Enforce RFC 7540 rules about stream weights

alexwlchan · alexwlchan · commit 35493f5b3da3 · 2017-01-22T12:44:47.000Z
diff --git a/src/priority/__init__.py b/src/priority/__init__.py
@@ -4,5 +4,5 @@
 """
 from .priority import (  # noqa
     Stream, PriorityTree, DeadlockError, PriorityLoop, DuplicateStreamError,
-    MissingStreamError, TooManyStreamsError
+    MissingStreamError, TooManyStreamsError, BadWeightError
 )
diff --git a/src/priority/priority.py b/src/priority/priority.py
@@ -53,6 +53,15 @@ class TooManyStreamsError(Exception):
     pass
 
 
+class BadWeightError(Exception):
+    """
+    An attempt was made to create a stream with an invalid weight.
+
+    .. versionadded:: 1.3.0
+    """
+    pass
+
+
 class Stream(object):
     """
     Priority information for a given stream.
@@ -70,6 +79,21 @@ def __init__(self, stream_id, weight=16):
         self.last_weight = 0
         self._deficit = 0
 
+    @property
+    def weight(self):
+        return self._weight
+
+    @weight.setter
+    def weight(self, value):
+        # RFC 7540 § 5.3.2: "All dependent streams are allocated an integer
+        # weight between 1 and 256 (inclusive)."
+        if not isinstance(value, int):
+            raise BadWeightError("Stream weight should be an integer")
+        elif not (1 <= value <= 256):
+            raise BadWeightError(
+                "Stream weight must be between 1 and 256 (inclusive)")
+        self._weight = value
+
     def add_child(self, child):
         """
         Add a stream that depends on this one.
diff --git a/test/test_priority.py b/test/test_priority.py
@@ -391,6 +391,39 @@ def test_can_insert_stream_with_exclusive_dependency_on_0(self,
         next_ten_ids = [next(p) for _ in range(0, 10)]
         assert next_ten_ids == [5] * 10
 
+    @pytest.mark.parametrize('weight', [
+        None,
+        0.5,
+        float('inf'),
+        'priority',
+        object
+    ])
+    def test_insert_stream_with_non_integer_weight_is_error(self, weight):
+        """
+        Creating a stream with a non-integer weight is rejected.
+        """
+        p = priority.PriorityTree()
+        with pytest.raises(priority.BadWeightError) as err:
+            p.insert_stream(stream_id=1, weight=weight)
+        assert err.value.args[0] == 'Stream weight should be an integer'
+
+    @pytest.mark.parametrize('weight', [
+        0,
+        257,
+        1000,
+        -42,
+    ])
+    def test_insert_stream_with_out_of_bounds_weight_is_error(self, weight):
+        """
+        Creating a stream with an out-of-bounds integer weight is rejected.
+        """
+        p = priority.PriorityTree()
+        with pytest.raises(priority.BadWeightError) as err:
+            p.insert_stream(stream_id=1, weight=weight)
+        assert (
+            err.value.args[0] ==
+            'Stream weight must be between 1 and 256 (inclusive)')
+
 
 class TestPriorityTreeOutput(object):
     """

Original file line number	Diff line number	Diff line change
`@@ -4,5 +4,5 @@`
`4`	`4`	`"""`
`5`	`5`	`from .priority import ( # noqa`
`6`	`6`	`Stream, PriorityTree, DeadlockError, PriorityLoop, DuplicateStreamError,`
`7`		`- MissingStreamError, TooManyStreamsError`
	`7`	`+ MissingStreamError, TooManyStreamsError, BadWeightError`
`8`	`8`	`)`