What is this?

simpledeobf is a very simple and primitive command-line deobfuscator for Minecraft mods. You can use it to create dev versions of mod releases for debugging. Or anything else, really - it all depends on what inputs and mapping files you use. Feel free to get creative with it.

How to use it?

simpledeobf will need files from your Gradle cache which are created by ForgeGradle, so it's best to start with a ForgeGradle workspace already set up for your target Minecraft version.

Command-line options:

• --output The path to the resulting jar. You can only have one.

• --input The input jar you wish to deobfuscate. Can be repeated, but the files from all inputs will just end up in a single output jar.

• --mapFile The path to the MCP mapping file, found in your Gradle cache somewhere under minecraft/de/oceanlabs/mcp. You need to use the one that corresponds to the namespaces you are converting from and to, and also matches the ones you use in your project. Can be repeated, later files will overwrite mappings from previous ones.

• --map Defines a single explicit mapping. This option is treated as if it was a line in the MCP mapping file. Takes precedence over mappings read from MCP files. Can be repeated.

• --ref The path to a reference jar. Can be repeated. The classes inside are read only to determine the class hierarchy, which may be needed to properly deobfuscate certain jar files. The reference jar must be in the same namespace as the input.

  More precisely: you will need to provide a proper class hierarchy to deobfuscate overridden methods whose declaring classes or interfaces are 2 or more levels above the overriding class.

  When in doubt, try using a Minecraft jar of the proper namespace.

• --defaultPkg move all classes from the default package into this one. Having classes in the default package can mess with source attachment in the IDE.

• --forcePublic make all fields, methods and inner classes public. The poor man's access transformer.

• --xdeltaPrefix Prefix for xdelta files.

• --xdeltaPostfix Postfix for xdelta files. Must be used together with the previous option.

  Files that match the given pre/postfixes will be interpreted as patches. The same filename with pre/postfixes stripped from it will be searched for in the reference jars. If found, the patch will be applied to this file and the result used as if the patched version had been read from the input jar.

• --help or -? displays a quick overview of these options.

Have your favourite brand of decompiler ready, and be prepared to dig through the result, and make several iterations before you end up with something usable.

Also there's no guarantee that it's even possible to create a workable dev jar for any given mod. If it uses reflection and/or class transformation, chances are good that it will just crash anyway, unless it's specifically made to be environment agnostic.

Have OptiFine, will debug

As an example, here is a guide on getting OptiFine into your dev environment with simpledeobf. This is the prime use-case of simpledeobf, and the reason for its existence.

The following is the actual command I use for the deobfuscation itself, so you'll need to change the directory names. It's a single command, but I broke it up into lines for readability.

java -jar simpledeobf-0.5.jar
--input h:\Minecraft\mods\obf\OptiFine_1.8.8_HD_U_H2.jar
--output h:\Minecraft\mods\mcp\OptiFine_1.8.8_HD_U_H2-dev.jar
--mapFile h:\Minecraft\.gradle\caches\minecraft\de\oceanlabs\mcp\mcp_stable\20\srgs\notch-mcp.srg
--ref h:\Minecraft\.gradle\caches\minecraft\net\minecraft\minecraft_merged\1.8.8\minecraft_merged-1.8.8.jar
--map="CL: bet$1 net/minecraft/client/entity/AbstractClientPlayer$1"
--map="CL: b$8 net/minecraft/crash/CrashReport$8"
--forcePublic

This will give you a jar with the stable_20 mappings. The 2 map options are needed because OptiFine declares some extra inner classes that are not present in vanilla and have no mappings. If you want to do this for a different Minecraft version, you'll have to change these. Just start without manual mappings, and check if there are still obfuscated classes in the result. Check in the MCP files what the outer class is, and add a mapping. Rinse and repeat.

Open the resulting jar file, and delete the net/minecraftforge directory. There are dummy classes inside that are normally not loaded, but will cause problems in a dev environment. They need to go.

Now you have to create a tweaker and class transformer, because the default OptiFine ones will not work properly in a dev environment. Here is mine that I use in Better Foliage, you need something similar. The point is to change dots to slashes in the class names, so the OptiFine transformer can find the deobfuscated class files.

Edit the META-INF/MANIFEST.MF file. Change the TweakClass option to the tweaker you just made.

The jar is now ready. If you also want source attachment, which is highly recommended, just decompile it with your favourite tool (I prefer JD-GUI), and save a source jar. Make sure that "Realign line numbers" or the equivalent option is turned on.

Drop the jar in the mods folder of your workspace, manually add it to the project dependencies after all the Gradle stuff, set its source attachment, and you're ready. You can start your project with OptiFine thrown in the mix, debug, set breakpoints, and everything.

Note: Debugging into one of the vanilla classes that OptiFine overwrites may or may not give you some headache under Eclipse. I can only confirm it works fine under IDEA, which allows you to switch between sources on the fly if multiple jar files declare a class. A popup comes up saying "Alternative source available for the class blah blah blah", and you can switch to the OptiFine jar, which contains the class actually executing.

OptiFine H5 and beyond

Starting with release H5, OptiFine has adopted a patch-based approach. Instead of replacing the impacted class files with alternative ones, it supplies patches in the xdelta format that are applied at runtime.

Instead of transforming xdelta files, simpledeobf is able to create classic replacement-style deobfuscated jar files by applying the patches against the original Minecraft jar. Again, you'll need to create a class transformer that is able to load it like this.

Here is the example command line I use to deobfuscate OptiFine for 1.9.

java -jar simpledeobf-0.6.jar
--input h:\Minecraft\mods\obf\OptiFine_1.9.0_HD_U_B2_pre.jar
--output h:\Minecraft\mods\mcp\OptiFine_1.9.0_HD_U_B2_pre-dev.jar
--mapFile h:\Minecraft\.gradle\caches\minecraft\de\oceanlabs\mcp\mcp_snapshot\20160406\srgs\notch-mcp.srg
--ref h:\Minecraft\.gradle\caches\minecraft\net\minecraft\minecraft\1.9\minecraft-1.9.jar
--forcePublic
--xdeltaPrefix="patch/"
--xdeltaPostfix=".xdelta"

Note the use of the regular minecraft binary, instead of minecraft_merged.