BinaryenWasmMutator.swift

// Copyright 2026 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

import Foundation

/// A mutator that mutates Wasm modules inside the program using Binaryen's wasm-opt.
public class BinaryenWasmMutator: BaseInstructionMutator {
    private let logger = Logger(withLabel: "BinaryenWasmMutator")

    public init() {
        super.init(maxSimultaneousMutations: 1)
    }

    public override func canMutate(_ instr: Instruction) -> Bool {
        return instr.op is RawWasmModule
    }

    public override func mutate(_ instr: Instruction, _ b: ProgramBuilder) {
        let op = instr.op as! RawWasmModule
        let oldBytes = op.bytes
        let metadata = op.metadata  // Preserve the original metadata (signatures, exports)

        let extraArguments = [
            "--fuzz-preserve-imports-exports"
        ]

        let (mutatedBytes, _) = BinaryenRunner.runWasmOptWithTempFiles(
            fuzzer: b.fuzzer,
            inputBytes: oldBytes,
            extraArguments: extraArguments
        )

        // Create a new RawWasmModule operation with mutated bytes but same metadata
        let newOp = RawWasmModule(bytes: mutatedBytes, metadata: metadata)
        let newInstr = Instruction(newOp, inouts: instr.inouts)
        b.adopt(newInstr)
    }
}