TUN-8725: implement diagnostic procedure

## Summary
Add a function that orchestrates the diagnostic jobs producing a zip file at the end.

Closes TUN-8725

diagnostic/log_collector_utils.go

@@ -5,6 +5,7 @@ import (
 	"io"
 	"os"
 	"os/exec"
+	"path/filepath"
 )
 
 func PipeCommandOutputToFile(command *exec.Cmd, outputHandle *os.File) (*LogInformation, error) {
@@ -45,3 +46,45 @@ func PipeCommandOutputToFile(command *exec.Cmd, outputHandle *os.File) (*LogInfo
 
 	return NewLogInformation(outputHandle.Name(), true, false), nil
 }
+
+func CopyFilesFromDirectory(path string) (string, error) {
+	// rolling logs have as suffix the current date thus
+	// when iterating the path files they are already in
+	// chronological order
+	files, err := os.ReadDir(path)
+	if err != nil {
+		return "", fmt.Errorf("error reading directory %s: %w", path, err)
+	}
+
+	outputHandle, err := os.Create(filepath.Join(os.TempDir(), logFilename))
+	if err != nil {
+		return "", fmt.Errorf("creating file %s: %w", outputHandle.Name(), err)
+	}
+	defer outputHandle.Close()
+
+	for _, file := range files {
+		logHandle, err := os.Open(filepath.Join(path, file.Name()))
+		if err != nil {
+			return "", fmt.Errorf("error opening file %s:%w", file.Name(), err)
+		}
+		defer logHandle.Close()
+
+		_, err = io.Copy(outputHandle, logHandle)
+		if err != nil {
+			return "", fmt.Errorf("error copying file %s:%w", logHandle.Name(), err)
+		}
+	}
+
+	logHandle, err := os.Open(filepath.Join(path, "cloudflared.log"))
+	if err != nil {
+		return "", fmt.Errorf("error opening file %s:%w", logHandle.Name(), err)
+	}
+	defer logHandle.Close()
+
+	_, err = io.Copy(outputHandle, logHandle)
+	if err != nil {
+		return "", fmt.Errorf("error copying file %s:%w", logHandle.Name(), err)
+	}
+
+	return outputHandle.Name(), nil
+}