Python-CStruct
C-style structs for Python
Convert C struct/union definitions into Python classes with methods for serializing/deserializing. The usage is very simple: create a class subclassing cstruct.MemCStruct and add a C struct/union definition as a string in the struct field. The C struct/union definition is parsed at runtime and the struct format string is generated. The class offers the method "unpack" for deserializing an array of bytes into a Python object and the method "pack" for serializing the values into an array of bytes.
Example
The following program reads the DOS partition information from a disk.
#!/usr/bin/env python
import cstruct
class Position(cstruct.MemCStruct):
__byte_order__ = cstruct.LITTLE_ENDIAN
__def__ = """
struct {
unsigned char head;
unsigned char sector;
unsigned char cyl;
}
"""
class Partition(cstruct.MemCStruct):
__byte_order__ = cstruct.LITTLE_ENDIAN
__def__ = """
struct {
unsigned char status; /* 0x80 - active */
struct Position start;
unsigned char partition_type;
struct Position end;
unsigned int start_sect; /* starting sector counting from 0 */
unsigned int sectors; /* nr of sectors in partition */
}
"""
def print_info(self):
print("bootable: %s" % ((self.status & 0x80) and "Y" or "N"))
print("partition_type: %02X" % self.partition_type)
print("start: head: %X sectory: %X cyl: %X" % (self.start.head, self.start.sector, self.start.cyl))
print("end: head: %X sectory: %X cyl: %X" % (self.end.head, self.end.sector, self.end.cyl))
print("starting sector: %08X" % self.start_sect)
print("size MB: %s" % (self.sectors / 2 / 1024))
class MBR(cstruct.MemCStruct):
__byte_order__ = cstruct.LITTLE_ENDIAN
__def__ = """
struct {
char unused[440];
unsigned char disk_signature[4];
unsigned char usualy_nulls[2];
struct Partition partitions[4];
char signature[2];
}
"""
def print_info(self):
print("disk signature: %s" % "".join(["%02X" % x for x in self.disk_signature]))
print("usualy nulls: %s" % "".join(["%02X" % x for x in self.usualy_nulls]))
for i, partition in enumerate(self.partitions):
print("")
print("partition: %s" % i)
partition.print_info()
disk = "mbr"
with open(disk, "rb") as f:
mbr = MBR()
mbr.unpack(f)
mbr.print_info()