PNG Extra Embedder (PEE)
========================

Can embed any file in a PNG/WebM/GIF and upload it through 4chanX.
Requires 4chanX and violentmonkey.

How to Build
============

npm i and npm run build
then install the generated main.users.js

How to Install
==============

Or use the prebuilt main.user.js at the root of this repo.

How to use
==========

Posts with an embedded image/video will have an colored dashed line on their right. Golden means the file is external (ie. a booru), and pink means it was a file embedded in the post file.


![eye](settings.png)

In the quick reply form, a magnet icon will appear.
You need to select a png/webm/gif file to upload first, as you would normally (this is what the file will appear as), then click on the magnet to select a file to embed (can be anything).

![qr](screen.png)

Formats
======

PNG
---
This works by appending the file in the last IDAT chunk.
Metadata information is stored in a tEXt chunk, placed near the header so that a parser looking for that embedded information can bail out without having to parse the whole file.

Metadata in the tEXt has the following meaning:

CUM[null]0 -> The last IDAT chunk is formatted as [filename length[LE 4 bytes], filename, filedata]

CUM[null]X is reserved for future extensions

Possible workaround for 4chan jannies would be to assoome IDAT chunks don't go over a certain size, slightly harder workaround would be to check if the deflate stream yields enough pixels to fit the described dimensions of the image. 


Webm
----
The file is embedded in a SimpleTag tag, with a TagName of C00M and a TagBinary that contains the file content.
The Tags section of that file can contain a TagName with a value of COOMFILENAME and a TagString containing a filename

GIF
---

The embedded data is contained in an application extension chunk, usually right after the NETSCAPE extension.
The extension is named COOMTECH0.1, the rest of the bytes encode directly the file content, with no filename. The filesize is implicitely determined by a sentinel value that marks the end of the subchunk.

JPG
---

Can never be supported as 4chan reincodes them.

Third Eye
---------

Third eye filenames are supported.
Filename just need to be made of 32 hex characters that correspond to a filename in any of the supported boorus.

Other formats
=============

The format used by Zip anon won't be supported because:
- it isn't extensible (if change were to the storage format, an extension update wouldn't be backcompatible)
- requires parsing the whole file to know if it has an embedded file
- and includes a private chunk type that is functionally defective (stores the length of the last IDAT chunk as a mean to identify it, instead of assooming it's simply the last one)

Bugs
====

- fails to find files in new posts after a thread update
- more to come