From 2eaecd5ce7343b8df44f2cee6ae7a256e3ed64de Mon Sep 17 00:00:00 2001
From: Vincent Michel <vxgmichel@gmail.com>
Date: Sat, 16 Mar 2019 18:00:08 +0100
Subject: [PATCH] bpo-31062: Allow socket.makefile to handle line buffering
 properly

Line buffering is enabled by using the argument `buffering=1` as
defined in `io.open`.
---
 Lib/socket.py                                 |  7 ++++-
 Lib/test/test_socket.py                       | 29 ++++++++++++++-----
 .../2021-09-09-10-15-54.bpo-31062.tLeTkn.rst  |  2 ++
 3 files changed, 30 insertions(+), 8 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Library/2021-09-09-10-15-54.bpo-31062.tLeTkn.rst

diff --git a/Lib/socket.py b/Lib/socket.py
index ef82c496cb85a4..a4a96977657ff5 100755
--- a/Lib/socket.py
+++ b/Lib/socket.py
@@ -320,8 +320,12 @@ def makefile(self, mode="r", buffering=None, *,
             rawmode += "w"
         raw = SocketIO(self, rawmode)
         self._io_refs += 1
+        line_buffering = False
         if buffering is None:
             buffering = -1
+        if buffering == 1:
+            buffering = -1
+            line_buffering = True
         if buffering < 0:
             buffering = io.DEFAULT_BUFFER_SIZE
         if buffering == 0:
@@ -338,7 +342,8 @@ def makefile(self, mode="r", buffering=None, *,
         if binary:
             return buffer
         encoding = io.text_encoding(encoding)
-        text = io.TextIOWrapper(buffer, encoding, errors, newline)
+        text = io.TextIOWrapper(
+            buffer, encoding, errors, newline, line_buffering)
         text.mode = mode
         return text
 
diff --git a/Lib/test/test_socket.py b/Lib/test/test_socket.py
index 7ac92608f7ce80..31b768e66bbe78 100755
--- a/Lib/test/test_socket.py
+++ b/Lib/test/test_socket.py
@@ -4913,10 +4913,20 @@ def testReadline(self):
         # Performing file readline test
         line = self.read_file.readline()
         self.assertEqual(line, self.read_msg)
+        # Readline mode
+        if self.bufsize == 1 and self.read_mode == "r":
+            self.assertTrue(self.read_file.line_buffering)
 
     def _testReadline(self):
         self.write_file.write(self.write_msg)
-        self.write_file.flush()
+        # Readline mode: no need to flush
+        if self.bufsize == 1 and self.write_mode == "w":
+            self.assertTrue(self.write_file.line_buffering)
+        else:
+            self.write_file.flush()
+        # Prevent garbage collection from flushing
+        # until the server has finished
+        self.assertTrue(self.serv_finished.wait(5.0))
 
     def testCloseAfterMakefile(self):
         # The file returned by makefile should keep the socket open.
@@ -5072,11 +5082,6 @@ def _testWriteNonBlocking(self):
             self.serv_skipped = "failed to saturate the socket buffer"
 
 
-class LineBufferedFileObjectClassTestCase(FileObjectClassTestCase):
-
-    bufsize = 1 # Default-buffered for reading; line-buffered for writing
-
-
 class SmallBufferedFileObjectClassTestCase(FileObjectClassTestCase):
 
     bufsize = 2 # Exercise the buffering code
@@ -5112,6 +5117,16 @@ class UnicodeReadWriteFileObjectClassTestCase(FileObjectClassTestCase):
     newline = ''
 
 
+class UnicodeLineBufferedFileObjectClassTestCase(FileObjectClassTestCase):
+
+    bufsize = 1  # Default-buffered for reading; line-buffered for writing
+    read_mode = 'r'
+    read_msg = MSG.decode('utf-8')
+    write_mode = 'w'
+    write_msg = MSG.decode('utf-8')
+    newline = ''
+
+
 class NetworkConnectionTest(object):
     """Prove network connection."""
 
@@ -6649,11 +6664,11 @@ def test_main():
         NonBlockingTCPTests,
         FileObjectClassTestCase,
         UnbufferedFileObjectClassTestCase,
-        LineBufferedFileObjectClassTestCase,
         SmallBufferedFileObjectClassTestCase,
         UnicodeReadFileObjectClassTestCase,
         UnicodeWriteFileObjectClassTestCase,
         UnicodeReadWriteFileObjectClassTestCase,
+        UnicodeLineBufferedFileObjectClassTestCase,
         NetworkConnectionNoServer,
         NetworkConnectionAttributesTest,
         NetworkConnectionBehaviourTest,
diff --git a/Misc/NEWS.d/next/Library/2021-09-09-10-15-54.bpo-31062.tLeTkn.rst b/Misc/NEWS.d/next/Library/2021-09-09-10-15-54.bpo-31062.tLeTkn.rst
new file mode 100644
index 00000000000000..ef6421b957bd6a
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2021-09-09-10-15-54.bpo-31062.tLeTkn.rst
@@ -0,0 +1,2 @@
+Allow :meth:`socket.socket.makefile` to handle line buffering properly
+(``buffering=1``). This is done by mimicking the behavior of :func:`open`.