add parseJsonFields option

README.md

@@ -138,6 +138,7 @@ Key | Description
 `dest` or `storage` | Where to store the files
 `fileFilter` | Function to control which files are accepted
 `limits` | Limits of the uploaded data
+`parseJsonFields` | Parse fields that have the content-type `application/json`
 `preservePath` | Keep the full path of files instead of just the base name
 
 In an average web app, only `dest` might be required, and configured as shown in
@@ -299,6 +300,13 @@ function fileFilter (req, file, cb) {
 }
 ```
 
+### `parseJsonFields`
+
+Fields may also have a `Content-Type` header. If you set `parseJsonFields` to
+`true` these fields will be parsed using `JSON.parse()` instead of handled as
+plain text strings. This way you don't need to unroll complex JSON structures
+that are transmitted alongside uploaded files as url-encoded fields.
+
 ## Error handling
 
 When encountering an error, Multer will delegate the error to Express. You can

index.js

@@ -20,6 +20,7 @@ function Multer (options) {
   this.limits = options.limits
   this.preservePath = options.preservePath
   this.fileFilter = options.fileFilter || allowAll
+  this.parseJsonFields = !!options.parseJsonFields
 }
 
 Multer.prototype._makeMiddleware = function (fields, fileStrategy) {
@@ -49,7 +50,8 @@ Multer.prototype._makeMiddleware = function (fields, fileStrategy) {
       preservePath: this.preservePath,
       storage: this.storage,
       fileFilter: wrappedFileFilter,
-      fileStrategy: fileStrategy
+      fileStrategy: fileStrategy,
+      parseJsonFields: this.parseJsonFields
     }
   }
 
@@ -79,7 +81,8 @@ Multer.prototype.any = function () {
       preservePath: this.preservePath,
       storage: this.storage,
       fileFilter: this.fileFilter,
-      fileStrategy: 'ARRAY'
+      fileStrategy: 'ARRAY',
+      parseJsonFields: this.parseJsonFields
     }
   }
 

lib/make-middleware.js

@@ -24,6 +24,7 @@ function makeMiddleware (setup) {
     var fileFilter = options.fileFilter
     var fileStrategy = options.fileStrategy
     var preservePath = options.preservePath
+    var parseJsonFields = options.parseJsonFields
 
     req.body = Object.create(null)
 
@@ -80,7 +81,7 @@ function makeMiddleware (setup) {
     }
 
     // handle text field data
-    busboy.on('field', function (fieldname, value, fieldnameTruncated, valueTruncated) {
+    busboy.on('field', function (fieldname, value, fieldnameTruncated, valueTruncated, encoding, mimetype) {
       if (fieldname == null) return abortWithCode('MISSING_FIELD_NAME')
       if (fieldnameTruncated) return abortWithCode('LIMIT_FIELD_KEY')
       if (valueTruncated) return abortWithCode('LIMIT_FIELD_VALUE', fieldname)
@@ -90,6 +91,14 @@ function makeMiddleware (setup) {
         if (fieldname.length > limits.fieldNameSize) return abortWithCode('LIMIT_FIELD_KEY')
       }
 
+      if (parseJsonFields && mimetype === 'application/json') {
+        try {
+          value = JSON.parse(value)
+        } catch (error) {
+          return abortWithError(error)
+        }
+      }
+
       appendField(req.body, fieldname, value)
     })