--- a/mercurial/pure/charencode.py	Thu Aug 24 21:43:54 2017 -0700
+++ b/mercurial/pure/charencode.py	Sun Apr 23 16:10:51 2017 +0900
@@ -7,6 +7,12 @@
 
 from __future__ import absolute_import
 
+import array
+
+from .. import (
+    pycompat,
+)
+
 def asciilower(s):
     '''convert a string to lowercase if ASCII
 
@@ -20,3 +26,47 @@
     Raises UnicodeDecodeError if non-ASCII characters are found.'''
     s.decode('ascii')
     return s.upper()
+
+_jsonmap = []
+_jsonmap.extend("\\u%04x" % x for x in range(32))
+_jsonmap.extend(pycompat.bytechr(x) for x in range(32, 127))
+_jsonmap.append('\\u007f')
+_jsonmap[0x09] = '\\t'
+_jsonmap[0x0a] = '\\n'
+_jsonmap[0x22] = '\\"'
+_jsonmap[0x5c] = '\\\\'
+_jsonmap[0x08] = '\\b'
+_jsonmap[0x0c] = '\\f'
+_jsonmap[0x0d] = '\\r'
+_paranoidjsonmap = _jsonmap[:]
+_paranoidjsonmap[0x3c] = '\\u003c'  # '<' (e.g. escape "</script>")
+_paranoidjsonmap[0x3e] = '\\u003e'  # '>'
+_jsonmap.extend(pycompat.bytechr(x) for x in range(128, 256))
+
+def jsonescapeu8fast(u8chars, paranoid):
+    """Convert a UTF-8 byte string to JSON-escaped form (fast path)
+
+    Raises ValueError if non-ASCII characters have to be escaped.
+    """
+    if paranoid:
+        jm = _paranoidjsonmap
+    else:
+        jm = _jsonmap
+    try:
+        return ''.join(jm[x] for x in bytearray(u8chars))
+    except IndexError:
+        raise ValueError
+
+def jsonescapeu8fallback(u8chars, paranoid):
+    """Convert a UTF-8 byte string to JSON-escaped form (slow path)
+
+    Escapes all non-ASCII characters no matter if paranoid is False.
+    """
+    if paranoid:
+        jm = _paranoidjsonmap
+    else:
+        jm = _jsonmap
+    # non-BMP char is represented as UTF-16 surrogate pair
+    u16codes = array.array('H', u8chars.decode('utf-8').encode('utf-16'))
+    u16codes.pop(0)  # drop BOM
+    return ''.join(jm[x] if x < 128 else '\\u%04x' % x for x in u16codes)