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
+```

restapi/restapi.go

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+package main
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"net/http"
+	"time"
+
+	"collectd.org/api"
+	"collectd.org/plugin"
+	"go.uber.org/multierr"
+)
+
+const pluginName = "restapi"
+
+type restapi struct {
+	srv *http.Server
+}
+
+func init() {
+	mux := http.NewServeMux()
+	mux.HandleFunc("/valueList", valueListHandler)
+
+	api := restapi{
+		srv: &http.Server{
+			Addr:    ":8080",
+			Handler: mux,
+		},
+	}
+
+	go func() {
+		if err := api.srv.ListenAndServe(); !errors.Is(err, http.ErrServerClosed) {
+			plugin.Errorf("%s plugin: ListenAndServe(): %v", pluginName, err)
+		}
+	}()
+
+	plugin.RegisterShutdown(pluginName, api)
+}
+
+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
+	}
+}
+
+func (api restapi) Shutdown(ctx context.Context) error {
+	ctx, cancel := context.WithTimeout(ctx, 30*time.Second)
+	defer cancel()
+
+	return api.srv.Shutdown(ctx)
+}
+
+func main() {} // ignored