public fun parseBoundary()

in ktor-http/ktor-http-cio/jvm/src/io/ktor/http/cio/Multipart.kt [479:557]
67 lines of code
13 McCabe index (conditional complexity)

public fun parseBoundary(contentType: CharSequence): ByteBuffer {
    val boundaryParameter = findBoundary(contentType)

    if (boundaryParameter == -1) throw IOException("Failed to parse multipart: Content-Type's boundary parameter is missing")
    val boundaryStart = boundaryParameter + 9

    val boundaryBytes: ByteBuffer = ByteBuffer.allocate(74)
    boundaryBytes.put(0x0d)
    boundaryBytes.put(0x0a)
    boundaryBytes.put(PrefixChar)
    boundaryBytes.put(PrefixChar)

    var state = 0 // 0 - skipping spaces, 1 - unquoted characters, 2 - quoted no escape, 3 - quoted after escape

    loop@ for (i in boundaryStart until contentType.length) {
        val ch = contentType[i]
        val v = ch.toInt() and 0xffff
        if (v and 0xffff > 0x7f) throw IOException("Failed to parse multipart: wrong boundary byte 0x${v.toString(16)} - should be 7bit character")

        when (state) {
            0 -> {
                when (ch) {
                    ' ' -> {
                        // skip space
                    }
                    '"' -> {
                        state = 2 // start quoted string parsing
                    }
                    ';', ',' -> {
                        break@loop
                    }
                    else -> {
                        state = 1
                        boundaryBytes.put(v.toByte())
                    }
                }
            }
            1 -> { // non-quoted string
                if (ch == ' ' || ch == ',' || ch == ';') { // space, comma or semicolon (;)
                    break@loop
                } else if (boundaryBytes.hasRemaining()) {
                    boundaryBytes.put(v.toByte())
                } else {
                    //  RFC 2046, sec 5.1.1
                    throw IOException("Failed to parse multipart: boundary shouldn't be longer than 70 characters")
                }
            }
            2 -> {
                if (ch == '\\') {
                    state = 3
                } else if (ch == '"') {
                    break@loop
                } else if (boundaryBytes.hasRemaining()) {
                    boundaryBytes.put(v.toByte())
                } else {
                    //  RFC 2046, sec 5.1.1
                    throw IOException("Failed to parse multipart: boundary shouldn't be longer than 70 characters")
                }
            }
            3 -> {
                if (boundaryBytes.hasRemaining()) {
                    boundaryBytes.put(v.toByte())
                    state = 2
                } else {
                    //  RFC 2046, sec 5.1.1
                    throw IOException("Failed to parse multipart: boundary shouldn't be longer than 70 characters")
                }
            }
        }
    }

    boundaryBytes.flip()

    if (boundaryBytes.remaining() == 4) {
        throw IOException("Empty multipart boundary is not allowed")
    }

    return boundaryBytes
}