diff --git a/mercurial/archival.py b/mercurial/archival.py
--- a/mercurial/archival.py
+++ b/mercurial/archival.py
@@ -7,6 +7,7 @@
 
 
 import gzip
+import io
 import os
 import struct
 import tarfile
@@ -30,8 +31,6 @@
 
 from .utils import stringutil
 
-stringio = util.stringio
-
 # from unzip source code:
 _UNX_IFREG = 0x8000
 _UNX_IFLNK = 0xA000
@@ -115,7 +114,7 @@
         )
     }
 
-    out = util.stringio()
+    out = io.BytesIO()
 
     fm = formatter.formatter(repo.ui, out, b'archive', opts)
     fm.startitem()
@@ -184,7 +183,7 @@
             i.size = 0
         else:
             i.mode = mode
-            data = stringio(data)
+            data = io.BytesIO(data)
         self.z.addfile(i, data)
 
     def done(self):
diff --git a/mercurial/cmdutil.py b/mercurial/cmdutil.py
--- a/mercurial/cmdutil.py
+++ b/mercurial/cmdutil.py
@@ -8,6 +8,7 @@
 
 import copy as copymod
 import errno
+import io
 import os
 import re
 
@@ -73,8 +74,6 @@
     for t in (Any, Dict):
         assert t
 
-stringio = util.stringio
-
 # templates of common command options
 
 dryrunopts = [
@@ -575,7 +574,7 @@
                 util.copyfile(repo.wjoin(f), tmpname, copystat=True)
                 backups[f] = tmpname
 
-            fp = stringio()
+            fp = io.BytesIO()
             for c in chunks:
                 fname = c.filename()
                 if fname in backups:
@@ -3704,7 +3703,7 @@
         if tobackup is None:
             tobackup = set()
         # Apply changes
-        fp = stringio()
+        fp = io.BytesIO()
         # chunks are serialized per file, but files aren't sorted
         for f in sorted({c.header.filename() for c in chunks if ishunk(c)}):
             prntstatusmsg(b'revert', f)
diff --git a/mercurial/crecord.py b/mercurial/crecord.py
--- a/mercurial/crecord.py
+++ b/mercurial/crecord.py
@@ -9,6 +9,7 @@
 # (Itself based on Bryan O'Sullivan's record extension.)
 
 
+import io
 import os
 import re
 import signal
@@ -29,8 +30,6 @@
 )
 from .utils import stringutil
 
-stringio = util.stringio
-
 # patch comments based on the git one
 diffhelptext = _(
     b"""# To remove '-' lines, make them ' ' lines (context).
@@ -226,7 +225,7 @@
         self.hunks = [uihunk(h, self) for h in self.hunks]
 
     def prettystr(self):
-        x = stringio()
+        x = io.BytesIO()
         self.pretty(x)
         return x.getvalue()
 
@@ -463,7 +462,7 @@
     pretty = write
 
     def prettystr(self):
-        x = stringio()
+        x = io.BytesIO()
         self.pretty(x)
         return x.getvalue()
 
@@ -1799,7 +1798,7 @@
                 return None
 
             # write the initial patch
-            patch = stringio()
+            patch = io.BytesIO()
             patch.write(diffhelptext + hunkhelptext)
             chunk.header.write(patch)
             chunk.write(patch)
diff --git a/mercurial/patch.py b/mercurial/patch.py
--- a/mercurial/patch.py
+++ b/mercurial/patch.py
@@ -11,6 +11,7 @@
 import contextlib
 import copy
 import errno
+import io
 import os
 import re
 import shutil
@@ -45,8 +46,6 @@
     stringutil,
 )
 
-stringio = util.stringio
-
 gitre = re.compile(br'diff --git a/(.*) b/(.*)')
 tabsplitter = re.compile(br'(\t+|[^\t]+)')
 wordsplitter = re.compile(
@@ -74,7 +73,7 @@
         return len(l) == 2 and b' ' not in l[0]
 
     def chunk(lines):
-        return stringio(b''.join(lines))
+        return io.BytesIO(b''.join(lines))
 
     def hgsplit(stream, cur):
         inheader = True
@@ -107,7 +106,7 @@
 
     def mimesplit(stream, cur):
         def msgfp(m):
-            fp = stringio()
+            fp = io.BytesIO()
             # pytype: disable=wrong-arg-types
             g = mail.Generator(fp, mangle_from_=False)
             # pytype: enable=wrong-arg-types
@@ -290,7 +289,7 @@
 
             ui.debug(b'found patch at byte %d\n' % m.start(0))
             diffs_seen += 1
-            cfp = stringio()
+            cfp = io.BytesIO()
             for line in payload[: m.start(0)].splitlines():
                 if line.startswith(b'# HG changeset patch') and not hgpatch:
                     ui.debug(b'patch generated by hg export\n')
@@ -599,7 +598,7 @@
         self.created = 0
         self.maxsize = maxsize
         if self.maxsize is None:
-            self.maxsize = 4 * (2 ** 20)
+            self.maxsize = 4 * (2**20)
         self.size = 0
         self.data = {}
 
@@ -1258,7 +1257,7 @@
                         continue
                     # Remove comment lines
                     patchfp = open(patchfn, 'rb')
-                    ncpatchfp = stringio()
+                    ncpatchfp = io.BytesIO()
                     for line in patchfp:
                         line = util.fromnativeeol(line)
                         if not line.startswith(b'#'):
@@ -1677,7 +1676,7 @@
 
     >>> reversedhunks = reversehunks(hunkscomingfromfilterpatch)
     >>> from . import util
-    >>> fp = util.stringio()
+    >>> fp = io.BytesIO()
     >>> for c in reversedhunks:
     ...      c.write(fp)
     >>> fp.seek(0) or None
@@ -1734,7 +1733,7 @@
     ...  7
     ...  8
     ... +9'''
-    >>> out = util.stringio()
+    >>> out = io.BytesIO()
     >>> headers = parsepatch([rawpatch], maxcontext=1)
     >>> for header in headers:
     ...     header.write(out)
@@ -1841,7 +1840,7 @@
         }
 
     p = parser()
-    fp = stringio()
+    fp = io.BytesIO()
     fp.write(b''.join(originalchunks))
     fp.seek(0)
 
@@ -2030,7 +2029,7 @@
         pos = lr.fp.tell()
         fp = lr.fp
     except IOError:
-        fp = stringio(lr.fp.read())
+        fp = io.BytesIO(lr.fp.read())
     gitlr = linereader(fp)
     gitlr.push(firstline)
     gitpatches = readgitpatch(gitlr)
diff --git a/mercurial/profiling.py b/mercurial/profiling.py
--- a/mercurial/profiling.py
+++ b/mercurial/profiling.py
@@ -7,6 +7,7 @@
 
 
 import contextlib
+import io
 
 from .i18n import _
 from .pycompat import (
@@ -225,7 +226,7 @@
 
         try:
             if self._output == b'blackbox':
-                self._fp = util.stringio()
+                self._fp = io.BytesIO()
             elif self._output:
                 path = util.expandpath(self._output)
                 self._fp = open(path, b'wb')
diff --git a/mercurial/pure/mpatch.py b/mercurial/pure/mpatch.py
--- a/mercurial/pure/mpatch.py
+++ b/mercurial/pure/mpatch.py
@@ -10,9 +10,6 @@
 import struct
 
 
-stringio = io.BytesIO
-
-
 class mpatchError(Exception):
     """error raised when a delta cannot be decoded"""
 
@@ -71,7 +68,7 @@
     if not tl:
         return a
 
-    m = stringio()
+    m = io.BytesIO()
 
     # load our original text
     m.write(a)
diff --git a/mercurial/pure/parsers.py b/mercurial/pure/parsers.py
--- a/mercurial/pure/parsers.py
+++ b/mercurial/pure/parsers.py
@@ -25,8 +25,6 @@
 from ..revlogutils import nodemap as nodemaputil
 from ..revlogutils import constants as revlog_constants
 
-stringio = io.BytesIO
-
 
 _pack = struct.pack
 _unpack = struct.unpack
@@ -955,7 +953,7 @@
 
 
 def pack_dirstate(dmap, copymap, pl):
-    cs = stringio()
+    cs = io.BytesIO()
     write = cs.write
     write(b"".join(pl))
     for f, e in dmap.items():
diff --git a/mercurial/url.py b/mercurial/url.py
--- a/mercurial/url.py
+++ b/mercurial/url.py
@@ -9,6 +9,7 @@
 
 
 import base64
+import io
 import socket
 
 from .i18n import _
@@ -29,7 +30,6 @@
 )
 
 httplib = util.httplib
-stringio = util.stringio
 urlerr = util.urlerr
 urlreq = util.urlreq
 
@@ -276,7 +276,7 @@
         res.length = None
         res.chunked = 0
         res.will_close = 1
-        res.msg = httplib.HTTPMessage(stringio())
+        res.msg = httplib.HTTPMessage(io.BytesIO())
         return False
 
     res.msg = httplib.HTTPMessage(res.fp)
diff --git a/mercurial/wireprotoserver.py b/mercurial/wireprotoserver.py
--- a/mercurial/wireprotoserver.py
+++ b/mercurial/wireprotoserver.py
@@ -6,6 +6,7 @@
 
 
 import contextlib
+import io
 import struct
 import threading
 
@@ -24,8 +25,6 @@
     stringutil,
 )
 
-stringio = util.stringio
-
 urlerr = util.urlerr
 urlreq = util.urlreq
 
@@ -117,7 +116,7 @@
         oldout = self._ui.fout
         olderr = self._ui.ferr
 
-        out = util.stringio()
+        out = io.BytesIO()
 
         try:
             self._ui.fout = out