rust - 由于在 "thread '上出现了 'called ` main错误，导致无法创建通用JNIEnv结果:: unwrap()` on an ` Err`值

Question

我想用固定值的JNIEnv(例如“fake javastring”)创建一个通用的JObject(以及JString)，以测试一些需要JEnv和JObject才能正常工作的功能。我不想运行Java VM。

我尝试创建通用的None -value JNIEnv，但是由于错误而失败:

failures:

---- main_tests::Jstrings::return_fake_string stdout ----
thread 'main_tests::Jstrings::return_fake_string' panicked at 'called `Result::unwrap()` on an `Err` value: Error(NullPtr("from_raw ptr argument"), State { next_error: None, backtrace: InternalBacktrace })', src/libcore/result.rs:999:5
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
stack backtrace:
   0: std::sys::unix::backtrace::tracing::imp::unwind_backtrace
             at src/libstd/sys/unix/backtrace/tracing/gcc_s.rs:39
   1: std::sys_common::backtrace::_print
             at src/libstd/sys_common/backtrace.rs:71
   2: std::panicking::default_hook::{{closure}}
             at src/libstd/sys_common/backtrace.rs:59
             at src/libstd/panicking.rs:197
   3: std::panicking::default_hook
             at src/libstd/panicking.rs:208
   4: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:474
   5: std::panicking::continue_panic_fmt
             at src/libstd/panicking.rs:381
   6: rust_begin_unwind
             at src/libstd/panicking.rs:308
   7: core::panicking::panic_fmt
             at src/libcore/panicking.rs:85
   8: core::result::unwrap_failed
             at /rustc/a53f9df32fbb0b5f4382caaad8f1a46f36ea887c/src/libcore/macros.rs:18
   9: core::result::Result<T,E>::unwrap
             at /rustc/a53f9df32fbb0b5f4382caaad8f1a46f36ea887c/src/libcore/result.rs:800
  10: rust::empty_jnienv
             at src/main.rs:10
  11: rust::main_tests::Jstrings::return_fake_string
             at src/main.rs:29
  12: rust::main_tests::Jstrings::return_fake_string::{{closure}}
             at src/main.rs:27
  13: core::ops::function::FnOnce::call_once
             at /rustc/a53f9df32fbb0b5f4382caaad8f1a46f36ea887c/src/libcore/ops/function.rs:231
  14: <alloc::boxed::Box<F> as core::ops::function::FnOnce<A>>::call_once
             at /rustc/a53f9df32fbb0b5f4382caaad8f1a46f36ea887c/src/liballoc/boxed.rs:704
  15: __rust_maybe_catch_panic
             at src/libpanic_unwind/lib.rs:85
  16: test::run_test::run_test_inner::{{closure}}
             at /rustc/a53f9df32fbb0b5f4382caaad8f1a46f36ea887c/src/libstd/panicking.rs:272
             at /rustc/a53f9df32fbb0b5f4382caaad8f1a46f36ea887c/src/libstd/panic.rs:394
             at src/libtest/lib.rs:1468

我的代码-Cargo.toml

[package]
name = "rust"
version = "0.1.0"
edition = "2018"

[dependencies]
libc = "0.2"
jni = { version = "0.10.2", default-features = false }

主

mod backend;

extern crate libc;

use jni::objects::{JObject, JString};
use jni::JNIEnv;
use std::ptr;

pub unsafe fn empty_jnienv() -> jni::JNIEnv<'static> {
    jni::JNIEnv::from_raw(ptr::null_mut()).unwrap()
}

pub unsafe fn empty_jobj() -> jni::objects::JObject<'static> {
    jni::objects::JObject::null()
}

fn main() {}

#[cfg(test)]
mod main_tests {
    use super::*;

    mod Jstrings {
        use super::*;

        #[test]
        fn return_fake_string() {
            let this_string = "fake javastring";
            let jenv = unsafe { empty_jnienv() };
            let jobj = unsafe { empty_jobj() };
            let jstr: jni::objects::JString = jenv.new_string(this_string.to_owned()).unwrap();
            assert!(unsafe {
                backend::Java_com_example_android_MainActivity_test(jenv, jobj, jstr) == true
            });
        }
    }
}

后端

use jni::objects::{JObject, JString};
use jni::JNIEnv;
use std::ffi::{CStr, CString};

#[no_mangle]
pub unsafe extern "C" fn Java_com_example_android_MainActivity_test(
    env: JNIEnv,
    _: JObject,
    j_recipient: JString,
) -> bool {
    let mut this_return = false;
    let recipient = CString::from(CStr::from_ptr(
        env.get_string(j_recipient).unwrap().as_ptr(),
    ));

    if recipient.to_str().unwrap() == "fake javastring" {
        this_return = true;
    }
    this_return
}

有没有一种方法可以解决此问题而无需运行Java VM来创建 JNIEnv和 JObject？

Answer 1

如果查看jni.h，您会看到JNIEnv*是一个充满函数指针的大结构:

struct JNINativeInterface_ {
    void *reserved0;
    void *reserved1;
    void *reserved2;

    void *reserved3;
    jint (JNICALL *GetVersion)(JNIEnv *env);

    jclass (JNICALL *DefineClass)
      (JNIEnv *env, const char *name, jobject loader, const jbyte *buf,
       jsize len);
    jclass (JNICALL *FindClass)
      (JNIEnv *env, const char *name);

    // and so on
};

typedef const struct JNINativeInterface_ *JNIEnv;

如果您真的想走这条路，则可以仅实现代码所需的功能，然后将它们分配给 JNINativeInterface_的各个成员。
我对您使用的Rust桥梁了解不多，但是转换这样的 JNIEnv指针应该可以工作。

当然，最后一个问题是:您到底要测试什么？