loglist: thread context through FetchAll and fetchOne

FetchAll issued three sequential 30s-timeout HTTP fetches with no
context, so shutdown could stall up to ~90s waiting for the hourly
sync loop. runTailers already owns a cancellation context; pass it
through so cancelation aborts in-flight list fetches immediately.

First tests for the package: context cancellation and error status.

internal/loglist/loglist.go

@@ -1,6 +1,7 @@
 package loglist
 
 import (
+	"context"
 	"encoding/json"
 	"fmt"
 	"io"
@@ -83,7 +84,7 @@ func (l *Log) Endpoint() string {
 	}
 }
 
-func FetchAll(client *http.Client) ([]Log, error) {
+func FetchAll(ctx context.Context, client *http.Client) ([]Log, error) {
 	if client == nil {
 		client = &http.Client{Timeout: 30 * time.Second}
 	}
@@ -92,7 +93,10 @@ func FetchAll(client *http.Client) ([]Log, error) {
 	var order []string
 	var fetched int
 	for _, u := range urls {
-		list, err := fetchOne(client, u)
+		if ctx.Err() != nil {
+			break
+		}
+		list, err := fetchOne(ctx, client, u)
 		if err != nil {
 			continue
 		}
@@ -125,6 +129,9 @@ func FetchAll(client *http.Client) ([]Log, error) {
 		out = append(out, *seen[id])
 	}
 	if fetched == 0 {
+		if ctx.Err() != nil {
+			return nil, fmt.Errorf("log list fetch canceled: %w", ctx.Err())
+		}
 		return nil, fmt.Errorf("all %d log list sources failed", len(urls))
 	}
 	if fetched < len(urls) {
@@ -133,8 +140,12 @@ func FetchAll(client *http.Client) ([]Log, error) {
 	return out, nil
 }
 
-func fetchOne(client *http.Client, url string) (*List, error) {
-	resp, err := client.Get(url)
+func fetchOne(ctx context.Context, client *http.Client, url string) (*List, error) {
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
+	if err != nil {
+		return nil, err
+	}
+	resp, err := client.Do(req)
 	if err != nil {
 		return nil, err
 	}

internal/loglist/loglist_test.go

@@ -0,0 +1,41 @@
+package loglist
+
+import (
+	"context"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+	"time"
+)
+
+func TestFetchOneHonorsContext(t *testing.T) {
+	release := make(chan struct{})
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		<-release
+		w.Write([]byte(`{}`))
+	}))
+	defer func() {
+		close(release)
+		srv.Close()
+	}()
+
+	ctx, cancel := context.WithCancel(context.Background())
+	cancel()
+	start := time.Now()
+	if _, err := fetchOne(ctx, srv.Client(), srv.URL); err == nil {
+		t.Fatal("fetchOne with canceled context should fail")
+	}
+	if elapsed := time.Since(start); elapsed > time.Second {
+		t.Fatalf("canceled fetch took %v; want immediate return", elapsed)
+	}
+}
+
+func TestFetchOneRejectsBadStatus(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		http.Error(w, "nope", http.StatusInternalServerError)
+	}))
+	defer srv.Close()
+	if _, err := fetchOne(context.Background(), srv.Client(), srv.URL); err == nil {
+		t.Fatal("fetchOne should fail on 500")
+	}
+}

main.go

@@ -208,7 +208,7 @@ func cmdTail(args []string) error {
 func runTailers(ctx context.Context, st *store.Store, c *commonConfig, drain bool) {
 	t := &tailer.Tailer{Store: st, Interval: c.interval, Window: c.window, Drain: drain}
 	for {
-		logs, err := loglist.FetchAll(nil)
+		logs, err := loglist.FetchAll(ctx, nil)
 		if err == nil {
 			t.Sync(ctx, logs)
 			log.Printf("loglist sync: %d logs known", len(logs))