Add support for relative URLs to packages

pypi.org returns absolute URLs, but some servers might return relative
ones.

Author: chriskuehl

.gitignore

@@ -1,3 +1,4 @@
 *.py[co]
 /.coverage
+/cache
 /dist

Makefile

@@ -7,4 +7,4 @@ test:
 
 .PHONY: start-dev
 start-dev:
-	PYPI_BROWSER_DEBUG=1 poetry run uvicorn --reload --port 5000 pypi_browser.app:app
+	PYPI_BROWSER_DEBUG=1 PYPI_BROWSER_PACKAGE_CACHE_PATH=$(CURDIR)/cache poetry run uvicorn --reload --port 5000 pypi_browser.app:app

pypi_browser/pypi.py

@@ -4,6 +4,7 @@
 import itertools
 import os.path
 import typing
+import urllib.parse
 
 import aiofiles.os
 import httpx
@@ -83,7 +84,7 @@ async def downloaded_file_path(config: PyPIConfig, package: str, filename: str)
         # matching file.
         for file_ in itertools.chain.from_iterable(metadata['releases'].values()):
             if file_['filename'] == filename:
-                url = file_['url']
+                url = urllib.parse.urljoin(config.pypi_url, file_['url'])
                 break
         else:
             raise CannotFindFileError(package, filename)