From acc6793dea2e980786cb18a20f3deb66a80484d6 Mon Sep 17 00:00:00 2001 From: Adphi Date: Thu, 24 Mar 2022 15:26:15 +0100 Subject: [PATCH] bootstrap from example Signed-off-by: Adphi --- .gitignore | 1 + LICENSE | 201 ++++++++++++++++++++++++++++++++++++++++++++++++ README.md | 80 +++++++++++++++++++ example.go | 63 +++++++++++++++ example_test.go | 37 +++++++++ metrics.go | 20 +++++ ready.go | 5 ++ setup.go | 30 ++++++++ setup_test.go | 21 +++++ 9 files changed, 458 insertions(+) create mode 100644 .gitignore create mode 100644 LICENSE create mode 100644 README.md create mode 100644 example.go create mode 100644 example_test.go create mode 100644 metrics.go create mode 100644 ready.go create mode 100644 setup.go create mode 100644 setup_test.go diff --git a/.gitignore b/.gitignore new file mode 100644 index 0000000..485dee6 --- /dev/null +++ b/.gitignore @@ -0,0 +1 @@ +.idea diff --git a/LICENSE b/LICENSE new file mode 100644 index 0000000..8dada3e --- /dev/null +++ b/LICENSE @@ -0,0 +1,201 @@ + Apache License + Version 2.0, January 2004 + http://www.apache.org/licenses/ + + TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION + + 1. 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We also recommend that a + file or class name and description of purpose be included on the + same "printed page" as the copyright notice for easier + identification within third-party archives. + + Copyright {yyyy} {name of copyright owner} + + Licensed under the Apache License, Version 2.0 (the "License"); + you may not use this file except in compliance with the License. + You may obtain a copy of the License at + + http://www.apache.org/licenses/LICENSE-2.0 + + Unless required by applicable law or agreed to in writing, software + distributed under the License is distributed on an "AS IS" BASIS, + WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + See the License for the specific language governing permissions and + limitations under the License. diff --git a/README.md b/README.md new file mode 100644 index 0000000..4943273 --- /dev/null +++ b/README.md @@ -0,0 +1,80 @@ +# 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). diff --git a/example.go b/example.go new file mode 100644 index 0000000..03adf00 --- /dev/null +++ b/example.go @@ -0,0 +1,63 @@ +// 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) +} diff --git a/example_test.go b/example_test.go new file mode 100644 index 0000000..cd302e7 --- /dev/null +++ b/example_test.go @@ -0,0 +1,37 @@ +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) + } +} diff --git a/metrics.go b/metrics.go new file mode 100644 index 0000000..5a019d4 --- /dev/null +++ b/metrics.go @@ -0,0 +1,20 @@ +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 diff --git a/ready.go b/ready.go new file mode 100644 index 0000000..8175a9a --- /dev/null +++ b/ready.go @@ -0,0 +1,5 @@ +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 } diff --git a/setup.go b/setup.go new file mode 100644 index 0000000..d132fa9 --- /dev/null +++ b/setup.go @@ -0,0 +1,30 @@ +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 +} diff --git a/setup_test.go b/setup_test.go new file mode 100644 index 0000000..5893eda --- /dev/null +++ b/setup_test.go @@ -0,0 +1,21 @@ +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) + } +}