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32ea433a29
The rewrite plugin modifies DNS messages, affecting the request size observed in the coredns_dns_request_size_bytes metric. This change captures the original request size before any plugins can modify it. It adds a functional options pattern to Report() to pass this information while maintaining API compatibility. Tests have been added to verify the fix prevents rewrite from affecting the request size metrics. Docs included. Signed-off-by: Ville Vesilehto <ville@vesilehto.fi>
63 lines
1.9 KiB
Go
63 lines
1.9 KiB
Go
package metrics
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import (
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"context"
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"path/filepath"
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"github.com/coredns/coredns/plugin"
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"github.com/coredns/coredns/plugin/metrics/vars"
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"github.com/coredns/coredns/plugin/pkg/rcode"
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"github.com/coredns/coredns/request"
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"github.com/miekg/dns"
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)
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// ServeDNS implements the Handler interface.
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func (m *Metrics) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) {
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state := request.Request{W: w, Req: r}
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// Capture the original request size before any plugins modify it
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originalSize := r.Len()
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qname := state.QName()
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zone := plugin.Zones(m.ZoneNames()).Matches(qname)
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if zone == "" {
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zone = "."
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}
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// Record response to get status code and size of the reply.
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rw := NewRecorder(w)
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status, err := plugin.NextOrFailure(m.Name(), m.Next, ctx, rw, r)
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rc := rw.Rcode
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if !plugin.ClientWrite(status) {
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// when no response was written, fallback to status returned from next plugin as this status
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// is actually used as rcode of DNS response
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// see https://github.com/coredns/coredns/blob/master/core/dnsserver/server.go#L318
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rc = status
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}
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plugin := m.authoritativePlugin(rw.Caller)
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// Pass the original request size to vars.Report
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vars.Report(WithServer(ctx), state, zone, WithView(ctx), rcode.ToString(rc), plugin,
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rw.Len, rw.Start, vars.WithOriginalReqSize(originalSize))
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return status, err
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}
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// Name implements the Handler interface.
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func (m *Metrics) Name() string { return "prometheus" }
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// authoritativePlugin returns which of made the write, if none is found the empty string is returned.
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func (m *Metrics) authoritativePlugin(caller [3]string) string {
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// a b and c contain the full path of the caller, the plugin name 2nd last elements
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// .../coredns/plugin/whoami/whoami.go --> whoami
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// this is likely FS specific, so use filepath.
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for _, c := range caller {
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plug := filepath.Base(filepath.Dir(c))
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if _, ok := m.plugins[plug]; ok {
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return plug
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}
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}
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return ""
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}
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