feat(common): file type validator

packages/common/pipes/file/file-type.validator.ts

@@ -1,11 +1,15 @@
 import { FileValidator } from './file-validator.interface';
 
 export type FileTypeValidatorOptions = {
-  fileType: string;
+  fileType: string | RegExp;
 };
 
 /**
- * Defines the built-in FileType File Validator
+ * Defines the built-in FileType File Validator. It validates incoming files mime-type
+ * matching a string or a regular expression. Note that this validator uses a naive strategy
+ * to check the mime-type and could be fooled if the client provided a file with renamed extension.
+ * (for instance, renaming a 'malicious.bat' to 'malicious.jpeg'). To handle such security issues
+ * with more reliability, consider checking against the file's [magic-numbers](https://en.wikipedia.org/wiki/Magic_number_%28programming%29)
  *
  * @see [File Validators](https://docs.nestjs.com/techniques/file-upload#validators)
  *
@@ -25,6 +29,8 @@ export class FileTypeValidator extends FileValidator<FileTypeValidatorOptions> {
       return false;
     }
 
-    return (file.mimetype as string).endsWith(this.validationOptions.fileType);
+    return Boolean(
+      (file.mimetype as string).match(this.validationOptions.fileType),
+    );
   }
 }

packages/common/test/pipes/file/file-type.validator.spec.ts

@@ -27,6 +27,18 @@ describe('FileTypeValidator', () => {
       expect(fileTypeValidator.isValid(requestFile)).to.equal(true);
     });
 
+    it('should return true when the file mimetype matches the specified regexp', () => {
+      const fileTypeValidator = new FileTypeValidator({
+        fileType: /word/,
+      });
+
+      const requestFile = {
+        mimetype: 'application/msword',
+      };
+
+      expect(fileTypeValidator.isValid(requestFile)).to.equal(true);
+    });
+
     it('should return false when the file mimetype is different from the specified', () => {
       const fileTypeValidator = new FileTypeValidator({
         fileType: 'image/jpeg',
@@ -39,6 +51,18 @@ describe('FileTypeValidator', () => {
       expect(fileTypeValidator.isValid(requestFile)).to.equal(false);
     });
 
+    it('should return false when the file mimetype does not match the provided regexp', () => {
+      const fileTypeValidator = new FileTypeValidator({
+        fileType: /mp4/,
+      });
+
+      const requestFile = {
+        mimetype: 'image/png',
+      };
+
+      expect(fileTypeValidator.isValid(requestFile)).to.equal(false);
+    });
+
     it('should return false when the file mimetype was not provided', () => {
       const fileTypeValidator = new FileTypeValidator({
         fileType: 'image/jpeg',