app/internal/window: [Android] use correct JNI Call variant for registerFragment

While we're here,

- replace the registerFragment trampoline with a general variadic
CallVoidMethod trampoline.
- Use UTF-16 for passing strings to Java. Java's modified UTF-8 encoding differ
from Go's in corner cases.

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

app/internal/window/os_android.c

@@ -147,8 +147,8 @@ jint gio_jni_CallIntMethod(JNIEnv *env, jobject obj, jmethodID methodID) {
 	return (*env)->CallIntMethod(env, obj, methodID);
 }
 
-void gio_jni_CallVoidMethod(JNIEnv *env, jobject obj, jmethodID methodID) {
-	(*env)->CallVoidMethod(env, obj, methodID);
+void gio_jni_CallVoidMethod(JNIEnv *env, jobject obj, jmethodID methodID, const jvalue *args) {
+	(*env)->CallVoidMethodA(env, obj, methodID, args);
 }
 
 jbyte *gio_jni_GetByteArrayElements(JNIEnv *env, jbyteArray arr) {
@@ -163,7 +163,6 @@ jsize gio_jni_GetArrayLength(JNIEnv *env, jbyteArray arr) {
 	return (*env)->GetArrayLength(env, arr);
 }
 
-void gio_jni_RegisterFragment(JNIEnv *env, jobject view, jmethodID mid, char* del) {
-	jstring jdel = (*env)->NewStringUTF(env, del);
-	(*env)->CallObjectMethod(env, view, mid, jdel);
+jstring gio_jni_NewString(JNIEnv *env, const jchar *unicodeChars, jsize len) {
+	return (*env)->NewString(env, unicodeChars, len);
 }

app/internal/window/os_android.go

@@ -23,6 +23,7 @@ import (
 	"runtime/debug"
 	"sync"
 	"time"
+	"unicode/utf16"
 	"unsafe"
 
 	"gioui.org/f32"
@@ -57,6 +58,8 @@ type window struct {
 	mRegisterFragment              C.jmethodID
 }
 
+type jvalue uint64 // The largest JNI type fits in 64 bits.
+
 var dataDirChan = make(chan string, 1)
 
 var theJVM *C.JavaVM
@@ -212,7 +215,7 @@ func onFrameCallback(env *C.JNIEnv, class C.jclass, view C.jlong, nanos C.jlong)
 	w.mu.Unlock()
 	if anim {
 		runInJVM(func(env *C.JNIEnv) {
-			C.gio_jni_CallVoidMethod(env, w.view, w.mpostFrameCallback)
+			callVoidMethod(env, w.view, w.mpostFrameCallback)
 		})
 		w.draw(false)
 	}
@@ -306,7 +309,7 @@ func (w *window) SetAnimating(anim bool) {
 	w.mu.Unlock()
 	if anim {
 		runInJVM(func(env *C.JNIEnv) {
-			C.gio_jni_CallVoidMethod(env, w.view, w.mpostFrameCallbackOnMainThread)
+			callVoidMethod(env, w.view, w.mpostFrameCallbackOnMainThread)
 		})
 	}
 }
@@ -448,21 +451,39 @@ func (w *window) ShowTextInput(show bool) {
 	}
 	runInJVM(func(env *C.JNIEnv) {
 		if show {
-			C.gio_jni_CallVoidMethod(env, w.view, w.mshowTextInput)
+			callVoidMethod(env, w.view, w.mshowTextInput)
 		} else {
-			C.gio_jni_CallVoidMethod(env, w.view, w.mhideTextInput)
+			callVoidMethod(env, w.view, w.mhideTextInput)
 		}
 	})
 }
 
+func javaString(env *C.JNIEnv, str string) C.jstring {
+	if str == "" {
+		return 0
+	}
+	utf16Chars := utf16.Encode([]rune(str))
+	return C.gio_jni_NewString(env, (*C.jchar)(unsafe.Pointer(&utf16Chars[0])), C.int(len(utf16Chars)))
+}
+
 func (w *window) RegisterFragment(del string) {
 	runInJVM(func(env *C.JNIEnv) {
-		cdel := C.CString(del)
-		defer C.free(unsafe.Pointer(cdel))
-		C.gio_jni_RegisterFragment(env, w.view, w.mRegisterFragment, cdel)
+		jstr := javaString(env, del)
+		callVoidMethod(env, w.view, w.mRegisterFragment, jvalue(jstr))
 	})
 }
 
+func varArgs(args []jvalue) *C.jvalue {
+	if len(args) == 0 {
+		return nil
+	}
+	return (*C.jvalue)(unsafe.Pointer(&args[0]))
+}
+
+func callVoidMethod(env *C.JNIEnv, obj C.jobject, method C.jmethodID, args ...jvalue) {
+	C.gio_jni_CallVoidMethod(env, obj, method, varArgs(args))
+}
+
 func Main() {
 }
 

app/internal/window/os_android.h

@@ -12,8 +12,8 @@ __attribute__ ((visibility ("hidden"))) jmethodID gio_jni_GetMethodID(JNIEnv *en
 __attribute__ ((visibility ("hidden"))) jint gio_jni_CallStaticIntMethodII(JNIEnv *env, jclass clazz, jmethodID methodID, jint a1, jint a2);
 __attribute__ ((visibility ("hidden"))) jfloat gio_jni_CallFloatMethod(JNIEnv *env, jobject obj, jmethodID methodID);
 __attribute__ ((visibility ("hidden"))) jint gio_jni_CallIntMethod(JNIEnv *env, jobject obj, jmethodID methodID);
-__attribute__ ((visibility ("hidden"))) void gio_jni_CallVoidMethod(JNIEnv *env, jobject obj, jmethodID methodID);
+__attribute__ ((visibility ("hidden"))) void gio_jni_CallVoidMethod(JNIEnv *env, jobject obj, jmethodID methodID, const jvalue *args);
 __attribute__ ((visibility ("hidden"))) jbyte *gio_jni_GetByteArrayElements(JNIEnv *env, jbyteArray arr);
 __attribute__ ((visibility ("hidden"))) void gio_jni_ReleaseByteArrayElements(JNIEnv *env, jbyteArray arr, jbyte *bytes);
 __attribute__ ((visibility ("hidden"))) jsize gio_jni_GetArrayLength(JNIEnv *env, jbyteArray arr);
-__attribute__ ((visibility ("hidden"))) void gio_jni_RegisterFragment(JNIEnv *env, jobject view, jmethodID mid, char* del);
+__attribute__ ((visibility ("hidden"))) jstring gio_jni_NewString(JNIEnv *env, const jchar *unicodeChars, jsize len);