Support redirecting stdout/stdin/stderr to/from other sources

auxiliary.go

@@ -492,7 +492,7 @@ func LoadFile(l *State, fileName, mode string) error {
 	}
 	if fileName == "" {
 		l.PushString("=stdin")
-		f = os.Stdin
+		f = l.stdin
 	} else {
 		l.PushString("@" + fileName)
 		var err error
@@ -509,7 +509,7 @@ func LoadFile(l *State, fileName, mode string) error {
 	}
 	s, _ := l.ToString(-1)
 	err := l.Load(r, s, mode)
-	if f != os.Stdin {
+	if f != l.stdin {
 		_ = f.Close()
 	}
 	switch err {
@@ -538,7 +538,7 @@ func NewStateEx() *State {
 	if l != nil {
 		_ = AtPanic(l, func(l *State) int {
 			s, _ := l.ToString(-1)
-			fmt.Fprintf(os.Stderr, "PANIC: unprotected error in call to Lua API (%s)\n", s)
+			fmt.Fprintf(l.stderr, "PANIC: unprotected error in call to Lua API (%s)\n", s)
 			return 0
 		})
 	}

base.go

@@ -2,7 +2,6 @@ package lua
 
 import (
 	"io"
-	"os"
 	"runtime"
 	"strconv"
 	"strings"
@@ -215,13 +214,13 @@ var baseLibrary = []RegistryFunction{
 				panic("unreachable")
 			}
 			if i > 1 {
-				os.Stdout.WriteString("\t")
+				l.writeToStdout("\t")
 			}
-			os.Stdout.WriteString(s)
+			l.writeToStdout(s)
 			l.Pop(1) // pop result
 		}
-		os.Stdout.WriteString("\n")
-		os.Stdout.Sync()
+		l.writeToStdout("\n")
+		l.stdout.Sync()
 		return 0
 	}},
 	{"rawequal", func(l *State) int {
@@ -328,3 +327,11 @@ func BaseOpen(l *State) int {
 	l.SetField(-2, "_VERSION")
 	return 1
 }
+
+func (l *State) writeToStdout(s string) {
+	_, err := l.stdout.WriteString(s)
+	if err != nil {
+		Errorf(l, "failed writing to stdout: %v", err)
+		panic("unreachable")
+	}
+}

go.mod

@@ -1,3 +1,11 @@
 module github.com/Shopify/go-lua
 
 go 1.22
+
+require github.com/stretchr/testify v1.9.0
+
+require (
+	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/pmezard/go-difflib v1.0.0 // indirect
+	gopkg.in/yaml.v3 v3.0.1 // indirect
+)

go.sum

@@ -0,0 +1,10 @@
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/stretchr/testify v1.9.0 h1:HtqpIVDClZ4nwg75+f6Lvsy/wHu+3BoSGCbBAcpTsTg=
+github.com/stretchr/testify v1.9.0/go.mod h1:r2ic/lqez/lEtzL7wO/rwa5dbSLXVDPFyf8C91i36aY=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
+gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

io.go

@@ -316,9 +316,9 @@ func IOOpen(l *State) int {
 	SetFunctions(l, fileHandleMethods, 0)
 	l.Pop(1)
 
-	registerStdFile(l, os.Stdin, input, "stdin")
-	registerStdFile(l, os.Stdout, output, "stdout")
-	registerStdFile(l, os.Stderr, "", "stderr")
+	registerStdFile(l, l.stdin, input, "stdin")
+	registerStdFile(l, l.stdout, output, "stdout")
+	registerStdFile(l, l.stderr, "", "stderr")
 
 	return 1
 }

lua.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"io"
 	"math"
+	"os"
 	"strings"
 )
 
@@ -239,6 +240,7 @@ type State struct {
 	errorFunction         int      // current error handling function (stack index)
 	baseCallInfo          callInfo // callInfo for first level (go calling lua)
 	protectFunction       func()
+	stdout, stderr, stdin *os.File
 }
 
 type globalState struct {
@@ -455,7 +457,7 @@ func (l *State) Dump(w io.Writer) error {
 // http://www.lua.org/manual/5.2/manual.html#lua_newstate
 func NewState() *State {
 	v := float64(VersionNumber)
-	l := &State{allowHook: true, error: nil, nonYieldableCallCount: 1}
+	l := &State{allowHook: true, error: nil, nonYieldableCallCount: 1, stdout: os.Stdout, stderr: os.Stderr, stdin: os.Stdin}
 	g := &globalState{mainThread: l, registry: newTable(), version: &v, memoryErrorMessage: "not enough memory"}
 	l.global = g
 	l.initializeStack()
@@ -1529,3 +1531,12 @@ func (l *State) IsNoneOrNil(index int) bool { return l.TypeOf(index) <= TypeNil
 //
 // http://www.lua.org/manual/5.2/manual.html#lua_pushglobaltable
 func (l *State) PushGlobalTable() { l.RawGetInt(RegistryIndex, RegistryIndexGlobals) }
+
+// SetStdout redirects interpreter stdout to the given *os.File
+func (l *State) SetStdout(stdout *os.File) { l.stdout = stdout }
+
+// SetStderr redirects interpreter stderr to the given *os.File
+func (l *State) SetStderr(stderr *os.File) { l.stderr = stderr }
+
+// SetStdin redirects interpreter stdin from the given *os.File
+func (l *State) SetStdin(stdin *os.File) { l.stdin = stdin }

lua_test.go

@@ -1,23 +1,28 @@
-package lua
+package lua_test
 
 import (
 	"fmt"
+	"io"
+	"os"
 	"testing"
+
+	"github.com/Shopify/go-lua"
+	"github.com/stretchr/testify/assert"
 )
 
 func TestPushFStringPointer(t *testing.T) {
-	l := NewState()
+	l := lua.NewState()
 	l.PushFString("%p %s", l, "test")
 
 	expected := fmt.Sprintf("%p %s", l, "test")
-	actual := CheckString(l, -1)
+	actual := lua.CheckString(l, -1)
 	if expected != actual {
 		t.Errorf("PushFString, expected \"%s\" but found \"%s\"", expected, actual)
 	}
 }
 
 func TestToBooleanOutOfRange(t *testing.T) {
-	l := NewState()
+	l := lua.NewState()
 	l.SetTop(0)
 	l.PushBoolean(false)
 	l.PushBoolean(true)
@@ -29,3 +34,57 @@ func TestToBooleanOutOfRange(t *testing.T) {
 		}
 	}
 }
+
+func TestInputOutputErrorRedirect(t *testing.T) {
+	t.Run("test redirect stdout", func(t *testing.T) {
+		// use a variable as stdout
+		reader, writer, err := os.Pipe()
+		assert.Nil(t, err)
+
+		// setup runtime state
+		l := lua.NewState()
+		l.SetStdout(writer)
+		lua.OpenLibraries(l)
+
+		// run lua code
+		err = lua.DoString(l, "print(1 + 1)")
+		assert.Nil(t, err)
+
+		writer.Close()
+		output, err := io.ReadAll(reader)
+		assert.Nil(t, err)
+
+		assert.Equal(t, "2\n", string(output))
+	})
+
+	t.Run("test std redirect", func(t *testing.T) {
+		// create a pipe to stdin and add some lua code it it
+		inputReader, inputWriter, err := os.Pipe()
+		assert.Nil(t, err)
+
+		outputReader, outputWriter, err := os.Pipe()
+		assert.Nil(t, err)
+
+		// setup runtime state
+		l := lua.NewState()
+		l.SetStdin(inputReader)
+		l.SetStdout(outputWriter)
+		lua.OpenLibraries(l)
+
+		// write to the file input
+		_, err = inputWriter.Write([]byte("print(1 + 1)"))
+		assert.Nil(t, err)
+		assert.Nil(t, inputWriter.Close())
+
+		// run lua code
+		err = lua.DoFile(l, "")
+		assert.Nil(t, err)
+		assert.Nil(t, outputWriter.Close())
+
+		output, err := io.ReadAll(outputReader)
+		assert.Nil(t, err)
+
+		assert.Equal(t, "2\n", string(output))
+	})
+
+}