Add STDOut Consumer

Add an STDOut consumer for usecases where streaming the bytes to another
process is appropriate. If the consumer is STDOUT we are restricted to a
single file download concurrently in multifile mode.

cmd/multifile/multifile.go

@@ -97,6 +97,8 @@ func maxConcurrentFiles() int {
 }
 
 func multifileExecute(ctx context.Context, manifest pget.Manifest) error {
+	logger := logging.GetLogger()
+
 	chunkSize, err := humanize.ParseBytes(viper.GetString(config.OptChunkSize))
 	if err != nil {
 		return err
@@ -131,6 +133,13 @@ func multifileExecute(ctx context.Context, manifest pget.Manifest) error {
 		return fmt.Errorf("error getting consumer: %w", err)
 	}
 
+	// Special case, if we're writing to stdout, we only want to download one file at a time, since we can only stream
+	// a single bytestream to STDOUT
+	if viper.GetString(config.OptOutputConsumer) == config.ConsumerSTDOUT {
+		logger.Info().Msg("Using single file mode for STDOUT consumer")
+		pgetOpts.MaxConcurrentFiles = 1
+	}
+
 	getter := &pget.Getter{
 		Downloader: download.GetBufferMode(downloadOpts),
 		Consumer:   consumer,
@@ -158,7 +167,6 @@ func multifileExecute(ctx context.Context, manifest pget.Manifest) error {
 	}
 
 	throughput := float64(totalFileSize) / elapsedTime.Seconds()
-	logger := logging.GetLogger()
 	logger.Info().
 		Int("file_count", len(manifest)).
 		Str("total_bytes_downloaded", humanize.Bytes(uint64(totalFileSize))).

pkg/config/config.go

@@ -20,6 +20,7 @@ const (
 	ConsumerFile         = "file"
 	ConsumerTarExtractor = "tar-extractor"
 	ConsumerNull         = "null"
+	ConsumerSTDOUT       = "stdout"
 )
 
 var (
@@ -153,6 +154,8 @@ func GetConsumer() (consumer.Consumer, error) {
 		return &consumer.TarExtractor{Overwrite: enableOverwrite}, nil
 	case ConsumerNull:
 		return &consumer.NullWriter{}, nil
+	case ConsumerSTDOUT:
+		return &consumer.StdoutConsumer{}, nil
 	default:
 		return nil, fmt.Errorf("invalid consumer specified: %s", consumerName)
 	}

pkg/consumer/stdout.go

@@ -0,0 +1,20 @@
+package consumer
+
+import (
+	"fmt"
+	"io"
+	"os"
+)
+
+var _ Consumer = &StdoutConsumer{}
+
+type StdoutConsumer struct {
+}
+
+func (s StdoutConsumer) Consume(reader io.Reader, destPath string) error {
+	_, err := io.Copy(os.Stdout, reader)
+	if err != nil {
+		return fmt.Errorf("error writing to stdout: %w", err)
+	}
+	return nil
+}