Add Unpack class

TODO.md

@@ -1,7 +1,6 @@
 Things We Need To Do
 ====================
 
-* `unpack.py` like golang's `encoding/binary`
 * documentation
 * remove lingering py2-isms
 * more logical way to chain together dispatcher, tcp resequencer

netarch/unpack.py

@@ -0,0 +1,73 @@
+#! /usr/bin/python3
+
+ENDIAN_LITTLE = 1
+ENDIAN_BIG = 2
+ENDIAN_MIDDLE = 3
+ENDIAN_NETWORK = ENDIAN_BIG
+
+class Unpacker:
+    """Class that lets you peel values off
+    
+    >>> u = Unpacker(bytes((1, 0,2, 0,0,0,3, 0,0,0,0,0,0,0,4)))
+    >>> u.uint8()
+    1
+    >>> u.uint16()
+    2
+    >>> u.uint32()
+    3
+    >>> u.uint64()
+    4
+    
+    >>> u = Unpacker(bytes((1,0, 104,105)), ENDIAN_LITTLE)
+    >>> u.uint16()
+    1
+    >>> u.buf
+    b'hi'
+
+    >>> u = Unpacker(bytes((1,0, 0,2)))
+    >>> u.uint16(ENDIAN_LITTLE)
+    1
+    >>> u.uint(16, ENDIAN_BIG)
+    2
+    
+    >>> u = Unpacker(bytes((0,1,2,3)), ENDIAN_MIDDLE)
+    >>> '%08x' % u.uint32()
+    '01000302'
+    """
+    
+    def __init__(self, buf, endian=ENDIAN_NETWORK):
+        self.endian = endian
+        self.buf = buf
+
+    def uint(self, size, endian=None):
+        endian = endian or self.endian
+        if size not in (8, 16, 32, 64):
+            # XXX: I'm pretty sure this can be done, but I don't want to code it up right now.
+            raise ValueError("Can't do weird sizes")
+        noctets = size // 8
+        if endian == ENDIAN_BIG:
+            r = range(0, noctets)
+        elif endian == ENDIAN_LITTLE:
+            r = range(noctets-1, -1, -1)
+        elif endian == ENDIAN_MIDDLE:
+            r = (1, 0, 3, 2,   5, 4, 7, 6)[:noctets]
+        else:
+            raise ValueError("Unsupported byte order")
+        pull, self.buf = self.buf[:noctets], self.buf[noctets:]
+        acc = 0
+        for i in r:
+            acc = (acc << 8) | pull[i]
+        return acc
+        
+    def uint8(self):
+        return self.uint(8)
+    def uint16(self, endian=None):
+        return self.uint(16, endian)
+    def uint32(self, endian=None):
+        return self.uint(32, endian)
+    def uint64(self, endian=None):
+        return self.uint(64, endian)
+
+if __name__ == "__main__":
+    import doctest
+    doctest.testmod()