diff --git a/hgext/absorb.py b/hgext/absorb.py
--- a/hgext/absorb.py
+++ b/hgext/absorb.py
@@ -33,6 +33,7 @@
 
 
 import collections
+import io
 
 from mercurial.i18n import _
 from mercurial.node import (
@@ -968,7 +969,7 @@
     a1 = hunk.fromline + len(hunk.before) - 1
     # remove before and after context
     hunk.before = hunk.after = []
-    buf = util.stringio()
+    buf = io.BytesIO()
     hunk.write(buf)
     patchlines = mdiff.splitnewlines(buf.getvalue())
     # hunk.prettystr() will update hunk.removed
diff --git a/hgext/convert/cvs.py b/hgext/convert/cvs.py
--- a/hgext/convert/cvs.py
+++ b/hgext/convert/cvs.py
@@ -6,6 +6,7 @@
 # GNU General Public License version 2 or any later version.
 
 import errno
+import io
 import os
 import re
 import socket
@@ -18,7 +19,6 @@
 from mercurial import (
     encoding,
     error,
-    util,
 )
 from mercurial.utils import (
     dateutil,
@@ -30,7 +30,6 @@
     cvsps,
 )
 
-stringio = util.stringio
 checktool = common.checktool
 commit = common.commit
 converter_source = common.converter_source
@@ -260,7 +259,7 @@
             # file-objects returned by socket.makefile() do not handle
             # large read() requests very well.
             chunksize = 65536
-            output = stringio()
+            output = io.BytesIO()
             while count > 0:
                 data = fp.read(min(count, chunksize))
                 if not data:
diff --git a/hgext/convert/hg.py b/hgext/convert/hg.py
--- a/hgext/convert/hg.py
+++ b/hgext/convert/hg.py
@@ -17,6 +17,7 @@
 #   the converted revision to have a different identity than the
 #   source.
 
+import io
 import os
 import re
 import time
@@ -43,8 +44,6 @@
 )
 from mercurial.utils import dateutil
 
-stringio = util.stringio
-
 from . import common
 
 mapfile = common.mapfile
@@ -149,7 +148,7 @@
             self.before()
 
     def _rewritetags(self, source, revmap, data):
-        fp = stringio()
+        fp = io.BytesIO()
         for line in data.splitlines():
             s = line.split(b' ', 1)
             if len(s) != 2:
@@ -169,7 +168,7 @@
         return fp.getvalue()
 
     def _rewritesubstate(self, source, data):
-        fp = stringio()
+        fp = io.BytesIO()
         for line in data.splitlines():
             s = line.split(b' ', 1)
             if len(s) != 2:
diff --git a/hgext/convert/subversion.py b/hgext/convert/subversion.py
--- a/hgext/convert/subversion.py
+++ b/hgext/convert/subversion.py
@@ -3,6 +3,7 @@
 # Copyright(C) 2007 Daniel Holth et al
 
 import codecs
+import io
 import locale
 import os
 import pickle
@@ -26,7 +27,6 @@
 
 from . import common
 
-stringio = util.stringio
 propertycache = util.propertycache
 urlerr = util.urlerr
 urlreq = util.urlreq
@@ -1267,12 +1267,12 @@
             if self.module != new_module:
                 self.module = new_module
                 self.reparent(self.module)
-            io = stringio()
-            info = svn.ra.get_file(self.ra, file, revnum, io)
-            data = io.getvalue()
+            bio = io.BytesIO()
+            info = svn.ra.get_file(self.ra, file, revnum, bio)
+            data = bio.getvalue()
             # ra.get_file() seems to keep a reference on the input buffer
             # preventing collection. Release it explicitly.
-            io.close()
+            bio.close()
             if isinstance(info, list):
                 info = info[-1]
             mode = (b"svn:executable" in info) and b'x' or b''
diff --git a/hgext/infinitepush/bundleparts.py b/hgext/infinitepush/bundleparts.py
--- a/hgext/infinitepush/bundleparts.py
+++ b/hgext/infinitepush/bundleparts.py
@@ -3,6 +3,7 @@
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 
+import io
 
 from mercurial.i18n import _
 from mercurial.node import hex
@@ -13,7 +14,6 @@
     error,
     extensions,
     revsetlang,
-    util,
 )
 
 from . import common
@@ -114,7 +114,7 @@
         self.params = part.params
         self.mandatorykeys = part.mandatorykeys
         # copy the buffer
-        self._io = util.stringio(part.read())
+        self._io = io.BytesIO(part.read())
 
     def consume(self):
         return
diff --git a/hgext/patchbomb.py b/hgext/patchbomb.py
--- a/hgext/patchbomb.py
+++ b/hgext/patchbomb.py
@@ -77,6 +77,7 @@
 import email.mime.multipart as emimemultipart
 import email.utils as eutil
 import errno
+import io
 import os
 import socket
 
@@ -104,8 +105,6 @@
     urlutil,
 )
 
-stringio = util.stringio
-
 cmdtable = {}
 command = registrar.command(cmdtable)
 
@@ -228,7 +227,7 @@
     tmpl = ui.config(b'patchbomb', b'flagtemplate')
     if not tmpl:
         return b' '.join(flags)
-    out = util.stringio()
+    out = io.BytesIO()
     spec = formatter.literal_templatespec(templater.unquotestring(tmpl))
     with formatter.templateformatter(ui, out, b'patchbombflag', {}, spec) as fm:
         fm.startitem()
@@ -360,7 +359,7 @@
     for r in revs:
         if r == prev and (repo[None].files() or repo[None].deleted()):
             ui.warn(_(b'warning: working directory has uncommitted changes\n'))
-        output = stringio()
+        output = io.BytesIO()
         cmdutil.exportfile(
             repo, [r], output, opts=patch.difffeatureopts(ui, opts, git=True)
         )
@@ -995,7 +994,7 @@
             if not mbox:
                 # Exim does not remove the Bcc field
                 del m['Bcc']
-            fp = stringio()
+            fp = io.BytesIO()
             generator = mail.Generator(fp, mangle_from_=False)
             generator.flatten(m, False)
             alldests = to + bcc + cc
diff --git a/hgext/phabricator.py b/hgext/phabricator.py
--- a/hgext/phabricator.py
+++ b/hgext/phabricator.py
@@ -660,7 +660,7 @@
 
 def getdiff(basectx, ctx, diffopts):
     """plain-text diff without header (user, commit message, etc)"""
-    output = util.stringio()
+    output = io.BytesIO()
     for chunk, _label in patch.diffui(
         ctx.repo(), basectx.p1().node(), ctx.node(), None, opts=diffopts
     ):