webhooker/internal/handlers/webhook.go

package handlers

import (
	"encoding/json"
	"io"
	"net/http"

	"github.com/go-chi/chi"
	"sneak.berlin/go/webhooker/internal/database"
	"sneak.berlin/go/webhooker/internal/middleware"
)

const (
	// maxWebhookBodySize is the maximum allowed webhook
	// request body (1 MB).
	maxWebhookBodySize = 1 << maxBodyShift
)

// HandleWebhook handles incoming webhook requests at entrypoint
// URLs.
func (h *Handlers) HandleWebhook() http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		if r.Method != http.MethodPost {
			w.Header().Set("Allow", "POST")
			http.Error(
				w,
				"Method Not Allowed",
				http.StatusMethodNotAllowed,
			)

			return
		}

		entrypointUUID := chi.URLParam(r, "uuid")
		if entrypointUUID == "" {
			http.NotFound(w, r)

			return
		}

		entrypoint, ok := h.lookupEntrypoint(
			w, r, entrypointUUID,
		)
		if !ok {
			return
		}

		// Logged only once the lookup has found the entrypoint, so
		// an invented path writes no INFO line; a miss is logged at
		// DEBUG. The entrypoint is named by its ID: the UUID is its
		// credential and is never logged.
		h.log.Info("webhook request received",
			"entrypoint_id", entrypoint.ID,
			"webhook_id", entrypoint.WebhookID,
			"method", r.Method,
			"remoteIP", middleware.RemoteIP(r),
			"clientIP", middleware.ClientIP(r),
		)

		if !entrypoint.Active {
			http.Error(w, "Gone", http.StatusGone)

			return
		}

		h.processWebhookRequest(w, r, entrypoint)
	}
}

// processWebhookRequest reads the request into an event and has the
// delivery engine store it, with a delivery for each of the webhook's
// active targets, and answers the sender.
//
// Nothing about the request itself is authenticated: the entrypoint
// UUID in the path is the credential, and reaching here means it
// matched an active entrypoint.
func (h *Handlers) processWebhookRequest(
	w http.ResponseWriter,
	r *http.Request,
	entrypoint database.Entrypoint,
) {
	body, ok := h.readWebhookBody(w, r)
	if !ok {
		return
	}

	headersJSON, err := json.Marshal(r.Header)
	if err != nil {
		h.receiverError(w, "failed to serialize headers", err)

		return
	}

	event := &database.Event{
		WebhookID:    entrypoint.WebhookID,
		EntrypointID: entrypoint.ID,
		Method:       r.Method,
		RawQuery:     r.URL.RawQuery,
		Headers:      string(headersJSON),
		ContentType:  r.Header.Get("Content-Type"),
		Body:         string(body),
	}

	deliveries, err := h.engine.StoreEvent(event)
	if err != nil {
		h.receiverError(w, "failed to store webhook event", err)

		return
	}

	h.finishWebhookResponse(w, event, entrypoint, deliveries)
}

// lookupEntrypoint finds an entrypoint by UUID path.
func (h *Handlers) lookupEntrypoint(
	w http.ResponseWriter,
	r *http.Request,
	entrypointUUID string,
) (database.Entrypoint, bool) {
	var entrypoint database.Entrypoint

	result := h.db.DB().Where(
		"path = ?", entrypointUUID,
	).First(&entrypoint)
	if result.Error != nil {
		// Not even an unknown UUID is logged. The receiver's log
		// lines never carry the path segment, which is a credential
		// whenever it names an entrypoint.
		h.log.Debug("entrypoint not found")
		http.NotFound(w, r)

		return entrypoint, false
	}

	return entrypoint, true
}

// readWebhookBody reads and validates the request body size. This is
// the receiver's only body cap: /h/{uuid} has no MaxBodySize
// middleware (see Server.setupWebhookRoutes).
func (h *Handlers) readWebhookBody(
	w http.ResponseWriter,
	r *http.Request,
) ([]byte, bool) {
	body, err := io.ReadAll(
		io.LimitReader(r.Body, maxWebhookBodySize+1),
	)
	if err != nil {
		h.log.Error(
			"failed to read request body", "error", err,
		)
		http.Error(
			w, "Bad request", http.StatusBadRequest,
		)

		return nil, false
	}

	if len(body) > maxWebhookBodySize {
		http.Error(
			w,
			"Request body too large",
			http.StatusRequestEntityTooLarge,
		)

		return nil, false
	}

	return body, true
}

// receiverError logs an error and answers the sender with a plain-text
// 500. The receiver's answers are for programs, so it never sends the
// error page the web UI uses.
func (h *Handlers) receiverError(
	w http.ResponseWriter, msg string, err error,
) {
	h.log.Error(msg, "error", err)
	http.Error(
		w, "Internal server error",
		http.StatusInternalServerError,
	)
}

// finishWebhookResponse logs the stored event, with how many
// deliveries it has, and writes the HTTP response.
func (h *Handlers) finishWebhookResponse(
	w http.ResponseWriter,
	event *database.Event,
	entrypoint database.Entrypoint,
	deliveries int,
) {
	h.log.Info("webhook event created",
		"event_id", event.ID,
		"webhook_id", entrypoint.WebhookID,
		"entrypoint_id", entrypoint.ID,
		"target_count", deliveries,
	)

	w.WriteHeader(http.StatusOK)

	_, err := w.Write([]byte(`{"status":"ok"}`))
	if err != nil {
		h.log.Error(
			"failed to write response", "error", err,
		)
	}
}