【网络通信】增量更新：资源差分包的生成与应用

---逐文件差分：变更清单驱动
function DiffPack.build(oldDir, newDir, outDir)
    local manifest = {}
    for _, f in ipairs(Scan.files(newDir)) do
        local oldHash = Manifest.hashOf(oldDir, f)
        local newHash = Manifest.hashOf(newDir, f)
        if oldHash ~= newHash then
            local rel = f
            if oldHash then
                -- 老文件存在：做二进制差分
                Bsdiff.make(oldDir .. "/" .. rel,
                    newDir .. "/" .. rel,
                    outDir .. "/" .. rel .. ".patch")
            else
                -- 新增文件：整份进包
                Copy.file(newDir .. "/" .. rel,
                    outDir .. "/" .. rel)
            end
            manifest[#manifest + 1] = {
                path = rel, kind = oldHash and "patch" or "new",
                hash = newHash,
            }
        end
    end
    Manifest.write(outDir .. "/manifest.json", manifest)
    return manifest
end

---客户端应用差分包
function DiffPack.apply(packDir)
    local manifest = Manifest.read(packDir .. "/manifest.json")
    -- 前置校验：本地基线必须匹配
    for _, m in ipairs(manifest) do
        if m.kind == "patch" then
            local localHash = Manifest.hashOf(Res.root, m.path)
            if localHash ~= m.expectOld then
                return false, "基线不符，请走整包"
            end
        end
    end
    for _, m in ipairs(manifest) do
        if m.kind == "patch" then
            Bspatch.apply(Res.root .. "/" .. m.path,
                packDir .. "/" .. m.path .. ".patch")
        else
            Copy.file(packDir .. "/" .. m.path,
                Res.root .. "/" .. m.path)
        end
    end
    return Res.verify(manifest)
end