Add xdrlib.py

Author: windelbouwman

Lib/xdrlib.py

@@ -0,0 +1,241 @@
+"""Implements (a subset of) Sun XDR -- eXternal Data Representation.
+
+See: RFC 1014
+
+"""
+
+import struct
+from io import BytesIO
+from functools import wraps
+
+__all__ = ["Error", "Packer", "Unpacker", "ConversionError"]
+
+# exceptions
+class Error(Exception):
+    """Exception class for this module. Use:
+
+    except xdrlib.Error as var:
+        # var has the Error instance for the exception
+
+    Public ivars:
+        msg -- contains the message
+
+    """
+    def __init__(self, msg):
+        self.msg = msg
+    def __repr__(self):
+        return repr(self.msg)
+    def __str__(self):
+        return str(self.msg)
+
+
+class ConversionError(Error):
+    pass
+
+def raise_conversion_error(function):
+    """ Wrap any raised struct.errors in a ConversionError. """
+
+    @wraps(function)
+    def result(self, value):
+        try:
+            return function(self, value)
+        except struct.error as e:
+            raise ConversionError(e.args[0]) from None
+    return result
+
+
+class Packer:
+    """Pack various data representations into a buffer."""
+
+    def __init__(self):
+        self.reset()
+
+    def reset(self):
+        self.__buf = BytesIO()
+
+    def get_buffer(self):
+        return self.__buf.getvalue()
+    # backwards compatibility
+    get_buf = get_buffer
+
+    @raise_conversion_error
+    def pack_uint(self, x):
+        self.__buf.write(struct.pack('>L', x))
+
+    @raise_conversion_error
+    def pack_int(self, x):
+        self.__buf.write(struct.pack('>l', x))
+
+    pack_enum = pack_int
+
+    def pack_bool(self, x):
+        if x: self.__buf.write(b'\0\0\0\1')
+        else: self.__buf.write(b'\0\0\0\0')
+
+    def pack_uhyper(self, x):
+        try:
+            self.pack_uint(x>>32 & 0xffffffff)
+        except (TypeError, struct.error) as e:
+            raise ConversionError(e.args[0]) from None
+        try:
+            self.pack_uint(x & 0xffffffff)
+        except (TypeError, struct.error) as e:
+            raise ConversionError(e.args[0]) from None
+
+    pack_hyper = pack_uhyper
+
+    @raise_conversion_error
+    def pack_float(self, x):
+        self.__buf.write(struct.pack('>f', x))
+
+    @raise_conversion_error
+    def pack_double(self, x):
+        self.__buf.write(struct.pack('>d', x))
+
+    def pack_fstring(self, n, s):
+        if n < 0:
+            raise ValueError('fstring size must be nonnegative')
+        data = s[:n]
+        n = ((n+3)//4)*4
+        data = data + (n - len(data)) * b'\0'
+        self.__buf.write(data)
+
+    pack_fopaque = pack_fstring
+
+    def pack_string(self, s):
+        n = len(s)
+        self.pack_uint(n)
+        self.pack_fstring(n, s)
+
+    pack_opaque = pack_string
+    pack_bytes = pack_string
+
+    def pack_list(self, list, pack_item):
+        for item in list:
+            self.pack_uint(1)
+            pack_item(item)
+        self.pack_uint(0)
+
+    def pack_farray(self, n, list, pack_item):
+        if len(list) != n:
+            raise ValueError('wrong array size')
+        for item in list:
+            pack_item(item)
+
+    def pack_array(self, list, pack_item):
+        n = len(list)
+        self.pack_uint(n)
+        self.pack_farray(n, list, pack_item)
+
+
+
+class Unpacker:
+    """Unpacks various data representations from the given buffer."""
+
+    def __init__(self, data):
+        self.reset(data)
+
+    def reset(self, data):
+        self.__buf = data
+        self.__pos = 0
+
+    def get_position(self):
+        return self.__pos
+
+    def set_position(self, position):
+        self.__pos = position
+
+    def get_buffer(self):
+        return self.__buf
+
+    def done(self):
+        if self.__pos < len(self.__buf):
+            raise Error('unextracted data remains')
+
+    def unpack_uint(self):
+        i = self.__pos
+        self.__pos = j = i+4
+        data = self.__buf[i:j]
+        if len(data) < 4:
+            raise EOFError
+        return struct.unpack('>L', data)[0]
+
+    def unpack_int(self):
+        i = self.__pos
+        self.__pos = j = i+4
+        data = self.__buf[i:j]
+        if len(data) < 4:
+            raise EOFError
+        return struct.unpack('>l', data)[0]
+
+    unpack_enum = unpack_int
+
+    def unpack_bool(self):
+        return bool(self.unpack_int())
+
+    def unpack_uhyper(self):
+        hi = self.unpack_uint()
+        lo = self.unpack_uint()
+        return int(hi)<<32 | lo
+
+    def unpack_hyper(self):
+        x = self.unpack_uhyper()
+        if x >= 0x8000000000000000:
+            x = x - 0x10000000000000000
+        return x
+
+    def unpack_float(self):
+        i = self.__pos
+        self.__pos = j = i+4
+        data = self.__buf[i:j]
+        if len(data) < 4:
+            raise EOFError
+        return struct.unpack('>f', data)[0]
+
+    def unpack_double(self):
+        i = self.__pos
+        self.__pos = j = i+8
+        data = self.__buf[i:j]
+        if len(data) < 8:
+            raise EOFError
+        return struct.unpack('>d', data)[0]
+
+    def unpack_fstring(self, n):
+        if n < 0:
+            raise ValueError('fstring size must be nonnegative')
+        i = self.__pos
+        j = i + (n+3)//4*4
+        if j > len(self.__buf):
+            raise EOFError
+        self.__pos = j
+        return self.__buf[i:i+n]
+
+    unpack_fopaque = unpack_fstring
+
+    def unpack_string(self):
+        n = self.unpack_uint()
+        return self.unpack_fstring(n)
+
+    unpack_opaque = unpack_string
+    unpack_bytes = unpack_string
+
+    def unpack_list(self, unpack_item):
+        list = []
+        while 1:
+            x = self.unpack_uint()
+            if x == 0: break
+            if x != 1:
+                raise ConversionError('0 or 1 expected, got %r' % (x,))
+            item = unpack_item()
+            list.append(item)
+        return list
+
+    def unpack_farray(self, n, unpack_item):
+        list = []
+        for i in range(n):
+            list.append(unpack_item())
+        return list
+
+    def unpack_array(self, unpack_item):
+        n = self.unpack_uint()
+        return self.unpack_farray(n, unpack_item)

tests/snippets/test_xdrlib.py

@@ -0,0 +1,13 @@
+
+# This probably will be superceeded by the python unittests when that works.
+
+import xdrlib
+
+p = xdrlib.Packer()
+p.pack_int(1337)
+
+d = p.get_buffer()
+
+print(d)
+
+assert d == b'\x00\x00\x059'