Merge pull request #1469 from openziti/fix.config.template.tests

fixes template config tests on windows due to Stdout backpressure

ziti/cmd/create/create_config_controller.go

@@ -173,10 +173,12 @@ func (options *CreateConfigControllerOptions) run(data *ConfigTemplateValues) er
 		if err != nil {
 			return errors.Wrapf(err, "unable to create config file: %s", options.Output)
 		}
+
+		//only close things we open
+		defer func() { _ = f.Close() }()
 	} else {
 		f = os.Stdout
 	}
-	defer func() { _ = f.Close() }()
 
 	if err := tmpl.Execute(f, data); err != nil {
 		return errors.Wrap(err, "unable to execute template")

ziti/cmd/create/create_config_test.go

@@ -1,7 +1,6 @@
 package create
 
 import (
-	"bytes"
 	"fmt"
 	"github.com/stretchr/testify/assert"
 	"io"
@@ -247,18 +246,61 @@ func contains(s []string, str string) bool {
 	return false
 }
 
+// captureOutput hot-swaps os.Stdout in order to redirect all output to a memory buffer. Where possible, do not use
+// this function and instead create optional arguments/configuration to redirect output to io.Writer instances. This
+// should only be used for functionality that we do not control. Many instances of its usage are unnecessary and should
+// be remedied with the aforementioned solution where possible.
 func captureOutput(function func()) string {
-	var buffer bytes.Buffer
 	oldStdOut := os.Stdout
 	r, w, _ := os.Pipe()
 	os.Stdout = w
 
+	defer func() {
+		_ = r.Close()
+	}()
+
+	type readResult struct {
+		out []byte
+		err error
+	}
+
+	defer func() {
+		os.Stdout = oldStdOut
+	}()
+
+	var output []byte
+	var outputErr error
+
+	outChan := make(chan *readResult, 1)
+
+	// Start reading before writing, so we do not create backpressure that is never relieved in OSs with smaller buffers
+	// than the resulting configuration file (i.e. Windows). Go will not yield to other routines unless there is
+	// a system call. The fake os.Stdout will never yield and some code paths executed as `function()` may not
+	// have syscalls.
+	go func() {
+		output, outputErr = io.ReadAll(r)
+		outChan <- &readResult{
+			output,
+			outputErr,
+		}
+	}()
+
 	function()
 
-	_ = w.Close()
 	os.Stdout = oldStdOut
-	_, _ = io.Copy(&buffer, r)
-	return buffer.String()
+	_ = w.Close()
+
+	result := <-outChan
+
+	if result == nil {
+		panic("no output")
+	}
+
+	if result.err != nil {
+		panic(result.err)
+	}
+
+	return string(result.out)
 }
 
 func setEnvByMap[K string, V string](m map[K]V) {