io.github.binaryfoo.decoders.EmvBitStringDecoder.kt Maven / Gradle / Ivy

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Some decoders for the data used in EMV credit card transactions.

There is a newer version: 0.1.8

package io.github.binaryfoo.decoders

import io.github.binaryfoo.DecodedData
import io.github.binaryfoo.Decoder
import io.github.binaryfoo.bit.*
import io.github.binaryfoo.bit.EmvBit
import io.github.binaryfoo.decoders.bit.BitStringField
import io.github.binaryfoo.decoders.bit.EmvBitStringParser
import io.github.binaryfoo.res.ClasspathIO
import io.github.binaryfoo.tlv.ISOUtil
import org.apache.commons.io.IOUtils

import java.io.IOException
import java.io.InputStream
import java.util.ArrayList

/**
 * Decoder based on the config language (DSL...).
 * 
 * Each line in fileName should be parseable in one of the 3 formats:
 * 

 *     Enumerated - a direct mapping from a set of bits to a name. Bits can be spread over multiple bytes.
 *     Full byte - similar to enumerated but only handles a single byte.
 *     Numeric - the left or right nibble in a byte is interpreted as an integer.
 * 
 */
open public class EmvBitStringDecoder(fileName: String, val showFieldHexInDecoding: Boolean) : Decoder {

    private val bitMappings: List
    private val maxLength: Int

    {
        val input = ClasspathIO.open(fileName)
        try {
            bitMappings = EmvBitStringParser.parse(IOUtils.readLines(input))
        } catch (e: IOException) {
            throw RuntimeException(e)
        } finally {
            IOUtils.closeQuietly(input)
        }
        this.maxLength = findMaxLengthInBytes() * 2
    }

    override fun getMaxLength(): Int = maxLength

    private fun findMaxLengthInBytes(): Int {
        if (bitMappings.empty) {
            return 0
        }
        fun max(a: Int, b: Int): Int = if ((a >= b)) a else b
        return bitMappings.map { it.getStartBytesOffset() + it.getLengthInBytes() }.reduce(::max)
    }

    override fun decode(input: String, startIndexInBytes: Int, session: DecodeSession): List {
        val decoded = ArrayList()
        val bits = fromHex(input)
        for (field in bitMappings) {
            val v = field.getValueIn(bits)
            if (v != null) {
                val fieldStartIndex = startIndexInBytes + field.getStartBytesOffset()
                decoded.add(DecodedData.primitive(field.getPositionIn(if (showFieldHexInDecoding) bits else null), v, fieldStartIndex, fieldStartIndex + field.getLengthInBytes()))
            }
        }
        return decoded
    }

    override fun validate(input: String?): String? {
        if (input == null || input.length() != maxLength) {
            return "Value must be exactly ${maxLength} characters"
        }
        if (!ISOUtil.isValidHexString(input)) {
            return "Value must contain only the characters 0-9 and A-F"
        }
        return null
    }

}