Support large mutable uploads in a memory-efficient manner.

src/allmydata/storage/http_server.py

@@ -9,6 +9,10 @@ from functools import wraps
 from base64 import b64decode
 import binascii
 from tempfile import TemporaryFile
+from os import SEEK_END, SEEK_SET
+from io import BytesIO
+import mmap
+import sys
 
 from cryptography.x509 import Certificate as CryptoCertificate
 from zope.interface import implementer
@@ -39,7 +43,7 @@ from cryptography.x509 import load_pem_x509_certificate
 
 
 # TODO Make sure to use pure Python versions?
-from cbor2 import dump, loads
+import cbor2
 from pycddl import Schema, ValidationError as CDDLValidationError
 from .server import StorageServer
 from .http_common import (
@@ -515,7 +519,7 @@ class HTTPServer(object):
         if accept.best == CBOR_MIME_TYPE:
             request.setHeader("Content-Type", CBOR_MIME_TYPE)
             f = TemporaryFile()
-            dump(data, f)
+            cbor2.dump(data, f)
 
             def read_data(offset: int, length: int) -> bytes:
                 f.seek(offset)
@@ -527,27 +531,47 @@ class HTTPServer(object):
             # https://tahoe-lafs.org/trac/tahoe-lafs/ticket/3861
             raise _HTTPError(http.NOT_ACCEPTABLE)
 
-    def _read_encoded(self, request, schema: Schema) -> Any:
+    def _read_encoded(
+        self, request, schema: Schema, max_size: int = 1024 * 1024
+    ) -> Any:
         """
         Read encoded request body data, decoding it with CBOR by default.
 
-        Somewhat arbitrarily, limit body size to 1MB; this may be too low, we
-        may want to customize per query type, but this is the starting point
-        for now.
+        Somewhat arbitrarily, limit body size to 1MiB by default.
         """
         content_type = get_content_type(request.requestHeaders)
-        if content_type == CBOR_MIME_TYPE:
-            # Read 1 byte more than 1MB. We expect length to be 1MB or
-            # less; if it's more assume it's not a legitimate message.
-            message = request.content.read(1024 * 1024 + 1)
-            if len(message) > 1024 * 1024:
-                raise _HTTPError(http.REQUEST_ENTITY_TOO_LARGE)
-            schema.validate_cbor(message)
-            result = loads(message)
-            return result
-        else:
+        if content_type != CBOR_MIME_TYPE:
             raise _HTTPError(http.UNSUPPORTED_MEDIA_TYPE)
 
+        # Make sure it's not too large:
+        request.content.seek(SEEK_END, 0)
+        if request.content.tell() > max_size:
+            raise _HTTPError(http.REQUEST_ENTITY_TOO_LARGE)
+        request.content.seek(SEEK_SET, 0)
+
+        # We don't want to load the whole message into memory, cause it might
+        # be quite large. The CDDL validator takes a read-only bytes-like
+        # thing. Luckily, for large request bodies twisted.web will buffer the
+        # data in a file, so we can use mmap() to get a memory view. The CDDL
+        # validator will not make a copy, so it won't increase memory usage
+        # beyond that.
+        try:
+            fd = request.content.fileno()
+        except (ValueError, OSError):
+            fd = -1
+        if fd > 0:
+            # It's a file, so we can use mmap() to save memory.
+            message = mmap.mmap(fd, 0, access=mmap.ACCESS_READ)
+        else:
+            message = request.content.read()
+        schema.validate_cbor(message)
+
+        # The CBOR parser will allocate more memory, but at least we can feed
+        # it the file-like object, so that if it's large it won't be make two
+        # copies.
+        request.content.seek(SEEK_SET, 0)
+        return cbor2.load(request.content)
+
     ##### Generic APIs #####
 
     @_authorized_route(_app, set(), "/storage/v1/version", methods=["GET"])
@@ -746,7 +770,9 @@ class HTTPServer(object):
     )
     def mutable_read_test_write(self, request, authorization, storage_index):
         """Read/test/write combined operation for mutables."""
-        rtw_request = self._read_encoded(request, _SCHEMAS["mutable_read_test_write"])
+        rtw_request = self._read_encoded(
+            request, _SCHEMAS["mutable_read_test_write"], max_size=2**48
+        )
         secrets = (
             authorization[Secrets.WRITE_ENABLER],
             authorization[Secrets.LEASE_RENEW],

src/allmydata/test/test_storage_http.py

@@ -1186,18 +1186,42 @@ class MutableHTTPAPIsTests(SyncTestCase):
         )
         return storage_index, write_secret, lease_secret
 
-    def test_write_can_be_read(self):
+    def test_write_can_be_read_small_data(self):
+        """
+        Small written data can be read using ``read_share_chunk``.
+        """
+        self.write_can_be_read(b"abcdef")
+
+    def test_write_can_be_read_large_data(self):
+        """
+        Large written data (50MB) can be read using ``read_share_chunk``.
+        """
+        self.write_can_be_read(b"abcdefghij" * 5 * 1024 * 1024)
+
+    def write_can_be_read(self, data):
         """
         Written data can be read using ``read_share_chunk``.
         """
-        storage_index, _, _ = self.create_upload()
-        data0 = self.http.result_of_with_flush(
-            self.mut_client.read_share_chunk(storage_index, 0, 1, 7)
+        lease_secret = urandom(32)
+        storage_index = urandom(16)
+        self.http.result_of_with_flush(
+            self.mut_client.read_test_write_chunks(
+                storage_index,
+                urandom(32),
+                lease_secret,
+                lease_secret,
+                {
+                    0: TestWriteVectors(
+                        write_vectors=[WriteVector(offset=0, data=data)]
+                    ),
+                },
+                [],
+            )
         )
-        data1 = self.http.result_of_with_flush(
-            self.mut_client.read_share_chunk(storage_index, 1, 0, 8)
+        read_data = self.http.result_of_with_flush(
+            self.mut_client.read_share_chunk(storage_index, 0, 0, len(data))
         )
-        self.assertEqual((data0, data1), (b"bcdef-0", b"abcdef-1"))
+        self.assertEqual(read_data, data)
 
     def test_read_before_write(self):
         """In combo read/test/write operation, reads happen before writes."""
@@ -1276,15 +1300,6 @@ class MutableHTTPAPIsTests(SyncTestCase):
             b"aXYZef-0",
         )
 
-    def test_too_large_write(self):
-        """
-        Writing too large of a chunk results in a REQUEST ENTITY TOO LARGE http
-        error.
-        """
-        with self.assertRaises(ClientException) as e:
-            self.create_upload(b"0123456789" * 1024 * 1024)
-        self.assertEqual(e.exception.code, http.REQUEST_ENTITY_TOO_LARGE)
-
     def test_list_shares(self):
         """``list_shares()`` returns the shares for a given storage index."""
         storage_index, _, _ = self.create_upload()