tlslite.utils.codec module

Classes for reading/writing binary data (such as TLS records).

class tlslite.utils.codec.Parser(bytes)

Bases: object

Parser for TLV and LV byte-based encodings.

Parser that can handle arbitrary byte-based encodings usually employed in Type-Length-Value or Length-Value binary encoding protocols like ASN.1 or TLS

Note: if the raw bytes don’t match expected values (like trying to read a 4-byte integer from a 2-byte buffer), most methods will raise a SyntaxError exception.

TODO: don’t use an exception used by language parser to indicate errors in application code.

Variables:
  • bytes (bytearray) – data to be interpreted (buffer)
  • index (int) – current position in the buffer
  • lengthCheck (int) – size of struct being parsed
  • indexCheck (int) – position at which the structure begins in buffer
__init__(bytes)

Bind raw bytes with parser.

Parameters:bytes (bytearray) – bytes to be parsed/interpreted
atLengthCheck()

Check if there is data in structure left for parsing.

Returns True if the whole structure was parsed, False if there is some data left.

Will raise an exception if overflow occured (amount of data read was greater than expected size)

get(length)

Read a single big-endian integer value encoded in ‘length’ bytes.

Parameters:length (int) – number of bytes in which the value is encoded in
Return type:int
getFixBytes(lengthBytes)

Read a string of bytes encoded in ‘lengthBytes’ bytes.

Parameters:lengthBytes (int) – number of bytes to return
Return type:bytearray
getFixList(length, lengthList)

Read a list of static length with same-sized ints.

Parameters:
  • length (int) – size in bytes of a single element in list
  • lengthList (int) – number of elements in list
Return type:

list of int
getRemainingLength()

Return amount of data remaining in struct being parsed.

getVarBytes(lengthLength)

Read a variable length string with a fixed length.

Parameters:lengthLength (int) – number of bytes in which the length of the string is encoded in
Return type:bytearray
getVarList(length, lengthLength)

Read a variable length list of same-sized integers.

Parameters:
  • length (int) – size in bytes of a single element
  • lengthLength (int) – size of the encoded length of the list
Return type:

list of int
getVarTupleList(elemLength, elemNum, lengthLength)

Read a variable length list of same sized tuples.

Parameters:
  • elemLength (int) – length in bytes of single tuple element
  • elemNum (int) – number of elements in tuple
  • lengthLength (int) – length in bytes of the list length variable
Return type:

list of tuple of int
setLengthCheck(length)

Set length of struct and start a length check for parsing.

Parameters:length (int) – expected size of parsed struct in bytes
startLengthCheck(lengthLength)

Read length of struct and start a length check for parsing.

Parameters:lengthLength (int) – number of bytes in which the length is encoded
stopLengthCheck()

Stop struct parsing, verify that no under- or overflow occurred.

In case the expected length was mismatched with actual length of processed data, raises an exception.

class tlslite.utils.codec.Writer

Bases: object

Serialisation helper for complex byte-based structures.

__init__()

Initialise the serializer with no data.

add(x, length)

Add a single positive integer value x, encode it in length bytes

Encode positive integer x in big-endian format using length bytes, add to the internal buffer.

Parameters:
  • x (int) – value to encode
  • length (int) – number of bytes to use for encoding the value
addFixSeq(seq, length)

Add a list of items, encode every item in length bytes

Uses the unbounded iterable seq to produce items, each of which is then encoded to length bytes

Parameters:
  • seq (iterable of int) – list of positive integers to encode
  • length (int) – number of bytes to which encode every element
addFour(val)

Add a four-byte wide element to buffer, see add().

addOne(val)

Add a single-byte wide element to buffer, see add().

addThree(val)

Add a three-byte wide element to buffer, see add().

addTwo(val)

Add a double-byte wide element to buffer, see add().

addVarSeq(seq, length, lengthLength)

Add a bounded list of same-sized values

Create a list of specific length with all items being of the same size

Parameters:
  • seq (list of int) – list of positive integers to encode
  • length (int) – amount of bytes in which to encode every item
  • lengthLength (int) – amount of bytes in which to encode the overall length of the array
addVarTupleSeq(seq, length, lengthLength)

Add a variable length list of same-sized element tuples.

Note that all tuples must have the same size.

Inverse of Parser.getVarTupleList()

Parameters:
  • seq (enumerable) – list of tuples
  • length (int) – length of single element in tuple
  • lengthLength (int) – length in bytes of overall length field