ShockwaveFlash.Avm1 1.1.0

ShockwaveFlash.Avm1

AVM1 (ActionScript 1/2 bytecode) support for ShockwaveFlash — decode DoAction bytecode to a typed action model, evaluate data scripts to a typed value tree, edit, and write the bytecode back.

Install

dotnet add package ShockwaveFlash.Avm1

Read a data table

Linear data scripts (localization / config tables, common in older games) are replayed to their global variables:

using ShockwaveFlash;
using ShockwaveFlash.Avm1;
using ShockwaveFlash.Tags.Action;

var swf = ShockwaveFlashFile.Disassemble(File.ReadAllBytes("emotes.swf"));
var version = swf.Header.Version;
var tag = swf.Tags.OfType<DoActionTag>().First();

Avm1Object globals = tag.Evaluate(version);
string name = globals["EM"].AsObject["1"].AsObject["n"].AsString;

Edit & write back

Avm1Object / Avm1Array are editable in place, and primitives convert implicitly:

var globals = tag.Evaluate(version);
var emotes = globals["EM"].AsObject;

emotes["1"].AsObject["n"] = "New name";                                             // change
emotes["24"] = new Avm1Object { Members = { ["n"] = "New emote", ["s"] = "new" } }; // add

var output = swf.ReplaceTag(tag, tag.WithGlobals(globals, version)).Assemble();
File.WriteAllBytes("emotes.swf", output.ToArray());

Raw actions

For surgical edits that preserve everything else byte-for-byte, go through the action list instead of the value tree:

var actions = tag.DecodeActions(version);       // IReadOnlyList<Action>
// ... inspect or modify actions ...
var newTag = tag.WithActions(actions, version); // re-encoded; byte-identical when unchanged

Value model

Evaluate returns an Avm1Object whose members are Avm1Values — Avm1String, Avm1Number, Avm1Boolean, Avm1Null, Avm1Undefined, Avm1Object, Avm1Array. Read them with AsObject / AsArray / AsString / AsNumber / AsBoolean.

Notes

• The decoder and encoder cover the documented AVM1 opcode set (SWF 1–7) and round-trip byte-for-byte.
• Avm1Machine is a focused evaluator for linear data scripts — no control-flow or function execution. Opcodes outside the supported subset are collected in UnsupportedOpcodes; pass strict: true to throw Avm1UnsupportedActionException instead of skipping them.

Part of the ShockwaveFlash project · MIT © Aerafal