fix(dkim-relaxed): Faster DKIM hash calculation for relaxed body if t…

…he body contains extremely long lines

lib/dkim/body/relaxed.js

@@ -122,24 +122,36 @@ class RelaxedHash {
         this._updateBodyHash(chunk);
     }
 
+    /**
+     * Performs the following modifications for a single line:
+     *  - Replace all <LF> chars with <CR><LF>
+     *  - Replace all spaces and tabs with a single space.
+     *  - Remove trailing whitespace
+     * @param {Buffer} line
+     * @returns {Buffer} fixed line
+     */
     fixLineBuffer(line) {
-        let resultLine = [];
+        // Allocate maximum expected buffer length
+        // If the line is only filled with <LF> bytes then we need 2 times the size of the line
+        let lineBuf = Buffer.alloc(line.length * 2);
+        // Start processing the line from the end to beginning
+        let writePos = lineBuf.length - 1;
 
         let nonWspFound = false;
         let prevWsp = false;
 
         for (let i = line.length - 1; i >= 0; i--) {
             if (line[i] === CHAR_LF) {
-                resultLine.unshift(line[i]);
+                lineBuf[writePos--] = line[i];
                 if (i === 0 || line[i - 1] !== CHAR_CR) {
                     // add missing carriage return
-                    resultLine.unshift(CHAR_CR);
+                    lineBuf[writePos--] = CHAR_CR;
                 }
                 continue;
             }
 
             if (line[i] === CHAR_CR) {
-                resultLine.unshift(line[i]);
+                lineBuf[writePos--] = line[i];
                 continue;
             }
 
@@ -151,19 +163,19 @@ class RelaxedHash {
             }
 
             if (prevWsp) {
-                resultLine.unshift(CHAR_SPACE);
+                lineBuf[writePos--] = CHAR_SPACE;
                 prevWsp = false;
             }
 
             nonWspFound = true;
-            resultLine.unshift(line[i]);
+            lineBuf[writePos--] = line[i];
         }
 
         if (prevWsp && nonWspFound) {
-            resultLine.unshift(CHAR_SPACE);
+            lineBuf[writePos--] = CHAR_SPACE;
         }
 
-        return Buffer.from(resultLine);
+        return lineBuf.subarray(writePos + 1);
     }
 
     update(chunk, final) {

test/dkim/body/relaxed-test.js

@@ -82,4 +82,18 @@ describe('DKIM RelaxedBody Tests', () => {
                 .digest('base64')
         );
     });
+
+    it('Should process a very long line', async () => {
+        const lineLen = 10 * 1024 * 1024;
+        const message = Buffer.alloc(lineLen);
+        // Fill the line with printable characters from 0x20 to 0x7E
+        for (let i = 1; i < lineLen + 1; i++) {
+            message[i] = (i % 95) + 0x20;
+        }
+
+        let s = new RelaxedHash('rsa-sha256');
+        let buf = s.fixLineBuffer(message);
+
+        expect(buf).to.exist;
+    });
 });