How to get "/title actionbar" or GuiIngame.overlayMessage text?

[olari]

I'm trying to get the text from the /title actionbar command to get some information that a server presents there.

From the Minecraft decompilation I've gathered that the text itself is kept and used in net.minecraft.client.gui.GuiIngame, but I don't have access to it.

public class GuiIngame {
	protected String overlayMessage; // text itself
	public void setOverlayMessage(...); // setter
	// no getter
}

The only way I can come up with to get this information is to catch the SPacketTitle itself when it arrives.
This seems like a pretty daunting task so I thought I'd ask here first for alternatives.

If networking is the only option, I would like some guidance on how to approach it.

[V0idWa1k3r]

  On 7/29/2018 at 1:42 PM, olari said:

The only way I can come up with to get this information is to catch the SPacketTitle itself when it arrives.

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You could always use reflection. Make sure to use ReflectionHelper.getPrivateValue and provide both the deobf name of the field as well as the SRG name.

[olari]

  On 7/29/2018 at 2:00 PM, V0idWa1k3r said:

You could always use reflection. Make sure to use ReflectionHelper.getPrivateValue and provide both the deobf name of the field as well as the SRG name.

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Thank you very much for the hasty reply. I'll look into using reflection.

[olari]

  On 7/29/2018 at 2:02 PM, olari said:

Thank you very much for the hasty reply. I'll look into using reflection.

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Got it working!

 

String title = ReflectionHelper.getPrivateValue(GuiIngame.class, mc.ingameGUI, 8);

 

Edited July 29, 2018 by olari

[V0idWa1k3r]

I don't recommend using index-based field getters. Indices can change if a particularly bad mod creates a field in the class using asm. Names can't.

[IceMetalPunk]

To elaborate, reflection is relatively slow/inefficient. (It's also generally a bad idea, but Minecraft's source code gives us no other options in some cases, as you've discovered.) Therefore, it should be used only when necessary, and its returned objects cached whenever possible.

[larsgerrits]

  On 7/29/2018 at 5:38 PM, IceMetalPunk said:

reflection is relatively slow/inefficient.

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If you do it correctly, it's pretty much as fast as normal field access.

[IceMetalPunk]

  On 7/29/2018 at 7:55 PM, larsgerrits said:

If you do it correctly, it's pretty much as fast as normal field access.

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Define "correctly"?

[larsgerrits]

  On 7/29/2018 at 8:51 PM, IceMetalPunk said:

Define "correctly"?

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Store the Field instance in a static field somewhere. Calling Field#get will pretty much be the same as normal field access performance wise.

[IceMetalPunk]

  On 7/29/2018 at 8:59 PM, larsgerrits said:

Store the Field instance in a static field somewhere. Calling Field#get will pretty much be the same as normal field access performance wise.

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So... cache it, like I said? XD The actual reflective call is only happening once in that case, which is why it's fast. But if you were to call the reflection access methods as often as you'd otherwise call a field name, the performance drops significantly.

[olari]

Here's the final code:
 

private Field overlayMessageField = null;

// Called at initialization
private void findOverlayTextField() {
    this.overlayMessageField = ReflectionHelper.findField(GuiIngame.class, "overlayMessage");
}

public String getActionbar() {
    try {
        return (String)this.overlayMessageField.get(mc.ingameGUI);
    } catch (IllegalAccessException e) {
        e.printStackTrace();
    }

    return null;
}

 

[Draco18s]

Return an empty string instead of null.

[Draco18s]

  On 7/31/2018 at 3:58 PM, diesieben07 said:

No. What even...

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Would I rather check validate that the string returned by this function is null, or display an empty string (or the string "null")?

I think I'd rather have a non-null string.

[Draco18s]

  On 8/1/2018 at 7:44 AM, diesieben07 said:

Neither should ever happen in this case.

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Oh I agree it should never happen.

But if there's one thing I know about programming. "Should never happen" is not as absolute as one would think.

Edited August 1, 2018 by Draco18s

[Draco18s]

  On 8/1/2018 at 5:54 PM, diesieben07 said:

True. But if it does happen, just carrying on as if nothing was wrong is not the way to go.

This is what crash reports are for.

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In which case, I would do something like this:

public String getActionbar() {
	try {
	        return (String)overlayMessageField.get(Minecraft.getMinecraft().ingameGUI);
	    } catch (IllegalAccessException e) {
	    	e.printStackTrace();
	        throw new RuntimeException("Get Message Overlay failed!");
	    }
}

If it should crash, then let it crash. Don't handle the exception, then return null, allowing other code to null-check and not crash.