Format errors from caller

consumer.go

@@ -115,6 +115,10 @@ func (c *Consumer) Scan(ctx context.Context, fn func(*kinesis.Record) bool) erro
 		return fmt.Errorf("describe stream error: %v", err)
 	}
 
+	if len(resp.StreamDescription.Shards) == 0 {
+		return fmt.Errorf("no shards available")
+	}
+
 	var (
 		wg   sync.WaitGroup
 		errc = make(chan error, 1)
@@ -125,8 +129,8 @@ func (c *Consumer) Scan(ctx context.Context, fn func(*kinesis.Record) bool) erro
 	for _, shard := range resp.StreamDescription.Shards {
 		go func(shardID string) {
 			defer wg.Done()
-			err := c.ScanShard(ctx, shardID, fn)
-			if err != nil {
+
+			if err := c.ScanShard(ctx, shardID, fn); err != nil {
 				select {
 				case errc <- fmt.Errorf("shard %s error: %v", shardID, err):
 					// first error to occur
@@ -134,6 +138,7 @@ func (c *Consumer) Scan(ctx context.Context, fn func(*kinesis.Record) bool) erro
 					// error has already occured
 				}
 			}
+
 			c.logger.Println("exiting", shardID)
 			cancel()
 		}(*shard.ShardId)
@@ -145,8 +150,8 @@ func (c *Consumer) Scan(ctx context.Context, fn func(*kinesis.Record) bool) erro
 }
 
 // ScanShard loops over records on a specific shard, calls the callback func
-// for each record and checkpoints after each page is processed.
-// Note: returning `false` from the callback func will end the scan.
+// for each record and checkpoints the progress of scan.
+// Note: Returning `false` from the callback func will end the scan.
 func (c *Consumer) ScanShard(ctx context.Context, shardID string, fn func(*kinesis.Record) bool) error {
 	c.logger.Println("scanning", shardID)
 
@@ -190,7 +195,7 @@ func (c *Consumer) ScanShard(ctx context.Context, shardID string, fn func(*kines
 
 						if ok := fn(r); !ok {
 							if err := c.setCheckpoint(shardID, lastSeqNum); err != nil {
-								return err
+								return fmt.Errorf("set checkpoint error: %v", err)
 							}
 							return nil
 						}
@@ -198,7 +203,7 @@ func (c *Consumer) ScanShard(ctx context.Context, shardID string, fn func(*kines
 				}
 
 				if err := c.setCheckpoint(shardID, lastSeqNum); err != nil {
-					return err
+					return fmt.Errorf("set checkpoint error: %v", err)
 				}
 			}
 
@@ -217,7 +222,7 @@ func (c *Consumer) ScanShard(ctx context.Context, shardID string, fn func(*kines
 func (c *Consumer) setCheckpoint(shardID, lastSeqNum string) error {
 	err := c.checkpoint.Set(c.streamName, shardID, lastSeqNum)
 	if err != nil {
-		return fmt.Errorf("set checkpoint error: %v", err)
+		return err
 	}
 	c.logger.Println("checkpoint", shardID)
 	c.counter.Add("checkpoints", 1)

examples/consumer/main.go

@@ -14,7 +14,7 @@ import (
 	checkpoint "github.com/harlow/kinesis-consumer/checkpoint/redis"
 )
 
-// kick off a server for exposing metrics
+// kick off a server for exposing scan metrics
 func init() {
 	sock, err := net.Listen("tcp", "localhost:8080")
 	if err != nil {
@@ -45,7 +45,8 @@ func main() {
 	}
 
 	// consumer
-	c, err := consumer.New(*stream,
+	c, err := consumer.New(
+		*stream,
 		consumer.WithCheckpoint(ck),
 		consumer.WithLogger(logger),
 		consumer.WithCounter(counter),