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46 lines
1.4 KiB
TypeScript
46 lines
1.4 KiB
TypeScript
/**
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* Unpad the buffer from its padding.
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* An error is thrown if there is no padding.
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* A padded buffer is
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* * whatever at start
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* * ends with 0x80 and any number of 0x00 until the end
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*/
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export function removeMessagePadding(paddedData: ArrayBuffer): ArrayBuffer {
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const paddedPlaintext = new Uint8Array(paddedData);
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for (let i = paddedPlaintext.length - 1; i >= 0; i -= 1) {
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if (paddedPlaintext[i] === 0x80) {
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const plaintext = new Uint8Array(i);
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plaintext.set(paddedPlaintext.subarray(0, i));
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return plaintext.buffer;
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} else if (paddedPlaintext[i] !== 0x00) {
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throw new Error('Invalid padding');
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}
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}
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throw new Error('Invalid padding');
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}
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/**
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* Add padding to a message buffer
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* @param messageBuffer The buffer to add padding to.
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*/
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export function addMessagePadding(messageBuffer: Uint8Array): Uint8Array {
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const plaintext = new Uint8Array(getPaddedMessageLength(messageBuffer.byteLength + 1) - 1);
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plaintext.set(new Uint8Array(messageBuffer));
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plaintext[messageBuffer.byteLength] = 0x80;
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return plaintext;
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}
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function getPaddedMessageLength(originalLength: number): number {
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const messageLengthWithTerminator = originalLength + 1;
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let messagePartCount = Math.floor(messageLengthWithTerminator / 160);
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if (messageLengthWithTerminator % 160 !== 0) {
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messagePartCount += 1;
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}
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return messagePartCount * 160;
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}
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