From 1fac994d61765db774c24aa74413145b242f62b2 Mon Sep 17 00:00:00 2001
From: Andrew Morgan <andrewm@matrix.org>
Date: Mon, 11 Jun 2018 13:25:03 +0100
Subject: [PATCH] Reduce cyclomatic complexity

---
 .../dendrite/appservice/types/types.go        |  9 ++-
 .../workers/transaction_scheduler.go          | 66 +++++++++----------
 2 files changed, 39 insertions(+), 36 deletions(-)

diff --git a/src/github.com/matrix-org/dendrite/appservice/types/types.go b/src/github.com/matrix-org/dendrite/appservice/types/types.go
index a013e8b2..ac83b264 100644
--- a/src/github.com/matrix-org/dendrite/appservice/types/types.go
+++ b/src/github.com/matrix-org/dendrite/appservice/types/types.go
@@ -20,11 +20,14 @@ import (
 	"github.com/matrix-org/dendrite/common/config"
 )
 
-// ApplicationServiceWorkerState is a type that pairs and application service with a
-// lockable condition, allowing the roomserver to notify appservice workers when
-// there are events ready to send externally to application services.
+// ApplicationServiceWorkerState is a type that couples an application service,
+// a lockable condition as well as some other state variables, allowing the
+// roomserver to notify appservice workers when there are events ready to send
+// externally to application services.
 type ApplicationServiceWorkerState struct {
 	AppService  config.ApplicationService
 	Cond        *sync.Cond
 	EventsReady bool
+	// Backoff exponent (2^x secs). Max 6, aka 64s.
+	Backoff int
 }
diff --git a/src/github.com/matrix-org/dendrite/appservice/workers/transaction_scheduler.go b/src/github.com/matrix-org/dendrite/appservice/workers/transaction_scheduler.go
index ba169a91..671824a1 100644
--- a/src/github.com/matrix-org/dendrite/appservice/workers/transaction_scheduler.go
+++ b/src/github.com/matrix-org/dendrite/appservice/workers/transaction_scheduler.go
@@ -81,9 +81,6 @@ func worker(db *storage.Database, ws types.ApplicationServiceWorkerState) {
 		Timeout: transactionTimeout,
 	}
 
-	// Initialize backoff exponent (2^x secs). Max 6, aka 64s.
-	backoff := 0
-
 	// Initial check for any leftover events to send from last time
 	eventCount, err := db.CountEventsWithAppServiceID(ctx, ws.AppService.ID)
 	if err != nil {
@@ -94,12 +91,7 @@ func worker(db *storage.Database, ws types.ApplicationServiceWorkerState) {
 
 	// Wait if there are no new events to go out
 	if eventCount == 0 {
-		ws.Cond.L.Lock()
-		if !ws.EventsReady {
-			// Wait for a broadcast about new events
-			ws.Cond.Wait()
-		}
-		ws.Cond.L.Unlock()
+		waitForEvents(&ws)
 	}
 
 	// Loop forever and keep waiting for more events to send
@@ -122,34 +114,22 @@ func worker(db *storage.Database, ws types.ApplicationServiceWorkerState) {
 		// Batch events up into a transaction
 		transactionJSON, err := createTransaction(events)
 		if err != nil {
-			log.WithError(err).Fatal("appservice %s worker unable to marshal events",
+			log.WithError(err).Fatalf("appservice %s worker unable to marshal events",
 				ws.AppService.ID)
 
 			return
 		}
 
 		// Send the events off to the application service
-		err = send(client, ws.AppService, transactionJSON, len(events))
+		err = send(client, ws.AppService, transactionJSON)
 		if err != nil {
-			// Calculate how long to backoff for
-			backoffDuration := time.Duration(math.Pow(2, float64(backoff)))
-			backoffSeconds := time.Second * backoffDuration
-			log.WithError(err).Warnf("unable to send transactions to %s, backing off for %ds",
-				ws.AppService.ID, backoffDuration)
-
-			// Increment backoff count
-			backoff++
-			if backoff > 6 {
-				backoff = 6
-			}
-
 			// Backoff
-			time.Sleep(backoffSeconds)
+			backoff(err, &ws)
 			continue
 		}
 
 		// We sent successfully, hooray!
-		backoff = 0
+		ws.Backoff = 0
 
 		// Remove sent events from the DB
 		err = db.RemoveEventsBeforeAndIncludingID(ctx, eventIDs[len(eventIDs)-1])
@@ -166,16 +146,37 @@ func worker(db *storage.Database, ws types.ApplicationServiceWorkerState) {
 				ws.AppService.ID)
 			return
 		}
-
-		ws.Cond.L.Lock()
-		if !ws.EventsReady {
-			// Wait for a broadcast about new events
-			ws.Cond.Wait()
-		}
-		ws.Cond.L.Unlock()
+		waitForEvents(&ws)
 	}
 }
 
+// waitForEvents pauses the calling goroutine while it waits for a broadcast message
+func waitForEvents(ws *types.ApplicationServiceWorkerState) {
+	ws.Cond.L.Lock()
+	if !ws.EventsReady {
+		// Wait for a broadcast about new events
+		ws.Cond.Wait()
+	}
+	ws.Cond.L.Unlock()
+}
+
+// backoff pauses the calling goroutine for a 2^some backoff exponent seconds
+func backoff(err error, ws *types.ApplicationServiceWorkerState) {
+	// Calculate how long to backoff for
+	backoffDuration := time.Duration(math.Pow(2, float64(ws.Backoff)))
+	backoffSeconds := time.Second * backoffDuration
+	log.WithError(err).Warnf("unable to send transactions to %s, backing off for %ds",
+		ws.AppService.ID, backoffDuration)
+
+	ws.Backoff++
+	if ws.Backoff > 6 {
+		ws.Backoff = 6
+	}
+
+	// Backoff
+	time.Sleep(backoffSeconds)
+}
+
 // createTransaction takes in a slice of AS events, stores them in an AS
 // transaction, and JSON-encodes the results.
 func createTransaction(
@@ -200,7 +201,6 @@ func send(
 	client *http.Client,
 	appservice config.ApplicationService,
 	transaction []byte,
-	count int,
 ) error {
 	// POST a transaction to our AS.
 	address := fmt.Sprintf("%s/transactions/%d", appservice.URL, currentTransactionID)