Add xmodem example

README.md

@@ -11,6 +11,9 @@ and room to grow these explorations into full-blown decoders.
 Get going
 =========
 
-Documentation sucks, sorry.
+Documentation doesn't exist. Sorry.
-The way we go about things is to copy `dumbdecode.py` to a new file,
+The way we go about things is to copy [dumbdecode](examples/dumbdecode.py) to a new file,
 and start hacking onto it.
+
+You may find the [example xmodem decoder](examples/xmodem.py) to be helpful!
+It illustrates a fair amount of what the library provides.

examples/dumbdecode.py

@@ -1,7 +1,6 @@
 #! /usr/bin/python3
 
 import netarch
-import sys
 
 class DumbPacket(netarch.Packet):
 	def parse(self, data):
@@ -10,4 +9,4 @@ class DumbPacket(netarch.Packet):
 class DumbSession(netarch.Session):
 	Packet = DumbPacket
 
-netarch.main(DumbSession, sys.argv[1:])
+netarch.main(DumbSession)

examples/xmodem.py

@@ -0,0 +1,45 @@
+#! /usr/bin/python3
+
+import netarch
+
+class XmodemPacket(netarch.Packet):
+    def parse(self, data):
+        datastream = netarch.Unpacker(data)
+        self.opcode = datastream.uint8()
+        self.payload = datastream.buf
+
+    def opcode_1(self):
+        "Xfer"
+        datastream = netarch.Unpacker(self.payload)
+        self["seq"] = datastream.uint8()
+        self["~seq"] = datastream.uint8()
+
+        assert self["seq"] == 255 - self["~seq"]
+        assert len(datastream.buf) == 0x81
+
+        self["checksum"] = datastream.uint8(pos=-1)
+        self.payload = datastream.buf
+
+    def opcode_4(self):
+        "EOT"
+
+    def opcode_6(self):
+        "ACK"
+
+    def opcode_21(self):
+        "Begin transmission?"
+
+class XmodemSession(netarch.Session):
+    Packet = XmodemPacket
+
+    def process(self, packet):
+        packet.show()
+
+        if packet.opcode == 21:
+            # Open a new file for output
+            self.out = self.open_out("data.bin")
+        elif packet.opcode == 1:
+            self.out.write(bytes(packet.payload))
+
+
+netarch.main(XmodemSession)

netarch/__init__.py

@@ -2,8 +2,9 @@
 
 import binascii
 import struct
+import sys
 from . import ip
-
+from .unpack import Unpacker
 
 
 def cstring(buf):
@@ -180,8 +181,10 @@ def _registry(encoding):
 
 codecs.register(_registry)
 
-def main(session, pcaps):
+def main(session, pcaps=None):
     s = None
+    if not pcaps:
+        pcaps = sys.argv[1:]
     reseq = ip.Dispatch(*pcaps)
     for _, d in reseq:
         srv, first, chunk = d

netarch/unpack.py

@@ -39,7 +39,7 @@ class Unpacker:
         self.endian = endian
         self.buf = buf
 
-    def uint(self, size, endian=None):
+    def uint(self, size, pos=0, 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.
@@ -53,20 +53,22 @@ class Unpacker:
             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:]
+        if pos < 0:
+            pos += len(self.buf)
+        pull, self.buf = self.buf[pos:pos+noctets], self.buf[:pos] + self.buf[pos+noctets:]
         acc = 0
         for i in r:
             acc = (acc << 8) | pull[i]
         return acc
         
-    def uint8(self):
+    def uint8(self, pos=0):
-        return self.uint(8)
+        return self.uint(8, pos)
-    def uint16(self, endian=None):
+    def uint16(self, pos=0, endian=None):
-        return self.uint(16, endian)
+        return self.uint(16, pos, endian)
-    def uint32(self, endian=None):
+    def uint32(self, pos=0, endian=None):
-        return self.uint(32, endian)
+        return self.uint(32, pos, endian)
-    def uint64(self, endian=None):
+    def uint64(self, pos=0, endian=None):
-        return self.uint(64, endian)
+        return self.uint(64, pos, endian)
 
 if __name__ == "__main__":
     import doctest

setup.py

@@ -38,7 +38,7 @@ setup(
     # For a discussion on single-sourcing the version across setup.py and the
     # project code, see
     # https://packaging.python.org/en/latest/single_source_version.html
-    version='1.0.1',  # Required
+    version='2.1.0',  # Required
 
     # This is a one-line description or tagline of what your project does. This
     # corresponds to the "Summary" metadata field: