ui/app: merge goString implementations and add test

Fixes gio#30

Signed-off-by: Elias Naur <mail@eliasnaur.com>

ui/app/egl_windows.go

@@ -4,7 +4,6 @@ package app
 
 import (
 	"os"
-	"reflect"
 	"unsafe"
 
 	syscall "golang.org/x/sys/windows"
@@ -135,27 +134,5 @@ func eglTerminate(disp _EGLDisplay) bool {
 
 func eglQueryString(disp _EGLDisplay, name _EGLint) string {
 	r, _, _ := _eglQueryString.Call(uintptr(disp), uintptr(name))
-	return goString(r)
-}
-
-func goString(s uintptr) string {
-	if s == 0 {
-		return ""
-	}
-	sh := reflect.SliceHeader{
-		Data: s,
-		Len:  1 << 30,
-		Cap:  1 << 30,
-	}
-	sl := *(*[]byte)(unsafe.Pointer(&sh))
-	var v string
-	for i, c := range sl {
-		if c == 0 {
-			if i > 0 {
-				v = string(sl[:i-1])
-			}
-			break
-		}
-	}
-	return v
+	return gl.GoString(gl.SliceOf(r))
 }

ui/app/internal/gl/gl_windows.go

@@ -4,7 +4,6 @@ package gl
 
 import (
 	"math"
-	"reflect"
 	"syscall"
 	"unsafe"
 
@@ -284,7 +283,7 @@ func (c *Functions) GetShaderInfoLog(s Shader) string {
 }
 func (c *Functions) GetString(pname Enum) string {
 	s, _, _ := syscall.Syscall(_glGetString.Addr(), 1, uintptr(pname), 0, 0)
-	return goString(s)
+	return GoString(SliceOf(s))
 }
 func (c *Functions) GetUniformLocation(p Program, name string) Uniform {
 	cname := cString(name)
@@ -365,25 +364,3 @@ func cString(s string) []byte {
 	copy(b, s)
 	return b
 }
-
-func goString(s uintptr) string {
-	if s == 0 {
-		return ""
-	}
-	sh := reflect.SliceHeader{
-		Data: s,
-		Len:  1 << 30,
-		Cap:  1 << 30,
-	}
-	sl := *(*[]byte)(unsafe.Pointer(&sh))
-	var v string
-	for i, c := range sl {
-		if c == 0 {
-			if i > 0 {
-				v = string(sl[:i-1])
-			}
-			break
-		}
-	}
-	return v
-}

ui/app/internal/gl/util.go

@@ -87,3 +87,28 @@ func ParseGLVersion(glVer string) ([2]int, error) {
 	}
 	return ver, fmt.Errorf("failed to parse OpenGL ES version (%s)", glVer)
 }
+
+func SliceOf(s uintptr) []byte {
+	if s == 0 {
+		return nil
+	}
+	sh := reflect.SliceHeader{
+		Data: s,
+		Len:  1 << 30,
+		Cap:  1 << 30,
+	}
+	return *(*[]byte)(unsafe.Pointer(&sh))
+}
+
+// GoString convert a NUL-terminated C string
+// to a Go string.
+func GoString(s []byte) string {
+	i := 0
+	for {
+		if s[i] == 0 {
+			break
+		}
+		i++
+	}
+	return string(s[:i])
+}

ui/app/internal/gl/util_test.go

@@ -0,0 +1,18 @@
+package gl
+
+import (
+	"testing"
+)
+
+func TestGoString(t *testing.T) {
+	tests := [][2]string{
+		{"Hello\x00", "Hello"},
+		{"\x00", ""},
+	}
+	for _, test := range tests {
+		got := GoString([]byte(test[0]))
+		if exp := test[1]; exp != got {
+			t.Errorf("expected %q got %q", exp, got)
+		}
+	}
+}