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cache: do the msg copy right (#4207)

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Not sure why this is proving so difficult.. pointers are hard? [Was
tempted to rollback all tweaks here, but the original issue we're fixing
it too important to not have a proper fix].

But we need to make a copy of the message at the earliest point in the
handler because we are changing it (adding an opt rr). If we do this on
the original message (which is a pointer) we change it (obvs). When
undoing those changes we do work on a copy.

Re: testing. There isn't a explicit test for this, so I've added on to
the top-level test/ directory, which indeed makes the issue visible:

master:

~~~
go test -v -run=TestLookupCacheWithoutEdns
=== RUN   TestLookupCacheWithoutEdns
    cache_test.go:154: Expected no OPT RR, but got:
        ;; OPT PSEUDOSECTION:
        ; EDNS: version 0; flags: do; udp: 2048
--- FAIL: TestLookupCacheWithoutEdns (0.01s)
FAIL
~~~

This branch:

~~~
% go test -v -run=TestLookupCacheWithoutEdns
=== RUN   TestLookupCacheWithoutEdns
--- PASS: TestLookupCacheWithoutEdns (0.01s)
PASS
ok  	github.com/coredns/coredns/test	0.109s
~~~

Signed-off-by: Miek Gieben <miek@miek.nl>
This commit is contained in:
Miek Gieben 2020-10-15 16:47:07 +02:00 • committed by GitHub
parent 6938dac21d
commit 268781d355
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3 changed files with 61 additions and 19 deletions
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45
test/cache_test.go
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@ -110,3 +110,48 @@ func testCaseDNSSEC(t *testing.T, name, addr string, bufsize int) {
}
}
}
func TestLookupCacheWithoutEdns(t *testing.T) {
name, rm, err := test.TempFile(".", exampleOrg)
if err != nil {
t.Fatalf("Failed to create zone: %s", err)
}
defer rm()
corefile := `example.org:0 {
file ` + name + `
}`
i, udp, _, err := CoreDNSServerAndPorts(corefile)
if err != nil {
t.Fatalf("Could not get CoreDNS serving instance: %s", err)
}
defer i.Stop()
// Start caching forward CoreDNS that we want to test.
corefile = `example.org:0 {
forward . ` + udp + `
cache 10
}`
i, udp, _, err = CoreDNSServerAndPorts(corefile)
if err != nil {
t.Fatalf("Could not get CoreDNS serving instance: %s", err)
}
defer i.Stop()
m := new(dns.Msg)
m.SetQuestion("example.org.", dns.TypeA)
resp, err := dns.Exchange(m, udp)
if err != nil {
t.Fatalf("Expected to receive reply, but didn't: %s", err)
}
if len(resp.Extra) == 0 {
return
}
if resp.Extra[0].Header().Rrtype == dns.TypeOPT {
t.Fatalf("Expected no OPT RR, but got: %s", resp.Extra[0])
}
t.Fatalf("Expected empty additional section, got %v", resp.Extra)
}