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	// n is the number of DATA bytes we're allowed to send.
12	// A flow is kept both on a conn and a per-stream.
13	n int32
14
15	// conn points to the shared connection-level flow that is
16	// shared by all streams on that conn. It is nil for the flow
17	// that's on the conn directly.
18	conn *flow
19}
20
21func (f *flow) setConnFlow(cf *flow) { f.conn = cf }
22
23func (f *flow) available() int32 {
24	n := f.n
25	if f.conn != nil && f.conn.n < n {
26		n = f.conn.n
27	}
28	return n
29}
30
31func (f *flow) take(n int32) {
32	if n > f.available() {
33		panic("internal error: took too much")
34	}
35	f.n -= n
36	if f.conn != nil {
37		f.conn.n -= n
38	}
39}
40
41// add adds n bytes (positive or negative) to the flow control window.
42// It returns false if the sum would exceed 2^31-1.
43func (f *flow) add(n int32) bool {
44	remain := (1<<31 - 1) - f.n
45	if n > remain {
46		return false
47	}
48	f.n += n
49	return true
50}
51