Loading Offline Resources in WKWebView with a Local Web Server

1. Background

The author mentioned in the article 《WKWebView》 that WKWebView performs network requests in a process independent of the app process, and the requested data does not pass through the main process. Therefore, using NSURLProtocol directly on WKWebView cannot intercept the request. Therefore, if you need to intercept requests, a feasible solution is to use the private API exposed by Apple's open source Webkit2 source code (see section 3 of the original article for details: NSURLProtocol issue).
However, using private API will inevitably bring about the following problems:

Audit risk
When intercepting http/https, the post request body is lost
If ajax hook is used, there may be post header character length limit, Put type request exception, etc.

From this point of view, before the arrival of iOS11 WKURLSchemeHandler [Explore], the private API was not so perfect.
Fortunately, through searching, we found that the iOS system has the ability to build a server, and it is theoretically possible to implement WKWebView offline resource loading.

2. Analysis

Local web server based on iOS currently has the following relatively complete frameworks:

CocoaHttpServer (Supports iOS, macOS and various network scenarios)
GCDWebServer (based on iOS, does not support https and webSocket)
Telegraph (Swift implementation, more complete functions than the above two categories)

Because most APPs currently support ATS, and most domestic project codes are still implemented using OC, this article will conduct experiments based on CocoaHttpSever.
Telegraph was born to supplement the shortcomings of CocoaHttpSever and GCDWebServer. For pure Swift projects, it is recommended to use Telegraph.

3. First Attempt

After adding CocoaHTTPServer to the project:

First implement a service management.

#import "LocalWebServerManager.h"

#import "HTTPServer.h"
#import "MyHTTPConnection.h"

@interface LocalWebServerManager ()
{
    HTTPServer *_httpServer;
}
@end

@implementation LocalWebServerManager

+ (instancetype)sharedInstance {
    static LocalWebServerManager *_sharedInstance = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        _sharedInstance = [[LocalWebServerManager alloc] init];
    });
    return _sharedInstance;
}

- (void)start {
    
    _port = 60000;
    
    if (!_httpServer) {
        _httpServer = [[HTTPServer alloc] init];
        [_httpServer setType:@"_http._tcp."];
        [_httpServer setPort:_port];
        NSString * webLocalPath = [[[NSBundle mainBundle] resourcePath] stringByAppendingPathComponent:@"Resource"];
        [_httpServer setDocumentRoot:webLocalPath];
        
        NSLog(@"Setting document root: %@", webLocalPath);
        
    }
    
    if (_httpServer && ![_httpServer isRunning]) {
        NSError *error;
        if([_httpServer start:&error]) {
            NSLog(@"start server success in port %d %@", [_httpServer listeningPort], [_httpServer publishedName]);
        } else {
            NSLog(@"Start failed");
        }
    }
    
}

- (void)stop {
    if (_httpServer && [_httpServer isRunning]) {
        [_httpServer stop];
    }
}

@end

Then select its startup time, usually in AppDelegate or before WKWebView request.

- (void)viewDidLoad {
    [super viewDidLoad];
    
    //Setup WKWebView
    WKWebViewConfiguration *configuration = [[WKWebViewConfiguration alloc] init];
    WKUserContentController *controller = [[WKUserContentController alloc] init];
    configuration.userContentController = controller;
    configuration.processPool = [[WKProcessPool alloc] init];
    
    _wkWebView = [[WKWebView alloc] initWithFrame:self.view.bounds
                                    configuration:configuration];
    _wkWebView.navigationDelegate = self;
    _wkWebView.UIDelegate = self;
    
    [self.view addSubview:_wkWebView];
    
    //Start local web server
    [[LocalWebServerManager sharedInstance] start];
    
    //Local request which use local resource
    [self loadLocalRequest];
    
    //Remote request which use local resource
//    [self loadRemoteRequest];
}

Add a referenced resource directory (the blue folder) to the project, then create index.html and hi.js in that directory.

<!DOCTYPE html>
<html>
<head>
	<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
	<title>Hello</title>
	<script type="text/javascript" src="http://localhost:60000/hi.js"></script>
</head>
<body bgcolor="#4F8FFF">
    <center>
        <h1><br><br><br><br><br><br>Congratulations! The server is running successfully!</h1>
        <h5><br>Click the button below to try it out</h5>
        <input type='button' value='Calls the method ' in the local js resource onclick='invokeAlert()'/>
    </center>
</body>
</html>

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function invokeAlert() {
    alert('Perfect!')
}

Access http://localhost:60000/index.html through WKWebView.

After the above 4 steps, you can start the iOS local http service and access local html resources through WKWebView.

However, the purpose of this article is "Implementing WKWebView offline resource loading based on LocalWebServer". The so-called offline resource loading refers to: the page resources are on the remote server, and some resources in the page are in the iOS local sandbox.
Based on the above example, that is, index.html should be run on remote services such as nginx or apache, and hi.js should be stored in the resource directory of the app.

Is this feasible? Let's give it a try.
Rename index.html to demo.html and configure it in http://smallfan.net for direct access

- (void)loadRemoteRequest {
    if (_wkWebView) {
        [_wkWebView loadRequest:[NSURLRequest requestWithURL:[NSURL URLWithString:@"http://smallfan.net/demo.html"]]];
    }
}

Experimental result: feasible.
That is to say, it is achieved in the following way: Resources in HTML pages allow requests to local servers.

1	<script type="text/javascript" src="http://localhost:60000/hi.js"></script>

4. Support https

As mentioned before: supporting ATS has become a correct and effective choice.

In Safari and Apple WebKit: In https pages, http requests are not allowed, otherwise they will be blocked.

So if https is already supported, then http://localhost:60000/hi.js in the page must also support https. The problem is that for the https page, we can use a legal certificate issued by the CA for two-way or one-way authentication, but localhost is not a legal host, which means we need to implement a self-signed certificate for it.

4.1 Implement local server self-signed certificate

Because iOS development uses MacOS, the following behavior assumes that OpenSSL has been installed on the system by default.

First go to OpenSSL official website to download the latest version, unzip it and find CA.sh in the app directory, copy it to the root directory, and then run

1	% sh ~/CA.sh -newca

After running, a demoCA directory will be generated, which stores the CA's certificate and private key. At the same time, remember the authorization password you set.
Create a directory

1	% mkdir server

Then create a private key

1	% openssl genrsa -out server/server-key.pem 2048

Create certificate request

1	% openssl req -new -out server/server-req.csr -key server/server-key.pem

At this time, the terminal will ask you to fill in the area, name and other information. Common Name This item must be filled in localhost or 127.0.0.1. If you fill in 127.0.0.1, then the request on the page can only use https://127.0.0.1:60000 and cannot be used. https://localhost:60000, and vice versa.

Self-signed certificate

1	% openssl x509 -req -in server/server-req.csr -out server/server-cert.pem -signkey server/server-key.pem -CA demoCA/cacert.pem -CAkey demoCA/private/cakey.pem -CAcreateserial -days 3650

Export the certificate to .p12 format supported by the browser, remember to export the password (this article is: b123456)

1	% openssl pkcs12 -export -clcerts -in server/server-cert.pem -inkey server/server-key.pem -out server/server.p12

Since then, the self-signed certificate has been generated.

4.2 Configure self-signed certificate

Import the P12 file into the project's resource directory.
Then create MyHttpConnection as a subclass of HttpConnection and override - (BOOL)isSecureServer and sslIdentityAndCertificates.

#import "MyHTTPConnection.h"

@implementation MyHTTPConnection

- (BOOL)isSecureServer {
    return YES;
}

- (NSArray *)sslIdentityAndCertificates {
    
    SecIdentityRef identityRef = NULL;
    SecCertificateRef certificateRef = NULL;
    SecTrustRef trustRef = NULL;
    
    //p12File resource path
    NSString *thePath = [[NSBundle bundleWithPath:[[[NSBundle mainBundle] resourcePath] stringByAppendingPathComponent:@"Resource"]] pathForResource:@"localhost" ofType:@"p12"];
    NSData *PKCS12Data = [[NSData alloc] initWithContentsOfFile:thePath];
    CFDataRef inPKCS12Data = (__bridge CFDataRef)PKCS12Data;
    //p12File export password
    CFStringRef password = CFSTR("b123456");
    const void *keys[] = { kSecImportExportPassphrase };
    const void *values[] = { password };
    CFDictionaryRef optionsDictionary = CFDictionaryCreate(NULL, keys, values, 1, NULL, NULL);
    CFArrayRef items = CFArrayCreate(NULL, 0, 0, NULL);
    
    OSStatus securityError = errSecSuccess;
    securityError =  SecPKCS12Import(inPKCS12Data, optionsDictionary, &items);
    if (securityError == 0) {
        CFDictionaryRef myIdentityAndTrust = CFArrayGetValueAtIndex (items, 0);
        const void *tempIdentity = NULL;
        tempIdentity = CFDictionaryGetValue (myIdentityAndTrust, kSecImportItemIdentity);
        identityRef = (SecIdentityRef)tempIdentity;
        const void *tempTrust = NULL;
        tempTrust = CFDictionaryGetValue (myIdentityAndTrust, kSecImportItemTrust);
        trustRef = (SecTrustRef)tempTrust;
    } else {
        NSLog(@"Failed with error code %d",(int)securityError);
        return nil;
    }
    
    SecIdentityCopyCertificate(identityRef, &certificateRef);
    NSArray *result = [[NSArray alloc] initWithObjects:(__bridge id)identityRef, (__bridge id)certificateRef, nil];
    
    return result;
}

@end

Place HTTPConnetion.m in the startConnection method

1	[settings setObject:(NSString )kCFStreamSocketSecurityLevelNegotiatedSSL forKey:(NSString )kCFStreamSSLLevel];

Replace with

1 2	[settings setObject:@"2" forKey:GCDAsyncSocketSSLProtocolVersionMin]; [settings setObject:@"2" forKey:GCDAsyncSocketSSLProtocolVersionMax];

At the same time, before starting HTTPServer (calling startServer), use the setConnectionClass method to replace HTTPConnecdtion with MyHTTPConnection

1	[_httpServer setConnectionClass:[MyHTTPConnection class]];

Since then, the https service configuration is completed.

4.3 WKWebView certificate configuration

For self-signed certificates, WKWebView needs to allow in the WKNavagationDelegate method:

-                   (void)webView:(WKWebView *)webView
didReceiveAuthenticationChallenge:(NSURLAuthenticationChallenge *)challenge
                completionHandler:(void (^)(NSURLSessionAuthChallengeDisposition disposition, NSURLCredential * _Nullable credential))completionHandler {
    
    if ([challenge.protectionSpace.authenticationMethod isEqualToString:NSURLAuthenticationMethodServerTrust]) {
        NSURLCredential *card = [[NSURLCredential alloc] initWithTrust:challenge.protectionSpace.serverTrust];
        completionHandler(NSURLSessionAuthChallengeUseCredential, card);
    }
}

4.4 ATS settings

In Info.plist, find the App Transport Security Settings item, add one item Allow Arbitrary Loads in Web Content and set it to YES

<key>NSAppTransportSecurity</key>
	<dict>
		<key>NSAllowsArbitraryLoadsForMedia</key>
		<true/>
		<key>NSAllowsArbitraryLoadsInWebContent</key>
		<true/>
		<key>NSAllowsArbitraryLoads</key>
		<false/>
	</dict>

Through the above configuration, you can achieve https request local resources

1	<script type="text/javascript" src="https://localhost:60000/hi.js"></script>

- (void)loadRemoteRequest {
    if (_wkWebView) {
        [_wkWebView loadRequest:[NSURLRequest requestWithURL:[NSURL URLWithString:@"https://smallfan.net/demo.html"]]];
    }
}

- (void)loadLocalRequest {
    if (_wkWebView) {
        [_wkWebView loadRequest:[NSURLRequest requestWithURL:[NSURL URLWithString:[NSString stringWithFormat:@"https://localhost:%ld/index.html", [[LocalWebServerManager sharedInstance] port] ] ]]];
    }
}

5. Summary

In fact, this method of implementing WKWebView offline loading is a strange trick. Because of Apple's closed ecosystem, it is often difficult to optimize some existing things, and we can only continue to explore.
From this perspective, Python is more fun, 23333…

Regarding some issues in local web server, the author has not had time to conduct more in-depth research in the future. Here are some possible issues. Everyone is welcome to discuss them:

Resource access permission security issues
When switching between the front and backend of the app, the service restart performance is time consuming.
When the service is running, power and CPU usage issues
Multi-threading and disk IO issues

Finally, throw out a Demo, Biu...
Demo address: LocalWebServer

一、背景

笔者在《WKWebView》一文中提到过，WKWebView 在独立于 app 进程之外的进程中执行网络请求，请求数据不经过主进程，因此，在 WKWebView 上直接使用 NSURLProtocol 无法拦截请求。所以如果需要使用到拦截请求，有种可行地方案是使用苹果开源的 Webkit2 源码暴露的私有API（详见原文第3小节：NSURLProtocol问题）。
但使用私有API，必然带来以下几个问题：

审核风险
拦截http/https时，post请求body丢失
如使用ajax hook方式，可能存在 post header字符长度限制 、Put类型请求异常 等

由此看来，在 iOS11 WKURLSchemeHandler [探究] 到来之前，私有API并不那么完美。
所幸通过寻找发现，iOS系统上具备搭建服务器能力，理论上对实现 WKWebView 离线资源加载 存在可能性。

二、分析

基于iOS的local web server，目前大致有以下几种较为完善的框架：

CocoaHttpServer (支持iOS、macOS及多种网络场景)
GCDWebServer （基于iOS，不支持 https 及 webSocket）
Telegraph （Swift实现，功能较上面两类更完善）

因为目前大部分APP已经支持ATS，且国内大部分项目代码仍采用OC实现，故本文将以 CocoaHttpSever 为基础进行实验。
Telegraph 是为补充 CocoaHttpSever 及 GCDWebServer 不足而诞生，对于纯Swift项目，推荐使用 Telegraph 。

三、初出茅驴

在 project工程文件中引入 CocoaHttpServer 之后，

首先实现一个服务管理。

#import "LocalWebServerManager.h"

#import "HTTPServer.h"
#import "MyHTTPConnection.h"

@interface LocalWebServerManager ()
{
    HTTPServer *_httpServer;
}
@end

@implementation LocalWebServerManager

+ (instancetype)sharedInstance {
    static LocalWebServerManager *_sharedInstance = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        _sharedInstance = [[LocalWebServerManager alloc] init];
    });
    return _sharedInstance;
}

- (void)start {
    
    _port = 60000;
    
    if (!_httpServer) {
        _httpServer = [[HTTPServer alloc] init];
        [_httpServer setType:@"_http._tcp."];
        [_httpServer setPort:_port];
        NSString * webLocalPath = [[[NSBundle mainBundle] resourcePath] stringByAppendingPathComponent:@"Resource"];
        [_httpServer setDocumentRoot:webLocalPath];
        
        NSLog(@"Setting document root: %@", webLocalPath);
        
    }
    
    if (_httpServer && ![_httpServer isRunning]) {
        NSError *error;
        if([_httpServer start:&error]) {
            NSLog(@"start server success in port %d %@", [_httpServer listeningPort], [_httpServer publishedName]);
        } else {
            NSLog(@"启动失败");
        }
    }
    
}

- (void)stop {
    if (_httpServer && [_httpServer isRunning]) {
        [_httpServer stop];
    }
}

@end

然后选择其启动时机，一般选择在 AppDelegate 中或 WKWebView 请求之前。

- (void)viewDidLoad {
    [super viewDidLoad];
    
    //Setup WKWebView
    WKWebViewConfiguration *configuration = [[WKWebViewConfiguration alloc] init];
    WKUserContentController *controller = [[WKUserContentController alloc] init];
    configuration.userContentController = controller;
    configuration.processPool = [[WKProcessPool alloc] init];
    
    _wkWebView = [[WKWebView alloc] initWithFrame:self.view.bounds
                                    configuration:configuration];
    _wkWebView.navigationDelegate = self;
    _wkWebView.UIDelegate = self;
    
    [self.view addSubview:_wkWebView];
    
    //Start local web server
    [[LocalWebServerManager sharedInstance] start];
    
    //Local request which use local resource
    [self loadLocalRequest];
    
    //Remote request which use local resource
//    [self loadRemoteRequest];
}

在 project工程中引入相对资源目录（蓝色文件夹），在该目录中实现一个 index.html 和 hi.js 资源文件

<!DOCTYPE html>
<html>
<head>
	<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
	<title>Hello</title>
	<script type="text/javascript" src="http://localhost:60000/hi.js"></script>
</head>
<body bgcolor="#4F8FFF">
    <center>
        <h1><br><br><br><br><br><br>恭喜你 服务器运行成功!</h1>
        <h5><br>点击下面按钮试一下</h5>
        <input type='button' value='调用本地js资源中的方法' onclick='invokeAlert()'/>
    </center>
</body>
</html>

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function invokeAlert() {
    alert('Perfect!')
}

通过WKWebView访问 http://localhost:60000/index.html 即可。

通过以上4步，即可开启iOS本地http服务，通过WKWebView访问本地的html资源。

不过本文目的是 “基于LocalWebServer实现WKWebView离线资源加载”，所谓离线资源加载，指的是：页面资源在远端服务器，而页面中的部分资源在iOS本地沙盒中。
放在上面的例子上，也就是 index.html 应该在远程的 nginx 或 apache 等服务上运行，而 hi.js 应该存放在APP的资源目录之中。

此举是否可行呢？我们试试看。
将 index.html 改名为 demo.html 配置在 http://smallfan.net 中，直接进行访问

- (void)loadRemoteRequest {
    if (_wkWebView) {
        [_wkWebView loadRequest:[NSURLRequest requestWithURL:[NSURL URLWithString:@"http://smallfan.net/demo.html"]]];
    }
}

实验结果：可行。
也就是说，通过以下该方式实现：HTML页面内资源允许请求本地服务器。

1	<script type="text/javascript" src="http://localhost:60000/hi.js"></script>

四、支持https

正如前面所提：支持ATS已经成为一个正确而有效的选择。

在 Safari 及 Apple WebKit 中：在https页面内，不允许http请求存在，否则一概会被block。

因此如果已经支持了https，那么页面中的 http://localhost:60000/hi.js 也必须支持https才行。问题是，页面https我们可以采用CA颁发的合法证书进行双向或单向认证，而localhost并不是一个合法的host，也就是说我们需要为它实现一个自签名证书。

4.1 实现local server自签名证书

因为iOS开发使用MacOS，以下行为默认系统已经安装OpenSSL。

首先到 OpenSSL官网下载最新版本，解压后在app目录中找到CA.sh，拷贝到根目录，然后运行

1	% sh ~/CA.sh -newca

运行完后会生成一个demoCA的目录，里面存放了CA的证书和私钥，同时记住自己设置的授权密码。
创建一个目录

1	% mkdir server

然后创建一个私钥

1	% openssl genrsa -out server/server-key.pem 2048

创建证书请求

1	% openssl req -new -out server/server-req.csr -key server/server-key.pem

此时终端会要求你填写地区、姓名等信息，Common Name 这一项必须填 localhost 或者 127.0.0.1 ，如果填写127.0.0.1，那么页面中请求只能使用https://127.0.0.1:60000 而不能使用 https://localhost:60000，反之相同。

自签署证书

1	% openssl x509 -req -in server/server-req.csr -out server/server-cert.pem -signkey server/server-key.pem -CA demoCA/cacert.pem -CAkey demoCA/private/cakey.pem -CAcreateserial -days 3650

将证书导出成浏览器支持的.p12格式，记得导出密码（本文为: b123456）

1	% openssl pkcs12 -export -clcerts -in server/server-cert.pem -inkey server/server-key.pem -out server/server.p12

自此，自签名证书生成完成。

4.2 配置自签名证书

将p12文件导入 project工程中的资源目录中，
同时新建一个 MyHttpConnection 继承于 HttpConnection ，重载 - (BOOL)isSecureServer 方法及 sslIdentityAndCertificates 方法。

#import "MyHTTPConnection.h"

@implementation MyHTTPConnection

- (BOOL)isSecureServer {
    return YES;
}

- (NSArray *)sslIdentityAndCertificates {
    
    SecIdentityRef identityRef = NULL;
    SecCertificateRef certificateRef = NULL;
    SecTrustRef trustRef = NULL;
    
    //p12文件资源路径
    NSString *thePath = [[NSBundle bundleWithPath:[[[NSBundle mainBundle] resourcePath] stringByAppendingPathComponent:@"Resource"]] pathForResource:@"localhost" ofType:@"p12"];
    NSData *PKCS12Data = [[NSData alloc] initWithContentsOfFile:thePath];
    CFDataRef inPKCS12Data = (__bridge CFDataRef)PKCS12Data;
    //p12文件导出密码
    CFStringRef password = CFSTR("b123456");
    const void *keys[] = { kSecImportExportPassphrase };
    const void *values[] = { password };
    CFDictionaryRef optionsDictionary = CFDictionaryCreate(NULL, keys, values, 1, NULL, NULL);
    CFArrayRef items = CFArrayCreate(NULL, 0, 0, NULL);
    
    OSStatus securityError = errSecSuccess;
    securityError =  SecPKCS12Import(inPKCS12Data, optionsDictionary, &items);
    if (securityError == 0) {
        CFDictionaryRef myIdentityAndTrust = CFArrayGetValueAtIndex (items, 0);
        const void *tempIdentity = NULL;
        tempIdentity = CFDictionaryGetValue (myIdentityAndTrust, kSecImportItemIdentity);
        identityRef = (SecIdentityRef)tempIdentity;
        const void *tempTrust = NULL;
        tempTrust = CFDictionaryGetValue (myIdentityAndTrust, kSecImportItemTrust);
        trustRef = (SecTrustRef)tempTrust;
    } else {
        NSLog(@"Failed with error code %d",(int)securityError);
        return nil;
    }
    
    SecIdentityCopyCertificate(identityRef, &certificateRef);
    NSArray *result = [[NSArray alloc] initWithObjects:(__bridge id)identityRef, (__bridge id)certificateRef, nil];
    
    return result;
}

@end

将 HTTPConnetion.m 的 startConnection 方法中

1	[settings setObject:(NSString )kCFStreamSocketSecurityLevelNegotiatedSSL forKey:(NSString )kCFStreamSSLLevel];

替换为

1 2	[settings setObject:@"2" forKey:GCDAsyncSocketSSLProtocolVersionMin]; [settings setObject:@"2" forKey:GCDAsyncSocketSSLProtocolVersionMax];

同时在启动 HTTPServer（调用 startServer ）之前，使用 setConnectionClass 方法将 HTTPConnecdtion 替换为 MyHTTPConnection

1	[_httpServer setConnectionClass:[MyHTTPConnection class]];

自此，https服务配置完成。

4.3 WKWebView证书配置

对于自签名证书，WKWebView需要在WKNavagationDelegate方法中允许使用：

-                   (void)webView:(WKWebView *)webView
didReceiveAuthenticationChallenge:(NSURLAuthenticationChallenge *)challenge
                completionHandler:(void (^)(NSURLSessionAuthChallengeDisposition disposition, NSURLCredential * _Nullable credential))completionHandler {
    
    if ([challenge.protectionSpace.authenticationMethod isEqualToString:NSURLAuthenticationMethodServerTrust]) {
        NSURLCredential *card = [[NSURLCredential alloc] initWithTrust:challenge.protectionSpace.serverTrust];
        completionHandler(NSURLSessionAuthChallengeUseCredential, card);
    }
}

4.4 ATS设置

在 Info.plist 中，找到 App Transport Security Settings 项，在其中增加一项 Allow Arbitrary Loads in Web Content 设为 YES

<key>NSAppTransportSecurity</key>
	<dict>
		<key>NSAllowsArbitraryLoadsForMedia</key>
		<true/>
		<key>NSAllowsArbitraryLoadsInWebContent</key>
		<true/>
		<key>NSAllowsArbitraryLoads</key>
		<false/>
	</dict>

通过以上配置，即可实现 https 请求本地资源

1	<script type="text/javascript" src="https://localhost:60000/hi.js"></script>

- (void)loadRemoteRequest {
    if (_wkWebView) {
        [_wkWebView loadRequest:[NSURLRequest requestWithURL:[NSURL URLWithString:@"https://smallfan.net/demo.html"]]];
    }
}

- (void)loadLocalRequest {
    if (_wkWebView) {
        [_wkWebView loadRequest:[NSURLRequest requestWithURL:[NSURL URLWithString:[NSString stringWithFormat:@"https://localhost:%ld/index.html", [[LocalWebServerManager sharedInstance] port] ] ]]];
    }
}

五、小结

实际上这种方式实现 WKWebView 离线加载，属于奇技淫巧。因为 Apple 封闭的生态，很多时候想优化一些既有的东西举步维艰，只能不断探索。
从这个角度来看，还是 Python 好玩点，23333 …

关于 local web server 中有些问题，笔者并未来得及作更深入研究，以下列举一些可能性问题，欢迎大家一起探讨：

资源访问权限安全问题
APP前后台切换时，服务重启性能耗时问题
服务运行时，电量及CPU占有率问题
多线程及磁盘IO问题

最后，丢个Demo出来，Biu…
Demo地址：LocalWebServer

Smallfan