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bootstrap from example

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Signed-off-by: Adphi <philippe.adrien.nousse@gmail.com>
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# example
## Name
*example* - prints "example" after a query is handled.
## Description
The example plugin prints "example" on every query that got handled by the server. It serves as
documentation for writing CoreDNS plugins.
## Compilation
This package will always be compiled as part of CoreDNS and not in a standalone way. It will require you to use `go get` or as a dependency on [plugin.cfg](https://github.com/coredns/coredns/blob/master/plugin.cfg).
The [manual](https://coredns.io/manual/toc/#what-is-coredns) will have more information about how to configure and extend the server with external plugins.
A simple way to consume this plugin, is by adding the following on [plugin.cfg](https://github.com/coredns/coredns/blob/master/plugin.cfg), and recompile it as [detailed on coredns.io](https://coredns.io/2017/07/25/compile-time-enabling-or-disabling-plugins/#build-with-compile-time-configuration-file).
~~~
example:github.com/coredns/example
~~~
Put this early in the plugin list, so that *example* is executed before any of the other plugins.
After this you can compile coredns by:
``` sh
go generate
go build
```
Or you can instead use make:
``` sh
make
```
## Syntax
~~~ txt
example
~~~
## Metrics
If monitoring is enabled (via the *prometheus* directive) the following metric is exported:
* `coredns_example_request_count_total{server}` - query count to the *example* plugin.
The `server` label indicated which server handled the request, see the *metrics* plugin for details.
## Ready
This plugin reports readiness to the ready plugin. It will be immediately ready.
## Examples
In this configuration, we forward all queries to 9.9.9.9 and print "example" whenever we receive
a query.
~~~ corefile
. {
forward . 9.9.9.9
example
}
~~~
Or without any external connectivity:
~~~ corefile
. {
whoami
example
}
~~~
## Also See
See the [manual](https://coredns.io/manual).

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// Package example is a CoreDNS plugin that prints "example" to stdout on every packet received.
//
// It serves as an example CoreDNS plugin with numerous code comments.
package example
import (
"context"
"github.com/coredns/coredns/plugin"
"github.com/coredns/coredns/plugin/metrics"
clog "github.com/coredns/coredns/plugin/pkg/log"
"github.com/miekg/dns"
)
// Define log to be a logger with the plugin name in it. This way we can just use log.Info and
// friends to log.
var log = clog.NewWithPlugin("example")
// Example is an example plugin to show how to write a plugin.
type Example struct {
Next plugin.Handler
}
// ServeDNS implements the plugin.Handler interface. This method gets called when example is used
// in a Server.
func (e Example) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) {
// This function could be simpler. I.e. just fmt.Println("example") here, but we want to show
// a slightly more complex example as to make this more interesting.
// Here we wrap the dns.ResponseWriter in a new ResponseWriter and call the next plugin, when the
// answer comes back, it will print "example".
// Debug log that we've have seen the query. This will only be shown when the debug plugin is loaded.
log.Debug("Received response")
// Wrap.
pw := NewResponsePrinter(w)
// Export metric with the server label set to the current server handling the request.
requestCount.WithLabelValues(metrics.WithServer(ctx)).Inc()
// Call next plugin (if any).
return plugin.NextOrFailure(e.Name(), e.Next, ctx, pw, r)
}
// Name implements the Handler interface.
func (e Example) Name() string { return "example" }
// ResponsePrinter wrap a dns.ResponseWriter and will write example to standard output when WriteMsg is called.
type ResponsePrinter struct {
dns.ResponseWriter
}
// NewResponsePrinter returns ResponseWriter.
func NewResponsePrinter(w dns.ResponseWriter) *ResponsePrinter {
return &ResponsePrinter{ResponseWriter: w}
}
// WriteMsg calls the underlying ResponseWriter's WriteMsg method and prints "example" to standard output.
func (r *ResponsePrinter) WriteMsg(res *dns.Msg) error {
log.Info("example")
return r.ResponseWriter.WriteMsg(res)
}

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package example
import (
"bytes"
"context"
golog "log"
"strings"
"testing"
"github.com/coredns/coredns/plugin/pkg/dnstest"
"github.com/coredns/coredns/plugin/test"
"github.com/miekg/dns"
)
func TestExample(t *testing.T) {
// Create a new Example Plugin. Use the test.ErrorHandler as the next plugin.
x := Example{Next: test.ErrorHandler()}
// Setup a new output buffer that is *not* standard output, so we can check if
// example is really being printed.
b := &bytes.Buffer{}
golog.SetOutput(b)
ctx := context.TODO()
r := new(dns.Msg)
r.SetQuestion("example.org.", dns.TypeA)
// Create a new Recorder that captures the result, this isn't actually used in this test
// as it just serves as something that implements the dns.ResponseWriter interface.
rec := dnstest.NewRecorder(&test.ResponseWriter{})
// Call our plugin directly, and check the result.
x.ServeDNS(ctx, rec, r)
if a := b.String(); !strings.Contains(a, "[INFO] plugin/example: example") {
t.Errorf("Failed to print '%s', got %s", "[INFO] plugin/example: example", a)
}
}

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package example
import (
"sync"
"github.com/coredns/coredns/plugin"
"github.com/prometheus/client_golang/prometheus"
"github.com/prometheus/client_golang/prometheus/promauto"
)
// requestCount exports a prometheus metric that is incremented every time a query is seen by the example plugin.
var requestCount = promauto.NewCounterVec(prometheus.CounterOpts{
Namespace: plugin.Namespace,
Subsystem: "example",
Name: "request_count_total",
Help: "Counter of requests made.",
}, []string{"server"})
var once sync.Once

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package example
// Ready implements the ready.Readiness interface, once this flips to true CoreDNS
// assumes this plugin is ready for queries; it is not checked again.
func (e Example) Ready() bool { return true }

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package example
import (
"github.com/coredns/caddy"
"github.com/coredns/coredns/core/dnsserver"
"github.com/coredns/coredns/plugin"
)
// init registers this plugin.
func init() { plugin.Register("example", setup) }
// setup is the function that gets called when the config parser see the token "example". Setup is responsible
// for parsing any extra options the example plugin may have. The first token this function sees is "example".
func setup(c *caddy.Controller) error {
c.Next() // Ignore "example" and give us the next token.
if c.NextArg() {
// If there was another token, return an error, because we don't have any configuration.
// Any errors returned from this setup function should be wrapped with plugin.Error, so we
// can present a slightly nicer error message to the user.
return plugin.Error("example", c.ArgErr())
}
// Add the Plugin to CoreDNS, so Servers can use it in their plugin chain.
dnsserver.GetConfig(c).AddPlugin(func(next plugin.Handler) plugin.Handler {
return Example{Next: next}
})
// All OK, return a nil error.
return nil
}

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package example
import (
"testing"
"github.com/coredns/caddy"
)
// TestSetup tests the various things that should be parsed by setup.
// Make sure you also test for parse errors.
func TestSetup(t *testing.T) {
c := caddy.NewTestController("dns", `example`)
if err := setup(c); err != nil {
t.Fatalf("Expected no errors, but got: %v", err)
}
c = caddy.NewTestController("dns", `example more`)
if err := setup(c); err == nil {
t.Fatalf("Expected errors, but got: %v", err)
}
}