79 lines
1.9 KiB
JavaScript
79 lines
1.9 KiB
JavaScript
// Default stream and parsers for Uint8TypedArray data type
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export const buildStream = uint8Data => ({
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data: uint8Data,
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pos: 0
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})
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export const readByte = () => stream => {
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return stream.data[stream.pos++]
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}
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export const peekByte = (offset = 0) => stream => {
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return stream.data[stream.pos + offset]
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}
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export const readBytes = length => stream => {
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return stream.data.subarray(stream.pos, (stream.pos += length))
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}
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export const peekBytes = length => stream => {
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return stream.data.subarray(stream.pos, stream.pos + length)
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}
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export const readString = length => stream => {
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return Array.from(readBytes(length)(stream))
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.map(value => String.fromCharCode(value))
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.join('')
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}
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export const readUnsigned = littleEndian => stream => {
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const bytes = readBytes(2)(stream)
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return littleEndian ? (bytes[1] << 8) + bytes[0] : (bytes[0] << 8) + bytes[1]
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}
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export const readArray = (byteSize, totalOrFunc) => (
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stream,
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result,
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parent
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) => {
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const total =
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typeof totalOrFunc === 'function'
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? totalOrFunc(stream, result, parent)
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: totalOrFunc
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const parser = readBytes(byteSize)
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const arr = new Array(total)
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for (var i = 0; i < total; i++) {
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arr[i] = parser(stream)
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}
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return arr
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}
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const subBitsTotal = (bits, startIndex, length) => {
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var result = 0
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for (var i = 0; i < length; i++) {
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result += bits[startIndex + i] && 2 ** (length - i - 1)
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}
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return result
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}
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export const readBits = schema => stream => {
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const byte = readByte()(stream)
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// convert the byte to bit array
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const bits = new Array(8)
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for (var i = 0; i < 8; i++) {
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bits[7 - i] = !!(byte & (1 << i))
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}
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// convert the bit array to values based on the schema
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return Object.keys(schema).reduce((res, key) => {
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const def = schema[key]
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if (def.length) {
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res[key] = subBitsTotal(bits, def.index, def.length)
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} else {
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res[key] = bits[def.index]
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}
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return res
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}, {})
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}
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