diff --git a/mercurial/store.py b/mercurial/store.py
--- a/mercurial/store.py
+++ b/mercurial/store.py
@@ -469,12 +469,36 @@ class StoreFile:
 
     def file_size(self, vfs):
         if self._file_size is None:
+            if vfs is None:
+                msg = b"calling vfs-less file_size without prior call: %s"
+                msg %= self.unencoded_path
+                raise error.ProgrammingError(msg)
             try:
                 self._file_size = vfs.stat(self.unencoded_path).st_size
             except FileNotFoundError:
                 self._file_size = 0
         return self._file_size
 
+    def get_stream(self, vfs, copies):
+        """return data "stream" information for this file
+
+        (unencoded_file_path, content_iterator, content_size)
+        """
+        size = self.file_size(None)
+
+        def get_stream():
+            actual_path = copies[vfs.join(self.unencoded_path)]
+            with open(actual_path, 'rb') as fp:
+                yield None  # ready to stream
+                if size <= 65536:
+                    yield fp.read(size)
+                else:
+                    yield from util.filechunkiter(fp, limit=size)
+
+        s = get_stream()
+        next(s)
+        return (self.unencoded_path, s, size)
+
 
 @attr.s(slots=True, init=False)
 class BaseStoreEntry:
@@ -485,6 +509,14 @@ class BaseStoreEntry:
     def files(self) -> List[StoreFile]:
         raise NotImplementedError
 
+    def get_streams(self, vfs, copies=None):
+        """return a list of data stream associated to files for this entry
+
+        return [(unencoded_file_path, content_iterator, content_size), …]
+        """
+        assert vfs is not None
+        return [f.get_stream(vfs, copies) for f in self.files()]
+
 
 @attr.s(slots=True, init=False)
 class SimpleStoreEntry(BaseStoreEntry):
diff --git a/mercurial/streamclone.py b/mercurial/streamclone.py
--- a/mercurial/streamclone.py
+++ b/mercurial/streamclone.py
@@ -11,7 +11,6 @@ import os
 import struct
 
 from .i18n import _
-from .pycompat import open
 from .interfaces import repository
 from . import (
     bookmarks,
@@ -658,36 +657,25 @@ def _emit2(repo, entries):
         totalbytecount = 0
 
         for src, vfs, e in entries:
-            for f in e.files():
+            for name, stream, size in e.get_streams(vfs, copies=copy):
                 yield src
-                name = f.unencoded_path
                 yield util.uvarintencode(len(name))
-                actual_path = copy[vfs.join(name)]
-                fp = open(actual_path, b'rb')
-                size = f.file_size(vfs)
+                yield util.uvarintencode(size)
+                yield name
                 bytecount = 0
-                try:
-                    yield util.uvarintencode(size)
-                    yield name
-                    if size <= 65536:
-                        chunks = (fp.read(size),)
-                    else:
-                        chunks = util.filechunkiter(fp, limit=size)
-                    for chunk in chunks:
-                        bytecount += len(chunk)
-                        totalbytecount += len(chunk)
-                        progress.update(totalbytecount)
-                        yield chunk
-                    if bytecount != size:
-                        # Would most likely be caused by a race due to `hg
-                        # strip` or a revlog split
-                        msg = _(
-                            b'clone could only read %d bytes from %s, but '
-                            b'expected %d bytes'
-                        )
-                        raise error.Abort(msg % (bytecount, name, size))
-                finally:
-                    fp.close()
+                for chunk in stream:
+                    bytecount += len(chunk)
+                    totalbytecount += len(chunk)
+                    progress.update(totalbytecount)
+                    yield chunk
+                if bytecount != size:
+                    # Would most likely be caused by a race due to `hg
+                    # strip` or a revlog split
+                    msg = _(
+                        b'clone could only read %d bytes from %s, but '
+                        b'expected %d bytes'
+                    )
+                    raise error.Abort(msg % (bytecount, name, size))
 
 
 def _test_sync_point_walk_1(repo):