 5e32488

  	class MockRequest:
  	"An HTTPRequest-like object for local file:/// requests."
  	def __init__(self, url):
  	self.url = url
  	class MockResponse:
  	"An HTTPResponse-like object for local file:/// requests."
  	def __init__(self, url, body, headers=None):
  	self.request = MockRequest(url)
  	self.body = body
  	self.headers = headers
  	self.error = None
  	if self.headers is None:
  	self.headers = {}
  	if 'Content-Type' not in self.headers:
  	self.headers.update(self._get_content_type_headers_from_url(url))
  	@staticmethod
  	def _get_content_type_headers_from_url(url):
  	# If the extension is not recognized, assume text/html
  	headers = {'Content-Type': 'text/html'}
  	content_type, content_encoding = mimetypes.guess_type(url)
  	if content_type is not None:
  	headers['Content-Type'] = content_type
  	if content_encoding is not None:
  	headers['Content-Encoding'] = content_encoding
  	return headers

• Routing configuration.

  web-monitoring-diff/web_monitoring_diff/server/server.py

  Lines 40 to 76 in 5e32488

  	# Map tokens in the REST API to functions in modules.
  	# The modules do not have to be part of the web_monitoring_diff package.
  	DIFF_ROUTES = {
  	"length": basic_diffs.compare_length,
  	"identical_bytes": basic_diffs.identical_bytes,
  	"side_by_side_text": basic_diffs.side_by_side_text,
  	"links": html_links_diff.links_diff_html,
  	"links_json": html_links_diff.links_diff_json,
  	# applying diff-match-patch (dmp) to strings (no tokenization)
  	"html_text_dmp": basic_diffs.html_text_diff,
  	"html_source_dmp": basic_diffs.html_source_diff,
  	# three different approaches to the same goal:
  	"html_token": html_render_diff.html_diff_render,
  	# deprecated synonyms
  	"links_diff": html_links_diff.links_diff,
  	"html_text_diff": basic_diffs.html_text_diff,
  	"html_source_diff": basic_diffs.html_source_diff,
  	"html_visual_diff": html_render_diff.html_diff_render,
  	}
  	# Optional, experimental diffs.
  	try:
  	from ..experimental import htmltreediff
  	DIFF_ROUTES["html_tree"] = htmltreediff.diff
  	# Deprecated synonym
  	DIFF_ROUTES["html_tree_diff"] = htmltreediff.diff
  	except ModuleNotFoundError:
  	...
  	try:
  	from ..experimental import htmldiffer
  	DIFF_ROUTES["html_perma_cc"] = htmldiffer.diff
  	# Deprecated synonym
  	DIFF_ROUTES["html_differ"] = htmldiffer.diff
  	except ModuleNotFoundError:
  	...

• Other custom classes, e.g. PublicError:

  web-monitoring-diff/web_monitoring_diff/server/server.py

  Lines 135 to 168 in 5e32488

  	class PublicError(tornado.web.HTTPError):
  	"""
  	Customized version of Tornado's HTTP error designed for reporting publicly
  	visible error messages. Please always raise this instead of calling
  	`send_error()` directly, since it lets you attach a user-visible
  	explanation of what went wrong.
  	Parameters
  	----------
  	status_code : int, optional
  	Status code for the response. Defaults to `500`.
  	public_message : str, optional
  	Textual description of the error. This will be publicly visible in
  	production mode, unlike `log_message`.
  	log_message : str, optional
  	Error message written to logs and to error tracking service. Will be
  	included in the HTTP response only in debug mode. Same as the
  	`log_message` parameter to `tornado.web.HTTPError`, but with no
  	interpolation.
  	extra : dict, optional
  	Dict of additional keys and values to include in the error response.
  	"""
  	def __init__(self, status_code=500, public_message=None, log_message=None,
  	extra=None, **kwargs):
  	self.extra = extra or {}
  	if public_message is not None:
  	if 'error' not in self.extra:
  	self.extra['error'] = public_message
  	if log_message is None:
  	log_message = public_message
  	super().__init__(status_code, log_message, **kwargs)

• Body decoding logic.

• Possibly DiffHandler; it’s huge. It’s possible there are good ways to break it up, too.