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import sys
from collections import defaultdict
from tempfile import SpooledTemporaryFile
from asgiref.sync import AsyncToSync, sync_to_async
class WsgiToAsgi:
"""
Wraps a WSGI application to make it into an ASGI application.
"""
def __init__(self, wsgi_application, duplicate_header_limit=100):
self.wsgi_application = wsgi_application
self.duplicate_header_limit = duplicate_header_limit
async def __call__(self, scope, receive, send):
"""
ASGI application instantiation point.
We return a new WsgiToAsgiInstance here with the WSGI app
and the scope, ready to respond when it is __call__ed.
"""
await WsgiToAsgiInstance(self.wsgi_application, self.duplicate_header_limit)(
scope, receive, send
)
class WsgiToAsgiInstance:
"""
Per-socket instance of a wrapped WSGI application
"""
def __init__(self, wsgi_application, duplicate_header_limit=100):
self.wsgi_application = wsgi_application
self.duplicate_header_limit = duplicate_header_limit
self.response_started = False
self.response_content_length = None
async def __call__(self, scope, receive, send):
if scope["type"] != "http":
raise ValueError("WSGI wrapper received a non-HTTP scope")
self.scope = scope
with SpooledTemporaryFile(max_size=65536) as body:
# Alright, wait for the http.request messages
while True:
message = await receive()
if message["type"] != "http.request":
raise ValueError("WSGI wrapper received a non-HTTP-request message")
body.write(message.get("body", b""))
if not message.get("more_body"):
break
body.seek(0)
# Wrap send so it can be called from the subthread
self.sync_send = AsyncToSync(send)
# Call the WSGI app
await self.run_wsgi_app(body)
def build_environ(self, scope, body):
"""
Builds a scope and request body into a WSGI environ object.
"""
script_name = scope.get("root_path", "").encode("utf8").decode("latin1")
path_info = scope["path"].encode("utf8").decode("latin1")
if path_info.startswith(script_name):
path_info = path_info[len(script_name) :]
environ = {
"REQUEST_METHOD": scope["method"],
"SCRIPT_NAME": script_name,
"PATH_INFO": path_info,
"QUERY_STRING": scope["query_string"].decode("ascii"),
"SERVER_PROTOCOL": "HTTP/%s" % scope["http_version"],
"wsgi.version": (1, 0),
"wsgi.url_scheme": scope.get("scheme", "http"),
"wsgi.input": body,
"wsgi.errors": sys.stderr,
"wsgi.multithread": True,
"wsgi.multiprocess": True,
"wsgi.run_once": False,
}
# Get server name and port - required in WSGI, not in ASGI
if "server" in scope:
environ["SERVER_NAME"] = scope["server"][0]
environ["SERVER_PORT"] = str(scope["server"][1])
else:
environ["SERVER_NAME"] = "localhost"
environ["SERVER_PORT"] = "80"
if scope.get("client") is not None:
environ["REMOTE_ADDR"] = scope["client"][0]
# Go through headers and make them into environ entries
_headers = defaultdict(list)
for name, value in self.scope.get("headers", []):
name = name.decode("latin1")
if name == "content-length":
corrected_name = "CONTENT_LENGTH"
elif name == "content-type":
corrected_name = "CONTENT_TYPE"
else:
corrected_name = "HTTP_%s" % name.upper().replace("-", "_")
# HTTPbis say only ASCII chars are allowed in headers, but we latin1 just in case
value = value.decode("latin1")
if (
self.duplicate_header_limit
and len(_headers[corrected_name]) >= self.duplicate_header_limit
):
raise ValueError(
f"Too many duplicate headers: {corrected_name} exceeds limit of"
f"{self.duplicate_header_limit}"
)
_headers[corrected_name].append(value)
for name, values in _headers.items():
environ[name] = ",".join(values)
return environ
def start_response(self, status, response_headers, exc_info=None):
"""
WSGI start_response callable.
"""
# Don't allow re-calling once response has begun
if self.response_started:
raise exc_info[1].with_traceback(exc_info[2])
# Don't allow re-calling without exc_info
if hasattr(self, "response_start") and exc_info is None:
raise ValueError(
"You cannot call start_response a second time without exc_info"
)
# Extract status code
status_code, _ = status.split(" ", 1)
status_code = int(status_code)
# Extract headers
headers = [
(name.lower().encode("ascii"), value.encode("ascii"))
for name, value in response_headers
]
# Extract content-length
self.response_content_length = None
for name, value in response_headers:
if name.lower() == "content-length":
self.response_content_length = int(value)
# Build and send response start message.
self.response_start = {
"type": "http.response.start",
"status": status_code,
"headers": headers,
}
@sync_to_async
def run_wsgi_app(self, body):
"""
Called in a subthread to run the WSGI app. We encapsulate like
this so that the start_response callable is called in the same thread.
"""
# Translate the scope and incoming request body into a WSGI environ
try:
environ = self.build_environ(self.scope, body)
except ValueError:
# Return 400 Bad Request if header limit exceeded
self.sync_send(
{
"type": "http.response.start",
"status": 400,
"headers": [(b"content-type", b"text/plain")],
}
)
self.sync_send(
{
"type": "http.response.body",
"body": b"Bad Request: Too many duplicate headers",
}
)
return
# Run the WSGI app
bytes_sent = 0
for output in self.wsgi_application(environ, self.start_response):
# If this is the first response, include the response headers
if not self.response_started:
self.response_started = True
self.sync_send(self.response_start)
# If the application supplies a Content-Length header
if self.response_content_length is not None:
# The server should not transmit more bytes to the client than the header allows
bytes_allowed = self.response_content_length - bytes_sent
if len(output) > bytes_allowed:
output = output[:bytes_allowed]
self.sync_send(
{"type": "http.response.body", "body": output, "more_body": True}
)
bytes_sent += len(output)
# The server should stop iterating over the response when enough data has been sent
if bytes_sent == self.response_content_length:
break
# Close connection
if not self.response_started:
self.response_started = True
self.sync_send(self.response_start)
self.sync_send({"type": "http.response.body"})
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