43 lines
1.2 KiB
TypeScript
43 lines
1.2 KiB
TypeScript
export type ConcatInfo = {
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part: number;
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reference: number;
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total: number;
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};
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/**
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* Finds the concatenation information element in a User Data Header, walking the elements rather
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* than assuming the header holds nothing else — real SMSCs put ports, language indicators and more
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* alongside it.
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*
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* `message` is a short_message whose first octet is the UDH length.
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*/
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export function concatInfo(message: Buffer): ConcatInfo | undefined {
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const udhLength = message[0];
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if (udhLength === undefined) return undefined;
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const end = Math.min(udhLength + 1, message.length);
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let offset = 1;
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while (offset + 2 <= end) {
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const iei = message.readUInt8(offset);
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const ieLength = message.readUInt8(offset + 1);
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const data = message.subarray(offset + 2, offset + 2 + ieLength);
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if (offset + 2 + ieLength > end) return undefined;
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// 0x00 is an 8-bit concatenation reference, 0x08 a 16-bit one.
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if (iei === 0x00 && ieLength === 3) {
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return { part: data.readUInt8(2), reference: data.readUInt8(0), total: data.readUInt8(1) };
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}
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if (iei === 0x08 && ieLength === 4) {
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return { part: data.readUInt8(3), reference: data.readUInt16BE(0), total: data.readUInt8(2) };
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}
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offset += 2 + ieLength;
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}
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return undefined;
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}
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