1// Copyright 2014 The Go Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style
3// license that can be found in the LICENSE file.
4
5// Flow control
6
7package http2
8
9// flow is the flow control window's size.
10type flow struct {
11	_ incomparable
12
13	// n is the number of DATA bytes we're allowed to send.
14	// A flow is kept both on a conn and a per-stream.
15	n int32
16
17	// conn points to the shared connection-level flow that is
18	// shared by all streams on that conn. It is nil for the flow
19	// that's on the conn directly.
20	conn *flow
21}
22
23func (f *flow) setConnFlow(cf *flow) { f.conn = cf }
24
25func (f *flow) available() int32 {
26	n := f.n
27	if f.conn != nil && f.conn.n < n {
28		n = f.conn.n
29	}
30	return n
31}
32
33func (f *flow) take(n int32) {
34	if n > f.available() {
35		panic("internal error: took too much")
36	}
37	f.n -= n
38	if f.conn != nil {
39		f.conn.n -= n
40	}
41}
42
43// add adds n bytes (positive or negative) to the flow control window.
44// It returns false if the sum would exceed 2^31-1.
45func (f *flow) add(n int32) bool {
46	sum := f.n + n
47	if (sum > n) == (f.n > 0) {
48		f.n = sum
49		return true
50	}
51	return false
52}
53