tests/form_pages/test_file_field.py

@@ -332,6 +332,44 @@ def test_form_file_field_submit_wrong_mimetype(pub):
     assert resp.text == '%PDF-1.4 ...'
 
 
+def test_form_file_field_submit_garbage_pdf(pub):
+    FormDef.wipe()
+    formdef = FormDef()
+    formdef.name = 'test'
+    formdef.fields = [
+        fields.FileField(
+            id='0',
+            label='file',
+            document_type={
+                'id': 1,
+                'mimetypes': ['application/pdf'],
+                'label': 'PDF files',
+            },
+        )
+    ]
+    formdef.store()
+    formdef.data_class().wipe()
+
+    upload = Upload('test.pdf', b'x' * 500, 'application/pdf')
+    resp = get_app(pub).get('/test/')
+    resp.forms[0]['f0$file'] = upload
+    resp = resp.forms[0].submit('submit')
+    assert resp.pyquery('#form_error_f0').text() == 'invalid file type'
+
+    upload = Upload('test.pdf', b'x' * 500 + b'%PDF-1.4 ...', 'application/pdf')
+    resp = get_app(pub).get('/test/')
+    resp.forms[0]['f0$file'] = upload
+    resp = resp.forms[0].submit('submit')
+    assert 'Check values then click submit.' in resp.text
+    resp = resp.forms[0].submit('submit').follow()
+    assert 'The form has been recorded' in resp.text
+    resp = resp.click('test.pdf')
+    assert resp.location.endswith('/test.pdf')
+    resp = resp.follow()
+    assert resp.content_type == 'application/pdf'
+    assert '%PDF-1.4' in resp.text
+
+
 def test_form_file_field_submit_blacklist(pub):
     FormDef.wipe()
     formdef = FormDef()

wcs/qommon/form.py

@@ -903,6 +903,13 @@ class FileWithPreviewWidget(CompositeWidget):
         elif magic and self.value.fp:
             mime = magic.Magic(mime=True)
             filetype = mime.from_file(self.value.fp.name)
+            if filetype in ('application/octet-stream', 'text/plain'):
+                # second-guess libmagic as we want to accept PDF files
+                # with some garbage at start.
+                with open(self.value.fp.name, 'rb') as fd:
+                    first_bytes = fd.read(1024)
+                    if b'%PDF' in first_bytes:
+                        filetype = 'application/pdf'
         else:
             filetype = getattr(self.value, 'storage_attrs', {}).get('content_type')
             if not filetype: