add MIME encoding operation

src/core/config/Categories.json

@@ -83,6 +83,7 @@
             "Rison Decode",
             "To Modhex",
             "From Modhex",
+            "MIME Encoding",
             "MIME Decoding"
         ]
     },

src/core/operations/MIMEEncoding.mjs

@@ -0,0 +1,149 @@
+/**
+ * @author skyswordw
+ * @copyright Crown Copyright 2026
+ * @license Apache-2.0
+ */
+
+import Operation from "../Operation.mjs";
+import OperationError from "../errors/OperationError.mjs";
+import {toBase64} from "../lib/Base64.mjs";
+import cptable from "codepage";
+
+const CHARSET_CODEPAGES = {
+        "UTF-8": 65001,
+        "US-ASCII": 20127,
+        "ISO-8859-1": 28591,
+        "ISO-8859-2": 28592,
+        "ISO-8859-3": 28593,
+        "ISO-8859-4": 28594,
+        "ISO-8859-5": 28595,
+        "ISO-8859-6": 28596,
+        "ISO-8859-7": 28597,
+        "ISO-8859-8": 28598,
+        "ISO-8859-9": 28599,
+        "ISO-8859-10": 28600,
+        "ISO-8859-11": 28601,
+        "ISO-8859-13": 28603,
+        "ISO-8859-14": 28604,
+        "ISO-8859-15": 28605,
+        "ISO-8859-16": 28606,
+    },
+    TRANSFER_ENCODINGS = ["Base64", "Q-encoding"],
+    MAX_ENCODED_WORD_LENGTH = 75;
+
+/**
+ * MIME Encoding operation
+ */
+class MIMEEncoding extends Operation {
+
+    /**
+     * MIMEEncoding constructor
+     */
+    constructor() {
+        super();
+
+        this.name = "MIME Encoding";
+        this.module = "Default";
+        this.description = "Encodes text as MIME encoded-words for non-ASCII email header values.";
+        this.infoURL = "https://tools.ietf.org/html/rfc2047";
+        this.inputType = "string";
+        this.outputType = "string";
+        this.args = [
+            {
+                name: "Charset",
+                type: "option",
+                value: Object.keys(CHARSET_CODEPAGES)
+            },
+            {
+                name: "Transfer encoding",
+                type: "option",
+                value: TRANSFER_ENCODINGS
+            }
+        ];
+    }
+
+    /**
+     * @param {string} input
+     * @param {Object[]} args
+     * @returns {string}
+     */
+    run(input, args) {
+        const [charset, encoding] = args,
+            codepage = CHARSET_CODEPAGES[charset];
+
+        if (!codepage) throw new OperationError("Invalid charset");
+        if (!TRANSFER_ENCODINGS.includes(encoding)) throw new OperationError("Invalid transfer encoding");
+        if (!input.length) return "";
+
+        return input.split(/\r\n|\n|\r/).map(line => {
+            return this.encodeLine(line, charset, codepage, encoding);
+        }).join("\r\n");
+    }
+
+    /**
+     * @param {string} input
+     * @param {string} charset
+     * @param {number} codepage
+     * @param {string} encoding
+     * @returns {string}
+     */
+    encodeLine(input, charset, codepage, encoding) {
+        const encodedWords = [];
+        let chunk = "";
+
+        for (const char of input) {
+            const next = chunk + char;
+            if (chunk && this.encodedWord(charset, codepage, encoding, next).length > MAX_ENCODED_WORD_LENGTH) {
+                encodedWords.push(this.encodedWord(charset, codepage, encoding, chunk));
+                chunk = char;
+            } else {
+                chunk = next;
+            }
+        }
+
+        if (chunk) encodedWords.push(this.encodedWord(charset, codepage, encoding, chunk));
+        return encodedWords.join("\r\n ");
+    }
+
+    /**
+     * @param {string} charset
+     * @param {number} codepage
+     * @param {string} encoding
+     * @param {string} input
+     * @returns {string}
+     */
+    encodedWord(charset, codepage, encoding, input) {
+        const encodedText = encoding === "Base64" ?
+            toBase64(cptable.utils.encode(codepage, input)) :
+            this.qEncode(cptable.utils.encode(codepage, input));
+
+        return `=?${charset}?${encoding === "Base64" ? "B" : "Q"}?${encodedText}?=`;
+    }
+
+    /**
+     * @param {Uint8Array|byteArray} input
+     * @returns {string}
+     */
+    qEncode(input) {
+        let output = "";
+        for (const byte of input) {
+            if (byte === 0x20) {
+                output += "_";
+            } else if (
+                byte >= 0x21 &&
+                byte <= 0x7e &&
+                byte !== 0x3d &&
+                byte !== 0x3f &&
+                byte !== 0x5f
+            ) {
+                output += String.fromCharCode(byte);
+            } else {
+                output += `=${byte.toString(16).toUpperCase().padStart(2, "0")}`;
+            }
+        }
+        return output;
+    }
+
+}
+
+export default MIMEEncoding;

tests/node/tests/operations.mjs

@@ -681,6 +681,13 @@ WWFkYSBZYWRh\r
         assert.strictEqual(chef.LZNT1Decompress("\x1a\xb0\x00compress\x00edtestda\x04ta\x07\x88alot").toString(), "compressedtestdatacompressedalot");
     }),
 
+    it("MIME Encoding", () => {
+        assert.strictEqual(chef.MIMEEncoding("Keld Jørn Simonsen", {
+            charset: "ISO-8859-1",
+            transferEncoding: "Q-encoding",
+        }).toString(), "=?ISO-8859-1?Q?Keld_J=F8rn_Simonsen?=");
+    }),
+
     it("MD6", () => {
         assert.strictEqual(chef.MD6("Head Over Heels", {key: "arty"}).toString(), "d8f7fe4931fbaa37316f76283d5f615f50ddd54afdc794b61da522556aee99ad");
     }),
@@ -1178,4 +1185,3 @@ ExifImageHeight: 57`);
 
 
 ]);
-

tests/operations/tests/MIMEDecoding.mjs

@@ -1,5 +1,5 @@
 /**
- * MIME Header Decoding tests
+ * MIME Header Encoding and Decoding tests
  *
  * @author mshwed [m@ttshwed.com]
  * @copyright Crown Copyright 2019
@@ -9,6 +9,65 @@
 import TestRegister from "../../lib/TestRegister.mjs";
 
 TestRegister.addTests([
+    {
+        name: "MIME Encoding: UTF-8 Base64",
+        input: "Éric <eric@example.org>",
+        expectedOutput: "=?UTF-8?B?w4lyaWMgPGVyaWNAZXhhbXBsZS5vcmc+?=",
+        recipeConfig: [
+            {
+                "op": "MIME Encoding",
+                "args": ["UTF-8", "Base64"]
+            }
+        ]
+    },
+    {
+        name: "MIME Encoding: UTF-8 Q-encoding",
+        input: "Éric <eric@example.org>",
+        expectedOutput: "=?UTF-8?Q?=C3=89ric_<eric@example.org>?=",
+        recipeConfig: [
+            {
+                "op": "MIME Encoding",
+                "args": ["UTF-8", "Q-encoding"]
+            }
+        ]
+    },
+    {
+        name: "MIME Encoding: ISO-8859-1 Q-encoding",
+        input: "Keld Jørn Simonsen",
+        expectedOutput: "=?ISO-8859-1?Q?Keld_J=F8rn_Simonsen?=",
+        recipeConfig: [
+            {
+                "op": "MIME Encoding",
+                "args": ["ISO-8859-1", "Q-encoding"]
+            }
+        ]
+    },
+    {
+        name: "MIME Encoding: long Q-encoded header round trip",
+        input: "This is a deliberately long MIME header value with Éric and Anaïs in it.",
+        expectedOutput: "This is a deliberately long MIME header value with Éric and Anaïs in it.",
+        recipeConfig: [
+            {
+                "op": "MIME Encoding",
+                "args": ["UTF-8", "Q-encoding"]
+            },
+            {
+                "op": "MIME Decoding",
+                "args": []
+            }
+        ]
+    },
+    {
+        name: "MIME Encoding: long Base64 header is folded",
+        input: "This is a deliberately long MIME header value with Eric and Anais in it.",
+        expectedOutput: "=?US-ASCII?B?VGhpcyBpcyBhIGRlbGliZXJhdGVseSBsb25nIE1JTUUgaGVhZGVyIHZhbHVl?=\r\n =?US-ASCII?B?IHdpdGggRXJpYyBhbmQgQW5haXMgaW4gaXQu?=",
+        recipeConfig: [
+            {
+                "op": "MIME Encoding",
+                "args": ["US-ASCII", "Base64"]
+            }
+        ]
+    },
     {
         name: "Encoded comments",
         input: "(=?ISO-8859-1?Q?a?=)",