provide mechanisms to forward output from jnlp app

launcher/jnlp/launcher.go

@@ -299,6 +299,22 @@ func (launcher *Launcher) exec() error {
 	if launcher.gui.Closed() {
 		return errCancelled
 	}
+
+	if launcher.options != nil && launcher.options.StdoutHandler != nil {
+		pipe, err := cmd.StdoutPipe()
+		if err != nil {
+			return errors.Wrap(err, "failed to create stdout pipe to application")
+		}
+		go launcher.options.StdoutHandler(pipe)
+	}
+
+	if launcher.options != nil && launcher.options.StderrHandler != nil {
+		pipe, err := cmd.StderrPipe()
+		if err != nil {
+			return errors.Wrap(err, "failed to create stderr pipe to application")
+		}
+		go launcher.options.StderrHandler(pipe)
+	}
 	return cmd.Start()
 }
 

launcher/launcher.go

@@ -1,6 +1,7 @@
 package launcher
 
 import (
+	"io"
 	"net/url"
 	"strings"
 
@@ -23,12 +24,22 @@ type Launcher interface {
 	SetLogFile(logFile string)
 }
 
+// OutputHandler is invoked with the read end of a pipe to which the Launcher forwards
+// output (stdout or stderr). Each instance of an OutputHandler will be provided its own
+// goroutine, so it may block as necessary.
+type OutputHandler = func(pipe io.ReadCloser)
+
 type Options struct {
 	IsRunningFromBrowser          bool
 	JavaDir                       string
 	ShowConsole                   bool
 	DisableVerification           bool
 	DisableVerificationSameOrigin bool
+
+	// If non-nil, processes output from stdout of the launched process
+	StdoutHandler OutputHandler
+	// If non-nil, processes output from stderr of the launched process
+	StderrHandler OutputHandler
 }
 
 func RegisterProtocol(scheme string, launcher Launcher) {