vendor-ed skydns

vendor/github.com/skynetservices/skydns/server/msg.go

@@ -0,0 +1,54 @@
+// Copyright (c) 2014 The SkyDNS Authors. All rights reserved.
+// Use of this source code is governed by The MIT License (MIT) that can be
+// found in the LICENSE file.
+
+package server
+
+import "github.com/miekg/dns"
+
+// Fit will make m fit the size. If a message is larger than size then entire
+// additional section is dropped. If it is still to large and the transport
+// is udp we return a truncated message.
+// If the transport is tcp we are going to drop RR from the answer section
+// until it fits. When this is case the returned bool is true.
+func Fit(m *dns.Msg, size int, tcp bool) (*dns.Msg, bool) {
+	if m.Len() > size {
+		// Check for OPT Records at the end and keep those. TODO(miek)
+		m.Extra = nil
+	}
+	if m.Len() < size {
+		return m, false
+	}
+
+	// With TCP setting TC does not mean anything.
+	if !tcp {
+		m.Truncated = true
+		// fall through here, so we at least return a message that can
+		// fit the udp buffer.
+	}
+
+	// Additional section is gone, binary search until we have length that fits.
+	min, max := 0, len(m.Answer)
+	original := make([]dns.RR, len(m.Answer))
+	copy(original, m.Answer)
+	for {
+		if min == max {
+			break
+		}
+
+		mid := (min + max) / 2
+		m.Answer = original[:mid]
+
+		if m.Len() < size {
+			min++
+			continue
+		}
+		max = mid
+
+	}
+	if max > 1 {
+		max--
+	}
+	m.Answer = m.Answer[:max]
+	return m, true
+}