今天要整理的是：NSURLProtocol
NSURLProtocol是 URL Loading System的一部分，它是一个抽象类，想要使用子类继承并实现、然后注册。
URLLoadingSystem.png
它能干嘛？
拦截基于系统的NSUIConnection或者NSUISession进行封装的网络请求（如使用WKWebView、UIWebView）
单单一个拦截，这里就可以实现很多你想要实现的功能，例如：
- 解决dns域名劫持（白名单或黑名单）
- 加载本地缓存、本地js、css、image等静态资源
- 修改request，重定向
实现
首先实现是继承的NSURLProtocol的子类
#import <Foundation/Foundation.h>
@interface NSURLProtocolCustom : NSURLProtocol
@end
然后在合适的地方进行注册
[NSURLProtocol registerClass:[CustomURLProtocol class]];
一经注册之后，所有交给URL Loading system的网络请求都会被拦截，所以当不需要拦截的时候，要进行注销
[NSURLProtocol unregisterClass:[NSURLProtocolCustom class]];
在CustomURLProtocol里必须要实现的方法：
canInitWithRequest.png
canInitWithRequest 简单的说是请求的入口，所有的请求都会先进入到这里，如果希望拦截下来自己处理，那么就返回YES，否则就返回NO。
需要注意的地方是，当自己去处理这个请求的时候，由于URL Loading System会创建一个CustomURLProtocol实例后通过NSURLConnection去获取数据，NSURLConnection又会调用URL Loading System，这样会造成死循环，解决的方法是通过setProperty:forKey:inRequest:标记那些已经处理过的request，如果是已经处理的就返回NO。
canonicalRequestForRequest.png
通常canonicalRequestForRequest方法你可以直接返回request，但也可以在这里做修改，比如添加header，修改host等
loading.png
当需要自己处理该请求的时候，startLoading便会被调起，在这里你可以处理自己的逻辑。
加载本地js、css资源，缓存h5图片
在实际项目运行中，很多时候我们需要加载h5，但由于h5里有很多基础的js与css，这些基础资源基本不会有变化或者有些资源过大，网络不稳定的情况下会出现加载中断，所以在做webview优化的时候，我们可以抽离出这部分的资源文件，打包到项目里来，然后使用NSURLProtocol来进行加载，以减少这部分文件的网络请求。同样的，h5里的图片资源也可以通过NSURLProtocol加上SDWebImage进行加载并且缓存。
代码：
#import "NSURLProtocolCustom.h"
#import "NSString+PJR.h"
#import "UIImageView+WebCache.h"
#import "NSData+ImageContentType.h"
#import "UIImage+MultiFormat.h"
static NSString* const FilteredKey = @"FilteredKey";
@interface NSURLProtocolCustom ()
@property (nonatomic, strong) NSMutableData *responseData;
@property (nonatomic, strong) NSURLConnection *connection;
@end
@implementation NSURLProtocolCustom
+ (BOOL)canInitWithRequest:(NSURLRequest *)request
{
NSURL *url = request.URL;
NSString *scheme = [url scheme];
if ( ([scheme caseInsensitiveCompare:@"http"] == NSOrderedSame ||
[scheme caseInsensitiveCompare:@"https"] == NSOrderedSame))
{
NSString *requestUrl = url.absoluteString;
NSLog(@"HTTPMethod:%@",request.HTTPMethod);
NSLog(@"Protocol URL:%@",requestUrl);
NSString *extension = url.pathExtension;
if ([requestUrl containsString:@"://resource"]) {
//基础静态资源，h5上已经做了统一路径处理，可以以此：://resource 前序来判断是否需要拦截
if ([extension isEqualToString:@"js"] || [extension isEqualToString:@"css"]) {
NSString *fileName = [[request.URL.absoluteString componentsSeparatedByString:@"/"].lastObject componentsSeparatedByString:@"?"][0];
NSLog(@"fileName is %@",fileName);
//从bundle中读取
NSString *path = [[NSBundle mainBundle] pathForResource:fileName ofType:nil];
//从沙箱读取
// NSString *docPath = [NSHomeDirectory() stringByAppendingPathComponent:@"Documents"];
// NSString *path = [docPath stringByAppendingPathComponent:fileName];
if (path) {
NSLog(@"the file is local file");
return [NSURLProtocol propertyForKey:FilteredKey inRequest:request] == nil;
}
}
}
if ([extension isPicResource]) {
//用sdwebimage来加载图片，间接实现h5图片缓存功能
return [NSURLProtocol propertyForKey:FilteredKey inRequest:request]== nil;
}
}
return NO;
}
+ (NSURLRequest *)canonicalRequestForRequest:(NSURLRequest *)request
{
return request;
}
- (void)startLoading
{
NSURL *url = super.request.URL;
NSString *requestUrl = url.absoluteString;
NSString *extension = url.pathExtension;
NSMutableURLRequest *mutableReqeust = [[self request] mutableCopy];
//标记该请求已经处理
[NSURLProtocol setProperty:@YES forKey:FilteredKey inRequest:mutableReqeust];
if ([requestUrl containsString:@"://resource"]) {
//获取本地资源路径
NSString *fileName = [[requestUrl componentsSeparatedByString:@"/"].lastObject componentsSeparatedByString:@"?"][0];
//从bundle中读取
NSString *path = [[NSBundle mainBundle] pathForResource:fileName ofType:nil];
//从沙箱读取
// NSString *docPath = [NSHomeDirectory() stringByAppendingPathComponent:@"Documents"];
// NSString *path = [docPath stringByAppendingPathComponent:fileName];
if (path) {
//根据路径获取MIMEType
CFStringRef pathExtension = (__bridge_retained CFStringRef)[path pathExtension];
CFStringRef type = UTTypeCreatePreferredIdentifierForTag(kUTTagClassFilenameExtension, pathExtension, NULL);
CFRelease(pathExtension);
//The UTI can be converted to a mime type:
NSString *mimeType = (__bridge_transfer NSString *)UTTypeCopyPreferredTagWithClass(type, kUTTagClassMIMEType);
if (type != NULL)
CFRelease(type);
//加载本地资源
NSData *data = [NSData dataWithContentsOfFile:path];
[self sendResponseWithData:data mimeType:mimeType];
return;
}else{
NSLog(@"%@ is not find",fileName);
}
}else if([extension isPicResource]){
//处理图片缓存
NSString *key = [[SDWebImageManager sharedManager] cacheKeyForURL:url];
UIImage *img = [[SDImageCache sharedImageCache] imageFromDiskCacheForKey:key];
if (img) {
//存在图片缓存
NSData *data = nil;
if ([extension isEqualToString:@"png"]) {
data = UIImagePNGRepresentation(img);
}else{
data = UIImageJPEGRepresentation(img, 1);
}
NSString *mimeType = [NSData sd_contentTypeForImageData:data];
[self sendResponseWithData:data mimeType:mimeType];
return ;
}
self.connection = [NSURLConnection connectionWithRequest:mutableReqeust delegate:self];
}
}
- (void)stopLoading
{
NSLog(@"stopLoading from networld");
if (self.connection) {
[self.connection cancel];
}
}
- (void)sendResponseWithData:(NSData *)data mimeType:(nullable NSString *)mimeType
{
NSLog(@"sendResponseWithData start");
// 这里需要用到MIMEType
NSURLResponse *response = [[NSURLResponse alloc] initWithURL:super.request.URL
MIMEType:mimeType
expectedContentLength:data.length
textEncodingName:nil];
if ([self client]) {
if ([self.client respondsToSelector:@selector(URLProtocol:didReceiveResponse:cacheStoragePolicy:)]) {
[[self client] URLProtocol:self didReceiveResponse:response cacheStoragePolicy:NSURLCacheStorageNotAllowed];
}
if ([self.client respondsToSelector:@selector(URLProtocol:didLoadData:)]) {
[[self client] URLProtocol:self didLoadData:data];
}
if ([self.client respondsToSelector:@selector(URLProtocolDidFinishLoading:)]) {
[[self client] URLProtocolDidFinishLoading:self];
}
}
NSLog(@"sendResponseWithData end");
}
#pragma mark- NSURLConnectionDelegate
- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {
[self.client URLProtocol:self didFailWithError:error];
}
#pragma mark - NSURLConnectionDataDelegate
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
self.responseData = [[NSMutableData alloc] init];
[self.client URLProtocol:self didReceiveResponse:response cacheStoragePolicy:NSURLCacheStorageNotAllowed];
}
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
[self.responseData appendData:data];
[self.client URLProtocol:self didLoadData:data];
}
- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
//缓存图片
UIImage *cacheImage = [UIImage sd_imageWithData:self.responseData];
NSString *key = [[SDWebImageManager sharedManager] cacheKeyForURL:self.request.URL];
[[SDImageCache sharedImageCache] storeImage:cacheImage
recalculateFromImage:NO
imageData:self.responseData
forKey:key
toDisk:YES];
[self.client URLProtocolDidFinishLoading:self];
}
@end
最后
- 对于WKWebView，想要使用NSURLProtocol的话，注册的时候记得加上以下代码
Class cls = NSClassFromString(@"WKBrowsingContextController");
SEL sel = NSSelectorFromString(@"registerSchemeForCustomProtocol:");
if ([(id)cls respondsToSelector:sel]) {
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Warc-performSelector-leaks"
[(id)cls performSelector:sel withObject:@"http"];
[(id)cls performSelector:sel withObject:@"https"];
#pragma clang diagnostic pop
}
- 静态资源如果想要更新，可以单独开接口去下载，保存到沙箱中，同时将读取文件的方式由bundle改为沙箱。
demo
以上便是NSURLProtocol一些介绍，上面提到的加载本地资源文件demo MYLCustom也已经放到github，有兴趣的可以下载研究兼打个call。
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