Submit an empty file when leaving a file input blank

docs/ChangeLog.rst

@@ -14,6 +14,10 @@ Bug fixes
   ``disabled`` attribute from the element in the :class:`~mechanicalsoup.Form`
   object directly.
   [`#248 <https://github.com/MechanicalSoup/MechanicalSoup/issues/248>`__]
+* Upon submitting a form containing a file input field without uploading one,
+  an empty filename & content will be sent in compliance with regular web
+  browser behavior.
+  [`#250 <https://github.com/MechanicalSoup/MechanicalSoup/issues/250>`__]
 
 Version 0.11
 ============

mechanicalsoup/browser.py

@@ -180,11 +180,14 @@ def _request(self, form, url=None, **kwargs):
                     # in browsers, file upload only happens if the form
                     # (or submit button) enctype attribute is set to
                     # "multipart/form-data". We don't care, simplify.
-                    if not value:
-                        continue
-                    if isinstance(value, string_types):
-                        value = open(value, "rb")
-                    files[name] = value
+                    filename = value
+                    if filename != "" and isinstance(filename, string_types):
+                        content = open(filename, "rb")
+                    else:
+                        content = ""
+                    # If value is the empty string, we still pass it for
+                    # consistency with browsers (see #250).
+                    files[name] = (filename, content)
                 else:
                     data.append((name, value))
 

tests/test_browser.py

@@ -3,6 +3,7 @@
 import sys
 from bs4 import BeautifulSoup
 import tempfile
+import os
 from requests.cookies import RequestsCookieJar
 import pytest
 
@@ -56,7 +57,6 @@ def test__request(httpbin):
         <p><input type=checkbox name="topping" value="onion" checked>Onion</p>
         <p><input type=checkbox name="topping" value="mushroom">Mushroom</p>
       </fieldset>
-      <input name="pic" type="FiLe">
       <select name="shape">
         <option value="round">Round</option>
         <option value="square" selected>Square</option>
@@ -81,20 +81,25 @@ def test__request(httpbin):
         "Content-Type"]
 
 
-def test__request_file(httpbin):
+@pytest.mark.parametrize('expected_content, set_value', [
+    (b":-)", True),
+    (b"", False)
+])
+def test__request_file(httpbin, expected_content, set_value):
     form_html = """
     <form method="post" action="{}/post">
       <input name="pic" type="file" />
     </form>
     """.format(httpbin.url)
     form = BeautifulSoup(form_html, "lxml").form
 
-    # create a temporary file for testing file upload
-    pic_path = tempfile.mkstemp()[1]
-    with open(pic_path, "w") as f:
-        f.write(":-)")
+    if set_value:
+        # create a temporary file for testing file upload
+        pic_filedescriptor, pic_path = tempfile.mkstemp()
+        os.write(pic_filedescriptor, expected_content)
+        os.close(pic_filedescriptor)
 
-    form.find("input", {"name": "pic"})["value"] = pic_path
+        form.find("input", {"name": "pic"})["value"] = pic_path
 
     browser = mechanicalsoup.Browser()
     response = browser._request(form)
@@ -103,14 +108,29 @@ def test__request_file(httpbin):
     found = False
     for key, value in response.json().items():
         if key == "files":
-            assert value["pic"] == ":-)"
-            found = True
+            if "pic" in value:
+                if value["pic"].encode() == expected_content:
+                    # If pic is found twice, an error will occur
+                    assert not found
+                    found = True
+        # One would expect to find "pic" in files, but as of writing,
+        # httpbin puts it in form when the filename is empty:
+        elif key == "form":
+            if "pic" in value:
+                if value["pic"].encode() == expected_content:
+                    assert not found
+                    found = True
+                    assert b"filename=\"\"" in response.request.body
         else:
             assert (value is None) or ("pic" not in value)
 
     assert found
     assert "multipart/form-data" in response.request.headers["Content-Type"]
 
+    # In case we created a file for upload, we need to close & delete it
+    if set_value:
+        os.remove(pic_path)
+
 
 def test__request_select_none(httpbin):
     """Make sure that a <select> with no options selected