Binary edit a file from data folder

[magic]

Hi,

I try to edit a file in data folder with

Local file:=FileStream.Open( "cerberus://data/test.bin","r" )
Local i:=file.ReadInt()
DrawText i,100,100
file.Close

The stream seem Null. I check the file is there. m I missing anything?
Btw.. I'm in android

 

[Holzchopf]

Seems FileStream.Open can only access cerberus://internal/ - see here

Apparently you're supposed to use DataBuffer.Load instead.

 

[magic]

Oh thank you for the info.
Can we save the DataBuffer to a file?

 

[MikeHart]

Oh thank you for the info.
Can we save the DataBuffer to a file?

Use a FileStream . And with it, look into its Write methods.

 

[SLotman]

Did something change from Monkey? Because I had code written in Monkey that would read a file from the data folder...

I just did a

fs = FileStream.Open("data/" + file,"r")

and I know it worked on Monkey, because I have an old APK from this same project that still works (I'm loading a map)

Moved the file to Cerberus, compile it to Android and it doesn't anymore...?! (It is running on my own target, old from mojo1)

 

[magic]

FileStream.Open("data/" + file,"r")

may be that "data/" is change. I think something cerberus://blabla/ .. I can't remember. You can check doc

 

[SLotman]

I've tried cerberus://data/ no change. tried ./assets/cerberus/ and nothing.

 

[SLotman]

This probably won't work either: https://www.cerberus-x.com/community/index.php?threads/ini-file-handler.1249/

 

[Phil7]

I can look into this tomorrow. @SLotman Do you know the monkey version you built it with?
I can remember some changes/bug fixes regarding fixPath() but nothing that should break stuff

 

[SLotman]

Yeah, another project with a JSON reader I have here is failing too. Weird that reading and writeing from internal:// works, but not reading from cerberus://data/ ?!

 

[SLotman]

I was trying the old monkey version I have - and surprise - its failiing on v87 as well.

Weird that I'm looking at old sources, and PathToFilePath is exactly the same as the one in Cerberus - so thats not the culprit

 

[SLotman]

There is something really weird going on. I just altered another project on Monkey that uses JsonParser...works on Monkey 87, on Cerberus its throwing 'invalid Json' - maybe some android permission thing needed?

 

[Phil7]

Well Cerberus is definitely using a newer Android Api which introduces more and more finegrained permissions often with runtime popups.

 

[SLotman]

Hmmm...

I think this is the problem: Android does not permit to use RandomAcessFile outside of the internal storage, and thats exactly what Cerberus is doing when the filenotfound exception is raised:

    public RandomAccessFile OpenFile( String path,String mode ){
        try{
            return new RandomAccessFile( PathToFilePath( path ),mode );
        }catch( IOException ex ){
        }
        return null;
    }

I really don't know if there is a solution to this, other than the nasty one presented as to "copy" the desired file to internal and then read it from there :/

 

[Phil7]

Yes hmmm...
I had a search in the old monkey repo and found that in 2014 there was a commit that saved asset files to an external folder and also had a PathToFilePath() that returned PathToAssetPath()
But this was ditched before the OpenSource release of Monkey. I am not sure we should incorporate that hack again ...

 

[SLotman]

The 'PathToAssetPath' function seems to be in the android target, even in Cerberus...! The only difference is the last line, of PathToFilePath returning

return PathToAssetPath(path);

instead of

return ""

I've made the change here, but it didn't help, still returning null to filestream.open()

 

[Phil7]

I was referring to a larger commit (April 2014) that also includes the functionality of copying the asset file to a external location first. The PathToAssetPath() function on its own doesn't solve anything as it just removes some clutter in the string.

That's what I found out about the issue so far:

• The reason random access for the data folder is not supported by android is that all asset files are compressed inside the apk (not as simple files in a folder) and therefore only accessible for sequential access.
• So if we need real RandomAccessFile functionality on an asset file we have to copy it, which means extracting it to a different location. That seems to be the only way of having real random access performance.
• There might be a direct way to get the functionality of random access while still using the asset file itself for reading data by using the AssetFileDescriptor for getting to a certain location in a file but it still sits on the sequential loading process and leads to performance issues. - I am not sure if this would be an option at all!

All in all I tend to say I would implement that copy-to-internal functionality with a warning of that extracting process happening in the background.

 

[SLotman]

I ended up replacing it with a databuffer in my code. But if there was a way to just read it sequentially (like a fileStream, without seek, just readbyte, readint, readstring, etc) - I think that could be a good compromise (and something better than databuffer, specially when its a large file and you can't read it all into memory)

 

[Phil7]

But if there was a way to just read it sequentially (like a fileStream, without seek, just readbyte, readint, readstring, etc) - I think that could be a good compromise

That's a good idea! I will see if I can get a poor mans InputFileStream in CX running that can use most of the functionality of CX FileStream, probably except seek() and eof() and certainly all write commands.

 

[Phil7]

@SLotman I made a FileInputStream Class as a module for CX. At the moment it only supports Android and Desktop for now and on Desktop it is just a cheap copy of the regular FileStream restricted to read access. It's in this branch on Github until it gets merged.