def logFramesIfEnabled()

in http-core/src/main/scala/org/apache/pekko/http/impl/engine/http2/FrameLogger.scala [35:121]
70 lines of code
23 McCabe index (conditional complexity)

  def logFramesIfEnabled(shouldLog: Boolean): BidiFlow[FrameEvent, FrameEvent, FrameEvent, FrameEvent, NotUsed] =
    if (shouldLog) bidi
    else BidiFlow.identity

  def bidi: BidiFlow[FrameEvent, FrameEvent, FrameEvent, FrameEvent, NotUsed] =
    BidiFlow.fromFlows(
      Flow[FrameEvent].log(s"${Console.RED}DOWN${Console.RESET}", FrameLogger.logEvent),
      Flow[FrameEvent].log(s"${Console.GREEN} UP ${Console.RESET}", FrameLogger.logEvent))
      .addAttributes(Attributes(LogLevels(Logging.DebugLevel, Logging.DebugLevel, Logging.DebugLevel)))

  def logEvent(frameEvent: FrameEvent): String = {
    case class LogEntry(
        streamId: Int,
        shortFrameType: String,
        extraInfo: String,
        flags: Option[String]*)

    def flag(value: Boolean, name: String): Option[String] = if (value) Some(name) else None
    def hex(bytes: ByteString): String = {
      val num = math.min(maxBytes, bytes.size)

      val ellipsis =
        if (num < bytes.size) s" [... ${bytes.size - num} more bytes]"
        else ""

      bytes
        .take(num)
        .map("%02x" format _)
        .mkString(" ") + ellipsis
    }

    def entryForFrame(frameEvent: FrameEvent): LogEntry =
      frameEvent match {
        case PingFrame(false, data) => LogEntry(0, "PING", hex(data))
        case PingFrame(true, data)  => LogEntry(0, "PONG", hex(data))
        case HeadersFrame(streamId, endStream, endHeaders, payload, prio) =>
          val prioInfo = if (prio.isDefined) display(entryForFrame(prio.get)) + " " else ""

          LogEntry(streamId, "HEAD", prioInfo + hex(payload), flag(endStream, "ES"), flag(endHeaders, "EH"))
        case ContinuationFrame(streamId, endHeaders, payload) =>
          LogEntry(streamId, "CONT", hex(payload), flag(endHeaders, "EH"))
        case DataFrame(streamId, endStream, payload) =>
          LogEntry(streamId, "DATA", hex(payload), flag(endStream, "ES"))

        case GoAwayFrame(lastStreamId, errorCode, debug) =>
          LogEntry(0, "GOAY", s"lastStreamId = $lastStreamId, errorCode = $errorCode, debug = ${debug.utf8String}")

        case ParsedHeadersFrame(streamId, endStream, kvPairs, prio) =>
          val prioInfo = if (prio.isDefined) display(entryForFrame(prio.get)) + " " else ""
          val kvInfo = kvPairs.map {
            case (key, value) => s"$key -> $value"
          }.mkString(", ")
          LogEntry(streamId, "HEAD", prioInfo + kvInfo, flag(endStream, "ES"))

        case PriorityFrame(streamId, exclusive, streamDependency, weight) =>
          LogEntry(streamId, "PRIO", s"streamDependency = $streamDependency, weight: $weight", flag(exclusive, "EX"))

        case RstStreamFrame(streamId, errorCode) =>
          LogEntry(streamId, "RSET", errorCode.toString)

        case SettingsFrame(settings) =>
          val settingsInfo = settings.map {
            case Setting(id, value) => s"$id -> $value"
          }.mkString(", ")
          LogEntry(0, "SETT", settingsInfo)

        case SettingsAckFrame(s) =>
          val acksInfo = formatSettings(s)
          LogEntry(0, "SETA", acksInfo)

        case WindowUpdateFrame(streamId, windowSizeIncrement) =>
          LogEntry(streamId, "WIND", s"+ $windowSizeIncrement")

        case other: StreamFrameEvent =>
          LogEntry(other.streamId, "UNKN", other.toString)
        case other =>
          LogEntry(0, "UNKN", other.toString)
      }

    def display(entry: LogEntry): String = {
      import entry._

      import Console._
      f"$GREEN$streamId%4d $YELLOW$shortFrameType%s $RED${flags.flatMap(x => x).mkString(" ")} $RESET$extraInfo"
    }
    display(entryForFrame(frameEvent))
  }