| // Copyright 2018 The gVisor Authors. |
| // |
| // Licensed under the Apache License, Version 2.0 (the "License"); |
| // you may not use this file except in compliance with the License. |
| // You may obtain a copy of the License at |
| // |
| // http://www.apache.org/licenses/LICENSE-2.0 |
| // |
| // Unless required by applicable law or agreed to in writing, software |
| // distributed under the License is distributed on an "AS IS" BASIS, |
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| // See the License for the specific language governing permissions and |
| // limitations under the License. |
| |
| package tcp |
| |
| import ( |
| "gvisor.dev/gvisor/pkg/tcpip/header" |
| "gvisor.dev/gvisor/pkg/tcpip/seqnum" |
| ) |
| |
| const ( |
| // MaxSACKBlocks is the maximum number of SACK blocks stored |
| // at receiver side. |
| MaxSACKBlocks = 6 |
| ) |
| |
| // UpdateSACKBlocks updates the list of SACK blocks to include the segment |
| // specified by segStart->segEnd. If the segment happens to be an out of order |
| // delivery then the first block in the sack.blocks always includes the |
| // segment identified by segStart->segEnd. |
| func UpdateSACKBlocks(sack *SACKInfo, segStart seqnum.Value, segEnd seqnum.Value, rcvNxt seqnum.Value) { |
| newSB := header.SACKBlock{Start: segStart, End: segEnd} |
| |
| // Ignore any invalid SACK blocks or blocks that are before rcvNxt as |
| // those bytes have already been acked. |
| if newSB.End.LessThanEq(newSB.Start) || newSB.End.LessThan(rcvNxt) { |
| return |
| } |
| |
| if sack.NumBlocks == 0 { |
| sack.Blocks[0] = newSB |
| sack.NumBlocks = 1 |
| return |
| } |
| var n = 0 |
| for i := 0; i < sack.NumBlocks; i++ { |
| start, end := sack.Blocks[i].Start, sack.Blocks[i].End |
| if end.LessThanEq(rcvNxt) { |
| // Discard any sack blocks that are before rcvNxt as |
| // those have already been acked. |
| continue |
| } |
| if newSB.Start.LessThanEq(end) && start.LessThanEq(newSB.End) { |
| // Merge this SACK block into newSB and discard this SACK |
| // block. |
| if start.LessThan(newSB.Start) { |
| newSB.Start = start |
| } |
| if newSB.End.LessThan(end) { |
| newSB.End = end |
| } |
| } else { |
| // Save this block. |
| sack.Blocks[n] = sack.Blocks[i] |
| n++ |
| } |
| } |
| if rcvNxt.LessThan(newSB.Start) { |
| // If this was an out of order segment then make sure that the |
| // first SACK block is the one that includes the segment. |
| // |
| // See the first bullet point in |
| // https://tools.ietf.org/html/rfc2018#section-4 |
| if n == MaxSACKBlocks { |
| // If the number of SACK blocks is equal to |
| // MaxSACKBlocks then discard the last SACK block. |
| n-- |
| } |
| for i := n - 1; i >= 0; i-- { |
| sack.Blocks[i+1] = sack.Blocks[i] |
| } |
| sack.Blocks[0] = newSB |
| n++ |
| } |
| sack.NumBlocks = n |
| } |
| |
| // TrimSACKBlockList updates the sack block list by removing/modifying any block |
| // where start is < rcvNxt. |
| func TrimSACKBlockList(sack *SACKInfo, rcvNxt seqnum.Value) { |
| n := 0 |
| for i := 0; i < sack.NumBlocks; i++ { |
| if sack.Blocks[i].End.LessThanEq(rcvNxt) { |
| continue |
| } |
| if sack.Blocks[i].Start.LessThan(rcvNxt) { |
| // Shrink this SACK block. |
| sack.Blocks[i].Start = rcvNxt |
| } |
| sack.Blocks[n] = sack.Blocks[i] |
| n++ |
| } |
| sack.NumBlocks = n |
| } |