55 lines
1.3 KiB
Go
55 lines
1.3 KiB
Go
// Copyright (c) 2014 The SkyDNS Authors. All rights reserved.
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// Use of this source code is governed by The MIT License (MIT) that can be
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// found in the LICENSE file.
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package server
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import "github.com/miekg/dns"
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// Fit will make m fit the size. If a message is larger than size then entire
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// additional section is dropped. If it is still to large and the transport
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// is udp we return a truncated message.
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// If the transport is tcp we are going to drop RR from the answer section
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// until it fits. When this is case the returned bool is true.
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func Fit(m *dns.Msg, size int, tcp bool) (*dns.Msg, bool) {
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if m.Len() > size {
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// Check for OPT Records at the end and keep those. TODO(miek)
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m.Extra = nil
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}
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if m.Len() < size {
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return m, false
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}
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// With TCP setting TC does not mean anything.
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if !tcp {
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m.Truncated = true
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// fall through here, so we at least return a message that can
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// fit the udp buffer.
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}
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// Additional section is gone, binary search until we have length that fits.
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min, max := 0, len(m.Answer)
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original := make([]dns.RR, len(m.Answer))
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copy(original, m.Answer)
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for {
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if min == max {
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break
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}
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mid := (min + max) / 2
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m.Answer = original[:mid]
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if m.Len() < size {
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min++
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continue
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}
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max = mid
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}
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if max > 1 {
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max--
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}
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m.Answer = m.Answer[:max]
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return m, true
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}
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