git-p4: encode/decode communication with git for python3

Under python3, calls to write() on the stream to `git fast-import` must
be encoded.  This patch wraps the IO object such that this encoding is
done transparently.

Conversely, any text data read from subprocesses must also be decoded
before running through the rest of the pipeline.

Signed-off-by: Yang Zhao <yang.zhao@skyboxlabs.com>
Reviewed-by: Ben Keene <seraphire@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-p4.py

@@ -183,10 +183,12 @@ def read_pipe_full(c):
     (out, err) = p.communicate()
     return (p.returncode, out, decode_text_stream(err))
 
-def read_pipe(c, ignore_error=False):
+def read_pipe(c, ignore_error=False, raw=False):
     """ Read output from  command. Returns the output text on
         success. On failure, terminates execution, unless
         ignore_error is True, when it returns an empty string.
+
+        If raw is True, do not attempt to decode output text.
     """
     (retcode, out, err) = read_pipe_full(c)
     if retcode != 0:
@@ -194,6 +196,8 @@ def read_pipe(c, ignore_error=False):
             out = ""
         else:
             die('Command failed: %s\nError: %s' % (str(c), err))
+    if not raw:
+        out = decode_text_stream(out)
     return out
 
 def read_pipe_text(c):
@@ -220,7 +224,6 @@ def read_pipe_lines(c):
     val = [decode_text_stream(line) for line in pipe.readlines()]
     if pipe.close() or p.wait():
         die('Command failed: %s' % str(c))
-
     return val
 
 def p4_read_pipe_lines(c):
@@ -616,7 +619,8 @@ def p4CmdList(cmd, stdin=None, stdin_mode='w+b', cb=None, skip_info=False,
             stdin_file.write(stdin)
         else:
             for i in stdin:
-                stdin_file.write(i + '\n')
+                stdin_file.write(encode_text_stream(i))
+                stdin_file.write(b'\n')
         stdin_file.flush()
         stdin_file.seek(0)
 
@@ -1245,7 +1249,7 @@ def generatePointer(self, contentFile):
             ['git', 'lfs', 'pointer', '--file=' + contentFile],
             stdout=subprocess.PIPE
         )
-        pointerFile = pointerProcess.stdout.read()
+        pointerFile = decode_text_stream(pointerProcess.stdout.read())
         if pointerProcess.wait():
             os.remove(contentFile)
             die('git-lfs pointer command failed. Did you install the extension?')
@@ -3538,6 +3542,15 @@ def openStreams(self):
         self.gitStream = self.importProcess.stdin
         self.gitError = self.importProcess.stderr
 
+        if bytes is not str:
+            # Wrap gitStream.write() so that it can be called using `str` arguments
+            def make_encoded_write(write):
+                def encoded_write(s):
+                    return write(s.encode() if isinstance(s, str) else s)
+                return encoded_write
+
+            self.gitStream.write = make_encoded_write(self.gitStream.write)
+
     def closeStreams(self):
         self.gitStream.close()
         if self.importProcess.wait() != 0: