events: Implement event system (#4912)

Co-authored-by: Matt Holt <mholt@users.noreply.github.com>

2 files changed, 20 insertions, 5 deletions

diff --git a/modules/caddyhttp/reverseproxy/healthchecks.go b/modules/caddyhttp/reverseproxy/healthchecks.go
index eb98638..cf22d26 100644
--- a/modules/caddyhttp/reverseproxy/healthchecks.go
+++ b/modules/caddyhttp/reverseproxy/healthchecks.go
@@ -284,6 +284,13 @@ func (h *Handler) doActiveHealthCheck(dialInfo DialInfo, hostAddr string, upstre
 		}
 	}
 
+	markUnhealthy := func() {
+		// dispatch an event that the host newly became unhealthy
+		if upstream.setHealthy(false) {
+			h.events.Emit(h.ctx, "unhealthy", map[string]any{"host": hostAddr})
+		}
+	}
+
 	// do the request, being careful to tame the response body
 	resp, err := h.HealthChecks.Active.httpClient.Do(req)
 	if err != nil {
@@ -291,7 +298,7 @@ func (h *Handler) doActiveHealthCheck(dialInfo DialInfo, hostAddr string, upstre
 			zap.String("host", hostAddr),
 			zap.Error(err),
 		)
-		upstream.setHealthy(false)
+		markUnhealthy()
 		return nil
 	}
 	var body io.Reader = resp.Body
@@ -311,7 +318,7 @@ func (h *Handler) doActiveHealthCheck(dialInfo DialInfo, hostAddr string, upstre
 				zap.Int("status_code", resp.StatusCode),
 				zap.String("host", hostAddr),
 			)
-			upstream.setHealthy(false)
+			markUnhealthy()
 			return nil
 		}
 	} else if resp.StatusCode < 200 || resp.StatusCode >= 400 {
@@ -319,7 +326,7 @@ func (h *Handler) doActiveHealthCheck(dialInfo DialInfo, hostAddr string, upstre
 			zap.Int("status_code", resp.StatusCode),
 			zap.String("host", hostAddr),
 		)
-		upstream.setHealthy(false)
+		markUnhealthy()
 		return nil
 	}
 
@@ -331,14 +338,14 @@ func (h *Handler) doActiveHealthCheck(dialInfo DialInfo, hostAddr string, upstre
 				zap.String("host", hostAddr),
 				zap.Error(err),
 			)
-			upstream.setHealthy(false)
+			markUnhealthy()
 			return nil
 		}
 		if !h.HealthChecks.Active.bodyRegexp.Match(bodyBytes) {
 			h.HealthChecks.Active.logger.Info("response body failed expectations",
 				zap.String("host", hostAddr),
 			)
-			upstream.setHealthy(false)
+			markUnhealthy()
 			return nil
 		}
 	}
@@ -346,6 +353,7 @@ func (h *Handler) doActiveHealthCheck(dialInfo DialInfo, hostAddr string, upstre
 	// passed health check parameters, so mark as healthy
 	if upstream.setHealthy(true) {
 		h.HealthChecks.Active.logger.Info("host is up", zap.String("host", hostAddr))
+		h.events.Emit(h.ctx, "healthy", map[string]any{"host": hostAddr})
 	}
 
 	return nil
diff --git a/modules/caddyhttp/reverseproxy/reverseproxy.go b/modules/caddyhttp/reverseproxy/reverseproxy.go
index b806dda..895682f 100644
--- a/modules/caddyhttp/reverseproxy/reverseproxy.go
+++ b/modules/caddyhttp/reverseproxy/reverseproxy.go
@@ -36,6 +36,7 @@ import (
 
 	"github.com/caddyserver/caddy/v2"
 	"github.com/caddyserver/caddy/v2/caddyconfig/caddyfile"
+	"github.com/caddyserver/caddy/v2/modules/caddyevents"
 	"github.com/caddyserver/caddy/v2/modules/caddyhttp"
 	"github.com/caddyserver/caddy/v2/modules/caddyhttp/headers"
 	"github.com/caddyserver/caddy/v2/modules/caddyhttp/rewrite"
@@ -193,6 +194,7 @@ type Handler struct {
 
 	ctx    caddy.Context
 	logger *zap.Logger
+	events *caddyevents.App
 }
 
 // CaddyModule returns the Caddy module information.
@@ -205,6 +207,11 @@ func (Handler) CaddyModule() caddy.ModuleInfo {
 
 // Provision ensures that h is set up properly before use.
 func (h *Handler) Provision(ctx caddy.Context) error {
+	eventAppIface, err := ctx.App("events")
+	if err != nil {
+		return fmt.Errorf("getting events app: %v", err)
+	}
+	h.events = eventAppIface.(*caddyevents.App)
 	h.ctx = ctx
 	h.logger = ctx.Logger(h)