upstream: fix h3 error handling

upstream/doh.go

@@ -350,8 +350,12 @@ func (p *dnsOverHTTPS) resetClient(resetErr error) (client *http.Client, err err
 	p.clientMu.Lock()
 	defer p.clientMu.Unlock()
 
-	if errors.Is(resetErr, quic.Err0RTTRejected) {
-		// Reset the TokenStore only if 0-RTT was rejected.
+	shouldResetQUIC := errors.Is(resetErr, quic.Err0RTTRejected)
+	var qAppErr *quic.ApplicationError
+	if errors.As(resetErr, &qAppErr) && qAppErr.ErrorCode == quic.ApplicationErrorCode(http3.ErrCodeNoError) {
+		shouldResetQUIC = true
+	}
+	if shouldResetQUIC {
 		p.resetQUICConfig()
 	}
 

upstream/doh_h3_error_internal_test.go

@@ -0,0 +1,62 @@
+package upstream
+
+import (
+	"sync"
+	"testing"
+
+	"github.com/AdguardTeam/dnsproxy/internal/bootstrap"
+	"github.com/AdguardTeam/golibs/errors"
+	"github.com/quic-go/quic-go"
+	"github.com/quic-go/quic-go/http3"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestDNSOverHTTPS_resetClient_H3NoError(t *testing.T) {
+	t.Parallel()
+
+	testCases := []struct {
+		name                string
+		resetErr            error
+		wantQUICConfigReset bool
+	}{{
+		name: "handles_H3_NO_ERROR_gracefully",
+		resetErr: &quic.ApplicationError{
+			ErrorCode: quic.ApplicationErrorCode(http3.ErrCodeNoError),
+		},
+		wantQUICConfigReset: true,
+	}, {
+		name:                "resets_connection_on_H3_NO_ERROR",
+		resetErr:            errors.Error("some error with H3_NO_ERROR"),
+		wantQUICConfigReset: false,
+	}, {
+		name:                "retries_on_H3_NO_ERROR",
+		resetErr:            quic.Err0RTTRejected,
+		wantQUICConfigReset: true,
+	}}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			u := &dnsOverHTTPS{
+				quicConf:   &quic.Config{},
+				quicConfMu: &sync.Mutex{},
+				clientMu:   &sync.Mutex{},
+				logger:     testLogger,
+				getDialer: func() (bootstrap.DialHandler, error) {
+					return nil, errors.Error("no dialer")
+				},
+			}
+
+			originalConf := u.quicConf
+
+			u.resetClient(tc.resetErr)
+
+			if tc.wantQUICConfigReset {
+				assert.NotSame(t, originalConf, u.quicConf)
+			} else {
+				assert.Same(t, originalConf, u.quicConf)
+			}
+		})
+	}
+}