luci-py: Tools for working with BSD style ar archives.

client/libs/ar/writer.py

Index: client/libs/ar/writer.py
diff --git a/client/libs/ar/writer.py b/client/libs/ar/writer.py
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+++ b/client/libs/ar/writer.py
@@ -0,0 +1,109 @@
+# Copyright 2016 The LUCI Authors. All rights reserved.
+# Use of this source code is governed under the Apache License, Version 2.0
+# that can be found in the LICENSE file.
+
+import shutil
+
+
+class ArWriter(object):
+  """Write an ar archive to the given output buffer."""
+
+  # Mode sentinels
+  MODE_HEADER = []

[M-A Ruel, 2016/06/14 13:26:17]

= object()

[mithro, 2016/06/16 11:37:11]

Obsolete.

+  MODE_CONTENTS = []
+
+  def __init__(self, obuf):
+    self.obuf = obuf

[M-A Ruel, 2016/06/14 13:26:17]

I'd prefer self._obuf and _ prefix for others too

[mithro, 2016/06/16 11:37:11]

Obsolete.

+    self.obuf.write('!<arch>\n')
+    self.mode = ArWriter.MODE_HEADER
+    self.needspadding = False
+    self.bytesrequired = 0
+
+  def header(self, fp, size, modtime, ownerid, groupid, filemod):
+    """Write a file information to the archive."""
+    assert self.mode == ArWriter.MODE_HEADER
+    assert self.bytesrequired == 0
+
+    # File name, 16 bytes
+    self.obuf.write('#1/%-13s' % str(len(fp)))

[M-A Ruel, 2016/06/14 13:26:17]

Can you use struct.pack() like you did with unpack in reader?

[mithro, 2016/06/16 11:37:11]

No stuct.pack doesn't do this style of output (left aligned integers).

+    # Modtime, 12 bytes
+    self.obuf.write('%-12i' % modtime)
+    # Owner ID, 6 bytes
+    self.obuf.write('%-6i' % ownerid)
+    # Group ID, 6 bytes
+    self.obuf.write('%-6i' % groupid)
+    # File mode, 8 bytes
+    self.obuf.write('%-8o' % filemod)
+
+    datasize = size+len(fp)
+    # File size, 10 bytes
+    self.obuf.write('%-10s' % datasize)
+    # File magic, 2 bytes
+    self.obuf.write('\x60\n')
+
+    # Filename - BSD variant
+    self.obuf.write(fp)
+
+    self.mode = ArWriter.MODE_CONTENTS
+    self.bytesrequired = size
+    self.needspadding = datasize % 2 != 0
+
+  def _write(self, ibuf=None, s=None):

[M-A Ruel, 2016/06/14 13:26:17]

I think I'd prefer two functions. This is confusing.

[mithro, 2016/06/16 11:37:11]

Obsolete.

+    assert self.mode == ArWriter.MODE_CONTENTS
+    assert ibuf is not None or s is not None
+
+    if ibuf is not None:
+      start = ibuf.tell()
+      shutil.copyfileobj(ibuf, self.obuf)
+      end = ibuf.tell()
+      self.bytesrequired -= end-start
+
+    if s is not None:
+      self.obuf.write(s)
+      self.bytesrequired -= len(s)
+
+    if self.bytesrequired == 0:

[M-A Ruel, 2016/06/14 13:26:17]

if not self._bytesrequired:

[mithro, 2016/06/16 11:37:11]

Obsolete.

+      if self.needspadding:
+        self.obuf.write('\n')
+      self.mode = ArWriter.MODE_HEADER
+
+  def write(self, ibuf_or_str):

[M-A Ruel, 2016/06/14 13:26:17]

I'd prefer a writestr() function and not try to guess, it would be cleaner, more
readable and slightly faster.

[mithro, 2016/06/16 11:37:11]

Obsolete.

+    """Write the file body to the archive."""
+    try:
+      self._write(ibuf=ibuf_or_str)
+    except AttributeError:
+      self._write(s=ibuf_or_str)
+
+  def close(self):
+    """Close the archive. Will close the output buffer."""
+    assert self.bytesrequired == 0
+    assert self.mode == ArWriter.MODE_HEADER
+    self.obuf.close()
+
+
+class ArDefaultWriter(ArWriter):
+  """Write an ar archive using defaults to the given output buffer.
+
+  Only a file's name and content are needed to create the archive, all of the
+  modification time, user, group and mode information will be set to default
+  values. This means that you don't need to perform an expensive stat the file.
+  """
+  DEFAULT_MODTIME = 1447140471
+  DEFAULT_USER = 1000
+  DEFAULT_GROUP = 1000
+  DEFAULT_MODE = 0100640 # 100640 -- Octal
+
+  def header(self, name, size,
+             modtime=None, ownerid=None, groupid=None, filemod=None):

[M-A Ruel, 2016/06/14 13:26:17]

I'd prefer to not expose these arguments at all.  Add a # pylint:
disable=foo-bar

[mithro, 2016/06/16 11:37:11]

Obsolete.

+    assert modtime is None
+    assert ownerid is None
+    assert groupid is None
+    assert filemod is None
+    ArWriter.header(
+      self, name, size,
+      self.DEFAULT_MODTIME, self.DEFAULT_USER, self.DEFAULT_GROUP,
+      self.DEFAULT_MODE)
+
+  def add(self, name, data):
+    self.header(name, len(data))
+    self._write(s=data)