1 files changed, 102 insertions, 0 deletions
diff --git a/comm/mailnews/base/src/MailStringUtils.jsm b/comm/mailnews/base/src/MailStringUtils.jsm
new file mode 100644
index 0000000000..c892c328e4
--- /dev/null
+++ b/comm/mailnews/base/src/MailStringUtils.jsm
@@ -0,0 +1,102 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+const EXPORTED_SYMBOLS = ["MailStringUtils"];
+
+var MailStringUtils = {
+  /**
+   * Convert a ByteString to a Uint8Array.
+   *
+   * @param {ByteString} str - The input string.
+   * @returns {Uint8Array} The output Uint8Array.
+   */
+  byteStringToUint8Array(str) {
+    let arr = new Uint8Array(str.length);
+    for (let i = 0; i < str.length; i++) {
+      arr[i] = str.charCodeAt(i);
+    }
+    return arr;
+  },
+
+  /**
+   * Convert a Uint8Array to a ByteString.
+   *
+   * @param {Uint8Array} arr - The input Uint8Array.
+   * @returns {ByteString} The output string.
+   */
+  uint8ArrayToByteString(arr) {
+    let str = "";
+    for (let i = 0; i < arr.length; i += 65536) {
+      str += String.fromCharCode.apply(null, arr.subarray(i, i + 65536));
+    }
+    return str;
+  },
+
+  /**
+   * Convert a ByteString to a string.
+   *
+   * @param {ByteString} str - The ByteString to convert.
+   * @returns {string} The converted string.
+   */
+  byteStringToString(str) {
+    return new TextDecoder().decode(this.byteStringToUint8Array(str));
+  },
+
+  /**
+   * Convert a string to a ByteString.
+   *
+   * @param {string} str - The string to convert.
+   * @returns {ByteString} The converted ByteString.
+   */
+  stringToByteString(str) {
+    return this.uint8ArrayToByteString(new TextEncoder().encode(str));
+  },
+
+  /**
+   * Detect the text encoding of a ByteString.
+   *
+   * @param {ByteString} str - The input string.
+   * @returns {string} The output charset name.
+   */
+  detectCharset(str) {
+    // Check the BOM.
+    let charset = "";
+    if (str.length >= 2) {
+      let byte0 = str.charCodeAt(0);
+      let byte1 = str.charCodeAt(1);
+      let byte2 = str.charCodeAt(2);
+      if (byte0 == 0xfe && byte1 == 0xff) {
+        charset = "UTF-16BE";
+      } else if (byte0 == 0xff && byte1 == 0xfe) {
+        charset = "UTF-16LE";
+      } else if (byte0 == 0xef && byte1 == 0xbb && byte2 == 0xbf) {
+        charset = "UTF-8";
+      }
+    }
+    if (charset) {
+      return charset;
+    }
+
+    // Use mozilla::EncodingDetector.
+    let compUtils = Cc[
+      "@mozilla.org/messengercompose/computils;1"
+    ].createInstance(Ci.nsIMsgCompUtils);
+    return compUtils.detectCharset(str);
+  },
+
+  /**
+   * Read and detect the charset of a file, then convert the file content to
+   * DOMString. If you're absolutely sure it's a UTF-8 encoded file, use
+   * IOUtils.readUTF8 instead.
+   *
+   * @param {string} path - An absolute file path.
+   * @returns {DOMString} The file content.
+   */
+  async readEncoded(path) {
+    let arr = await IOUtils.read(path);
+    let str = this.uint8ArrayToByteString(arr);
+    let charset = this.detectCharset(str);
+    return new TextDecoder(charset).decode(arr);
+  },
+};