[core] Add status / health check API

Signed-off-by: Knut Ahlers <knut@ahlers.me>

irc.go

@@ -96,6 +96,9 @@ func (i ircHandler) ExecutePart(channel string) {
 }
 
 func (i ircHandler) Handle(c *irc.Client, m *irc.Message) {
+	// We've received a message, update status check
+	statusIRCMessageReceived = time.Now()
+
 	go func(m *irc.Message) {
 		configLock.RLock()
 		defer configLock.RUnlock()

status.go

@@ -0,0 +1,107 @@
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"strconv"
+	"time"
+
+	"github.com/pkg/errors"
+
+	"github.com/Luzifer/twitch-bot/plugins"
+)
+
+const statusIRCMessageReceivedTimeout = 5 * time.Minute
+
+var statusIRCMessageReceived time.Time
+
+type (
+	statusResponse struct {
+		Checks               []statusResponseCheck `json:"checks"`
+		OverallStatusSuccess bool                  `json:"overall_status_success"`
+	}
+
+	statusResponseCheck struct {
+		Name        string `json:"name"`
+		Description string `json:"description"`
+		Success     bool   `json:"success"`
+		Error       string `json:"error,omitempty"`
+
+		checkFn func() error
+	}
+)
+
+func init() {
+	registerRoute(plugins.HTTPRouteRegistrationArgs{
+		HandlerFunc: handleStatusRequest,
+		Method:      http.MethodGet,
+		Module:      "status",
+		Path:        "/status.json",
+		QueryParams: []plugins.HTTPRouteParamDocumentation{
+			{
+				Description: "Set the response status for failing checks",
+				Name:        "fail-status",
+				Required:    false,
+				Type:        "integer",
+			},
+		},
+		RequiresWriteAuth: false,
+		ResponseType:      plugins.HTTPRouteResponseTypeJSON,
+	})
+}
+
+func handleStatusRequest(w http.ResponseWriter, r *http.Request) {
+	failStatus := http.StatusInternalServerError
+	if v, err := strconv.Atoi(r.FormValue("fail-status")); err == nil {
+		failStatus = v
+	}
+
+	output := statusResponse{
+		OverallStatusSuccess: true,
+	}
+
+	for _, chk := range []statusResponseCheck{
+		{
+			Name:        "IRC connection alive",
+			Description: fmt.Sprintf("IRC connection received a message in last %s", statusIRCMessageReceivedTimeout),
+			checkFn: func() error {
+				if time.Since(statusIRCMessageReceived) > statusIRCMessageReceivedTimeout {
+					return errors.New("message lifetime expired")
+				}
+				return nil
+			},
+		},
+		{
+			Name:        "Twitch Client Authorized",
+			Description: "Twitch Client is authorized and can fetch authorized user",
+			checkFn: func() error {
+				if twitchClient == nil {
+					return errors.New("not initialized")
+				}
+
+				_, err := twitchClient.GetAuthorizedUsername()
+				return errors.Wrap(err, "fetching username")
+			},
+		},
+	} {
+		err := chk.checkFn()
+		if err != nil {
+			chk.Error = err.Error()
+		}
+		chk.Success = err == nil
+
+		output.Checks = append(output.Checks, chk)
+		output.OverallStatusSuccess = output.OverallStatusSuccess && chk.Success
+	}
+
+	w.Header().Set("Content-Type", "application/json")
+	if !output.OverallStatusSuccess {
+		w.WriteHeader(failStatus)
+	}
+
+	if err := json.NewEncoder(w).Encode(output); err != nil {
+		http.Error(w, errors.Wrap(err, "encoding output").Error(), http.StatusInternalServerError)
+		return
+	}
+}