Provide a compatibility option for clients with broken data set order.

CHANGES.rst

@@ -1,6 +1,35 @@
 Changes
 =======
 
+0.7 (unreleased)
+----------------
+
+- Provide a compatibility option for clients that do not implement the "list of
+  tuples" processing according to the HTML spec's "Constructing the form data
+  set" algorithm.
+
+  To help those clients you can suffix each field name with a unique marker
+  so that they will properly preserver order and thus emulate the 
+  "list of tuples" behaviour. 
+
+  If your application relies on this, then provide the ``unique_key_separator``
+  argument to the parse function ``parse(fields, unique_key_separator=":"")`` and
+  suffix the input field names accordingly. The actual IDs do not matter,
+  as long as the combination of field name + id ends up as unique. :
+
+    <input type="hidden" name="__start__:1234" value="series:sequence"/>
+    <input type="hidden" name="name:1234" value="Bob" />
+    <input type="hidden" name="__end__:1234" />
+
+    <input type="hidden" name="__start__:1235" value="series:sequence"/>
+    <input type="hidden" name="name:1235" value="Ken" />
+    <input type="hidden" name="__end__:1235" />
+
+  For readability you can reuse the same ID on start/end markers, but they could
+  also be different and don't have to be numbers, UUIDs would work as well but
+  will increase payload size.
+
+
 0.6 (2018-08-24)
 ----------------
 

peppercorn/__init__.py

@@ -13,7 +13,7 @@ def data_type(value):
 TYPS = (SEQUENCE, MAPPING, RENAME, IGNORE)
 
 
-def parse(tokens):
+def parse(tokens, unique_key_separator=None):
     """ Infer a data structure from the ordered set of fields and
     return it."""
     target = typ = None
@@ -22,6 +22,9 @@ def parse(tokens):
 
     for token in tokens:
         key, val = token
+        if unique_key_separator:
+            key = key.rsplit(unique_key_separator, maxsplit=1)[0]
+
         if key == START:
             stack.append((target, typ, out))
             target, typ = data_type(val)
@@ -46,7 +49,7 @@ def parse(tokens):
             target = prev_target
             typ = prev_typ
         else:
-            out.append(token)
+            out.append((key, val))
 
     if stack:
         raise ValueError("Not enough end markers")

peppercorn/tests.py

@@ -2,9 +2,9 @@
 from peppercorn.compat import PY3
 
 class TestParse(unittest.TestCase):
-    def _callFUT(self, fields):
+    def _callFUT(self, fields, **kw):
         from peppercorn import parse
-        return parse(fields)
+        return parse(fields, **kw)
 
     def _makeEnviron(self, kw=None):
         if kw is None: # pragma: no cover
@@ -73,7 +73,43 @@ def test_bare(self):
         fields = self._getFields()
         result = self._callFUT(fields)
         self._assertFieldsResult(result)
-
+
+    def test_bare_with_marker(self):
+        i = 0
+        def next_id():
+            nonlocal i
+            i += 1
+            return str(i)
+        fields = [
+            (key + ":" + next_id(), value)
+            for key, value in self._getFields()]
+        result = self._callFUT(fields, unique_key_separator=":")
+        self._assertFieldsResult(result)
+
+    def test_bare_without_marker(self):
+        # This is proof that ":" isn't something special when we don't
+        # provide a unique key separator
+
+        from peppercorn import START, END, MAPPING
+
+        fields = []
+        for key, value in self._getFields():
+            if key not in [START, END]:
+                key = key + ":something"
+            fields.append((key, value))
+
+        result = self._callFUT(fields)
+
+        self.assertEqual(
+            result,
+            {'series':
+             {'name:something':'date series 1',
+              'dates': [['10', '12', '2008'],
+                        ['10', '12', '2009']],
+              },
+             'name:something': 'project1',
+             'title:something': 'Cool project'})
+
     def test_fieldstorage(self):
         fs = self._makeMultipartFieldStorage(self._getFields())