@aokiapp/tlv/dist/builder/basic-builder.js

Tag-Length-Value (TLV) parser and builder library with schema support. Provides both parsing and building APIs as submodules.

import { TagClass } from "../common/types.js";
/**
 * TLV構造体（Tag/Length/Value）を受け取り、DERエンコードされたArrayBufferを返す
 */
export class BasicTLVBuilder {
    /**
     * TLV構造体からDERエンコードバイト列を生成する
     * @param tlv - TLV構造体（tag, length, value）
     * @returns DERエンコード済みArrayBuffer
     */
    static build(tlv) {
        const { tag, value } = tlv;
        const { tagClass, tagNumber, constructed } = tag;
        if (tagNumber < 0 || tagNumber >= Number.MAX_SAFE_INTEGER) {
            throw new Error("Tag number is out of valid range.");
        }
        if (typeof tagClass !== "number" ||
            tagClass < TagClass.Universal ||
            tagClass > TagClass.Private) {
            throw new Error(`Invalid tag class: ${tagClass}`);
        }
        // 1. Encode Tag
        const tagBytes = [];
        let firstByte = (tagClass << 6) | (constructed ? 0x20 : 0x00);
        if (tagNumber < 31) {
            firstByte |= tagNumber;
            tagBytes.push(firstByte);
        }
        else {
            firstByte |= 0x1f;
            tagBytes.push(firstByte);
            const tagNumBytes = [];
            let num = tagNumber;
            do {
                tagNumBytes.unshift(num % 128);
                num = Math.floor(num / 128); // Use division for numbers > 32-bit
            } while (num > 0);
            for (let i = 0; i < tagNumBytes.length - 1; i++) {
                tagBytes.push(tagNumBytes[i] | 0x80);
            }
            tagBytes.push(tagNumBytes[tagNumBytes.length - 1]);
        }
        // 2. Encode Length
        const lengthBytes = [];
        const len = value.byteLength;
        if (len < 128) {
            lengthBytes.push(len);
        }
        else {
            const lenOfLenBytes = [];
            let tempLen = len;
            do {
                lenOfLenBytes.unshift(tempLen & 0xff);
                tempLen = Math.floor(tempLen / 256);
            } while (tempLen > 0);
            if (lenOfLenBytes.length > 126) {
                // The length of the length field can be at most 126 bytes in BER/DER.
                // (First byte is 0x80 | 126 = 0xFE). 0xFF is reserved.
                throw new Error("Value is too long to be encoded.");
            }
            lengthBytes.push(0x80 | lenOfLenBytes.length);
            lengthBytes.push(...lenOfLenBytes);
        }
        // 3. Concatenate T, L, V
        const totalLength = tagBytes.length + lengthBytes.length + len;
        const result = new Uint8Array(totalLength);
        const valueBytes = new Uint8Array(value);
        let offset = 0;
        result.set(tagBytes, offset);
        offset += tagBytes.length;
        result.set(lengthBytes, offset);
        offset += lengthBytes.length;
        result.set(valueBytes, offset);
        return result.buffer;
    }
}