jni/jni.go

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2020-06-19 16:07:37 -04:00
// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package jni
// Package jni implements various helper functions for communicating with the Android JVM
// though JNI.
import (
"errors"
"fmt"
"reflect"
"runtime"
"unicode/utf16"
"unsafe"
)
/*
#cgo CFLAGS: -Wall
#include <jni.h>
#include <stdlib.h>
#include "gojni.h"
*/
import "C"
type JVM struct {
jvm *C.JavaVM
}
type Env struct {
env *C.JNIEnv
}
type (
Class C.jclass
Object C.jobject
MethodID C.jmethodID
String C.jstring
ByteArray C.jbyteArray
Value uint64 // All JNI types fit into 64-bits.
)
func JVMFor(jvmPtr uintptr) JVM {
return JVM{
jvm: (*C.JavaVM)(unsafe.Pointer(jvmPtr)),
}
}
func EnvFor(envPtr uintptr) Env {
return Env{
env: (*C.JNIEnv)(unsafe.Pointer(envPtr)),
}
}
// Do invokes a function with a temporary JVM environment. The
// environment is not valid after the function returns.
func Do(vm JVM, f func(env Env) error) error {
runtime.LockOSThread()
defer runtime.UnlockOSThread()
var env *C.JNIEnv
if res := C._jni_GetEnv(vm.jvm, &env, C.JNI_VERSION_1_6); res != C.JNI_OK {
if res != C.JNI_EDETACHED {
panic(fmt.Errorf("JNI GetEnv failed with error %d", res))
}
if C._jni_AttachCurrentThread(vm.jvm, &env, nil) != C.JNI_OK {
panic(errors.New("runInJVM: AttachCurrentThread failed"))
}
defer C._jni_DetachCurrentThread(vm.jvm)
}
return f(Env{env})
}
func varArgs(args []Value) *C.jvalue {
if len(args) == 0 {
return nil
}
return (*C.jvalue)(unsafe.Pointer(&args[0]))
}
func IsSameObject(e Env, ref1, ref2 Object) bool {
same := C._jni_IsSameObject(e.env, C.jobject(ref1), C.jobject(ref2))
return same == C.JNI_TRUE
}
func CallStaticIntMethod(e Env, cls Class, method MethodID, args ...Value) (int, error) {
res := C._jni_CallStaticIntMethodA(e.env, C.jclass(cls), C.jmethodID(method), varArgs(args))
return int(res), exception(e)
}
func CallStaticVoidMethod(e Env, cls Class, method MethodID, args ...Value) error {
C._jni_CallStaticVoidMethodA(e.env, C.jclass(cls), C.jmethodID(method), varArgs(args))
return exception(e)
}
func CallVoidMethod(e Env, obj Object, method MethodID, args ...Value) error {
C._jni_CallVoidMethodA(e.env, C.jobject(obj), C.jmethodID(method), varArgs(args))
return exception(e)
}
func CallStaticObjectMethod(e Env, cls Class, method MethodID, args ...Value) (Object, error) {
res := C._jni_CallStaticObjectMethodA(e.env, C.jclass(cls), C.jmethodID(method), varArgs(args))
return Object(res), exception(e)
}
func CallObjectMethod(e Env, obj Object, method MethodID, args ...Value) (Object, error) {
res := C._jni_CallObjectMethodA(e.env, C.jobject(obj), C.jmethodID(method), varArgs(args))
return Object(res), exception(e)
}
func CallIntMethod(e Env, obj Object, method MethodID, args ...Value) (int32, error) {
res := C._jni_CallIntMethodA(e.env, C.jobject(obj), C.jmethodID(method), varArgs(args))
return int32(res), exception(e)
}
// GetByteArrayElements returns the contents of the array.
func GetByteArrayElements(e Env, jarr ByteArray) []byte {
size := C._jni_GetArrayLength(e.env, C.jarray(jarr))
elems := C._jni_GetByteArrayElements(e.env, C.jbyteArray(jarr))
defer C._jni_ReleaseByteArrayElements(e.env, C.jbyteArray(jarr), elems, 0)
backing := (*(*[1 << 30]byte)(unsafe.Pointer(elems)))[:size:size]
s := make([]byte, len(backing))
copy(s, backing)
return s
}
// NewByteArray allocates a Java byte array with the content. It
// panics if the allocation fails.
func NewByteArray(e Env, content []byte) ByteArray {
jarr := C._jni_NewByteArray(e.env, C.jsize(len(content)))
if jarr == 0 {
panic(fmt.Errorf("jni: NewByteArray(%d) failed", len(content)))
}
elems := C._jni_GetByteArrayElements(e.env, jarr)
defer C._jni_ReleaseByteArrayElements(e.env, jarr, elems, 0)
backing := (*(*[1 << 30]byte)(unsafe.Pointer(elems)))[:len(content):len(content)]
copy(backing, content)
return ByteArray(jarr)
}
// ClassLoader returns a reference to the Java ClassLoader associated
// with obj.
func ClassLoaderFor(e Env, obj Object) Object {
cls := GetObjectClass(e, obj)
getClassLoader := GetMethodID(e, cls, "getClassLoader", "()Ljava/lang/ClassLoader;")
clsLoader, err := CallObjectMethod(e, Object(obj), getClassLoader)
if err != nil {
// Class.getClassLoader should never fail.
panic(err)
}
return Object(clsLoader)
}
// LoadClass invokes the underlying ClassLoader's loadClass method and
// returns the class.
func LoadClass(e Env, loader Object, class string) (Class, error) {
cls := GetObjectClass(e, loader)
loadClass := GetMethodID(e, cls, "loadClass", "(Ljava/lang/String;)Ljava/lang/Class;")
name := JavaString(e, class)
loaded, err := CallObjectMethod(e, loader, loadClass, Value(name))
if err != nil {
return 0, err
}
return Class(loaded), exception(e)
}
// exception returns an error corresponding to the pending
// exception, and clears it. exceptionError returns nil if no
// exception is pending.
func exception(e Env) error {
thr := C._jni_ExceptionOccurred(e.env)
if thr == 0 {
return nil
}
C._jni_ExceptionClear(e.env)
cls := GetObjectClass(e, Object(thr))
toString := GetMethodID(e, cls, "toString", "()Ljava/lang/String;")
msg, err := CallObjectMethod(e, Object(thr), toString)
if err != nil {
return err
}
return errors.New(GoString(e, String(msg)))
}
// GetObjectClass returns the Java Class for an Object.
func GetObjectClass(e Env, obj Object) Class {
if obj == 0 {
panic("null object")
}
cls := C._jni_GetObjectClass(e.env, C.jobject(obj))
if err := exception(e); err != nil {
// GetObjectClass should never fail.
panic(err)
}
return Class(cls)
}
// GetStaticMethodID returns the id for a static method. It panics if the method
// wasn't found.
func GetStaticMethodID(e Env, cls Class, name, signature string) MethodID {
mname := C.CString(name)
defer C.free(unsafe.Pointer(mname))
msig := C.CString(signature)
defer C.free(unsafe.Pointer(msig))
m := C._jni_GetStaticMethodID(e.env, C.jclass(cls), mname, msig)
if err := exception(e); err != nil {
panic(err)
}
return MethodID(m)
}
// GetMethodID returns the id for a method. It panics if the method
// wasn't found.
func GetMethodID(e Env, cls Class, name, signature string) MethodID {
mname := C.CString(name)
defer C.free(unsafe.Pointer(mname))
msig := C.CString(signature)
defer C.free(unsafe.Pointer(msig))
m := C._jni_GetMethodID(e.env, C.jclass(cls), mname, msig)
if err := exception(e); err != nil {
panic(err)
}
return MethodID(m)
}
func NewGlobalRef(e Env, obj Object) Object {
return Object(C._jni_NewGlobalRef(e.env, C.jobject(obj)))
}
func DeleteGlobalRef(e Env, obj Object) {
C._jni_DeleteGlobalRef(e.env, C.jobject(obj))
}
// JavaString converts the string to a JVM jstring.
func JavaString(e Env, str string) String {
if str == "" {
return 0
}
utf16Chars := utf16.Encode([]rune(str))
res := C._jni_NewString(e.env, (*C.jchar)(unsafe.Pointer(&utf16Chars[0])), C.int(len(utf16Chars)))
return String(res)
}
// GoString converts the JVM jstring to a Go string.
func GoString(e Env, str String) string {
if str == 0 {
return ""
}
strlen := C._jni_GetStringLength(e.env, C.jstring(str))
chars := C._jni_GetStringChars(e.env, C.jstring(str))
var utf16Chars []uint16
hdr := (*reflect.SliceHeader)(unsafe.Pointer(&utf16Chars))
hdr.Data = uintptr(unsafe.Pointer(chars))
hdr.Cap = int(strlen)
hdr.Len = int(strlen)
utf8 := utf16.Decode(utf16Chars)
return string(utf8)
}