今日头条优化实践： iOS 包大小二进制优化，一行代码减少 60 MB 下载大小

{"type":"doc","content":[{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"摘要"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"苹果对 iOS App 大小有严格限制："},{"type":"text","marks":[{"type":"strong"}],"text":"下载大小"},{"type":"text","text":"超限会阻碍用户在蜂窝网络下载 App ，直接影响新用户转化；"},{"type":"text","marks":[{"type":"strong"}],"text":"可执行文件"},{"type":"text","text":"超限将导致 App 审核被拒，直接影响上架。今日头条探索实践 "},{"type":"text","marks":[{"type":"strong"}],"text":"__TEXT 段迁移"},{"type":"text","text":"技术，成功减小下载大小 "},{"type":"text","marks":[{"type":"strong"}],"text":"32%"},{"type":"text","text":"，并且解决了可执行文件大小受限问题。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"一、背景知识"}]},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"1. 下载大小限制"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"App 大小有下载大小和安装大小的概念。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"下载大小是指 App 压缩包（也就是 .ipa 文件）所占的空间，用户在下载 App 时，下载的是压缩包，这样做可以节省流量；当压缩包下载完成后，就会自动解压，解压过程也就是通常所说的安装过程；安装大小就是指压缩包解压后所占用的空间。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"安装大小在 App Store 上就可以看见 ，通常它会影响用户的下载意愿："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https:\/\/static001.infoq.cn\/resource\/image\/9f\/f9\/9f5e60c538443eae31158760716c55f9.png","alt":null,"title":"","style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":"","fromPaste":false,"pastePass":false}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"而下载大小只有研发人员在 App Store Connect 后台才可以看，用户看不见，它影响的是下载消耗的流量和时长："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https:\/\/static001.infoq.cn\/resource\/image\/c4\/fa\/c4e5c8fd2d0dc9ebd2481915434740fa.png","alt":null,"title":"","style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":"","fromPaste":false,"pastePass":false}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"若"},{"type":"text","marks":[{"type":"strong"}],"text":"下载大小"},{"type":"text","text":"超过限制，将无法使用蜂窝网络下载 App（ iOS 13 之前），会收到文件容量太大的提示，需通过 Wi-Fi 网络下载。如下，为苹果历年来对 App 下载大小限制的变化情况："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"bulletedlist","content":[{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"2008 年 7 月，搭载了 App Store 的 iPhone 3G 正式发售，下载限制仅为 10 MB"}]}]}]}]}