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Add net.LookipIP DNS provider implementation #208

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Add net.LookipIP DNS provider implementation #208

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30 changes: 30 additions & 0 deletions kv/memberlist/dnsprovider.go
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Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,8 @@ package memberlist

import (
"context"
"net"
"sync"
)

// DNSProvider supports storing or resolving a list of addresses.
Expand All @@ -13,3 +15,31 @@ type DNSProvider interface {
// Addresses returns the latest addresses present in the DNSProvider.
Addresses() []string
}

type dnsProvider struct {
sync.Mutex
addr []string
}

func NewDNSProvider() DNSProvider { return &dnsProvider{} }

func (d *dnsProvider) Resolve(ctx context.Context, addrs []string) error {
d.Lock()
defer d.Unlock()
for _, a := range addrs {
ips, err := net.LookupIP(a)
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Should the context be checked for cancellation on each iteration? That seems like it'd make this more responsive.

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Or perhaps just once before doing any DNS lookups?

if err != nil {
return err
}
for _, ip := range ips {
d.addr = append(d.addr, ip.String())
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Instead of doing an append(d.addr) in a loop, I'd rather see a new slice of addresses constructed and then swapped at the end. That prevents cases where an error is returned and d.addr is only half updated. This would also allow you to avoid holding the lock while doing network operations. Something like:

var addrs []string
for _, a: range addrs {
    // do the lookup
    addrs = append(addrs, ip.String())
}
d.Lock()
d.addrs = addrs
d.Unlock()
return nil

}
}
return nil
}

func (d *dnsProvider) Addresses() []string {
d.Lock()
defer d.Unlock()
return d.addr
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I think you need to make a copy of this otherwise the underlying storage of the slice can still be modified after the caller starts using it (I could be wrong, we do run tests with -race but this code feels like a race condition).

}
28 changes: 28 additions & 0 deletions kv/memberlist/dnsprovider_test.go
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Original file line number Diff line number Diff line change
@@ -0,0 +1,28 @@
package memberlist

import (
"context"
"testing"
)

func TestDNSProvider(t *testing.T) {
dns := &dnsProvider{}
if err := dns.Resolve(context.Background(), []string{"localhost"}); err != nil {
t.Fatal(err)
}
has127_0_0_1 := false
for _, addr := range dns.Addresses() {
if addr == "127.0.0.1" {
has127_0_0_1 = true
}
}
if !has127_0_0_1 {
t.Error("resolving localhost must result in 127.0.0.1 address", dns.Addresses())
}
if err := dns.Resolve(context.Background(), []string{"invalid dns"}); err == nil {
t.Error("resolving and invalid address must result in an error")
}
if len(dns.Addresses()) == 0 {
t.Error("DNSProvider must keep recent addresses on failure")
}
}