git-p4: add read_pipe_text() internal function

The existing read_pipe() function returns an empty string on
error, but also returns an empty string if the command returns
an empty string.

This leads to ugly constructions trying to detect error cases.

Add read_pipe_text() which just returns None on error.

Signed-off-by: Luke Diamand <luke@diamand.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/git-p4.py b/git-p4.py
index eab319d76e4597ebbb27019695fd9ce14d145285..584b817757f85f1f92927b5fca7403e7e4ed7b0a 100755 (executable)
--- a/git-p4.py
+++ b/git-p4.py
@@ -160,17 +160,42 @@ def p4_write_pipe(c, stdin):
     real_cmd = p4_build_cmd(c)
     return write_pipe(real_cmd, stdin)
 
-def read_pipe(c, ignore_error=False):
+def read_pipe_full(c):
+    """ Read output from  command. Returns a tuple
+        of the return status, stdout text and stderr
+        text.
+    """
     if verbose:
         sys.stderr.write('Reading pipe: %s\n' % str(c))
 
     expand = isinstance(c,basestring)
     p = subprocess.Popen(c, stdout=subprocess.PIPE, stderr=subprocess.PIPE, shell=expand)
     (out, err) = p.communicate()
-    if p.returncode != 0 and not ignore_error:
-        die('Command failed: %s\nError: %s' % (str(c), err))
+    return (p.returncode, out, err)
+
+def read_pipe(c, ignore_error=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.
+    """
+    (retcode, out, err) = read_pipe_full(c)
+    if retcode != 0:
+        if ignore_error:
+            out = ""
+        else:
+            die('Command failed: %s\nError: %s' % (str(c), err))
     return out
 
+def read_pipe_text(c):
+    """ Read output from a command with trailing whitespace stripped.
+        On error, returns None.
+    """
+    (retcode, out, err) = read_pipe_full(c)
+    if retcode != 0:
+        return None
+    else:
+        return out.rstrip()
+
 def p4_read_pipe(c, ignore_error=False):
     real_cmd = p4_build_cmd(c)
     return read_pipe(real_cmd, ignore_error)