Added tar plugin for better handling of tar files

src/binwalk/plugins/tar.py

+import time
+import math
+import binwalk.core.plugin
+
+class Plugin(binwalk.core.plugin.Plugin):
+
+    MODULES = ['Signature']
+
+    # "borrowed from pythons tarfile module"
+    TAR_BLOCKSIZE = 512
+
+    def nts(self, s):
+        """
+        Convert a null-terminated string field to a python string.
+        """
+        # Use the string up to the first null char.
+        p = s.find("\0")
+        if p == -1:
+            return s
+        return s[:p]
+
+    def nti(self, s):
+        """
+        Convert a number field to a python number.
+        """
+        # There are two possible encodings for a number field, see
+        # itn() below.
+        if s[0] != chr(0200):
+            try:
+                n = int(self.nts(s) or "0", 8)
+            except ValueError:
+                raise ValueError("invalid tar header")
+        else:
+            n = 0L
+            for i in xrange(len(s) - 1):
+                n <<= 8
+                n += ord(s[i + 1])
+        return n
+
+    def scan(self, result):
+        if result.description.lower().startswith('posix tar archive'):
+            is_tar = True
+            file_offset = result.offset
+            fd = self.module.config.open_file(result.file.name, offset=result.offset)
+
+            while is_tar:
+                # read in the tar header struct
+                buf = fd.read(self.TAR_BLOCKSIZE)
+                
+                # check to see if we are still in a tarball
+                if buf[257:262] == 'ustar':
+                    # get size of tarred file convert to blocks (plus 1 to include header)
+                    try:
+                        size = self.nti(buf[124:136])
+                        blocks = math.ceil(size/float(self.TAR_BLOCKSIZE)) + 1
+                    except ValueError as e:
+                        is_tar = False
+                        break
+
+                    # update file offset for next file in tarball
+                    file_offset += int(self.TAR_BLOCKSIZE*blocks)
+
+                    if file_offset >= result.file.size:
+                        # we hit the end of the file
+                        is_tar = False
+                    else:
+                        fd.seek(file_offset)
+                else:
+                    is_tar = False            
+
+            result.jump = file_offset