intel-hex/index.js

A JavaScript parser/writer for Intel HEX file format.

//Intel Hex record types
const DATA = 0,
	END_OF_FILE = 1,
	EXT_SEGMENT_ADDR = 2,
	START_SEGMENT_ADDR = 3,
	EXT_LINEAR_ADDR = 4,
	START_LINEAR_ADDR = 5;

const EMPTY_VALUE = 0xFF;

/* intel_hex.parse(data)
	- `data` - Intel Hex file (string in ASCII format or Buffer Object)
	- `bufferSize` - the size of the Buffer containing the data (optional)
	  The data exceeding the buffer size will be discarded
	- `addressOffset` - starting address offset (optional)
	  The data before the starting address will be discarded

	returns an Object with the following properties:

	- `data` - data as a Buffer Object, **padded with 0xFF
	  where data is empty**.
	- `startSegmentAddress` - the address provided by the last
	  start segment address record; null, if not given
	- `startLinearAddress` - the address provided by the last
	  start linear address record; null, if not given

	Special thanks to: http://en.wikipedia.org/wiki/Intel_HEX
*/
exports.parse = function parseIntelHex(data, bufferSize, addressOffset) {
	if(data instanceof Buffer)
		data = data.toString("ascii");
	//Initialization
	var buf = Buffer.alloc(bufferSize || 8192),
		bufLength = 0, //Length of data in the buffer
		highAddress = 0, //upper address
		startSegmentAddress = null,
		startLinearAddress = null,
		addressOffset = addressOffset || 0,
		lineNum = 0, //Line number in the Intel Hex string
		pos = 0; //Current position in the Intel Hex string

	const SMALLEST_LINE = 11;
	while(pos + SMALLEST_LINE <= data.length)
	{
		//Parse an entire line
		if(data.charAt(pos++) != ":")
			throw new Error("Line " + (lineNum+1) +
				" does not start with a colon (:).");
		else
			lineNum++;
		//Number of bytes (hex digit pairs) in the data field
		var dataLength = parseInt(data.substr(pos, 2), 16);
		pos += 2;
		//Get 16-bit address (big-endian)
		var lowAddress = parseInt(data.substr(pos, 4), 16);
		pos += 4;
		//Record type
		var recordType = parseInt(data.substr(pos, 2), 16);
		pos += 2;
		//Data field (hex-encoded string)
		var dataField = data.substr(pos, dataLength * 2),
			dataFieldBuf = Buffer.from(dataField, "hex");
		pos += dataLength * 2;
		//Checksum
		var checksum = parseInt(data.substr(pos, 2), 16);
		pos += 2;
		//Validate checksum
		var calcChecksum = (dataLength + (lowAddress >> 8) +
			lowAddress + recordType) & 0xFF;
		for(var i = 0; i < dataLength; i++)
			calcChecksum = (calcChecksum + dataFieldBuf[i]) & 0xFF;
		calcChecksum = (0x100 - calcChecksum) & 0xFF;
		if(checksum != calcChecksum)
			throw new Error("Invalid checksum on line " + lineNum +
				": got " + checksum + ", but expected " + calcChecksum);
		//Parse the record based on its recordType
		switch(recordType)
		{
			case DATA:
				var absoluteAddress = highAddress + lowAddress - addressOffset;
				//Expand buf, if necessary
				if(absoluteAddress + dataLength >= buf.length)
				{
					var tmp = Buffer.alloc((absoluteAddress + dataLength) * 2);
					buf.copy(tmp, 0, 0, bufLength);
					buf = tmp;
				}
				//Write over skipped bytes with EMPTY_VALUE
				if(absoluteAddress > bufLength)
					buf.fill(EMPTY_VALUE, bufLength, absoluteAddress);
				//Write the dataFieldBuf to buf
				dataFieldBuf.copy(buf, absoluteAddress);
				bufLength = Math.max(bufLength, absoluteAddress + dataLength);
				// Safely abort if the buffer length is already sufficient
				if(bufLength >= bufferSize) {
					return {
						"data": buf.slice(0, bufLength),
						"startSegmentAddress": startSegmentAddress,
						"startLinearAddress": startLinearAddress
					};
				}
				break;
			case END_OF_FILE:
				if(dataLength != 0)
					throw new Error("Invalid EOF record on line " +
						lineNum + ".");
				return {
					"data": buf.slice(0, bufLength),
					"startSegmentAddress": startSegmentAddress,
					"startLinearAddress": startLinearAddress
				};
				break;
			case EXT_SEGMENT_ADDR:
				if(dataLength != 2 || lowAddress != 0)
					throw new Error("Invalid extended segment address record on line " +
						lineNum + ".");
				highAddress = parseInt(dataField, 16) << 4;
				break;
			case START_SEGMENT_ADDR:
				if(dataLength != 4 || lowAddress != 0)
					throw new Error("Invalid start segment address record on line " +
						lineNum + ".");
				startSegmentAddress = parseInt(dataField, 16);
				break;
			case EXT_LINEAR_ADDR:
				if(dataLength != 2 || lowAddress != 0)
					throw new Error("Invalid extended linear address record on line " +
						lineNum + ".");
				highAddress = parseInt(dataField, 16) << 16;
				break;
			case START_LINEAR_ADDR:
				if(dataLength != 4 || lowAddress != 0)
					throw new Error("Invalid start linear address record on line " +
						lineNum + ".");
				startLinearAddress = parseInt(dataField, 16);
				break;
			default:
				throw new Error("Invalid record type (" + recordType +
					") on line " + lineNum);
				break;
		}
		//Advance to the next line
		if(data.charAt(pos) == "\r")
			pos++;
		if(data.charAt(pos) == "\n")
			pos++;
	}
	throw new Error("Unexpected end of input: missing or invalid EOF record.");
};