commonMain.aws.sdk.kotlin.runtime.protocol.eventstream.FrameDecoder.kt Maven / Gradle / Ivy

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Support for the vnd.amazon.event-stream content type

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/*
 * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
 * SPDX-License-Identifier: Apache-2.0.
 */

package aws.sdk.kotlin.runtime.protocol.eventstream

import aws.sdk.kotlin.runtime.InternalSdkApi
import aws.smithy.kotlin.runtime.io.Buffer
import aws.smithy.kotlin.runtime.io.SdkByteBuffer
import aws.smithy.kotlin.runtime.io.readFully

@InternalSdkApi
public class FrameDecoder {
    private var prelude: Prelude? = null

    /**
     * Reset the decoder discarding any intermediate state
     */
    public fun reset() { prelude = null }

    private fun isFrameAvailable(buffer: Buffer): Boolean {
        val totalLen = prelude?.totalLen ?: return false
        val remaining = totalLen - PRELUDE_BYTE_LEN_WITH_CRC
        return buffer.readRemaining >= remaining.toULong()
    }

    /**
     * Attempt to decode a [Message] from the buffer. This function expects to be called over and over again
     * with more data in the buffer each time its called. When there is not enough data to decode this function
     * returns null.
     * The decoder will consume the prelude when enough data is available. When it is invoked with enough
     * data it will consume the remaining message bytes.
     */
    public fun decodeFrame(buffer: Buffer): Message? {
        if (prelude == null && buffer.readRemaining >= PRELUDE_BYTE_LEN_WITH_CRC.toULong()) {
            prelude = Prelude.decode(buffer)
        }

        return when (isFrameAvailable(buffer)) {
            true -> {
                val currPrelude = checkNotNull(prelude)
                val messageBuf = SdkByteBuffer(currPrelude.totalLen.toULong())
                currPrelude.encode(messageBuf)
                buffer.readFully(messageBuf)
                reset()
                Message.decode(messageBuf)
            }
            else -> null
        }
    }
}