Add a 'download' language for fetching pre-built binaries

This commit implements https://github.com/pre-commit/pre-commit/issues/1453#issuecomment-1702880253

tests/languages/download_test.py

@@ -0,0 +1,132 @@
+from __future__ import annotations
+
+import platform
+from dataclasses import dataclass
+from http.server import BaseHTTPRequestHandler
+from http.server import HTTPServer
+from threading import Thread
+from typing import Collection
+from typing import Iterator
+
+import py.path
+from pytest import fixture
+
+import pre_commit.constants as C
+from pre_commit.languages import download
+from pre_commit.languages.download import ChecksumMismatchError
+from pre_commit.languages.download import SRI
+from pre_commit.languages.download import URI
+from pre_commit.prefix import Prefix
+
+
+@dataclass(frozen=True)
+class Script:
+    content: bytes
+    integrity: SRI
+
+
+@fixture
+def shell() -> Script:
+    content = b'#!/bin/sh\necho hello\nexit 123'
+    integrity = SRI('sha256-oRJkj6Cr8nWIivZ9d3W+rVZt/aSW1l9YtxSVh+GtIHM=')
+    return Script(content, integrity)
+
+
+@fixture
+def batch() -> Script:
+    content = b'@echo off\necho hello\nexit 123'
+    integrity = SRI('sha256-L63Nefq+fKVIm24IKqlcqbJmc1rrJD3dKhIvutFK+IA=')
+    return Script(content, integrity)
+
+
+@fixture
+def script(shell: Script, batch: Script) -> Script:
+    if platform.system() == 'Windows':
+        return batch
+    else:
+        return shell
+
+
+@dataclass(frozen=True)
+class Server:
+    uri: URI
+    script: Script
+
+
+@fixture
+def server(script: Script) -> Iterator[Server]:
+    class HTTPRequestHandler(BaseHTTPRequestHandler):
+        def do_GET(self):
+            self.send_response(200)
+            self.end_headers()
+            self.wfile.write(script.content)
+    httpd = HTTPServer(('localhost', 5555), HTTPRequestHandler)
+    thread = Thread(target=httpd.serve_forever, name='HTTP Server')
+    thread.start()
+    host, port = httpd.server_address
+    uri = URI(f'http://{str(host)}:{str(port)}')
+    try:
+        yield Server(uri, fixture)
+    finally:
+        httpd.shutdown()
+        httpd.server_close()
+        thread.join(1)
+        assert not thread.is_alive()
+
+
+@dataclass(frozen=True)
+class Fixture:
+    server: Server
+    dependencies: Collection[str]
+
+
+@fixture
+def healthy(server: Server, shell: Script, batch: Script) -> Fixture:
+    dependencies = (
+        f"""linux/amd64
+{shell.integrity}
+{server.uri}
+test.bat""",
+        f"""windows/amd64
+{batch.integrity}
+{server.uri}
+test.bat""",
+    )
+    return Fixture(server, dependencies)
+
+
+@fixture
+def unhealthy(server: Server, shell: Script, batch: Script) -> Fixture:
+    dependencies = (
+        f"""linux/amd64
+{batch.integrity}
+{server.uri}
+test.bat""",
+        f"""windows/amd64
+{shell.integrity}
+{server.uri}
+test.bat""",
+    )
+    return Fixture(server, dependencies)
+
+
+@fixture
+def prefix(tmpdir: py.path) -> Iterator[Prefix]:
+    with tmpdir.as_cwd():
+        directory = tmpdir.join('prefix').ensure_dir()
+        prefix = Prefix(str(directory))
+        yield prefix
+
+
+def test_download_healthy(prefix: Prefix, healthy: Fixture) -> None:
+    """Do a download test with healthy SRI checksum"""
+    download.install_environment(prefix, C.DEFAULT, healthy.dependencies)
+    assert download.health_check(prefix, C.DEFAULT) is None
+
+
+def test_download_unhealthy(prefix: Prefix, unhealthy: Fixture) -> None:
+    """Do a download test with unhealthy SRI checksum"""
+    try:
+        download.install_environment(prefix, C.DEFAULT, unhealthy.dependencies)
+    except ChecksumMismatchError:
+        pass