121 lines
3.3 KiB
Go
121 lines
3.3 KiB
Go
// Copyright 2014 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Flow control
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package http2
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// inflowMinRefresh is the minimum number of bytes we'll send for a
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// flow control window update.
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const inflowMinRefresh = 4 << 10
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// inflow accounts for an inbound flow control window.
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// It tracks both the latest window sent to the peer (used for enforcement)
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// and the accumulated unsent window.
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type inflow struct {
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avail int32
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unsent int32
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}
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// init sets the initial window.
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func (f *inflow) init(n int32) {
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f.avail = n
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}
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// add adds n bytes to the window, with a maximum window size of max,
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// indicating that the peer can now send us more data.
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// For example, the user read from a {Request,Response} body and consumed
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// some of the buffered data, so the peer can now send more.
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// It returns the number of bytes to send in a WINDOW_UPDATE frame to the peer.
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// Window updates are accumulated and sent when the unsent capacity
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// is at least inflowMinRefresh or will at least double the peer's available window.
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func (f *inflow) add(n int) (connAdd int32) {
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if n < 0 {
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panic("negative update")
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}
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unsent := int64(f.unsent) + int64(n)
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// "A sender MUST NOT allow a flow-control window to exceed 2^31-1 octets."
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// RFC 7540 Section 6.9.1.
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const maxWindow = 1<<31 - 1
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if unsent+int64(f.avail) > maxWindow {
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panic("flow control update exceeds maximum window size")
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}
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f.unsent = int32(unsent)
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if f.unsent < inflowMinRefresh && f.unsent < f.avail {
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// If there aren't at least inflowMinRefresh bytes of window to send,
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// and this update won't at least double the window, buffer the update for later.
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return 0
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}
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f.avail += f.unsent
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f.unsent = 0
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return int32(unsent)
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}
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// take attempts to take n bytes from the peer's flow control window.
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// It reports whether the window has available capacity.
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func (f *inflow) take(n uint32) bool {
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if n > uint32(f.avail) {
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return false
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}
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f.avail -= int32(n)
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return true
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}
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// takeInflows attempts to take n bytes from two inflows,
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// typically connection-level and stream-level flows.
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// It reports whether both windows have available capacity.
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func takeInflows(f1, f2 *inflow, n uint32) bool {
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if n > uint32(f1.avail) || n > uint32(f2.avail) {
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return false
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}
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f1.avail -= int32(n)
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f2.avail -= int32(n)
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return true
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}
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// outflow is the outbound flow control window's size.
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type outflow struct {
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_ incomparable
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// n is the number of DATA bytes we're allowed to send.
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// An outflow is kept both on a conn and a per-stream.
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n int32
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// conn points to the shared connection-level outflow that is
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// shared by all streams on that conn. It is nil for the outflow
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// that's on the conn directly.
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conn *outflow
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}
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func (f *outflow) setConnFlow(cf *outflow) { f.conn = cf }
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func (f *outflow) available() int32 {
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n := f.n
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if f.conn != nil && f.conn.n < n {
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n = f.conn.n
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}
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return n
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}
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func (f *outflow) take(n int32) {
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if n > f.available() {
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panic("internal error: took too much")
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}
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f.n -= n
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if f.conn != nil {
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f.conn.n -= n
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}
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}
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// add adds n bytes (positive or negative) to the flow control window.
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// It returns false if the sum would exceed 2^31-1.
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func (f *outflow) add(n int32) bool {
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sum := f.n + n
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if (sum > n) == (f.n > 0) {
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f.n = sum
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return true
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}
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return false
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}
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