agent-watcher/internal/source/webhook/webhook.go

// Package webhook implements the HTTP webhook Source.
//
// Listens on a loopback address and routes incoming POSTs to inbox events
// according to a routing table. Each route specifies recipient, type,
// priority, and a Go text/template that renders the payload from the request
// body decoded as JSON.
//
// v1 is loopback-only (127.0.0.1) — no authentication. The spec calls for
// Caddy + bearer-token reverse-proxy as the v2 upgrade path. Do NOT bind to
// 0.0.0.0 in v1.
//
// Per spec §3.5, the same listener also exposes /health with per-source
// counters.
package webhook

import (
	"bytes"
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"log/slog"
	"net"
	"net/http"
	"sync/atomic"
	"text/template"
	"time"

	"git.botbought.ai/foreman/agent-watcher/internal/inbox"
	"git.botbought.ai/foreman/agent-watcher/internal/source"
)

// Route maps a URL path to an emitted event.
type Route struct {
	// Recipient is the target inbox name.
	Recipient string

	// Type is one of INFO, NEEDS-RESPONSE, ACK-REQUEST.
	Type string

	// Priority is "normal" or "urgent". Empty defaults to "normal".
	Priority string

	// PayloadTemplate is a Go text/template rendered with the request body
	// (decoded as JSON into a map[string]any) as the dot. Plain strings
	// without {{}} render to themselves.
	PayloadTemplate string
}

// Config configures a webhook Source.
type Config struct {
	// Listen is the bind address, e.g. "127.0.0.1:18790".
	Listen string

	// Routes maps URL path → Route. Path includes the leading slash.
	Routes map[string]Route
}

// Source serves HTTP and emits an inbox event for each matched POST.
type Source struct {
	cfg    Config
	logger *slog.Logger

	tmpls map[string]*template.Template

	// counters
	received atomic.Uint64
	emitted  atomic.Uint64
	errors   atomic.Uint64
	startedAt time.Time
}

// New parses the route templates and returns a configured Source.
// Returns an error if any template fails to parse.
func New(cfg Config, logger *slog.Logger) (*Source, error) {
	if logger == nil {
		logger = slog.Default()
	}
	if cfg.Listen == "" {
		return nil, errors.New("webhook: listen address required")
	}
	if !isLoopback(cfg.Listen) {
		return nil, fmt.Errorf("webhook: listen %q is not a loopback address; v1 forbids non-loopback binds", cfg.Listen)
	}

	tmpls := make(map[string]*template.Template, len(cfg.Routes))
	for path, r := range cfg.Routes {
		if !validTypes[r.Type] {
			return nil, fmt.Errorf("webhook: route %s: invalid type %q", path, r.Type)
		}
		if r.Priority != "" && r.Priority != "normal" && r.Priority != "urgent" {
			return nil, fmt.Errorf("webhook: route %s: invalid priority %q", path, r.Priority)
		}
		t, err := template.New(path).Option("missingkey=zero").Parse(r.PayloadTemplate)
		if err != nil {
			return nil, fmt.Errorf("webhook: route %s: parse template: %w", path, err)
		}
		tmpls[path] = t
	}
	return &Source{
		cfg:       cfg,
		logger:    logger.With("source", "webhook", "listen", cfg.Listen),
		tmpls:     tmpls,
		startedAt: time.Now(),
	}, nil
}

func (s *Source) Name() string { return "webhook" }

// Run blocks until ctx is canceled.
func (s *Source) Run(ctx context.Context, emit source.Emit) error {
	mux := http.NewServeMux()
	mux.HandleFunc("/health", s.health)
	mux.HandleFunc("/", s.handler(emit))

	srv := &http.Server{
		Addr:              s.cfg.Listen,
		Handler:           mux,
		ReadHeaderTimeout: 5 * time.Second,
	}

	listenErr := make(chan error, 1)
	go func() {
		s.logger.Info("listening")
		listenErr <- srv.ListenAndServe()
	}()

	select {
	case <-ctx.Done():
		shutCtx, cancel := context.WithTimeout(context.Background(), 3*time.Second)
		defer cancel()
		_ = srv.Shutdown(shutCtx)
		return ctx.Err()
	case err := <-listenErr:
		if errors.Is(err, http.ErrServerClosed) {
			return nil
		}
		return fmt.Errorf("webhook: serve: %w", err)
	}
}

func (s *Source) handler(emit source.Emit) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		s.received.Add(1)

		if r.Method != http.MethodPost {
			http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
			return
		}
		route, ok := s.cfg.Routes[r.URL.Path]
		if !ok {
			http.Error(w, "no route", http.StatusNotFound)
			return
		}
		body, err := io.ReadAll(io.LimitReader(r.Body, 1<<20)) // 1 MiB cap
		if err != nil {
			s.errors.Add(1)
			s.logger.Warn("read body", "path", r.URL.Path, "err", err)
			http.Error(w, "read failed", http.StatusBadRequest)
			return
		}
		var data map[string]any
		if len(bytes.TrimSpace(body)) > 0 {
			if err := json.Unmarshal(body, &data); err != nil {
				s.errors.Add(1)
				s.logger.Warn("body not JSON", "path", r.URL.Path, "err", err)
				http.Error(w, "body must be JSON", http.StatusBadRequest)
				return
			}
		} else {
			data = map[string]any{}
		}

		var rendered bytes.Buffer
		if err := s.tmpls[r.URL.Path].Execute(&rendered, data); err != nil {
			s.errors.Add(1)
			s.logger.Warn("template render", "path", r.URL.Path, "err", err)
			http.Error(w, "render failed", http.StatusInternalServerError)
			return
		}
		priority := route.Priority
		if priority == "" {
			priority = "normal"
		}
		ev := &inbox.Event{
			From:     "collector",
			Type:     route.Type,
			Priority: priority,
			Payload:  rendered.String(),
			Source:   "webhook:" + r.URL.Path,
		}
		if err := emit(route.Recipient, ev); err != nil {
			s.errors.Add(1)
			s.logger.Error("emit", "path", r.URL.Path, "err", err)
			http.Error(w, "emit failed", http.StatusInternalServerError)
			return
		}
		s.emitted.Add(1)
		w.WriteHeader(http.StatusAccepted)
		_, _ = io.WriteString(w, "ok\n")
	}
}

// Stats returns the current counter snapshot. Safe to call from any goroutine.
type Stats struct {
	Received  uint64 `json:"received"`
	Emitted   uint64 `json:"emitted"`
	Errors    uint64 `json:"errors"`
	UptimeSec int64  `json:"uptime_sec"`
}

func (s *Source) Stats() Stats {
	return Stats{
		Received:  s.received.Load(),
		Emitted:   s.emitted.Load(),
		Errors:    s.errors.Load(),
		UptimeSec: int64(time.Since(s.startedAt).Seconds()),
	}
}

func (s *Source) health(w http.ResponseWriter, r *http.Request) {
	w.Header().Set("Content-Type", "application/json")
	_ = json.NewEncoder(w).Encode(s.Stats())
}

// validTypes mirrors agent-ping. Kept here (not imported from dropfolder) so
// the webhook source has no cross-source dependency.
var validTypes = map[string]bool{
	"INFO":           true,
	"NEEDS-RESPONSE": true,
	"ACK-REQUEST":    true,
}

// isLoopback returns true if addr binds only to a loopback interface.
// Accepts "127.0.0.1:port", "[::1]:port", "localhost:port".
func isLoopback(addr string) bool {
	host, _, err := net.SplitHostPort(addr)
	if err != nil {
		return false
	}
	if host == "localhost" {
		return true
	}
	ip := net.ParseIP(host)
	return ip != nil && ip.IsLoopback()
}