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package scodec.codecs
import scodec._
import scodec.bits.{ByteVector, BitVector}
/**
* Provides methods to create a "checksum codec" (encodes a bit-range to a bit-checksum and decodes bits to a bit-range).
*/
object ChecksumCodec {
/**
* Returns a codec that encodes a bit-range to a bit-checksum and decodes bits to a bit-range.
*
* @param encoder encodes a bit-range to a bit-checksum
* @param range decodes the size of a bit-range
* @return
*/
def apply(encoder: Encoder[BitVector], range: Decoder[Long]): Codec[BitVector] =
Codec(encoder, Decoder(
bits => range.decode(bits).flatMap(
size => bits.consumeThen(size.value)(
e => Attempt.failure(Err.InsufficientBits(size.value, bits.size, List(e))),
(range, remainder) => Attempt.successful(DecodeResult(range, remainder))))))
/**
* Returns a codec that encodes a bit-range to a bit-checksum and decodes bits to a bit-range.
*
* @param encoder encodes a bit-range to a bit-checksum
* @param range decodes the (un-padded) size of a bit-range
* @param padding size padding for the bit-range
* @return
*/
def apply(encoder: Encoder[BitVector], range: Decoder[Long], padding: Long): Codec[BitVector] =
apply(encoder, range map (_ + padding))
/**
* Returns a codec that encodes a bit-range to a bit-checksum and decodes bits to a bit-range.
*
* @param encoder encodes a byte-range to a byte-checksum
* @param range decodes the (un-padded) size of a byte-range
* @param padding size padding for the byte-range
* @return
*/
def apply(encoder: Encoder[ByteVector], range: Decoder[Int], padding: Int): Codec[BitVector] =
apply(encoder.contramap[BitVector](_.bytes), range.map(8L * _), 8l * padding)
/**
* Returns a codec that encodes a bit-range to a bit-checksum and decodes bits to a bit-range.
*
* @param length the bit-length of the checksum
* @param f computes bit-checksum
* @param range decodes the (un-padded) size of a bit-range
* @param padding size padding for the bit-range
* @return
*/
def apply(length: Long, f: BitVector => BitVector, range: Decoder[Long], padding: Long): Codec[BitVector] =
apply(new Encoder[BitVector] {
def encode(value: BitVector): Attempt[BitVector] = Attempt.successful(f(value))
def sizeBound: SizeBound = SizeBound.exact(length)
}, range, padding)
/**
* Returns a codec that encodes a bit-range to a bit-checksum and decodes bits to a bit-range.
*
* @param length the byte-length of the checksum
* @param f computes byte-checksum
* @param range decodes the (un-padded) size of a byte-range
* @param padding size padding for the byte-range
* @return
*/
def apply(length: Int, f: ByteVector => ByteVector, range: Decoder[Int], padding: Int): Codec[BitVector] =
apply(8L * length, (bits: BitVector) => f(bits.bytes).bits, range.map(8L + _), 8L * padding)
/**
* Returns a codec that encodes a bit-range to an XORed bit-checksum and decodes bits to a bit-range.
*
* @param length the bit-length of the checksum
* @param range decodes the (un-padded) size of a bit-range
* @param padding size padding for the bit-range
* @return
*/
def xor(length: Long, range: Decoder[Long], padding: Long): Codec[BitVector] =
apply(length, (bits: BitVector) => bits.grouped(length).foldLeft(BitVector.low(length))(_ xor _), range, padding)
/**
* Returns a codec that encodes a bit-range to an XORed bit-checksum and decodes bits to a bit-range.
*
* @param length the byte-length of the checksum
* @param range decodes the (un-padded) size of a byte-range
* @param padding size padding for the byte-range
* @return
*/
def xor(length: Int, range: Decoder[Int], padding: Int): Codec[BitVector] =
xor(8L * length, range.map(8L * _), 8L * padding)
case class Mismatch(bits: BitVector, expected: BitVector, actual: BitVector, context: List[String] = Nil) extends Err {
def message: String = s"checksum mismatch for bits: $bits, expected: $expected, actual: $actual"
def pushContext(ctx: String): Err = copy(context = ctx :: context)
}
}
