xhrupload: Use error messages from the endpoint, closes #303

src/core/Core.js

@@ -444,7 +444,11 @@ class Uppy {
 
     this.on('core:upload-error', (fileID, error) => {
       const fileName = this.state.files[fileID].name
-      this.info(`Failed to upload: ${fileName}`, 'error', 5000)
+      let message = `Failed to upload ${fileName}`
+      if (typeof error === 'object' && error.message) {
+        message = `${message}: ${error.message}`
+      }
+      this.info(message, 'error', 5000)
     })
 
     this.on('core:upload', () => {

src/plugins/XHRUpload.js

@@ -20,6 +20,9 @@ module.exports = class XHRUpload extends Plugin {
       headers: {},
       getResponseData (xhr) {
         return JSON.parse(xhr.response)
+      },
+      getResponseError (xhr) {
+        return new Error('Upload error')
       }
     }
 
@@ -88,8 +91,10 @@ module.exports = class XHRUpload extends Plugin {
 
           return resolve(file)
         } else {
-          this.core.emit('core:upload-error', file.id, xhr)
-          return reject('Upload error')
+          const error = opts.getResponseError(xhr) || new Error('Upload error')
+          error.request = xhr
+          this.core.emit('core:upload-error', file.id, error)
+          return reject(error)
         }
 
         // var upload = {}
@@ -103,7 +108,7 @@ module.exports = class XHRUpload extends Plugin {
 
       xhr.addEventListener('error', (ev) => {
         this.core.emit('core:upload-error', file.id)
-        return reject('Upload error')
+        return reject(new Error('Upload error'))
       })
 
       xhr.open(opts.method.toUpperCase(), opts.endpoint, true)