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plugin/grpc: fix span leak and deadline on error attempt #7487

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Merged
yongtang merged 1 commit into from
Sep 2, 2025
Merged

plugin/grpc: fix span leak and deadline on error attempt #7487

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27 changes: 16 additions & 11 deletions plugin/grpc/grpc.go
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Original file line number Diff line number Diff line change
Expand Up @@ -43,10 +43,10 @@ func (g *GRPC) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (
}

var (
span, child ot.Span
ret *dns.Msg
err error
i int
span ot.Span
ret *dns.Msg
err error
i int
)
span = ot.SpanFromContext(ctx)
list := g.list()
Expand All @@ -65,20 +65,25 @@ func (g *GRPC) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (
proxy := list[i]
i++

callCtx := ctx
var child ot.Span
if span != nil {
child = span.Tracer().StartSpan("query", ot.ChildOf(span.Context()))
ctx = ot.ContextWithSpan(ctx, child)
child, callCtx = ot.StartSpanFromContext(callCtx, "query")
}

ret, err = proxy.query(ctx, r)
if err != nil {
// Continue with the next proxy
continue
}
var cancel context.CancelFunc
callCtx, cancel = context.WithDeadline(callCtx, deadline)

ret, err = proxy.query(callCtx, r)
cancel()

if child != nil {
child.Finish()
}
if err != nil {
// Continue with the next proxy
continue
}

// Check if the reply is correct; if not return FormErr.
if !state.Match(ret) {
Expand Down
77 changes: 77 additions & 0 deletions plugin/grpc/grpc_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -5,13 +5,17 @@ import (
"errors"
"strings"
"testing"
"time"

"github.com/coredns/coredns/pb"
"github.com/coredns/coredns/plugin/pkg/dnstest"
"github.com/coredns/coredns/plugin/pkg/fall"
"github.com/coredns/coredns/plugin/test"

"github.com/miekg/dns"
ot "github.com/opentracing/opentracing-go"
"github.com/opentracing/opentracing-go/mocktracer"
grpcgo "google.golang.org/grpc"
)

func TestGRPC(t *testing.T) {
Expand Down Expand Up @@ -102,3 +106,76 @@ func TestGRPCFallthroughNoNext(t *testing.T) {
t.Errorf("Expected SERVFAIL when no backends and no next plugin, got: %d", rcode)
}
}

// deadlineCheckingClient records whether a deadline was attached to ctx.
type deadlineCheckingClient struct {
sawDeadline bool
lastDeadline time.Time
dnsPacket *pb.DnsPacket
err error
}

func (c *deadlineCheckingClient) Query(ctx context.Context, in *pb.DnsPacket, opts ...grpcgo.CallOption) (*pb.DnsPacket, error) {
if dl, ok := ctx.Deadline(); ok {
c.sawDeadline = true
c.lastDeadline = dl
}
return c.dnsPacket, c.err
}

// Test that on error paths we still finish child spans, and that we set a per-call deadline.
func TestGRPC_SpansOnErrorPath(t *testing.T) {
m := &dns.Msg{}
msgBytes, err := m.Pack()
if err != nil {
t.Fatalf("Error packing response: %s", err)
}
dnsPacket := &pb.DnsPacket{Msg: msgBytes}

// Proxy 1: returns error, we should still finish its child span and have a deadline
p1 := &deadlineCheckingClient{dnsPacket: nil, err: errors.New("kaboom")}
// Proxy 2: returns success
p2 := &deadlineCheckingClient{dnsPacket: dnsPacket, err: nil}

g := newGRPC()
g.from = "."
g.proxies = []*Proxy{{client: p1}, {client: p2}}

// Ensure deterministic order of the retries: try p1 then p2
g.p = new(sequential)

// Set a parent span in context so ServeDNS creates child spans per attempt
tracer := mocktracer.New()
prev := ot.GlobalTracer()
ot.SetGlobalTracer(tracer)
defer ot.SetGlobalTracer(prev)

parent := tracer.StartSpan("parent")
ctx := ot.ContextWithSpan(t.Context(), parent)

rec := dnstest.NewRecorder(&test.ResponseWriter{})
if _, err := g.ServeDNS(ctx, rec, m); err != nil {
t.Fatalf("ServeDNS returned error: %v", err)
}

// Assert both attempts finished child spans with retries
// (2 query spans: error + success)
finished := tracer.FinishedSpans()
var finishedQueries int
for _, s := range finished {
if s.OperationName == "query" {
finishedQueries++
}
}
if finishedQueries != 2 {
t.Fatalf("expected 2 finished 'query' spans, got %d (finished: %v)", finishedQueries, finished)
}

// Assert we set a deadline on the call contexts
if !p1.sawDeadline {
t.Fatalf("expected deadline to be set on first proxy call context")
}
if !p2.sawDeadline {
t.Fatalf("expected deadline to be set on second proxy call context")
}
}