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112 lines
3.7 KiB
Go
112 lines
3.7 KiB
Go
// Package plugin provides some types and functions common among plugin.
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package plugin
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import (
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"context"
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"errors"
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"fmt"
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"github.com/miekg/dns"
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ot "github.com/opentracing/opentracing-go"
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"github.com/prometheus/client_golang/prometheus"
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)
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type (
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// Plugin is a middle layer which represents the traditional
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// idea of plugin: it chains one Handler to the next by being
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// passed the next Handler in the chain.
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Plugin func(Handler) Handler
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// Handler is like dns.Handler except ServeDNS may return an rcode
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// and/or error.
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//
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// If ServeDNS writes to the response body, it should return a status
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// code. If the status code is not one of the following:
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//
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// * SERVFAIL (dns.RcodeServerFailure)
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//
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// * REFUSED (dns.RecodeRefused)
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//
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// * FORMERR (dns.RcodeFormatError)
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//
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// * NOTIMP (dns.RcodeNotImplemented)
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//
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// CoreDNS assumes *no* reply has yet been written. All other response
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// codes signal other handlers above it that the response message is
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// already written, and that they should not write to it also.
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//
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// If ServeDNS encounters an error, it should return the error value
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// so it can be logged by designated error-handling plugin.
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//
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// If writing a response after calling another ServeDNS method, the
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// returned rcode SHOULD be used when writing the response.
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//
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// If handling errors after calling another ServeDNS method, the
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// returned error value SHOULD be logged or handled accordingly.
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//
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// Otherwise, return values should be propagated down the plugin
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// chain by returning them unchanged.
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Handler interface {
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ServeDNS(context.Context, dns.ResponseWriter, *dns.Msg) (int, error)
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Name() string
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}
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// HandlerFunc is a convenience type like dns.HandlerFunc, except
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// ServeDNS returns an rcode and an error. See Handler
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// documentation for more information.
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HandlerFunc func(context.Context, dns.ResponseWriter, *dns.Msg) (int, error)
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)
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// ServeDNS implements the Handler interface.
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func (f HandlerFunc) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) {
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return f(ctx, w, r)
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}
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// Name implements the Handler interface.
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func (f HandlerFunc) Name() string { return "handlerfunc" }
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// Error returns err with 'plugin/name: ' prefixed to it.
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func Error(name string, err error) error { return fmt.Errorf("%s/%s: %s", "plugin", name, err) }
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// NextOrFailure calls next.ServeDNS when next is not nill, otherwise it will return, a ServerFailure and a nil error.
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func NextOrFailure(name string, next Handler, ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) { // nolint: golint
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if next != nil {
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if span := ot.SpanFromContext(ctx); span != nil {
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child := span.Tracer().StartSpan(next.Name(), ot.ChildOf(span.Context()))
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defer child.Finish()
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ctx = ot.ContextWithSpan(ctx, child)
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}
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return next.ServeDNS(ctx, w, r)
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}
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return dns.RcodeServerFailure, Error(name, errors.New("no next plugin found"))
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}
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// ClientWrite returns true if the response has been written to the client.
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// Each plugin to adhire to this protocol.
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func ClientWrite(rcode int) bool {
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switch rcode {
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case dns.RcodeServerFailure:
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fallthrough
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case dns.RcodeRefused:
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fallthrough
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case dns.RcodeFormatError:
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fallthrough
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case dns.RcodeNotImplemented:
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return false
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}
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return true
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}
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// Namespace is the namespace used for the metrics.
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const Namespace = "coredns"
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// TimeBuckets is based on Prometheus client_golang prometheus.DefBuckets
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var TimeBuckets = prometheus.ExponentialBuckets(0.00025, 2, 16) // from 0.25ms to 8 seconds
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// ErrOnce is returned when a plugin doesn't support multiple setups per server.
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var ErrOnce = errors.New("this plugin can only be used once per Server Block")
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// ServerCtx is the context key to pass server address context to the plugins handling the request.
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type ServerCtx struct{}
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