Regarding scodec performance

Benchmark.sc

//> using scala 3.6.3
//> using dep org.scodec::scodec-bits:1.2.1
//> using dep org.scodec::scodec-core:2.3.2

import scodec.bits.*
import scodec.codecs.*

val iterations = 10000

val str = "Hello World!"
val lengthBits = BitVector(str.length)
val stringBits = BitVector.encodeUtf8(str).toOption.get // Not safe, but only used for verification.
val bits = lengthBits ++ stringBits

// warm up
for (i <- 0 until 10000) {
  decodeByCodecs()
  decodeBySplitAt()
}

val benchmark1Start = System.nanoTime()
for (i <- 0 until iterations) {
  decodeByCodecs()
}
val benchmark1End = System.nanoTime() - benchmark1Start

val benchmark2Start = System.nanoTime()
for (i <- 0 until iterations) {
  decodeBySplitAt()
}
val benchmark2End = System.nanoTime() - benchmark2Start

println(s"benchmark1: ${benchmark1End / 1000000} ms") // 5 ms
println(s"benchmark2: ${benchmark2End / 1000000} ms") // 2 ms

def decodeByCodecs(): String =
  (for
    length <- uint8
    str <- bytes(length)
  yield new String(str.toArray, "UTF-8")).decode(bits).require.value

def decodeBySplitAt(): String =
  val (lengthBits, postLengthBits) = bits.splitAt(8)
  val length = lengthBits.toInt(false)
  val strBits = postLengthBits.take(length * 8L)
  new String(strBits.toByteArray, "UTF-8")

I also verified the process when using Array and Chunk.

  val byteArray = bits.toByteArray
  val chunk = fs2.Chunk(byteArray *)
  
  def decodeByStandard(): String =
    val length = byteArray(0).toInt & 0xFF
    new String(byteArray, 1, length, "UTF-8")

  def decodeByChunk(): String =
    val length = chunk(0).toInt & 0xFF
    val strBytes = chunk.drop(1).take(length).toArray
    new String(strBytes, "UTF-8")

The results were as follows, with the direct decoding of Chunk being the fastest.

codecs:  9 ms
splitAt: 3 ms
chunk:   1 ms
array:   4 ms

Full code

//> using scala 3.6.3
//> using dep co.fs2::fs2-core:3.11.0
//> using dep org.scodec::scodec-bits:1.2.1
//> using dep org.scodec::scodec-core:2.3.2

import scodec.bits.*
import scodec.codecs.*

val iterations = 10000

val str = "Hello World!"
val lengthBits = BitVector(str.length)
val stringBits = BitVector.encodeUtf8(str).toOption.get // Not safe, but only used for verification.
val bits = lengthBits ++ stringBits
val byteArray = bits.toByteArray
val chunk = fs2.Chunk(byteArray*)

// warm up
for (i <- 0 until 100000000) {
  decodeByCodecs()
  decodeBySplitAt()
  decodeByChunk()
  decodeByStandard()
}

val benchmark1Start = System.nanoTime()
for (i <- 0 until iterations) {
  decodeByCodecs()
}
val benchmark1End = System.nanoTime() - benchmark1Start

val benchmark2Start = System.nanoTime()
for (i <- 0 until iterations) {
  decodeBySplitAt()
}
val benchmark2End = System.nanoTime() - benchmark2Start

val benchmark3Start = System.nanoTime()
for (i <- 0 until iterations) {
  decodeByChunk()
}
val benchmark3End = System.nanoTime() - benchmark3Start

val benchmark4Start = System.nanoTime()
for (i <- 0 until iterations) {
  decodeByStandard()
}
val benchmark4End = System.nanoTime() - benchmark4Start

println(s"benchmark1: ${benchmark1End / 1000000} ms") // 9 ms
println(s"benchmark2: ${benchmark2End / 1000000} ms") // 3 ms
println(s"benchmark3: ${benchmark3End / 1000000} ms") // 1 ms
println(s"benchmark4: ${benchmark4End / 1000000} ms") // 4 ms

def decodeByCodecs(): String =
  val decoded = uint8.decode(bits).require
  val length = decoded.value
  val str = bytes(length).decode(decoded.remainder).require.value
  new String(str.toArray, "UTF-8")

def decodeBySplitAt(): String =
  val (lengthBits, postLengthBits) = bits.splitAt(8)
  val length = lengthBits.toInt(false)
  val strBits = postLengthBits.take(length * 8L)
  new String(strBits.toByteArray, "UTF-8")

def decodeByStandard(): String =
  val length = byteArray(0).toInt & 0xFF
  new String(byteArray, 1, length, "UTF-8")

def decodeByChunk(): String =
  val length = chunk(0).toInt & 0xFF
  val strBytes = chunk.drop(1).take(length).toArray
  new String(strBytes, "UTF-8")