Wrong JNI type in getField: Not Long but Java Object

[vonox7]

When setting a ConnectionLogger or OperationQueueListener to SMTPSession the setupNative function fails with the following error:
JNI GetObjectField called with pending exception java.lang.NoSuchFieldError: no "J" field "connectionLogger" in class "Lcom/libmailcore/SMTPSession;" or its superclasses

The connectionLogger/operationQueueListener field in SMTPSession is not a Long ("J") but an Object ("L..."), therefore the JNI GetFieldID function fails.

In File JavaHandle.cpp the function getField fetches through JNI an object, but GetFieldID falsly assumes that the type to search is a Long instead of an Java Object:

static jfieldID getField(JNIEnv * env, jobject obj, const char * fieldName)
{
    jclass c = env->GetObjectClass(obj);
    return env->GetFieldID(c, fieldName, "J");
}

The getField function is only called by getObjectField():

jobject mailcore::getObjectField(JNIEnv *env, jobject obj, const char * fieldName)
{
    return env->GetObjectField(obj, getField(env, obj, fieldName));
}

Expected code:
jclass c = env->GetFieldID(c, fieldName, "Lcom/libmailcore/ConnectionLogger;")
and
jclass c = env->GetFieldID(c, fieldName, "Lcom/libmailcore/OperationQueueListener;")

To solve this issue for all functions that use the getObjectField function, we would need an additional parameter that specifies the Java class we are looking for. (ConnectionLogger, OperationQueueListener...).

[functionaldude]

+1

[dinhvh]

Could you send a pull request to fix it?
Thanks!

[vonox7]

I tried to fix it, but apparently there are more bugs related to that issue.

[dinhvh]

@vonox7, would the following work?

static jfieldID getFieldForObject(JNIEnv * env, jobject obj, const char * fieldName)
{
    jclass c = env->GetObjectClass(obj);
    return env->GetFieldID(c, fieldName, "Ljava/lang/Object;");
}

jobject mailcore::getObjectField(JNIEnv *env, jobject obj, const char * fieldName)
{
    return env->GetObjectField(obj, getFieldForObject(env, obj, fieldName));
}

[vonox7]

Unfortunately, "Ljava/lang/Object;" won't work, as we get an NoSuchFieldError, see stacktrace: https://gist.github.com/vonox7/90f9bdd4c422f4925f99ba1933f7145e

By using the followig hack we get the correct field (connectionLogger/operationQueueListener), but then there seems to be some threading issues, have a look at the stacktrace: https://gist.github.com/vonox7/5868369b8ce76f254e1c72c6a3edf3bb
Hacky solution in getFieldForObject:

if (strcmp ("connectionLogger", fieldName) == 0) {
        return env->GetFieldID(c, fieldName, "Lcom/libmailcore/ConnectionLogger;");
    } else if (strcmp ("operationQueueListener", fieldName) == 0) {
        return env->GetFieldID(c, fieldName, "Lcom/libmailcore/OperationQueueListener;");
    }
}

[dinhvh]

Could you create a specific method for connectionLogger and send a pull request?

[vonox7]

As said above, even with the specific object call it will crash because of threading issues. Can you have a look into that threading issue? https://gist.github.com/vonox7/5868369b8ce76f254e1c72c6a3edf3bb

[dinhvh]

Ah ok. We probably need to fix mailcore::JavaConnectionLogger::log() to lookup properly connectionLogger from a thread.

[beczesz]

Any news about this issue?

[BigNateBombBomb]

Same boat here. Having issues with Office365 SMTP and would love to be able to see the actual responses so I can pinpoint the issue better

[filippo-orru]

I'd also really benefit from this. I'm trying to debug why creating a "manual" IMAP connection works, but mailcore doesn't