From 291f8e196ccb4343e2539a55d480b0b5a76d1e87 Mon Sep 17 00:00:00 2001
From: Michael Merickel <michael@merickel.org>
Date: Fri, 5 Apr 2019 13:19:13 -0500
Subject: simplify rotation

---
 waitress/channel.py            | 17 ++++++-----------
 waitress/tests/test_channel.py | 23 ++++++++++++++---------
 2 files changed, 20 insertions(+), 20 deletions(-)

diff --git a/waitress/channel.py b/waitress/channel.py
index 27eb532..6f20742 100644
--- a/waitress/channel.py
+++ b/waitress/channel.py
@@ -222,7 +222,7 @@ class HTTPChannel(wasyncore.dispatcher, object):
         while True:
             outbuf = self.outbufs[0]
             # use outbuf.__len__ rather than len(outbuf) FBO of not getting
-             # OverflowError on 32-bit Python
+            # OverflowError on 32-bit Python
             outbuflen = outbuf.__len__()
             while outbuflen > 0:
                 chunk = outbuf.get(self.sendbuf_len)
@@ -303,7 +303,7 @@ class HTTPChannel(wasyncore.dispatcher, object):
             # the async mainloop might be popping data off outbuf; we can
             # block here waiting for it because we're in a task thread
             with self.outbuf_lock:
-                overflowed = self._flush_outbufs_below_high_watermark()
+                self._flush_outbufs_below_high_watermark()
                 if not self.connected:
                     raise ClientDisconnected
                 if data.__class__ is ReadOnlyFileBasedBuffer:
@@ -313,12 +313,9 @@ class HTTPChannel(wasyncore.dispatcher, object):
                     self.outbufs.append(nextbuf)
                     self.current_outbuf_count = 0
                 else:
-                    # if we overflowed then start a new buffer to ensure
-                    # the original eventually gets pruned otherwise it may
-                    # grow unbounded
-                    if overflowed or (
-                        self.current_outbuf_count > self.adj.outbuf_high_watermark
-                    ):
+                    # if we overflowed then start a new buffer to ensure avoid
+                    # this buffer growing unbounded
+                    if self.current_outbuf_count > self.adj.outbuf_high_watermark:
                         nextbuf = OverflowableBuffer(self.adj.outbuf_overflow)
                         self.outbufs.append(nextbuf)
                         self.current_outbuf_count = 0
@@ -334,16 +331,14 @@ class HTTPChannel(wasyncore.dispatcher, object):
         return 0
 
     def _flush_outbufs_below_high_watermark(self):
-        overflowed = self.total_outbufs_len > self.adj.outbuf_high_watermark
         # check first to avoid locking if possible
-        if overflowed:
+        if self.total_outbufs_len > self.adj.outbuf_high_watermark:
             with self.outbuf_lock:
                 while (
                     self.connected and
                     self.total_outbufs_len > self.adj.outbuf_high_watermark
                 ):
                     self.outbuf_lock.wait()
-        return overflowed
 
     def service(self):
         """Execute all pending requests """
diff --git a/waitress/tests/test_channel.py b/waitress/tests/test_channel.py
index ff3bba6..35fccf6 100644
--- a/waitress/tests/test_channel.py
+++ b/waitress/tests/test_channel.py
@@ -239,18 +239,27 @@ class TestHTTPChannel(unittest.TestCase):
     def test_write_soon_rotates_outbuf_on_overflow(self):
         inst, sock, map = self._makeOneWithMap()
         inst.adj.outbuf_high_watermark = 3
-        inst.outbufs = [DummyBuffer(b'abcd')]
-        inst.total_outbufs_len = sum(len(x) for x in inst.outbufs)
+        inst.current_outbuf_count = 4
+        wrote = inst.write_soon(b'xyz')
+        self.assertEqual(wrote, 3)
+        self.assertEqual(len(inst.outbufs), 2)
+        self.assertEqual(inst.outbufs[0].get(), b'')
+        self.assertEqual(inst.outbufs[1].get(), b'xyz')
+
+    def test_write_soon_waits_on_backpressure(self):
+        inst, sock, map = self._makeOneWithMap()
+        inst.adj.outbuf_high_watermark = 3
+        inst.total_outbufs_len = 4
+        inst.current_outbuf_count = 4
         class Lock(DummyLock):
             def wait(self):
-                inst.outbufs[0].prune()
-                inst.total_outbufs_len = sum(len(x) for x in inst.outbufs)
+                inst.total_outbufs_len = 0
                 super(Lock, self).wait()
         inst.outbuf_lock = Lock()
         wrote = inst.write_soon(b'xyz')
         self.assertEqual(wrote, 3)
         self.assertEqual(len(inst.outbufs), 2)
-        self.assertTrue(inst.outbufs[0].pruned)
+        self.assertEqual(inst.outbufs[0].get(), b'')
         self.assertEqual(inst.outbufs[1].get(), b'xyz')
         self.assertTrue(inst.outbuf_lock.waited)
 
@@ -753,10 +762,6 @@ class DummyBuffer(object):
     def skip(self, num, x):
         self.skipped = num
 
-    def prune(self):
-        self.pruned = True
-        self.data = b''
-
     def __len__(self):
         return len(self.data)
 
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