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modification to AlignedListOfN to accomodate a variable codec for the length

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FateJH 2016-10-02 01:15:35 -04:00
parent b1615aa4d9
commit 29b4eaa4e4
1 changed files with 16 additions and 21 deletions
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37
common/src/main/scala/net/psforever/packet/PSPacket.scala
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@ -211,16 +211,16 @@ object PacketHelpers {
* Encode and decode a byte-aligned `List`.<br>
* <br>
* This function is copied almost verbatim from its source, with exception of swapping the normal `ListCodec` for a new `AlignedListCodec`.
* @param countCodec the codec that represents the prefixed size of the List
* @param alignment the number of bits padded between the List size and the List contents
* @param valueCodec a codec that describes each of the contents of the List
* @tparam A the type of the List contents
* @param countCodec the codec that represents the prefixed size of the `List`
* @param alignment the number of bits padded between the `List` size and the `List` contents
* @param valueCodec a codec that describes each of the contents of the `List`
* @tparam A the type of the `List` contents
* @see codec\package.scala, listOfN
* @return a codec that works on a List of A
*/
def listOfNAligned[A](countCodec: Codec[Int], alignment : Int, valueCodec: Codec[A]): Codec[List[A]] = {
countCodec.
flatZip { count => new AlignedListCodec(valueCodec, alignment, Some(count)) }.
flatZip { count => new AlignedListCodec(countCodec, valueCodec, alignment, Some(count)) }.
narrow[List[A]]({ case (cnt, xs) =>
if (xs.size == cnt) Attempt.successful(xs)
else Attempt.failure(Err(s"Insufficient number of elements: decoded ${xs.size} but should have decoded $cnt"))
@ -233,35 +233,30 @@ object PacketHelpers {
* The codec that encodes and decodes a byte-aligned `List`.<br>
* <br>
* This class is copied almost verbatim from its source, with only heavy modifications to its `encode` process.
* @param codec a codec that describes each of the contents of the `List`
* @param countCodec the codec that represents the prefixed size of the `List`
* @param valueCodec a codec that describes each of the contents of the `List`
* @param alignment the number of bits padded between the `List` size and the `List` contents (on successful)
* @param limit the number of elements in the `List`
* @tparam A the type of the `List` contents
* @see ListCodec.scala
*/
private class AlignedListCodec[A](codec: Codec[A], alignment : Int, limit: Option[Int] = None) extends Codec[List[A]] {
private class AlignedListCodec[A](countCodec : Codec[Int], valueCodec: Codec[A], alignment : Int, limit: Option[Int] = None) extends Codec[List[A]] {
/**
* Convert a `List` of elements into a byte-aligned `BitVector`.<br>
* <br>
* Bit padding after the encoded size of the `List` is only added if the `alignment` value is greater than zero and the initial encoding process was successful.
* The padding is rather heavy-handed and a completely different `BitVector` is returned if successful.
* Performance hits for this complexity are not expected to be significant.<br>
* <br>
* __Warning__:<br>
* A significant assumption is present in the code!
* The algorithm never confirms the bit size of the encoded size of the `List` and assumes it is equivalent to a `uint8`.
* The encoding is always split after its first eight bits.
* Obviously, if the bit size is a `uint16` or greater, the aligned encoding process will produce garbage.
* No `Exception`s will be thrown.
* Performance hits for this complexity are not expected to be significant.
* @param list the `List` to be encoded
* @return the `BitVector` encoding, if successful
*/
def encode(list: List[A]) : Attempt[BitVector] = {
val solve : Attempt[BitVector] = Encoder.encodeSeq(codec)(list)
override def encode(list : List[A]) : Attempt[BitVector] = {
val solve : Attempt[BitVector] = Encoder.encodeSeq(valueCodec)(list)
if(alignment > 0) {
solve match {
case Attempt.Successful(vector) =>
return Successful(vector.take(8L) ++ BitVector.fill(alignment)(false) ++ vector.drop(8L))
val countCodecSize : Long = countCodec.sizeBound.lowerBound
return Successful(vector.take(countCodecSize) ++ BitVector.fill(alignment)(false) ++ vector.drop(countCodecSize))
case _ =>
}
}
@ -273,7 +268,7 @@ private class AlignedListCodec[A](codec: Codec[A], alignment : Int, limit: Optio
* @param buffer the encoded bits in the `List`, preceded by the alignment bits
* @return the decoded `List`
*/
def decode(buffer: BitVector) = Decoder.decodeCollect[List, A](codec, limit)(buffer.drop(alignment))
def decode(buffer: BitVector) = Decoder.decodeCollect[List, A](valueCodec, limit)(buffer.drop(alignment))
/**
* The size of the encoded `List`.<br>
@ -283,7 +278,7 @@ private class AlignedListCodec[A](codec: Codec[A], alignment : Int, limit: Optio
*/
def sizeBound = limit match {
case None => SizeBound.unknown
case Some(lim) => codec.sizeBound * lim.toLong
case Some(lim) => valueCodec.sizeBound * lim.toLong
}
/**
@ -292,5 +287,5 @@ private class AlignedListCodec[A](codec: Codec[A], alignment : Int, limit: Optio
* Unchanged from original.
* @return the `String` representation
*/
override def toString = s"list($codec)"
override def toString = s"list($valueCodec)"
}