Plugin restapi: New plugin to provide a REST API.

restapi/README.md

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+# restapi
+
+Plugin **restapi** provides a REST API to communicate with the *collectd*
+daemon.
+
+## Description
+
+The *restapi plugin* starts a webserver and waits for incoming REST API
+requests.
+
+## Building
+
+To build this plugin, the collectd header files are required.
+
+On Debian and Ubuntu, the collectd headers are available from the
+`collectd-dev` package. Once installed, add the import paths to the
+`CGI_CPPFLAGS`:
+
+```bash
+export CGO_CPPFLAGS="-I/usr/include/collectd/core/daemon \
+-I/usr/include/collectd/core -I/usr/include/collectd"
+```
+
+Alternatively, you can grab the collectd sources, run the `configure` script,
+and reference the header files from there:
+
+```bash
+TOP_SRCDIR="${HOME}/collectd"
+export CGO_CPPFLAGS="-I${TOP_SRCDIR}/src -I${TOP_SRCDIR}/src/daemon"
+```
+
+Then build the plugin with the "c-shared" buildmode:
+
+```bash
+go build -buildmode=c-shared -o restapi.so
+```
+
+## Configuration
+
+### Synopsis
+
+```
+LoadPlugin restapi
+<Plugin "restapi">
+  Addr "::"
+  Port "8443"
+  CertFile "/path/to/cert_file.pem"
+  KeyFile "/path/to/key_file.pem"
+</Plugin>
+```
+
+### Options
+
+*   **Addr** *Network address*
+
+    Addredd to listen to. Defaults to `""` (any address).
+*   **Port** *Port*
+
+    Post to listen to. Defaults to `8080` (`8443` if **CertFile** is specified).
+*   **CertFile** *Path*<br>
+    **KeyFile** *Path*
+
+    TLS certificate and key files. Refer to
+    [`"net/http".ListenAndServeTLS`](https://golang.org/pkg/net/http/#ListenAndServeTLS)
+    for more information on the TLS setup.

restapi/restapi.go

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+package main
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"net"
+	"net/http"
+	"time"
+
+	"collectd.org/api"
+	"collectd.org/config"
+	"collectd.org/plugin"
+	"go.uber.org/multierr"
+)
+
+const pluginName = "restapi"
+
+type restapi struct {
+	srv *http.Server
+}
+
+func init() {
+	ra := &restapi{}
+
+	plugin.RegisterConfig(pluginName, ra)
+	plugin.RegisterShutdown(pluginName, ra)
+}
+
+func valueListHandler(w http.ResponseWriter, req *http.Request) {
+	if req.Method != http.MethodPost {
+		w.WriteHeader(http.StatusNotImplemented)
+		fmt.Fprintln(w, "Only POST is currently supported.")
+		return
+	}
+
+	var vls []api.ValueList
+	if err := json.NewDecoder(req.Body).Decode(&vls); err != nil {
+		w.WriteHeader(http.StatusBadRequest)
+		fmt.Fprintln(w, "parsing JSON failed:", err)
+		return
+	}
+
+	var errs error
+	for _, vl := range vls {
+		errs = multierr.Append(errs,
+			plugin.Write(req.Context(), &vl))
+	}
+
+	if errs != nil {
+		w.WriteHeader(http.StatusInternalServerError)
+		fmt.Fprintln(w, "plugin.Write():", errs)
+		return
+	}
+}
+
+type srvConfig struct {
+	Args     string // unused
+	Addr     string
+	Port     string
+	CertFile string
+	KeyFile  string
+}
+
+func (ra *restapi) Configure(_ context.Context, rawConfig config.Block) error {
+	cfg := srvConfig{}
+	if err := rawConfig.Unmarshal(&cfg); err != nil {
+		return err
+	}
+
+	if (cfg.CertFile == "") != (cfg.KeyFile == "") {
+		return fmt.Errorf("CertFile=%q, KeyFile=%q; need both for TLS setup",
+			cfg.CertFile, cfg.KeyFile)
+	}
+
+	if cfg.Port == "" {
+		cfg.Port = "8080"
+		if cfg.CertFile != "" {
+			cfg.Port = "8443"
+		}
+	}
+
+	mux := http.NewServeMux()
+	mux.HandleFunc("/valueList", valueListHandler)
+
+	ra.srv = &http.Server{
+		Addr:    net.JoinHostPort(cfg.Addr, cfg.Port),
+		Handler: mux,
+	}
+
+	go func() {
+		var err error
+		if cfg.CertFile != "" {
+			err = ra.srv.ListenAndServeTLS(cfg.CertFile, cfg.KeyFile)
+		} else {
+			err = ra.srv.ListenAndServe()
+		}
+		if !errors.Is(err, http.ErrServerClosed) {
+			plugin.Errorf("%s plugin: ListenAndServe(): %v", pluginName, err)
+		}
+	}()
+
+	return nil
+}
+
+func (ra *restapi) Shutdown(ctx context.Context) error {
+	if ra == nil || ra.srv == nil {
+		return nil
+	}
+
+	ctx, cancel := context.WithTimeout(ctx, 30*time.Second)
+	defer cancel()
+
+	return ra.srv.Shutdown(ctx)
+}
+
+func main() {} // ignored