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Fix data race between consumer of QueryParam.Entries and the sender #131

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Fix data race between consumer of QueryParam.Entries and the sender #131

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34 changes: 33 additions & 1 deletion client.go
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Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,7 @@
package mdns

import (
"bytes"
"context"
"fmt"
"log"
Expand Down Expand Up @@ -380,7 +381,7 @@ func (c *client) query(params *QueryParam) error {
}
inp.sent = true
select {
case params.Entries <- inp:
case params.Entries <- deepCopyServiceEntry(inp):
default:
}
} else {
Expand All @@ -398,6 +399,37 @@ func (c *client) query(params *QueryParam) error {
}
}

// deepCopyServiceEntry returns a deep copy of the given [ServiceEntry]. Since
// we send pointers back to callers via [QueryParam.Entries], they need to be
// copied so that neither of us are mutating/reading from the same pointer at
// the same time.
func deepCopyServiceEntry(se *ServiceEntry) *ServiceEntry {
info := make([]string, len(se.InfoFields))
copy(info, se.InfoFields)

var ipAddrV6 *net.IPAddr
if se.AddrV6IPAddr != nil {
ipAddrV6 = &net.IPAddr{
IP: bytes.Clone(se.AddrV6IPAddr.IP),
Zone: se.AddrV6IPAddr.Zone,
}
}

return &ServiceEntry{
hasTXT: se.hasTXT,
sent: se.sent,
Name: se.Name,
Host: se.Host,
AddrV4: bytes.Clone(se.AddrV4),
AddrV6: bytes.Clone(se.AddrV6),
Addr: bytes.Clone(se.Addr),
Port: se.Port,
Info: se.Info,
AddrV6IPAddr: ipAddrV6,
InfoFields: info,
}
}

// sendQuery is used to multicast a query out
func (c *client) sendQuery(q *dns.Msg) error {
buf, err := q.Pack()
Expand Down