[arch-dev-public] [PATCH 4/4] Reduce code duplication in open() calls

[Dan McGee]

The commit that created these very similar pair of functions did a
copy-paste job; this commit fixes up some of that to reduce code duplication
and keep all of the error handling code in once place so the actual work of
the two methods is much clearer.

Signed-off-by: Dan McGee <dan at archlinux.org>
---
 Namcap/util.py |   46 ++++++++++++++++------------------------------
 1 files changed, 16 insertions(+), 30 deletions(-)

diff --git a/Namcap/util.py b/Namcap/util.py
index 4568891..80d6857 100644
--- a/Namcap/util.py
+++ b/Namcap/util.py
@@ -21,18 +21,14 @@ import os
 import re
 import stat
 
-def is_elf(path):
-	"""
-	Given a file path, ensure it exists and peek at the first few bytes
-	to determine if it is an ELF file.
-	"""
+def read_carefully(path, readcall):
 	if not os.path.isfile(path):
 		return False
 	reset_perms = False
 	if not os.access(path, os.R_OK):
 		# don't mess with links we can't read
 		if os.path.islink(path):
-			return False
+			return None
 		reset_perms = True
 		# attempt to make it readable if possible
 		statinfo = os.stat(path)
@@ -40,14 +36,24 @@ def is_elf(path):
 		try:
 			os.chmod(path, newmode)
 		except IOError:
-			return False
+			return None
 	fd = open(path)
-	bytes = fd.read(4)
+	val = readcall(fd)
 	fd.close()
 	# reset permissions if necessary
 	if reset_perms:
 		# set file back to original permissions
 		os.chmod(path, statinfo.st_mode)
+	return val
+
+def is_elf(path):
+	"""
+	Given a file path, ensure it exists and peek at the first few bytes
+	to determine if it is an ELF file.
+	"""
+	bytes = read_carefully(path, lambda fd: fd.read(4))
+	if not bytes:
+		return False
 	# magic elf header, present in binaries and libraries
 	if bytes == "\x7FELF":
 		return True
@@ -59,29 +65,9 @@ supported_scripts = ['python', 'perl', 'ruby', 'wish', 'expect',
 
 def script_type(path):
 	global supported_scripts
-	if not os.path.isfile(path):
+	firstline = read_carefully(path, lambda fd: fd.readline())
+	if not firstline:
 		return None
-	reset_perms = False
-	if not os.access(path, os.R_OK):
-		# don't mess with links we can't read
-		if os.path.islink(path):
-			return None
-		reset_perms = True
-		# attempt to make it readable if possible
-		statinfo = os.stat(path)
-		newmode = statinfo.st_mode | stat.S_IRUSR
-		try:
-			os.chmod(path, newmode)
-		except IOError:
-			return None
-
-	fd = open(path)
-	firstline = fd.readline()
-	fd.close()
-	# reset permissions if necessary
-	if reset_perms:
-		# set file back to original permissions
-		os.chmod(path, statinfo.st_mode)
 	script = re.compile('#!.*/(.*)')
 	firstlinere = script.match(firstline)
 	if firstlinere != None:
-- 
1.7.1