目前iOS端比较常见的视频缓存的实现方式主要有两种:
1、使用iOS自带的AVURLAsset的AVAssetResourceLoader来实现。
2、在客户端搭建local服务器,local服务器作为中间者,代替客户端请求服务器数据,并将获取到的数据缓存,再提供给客户端。
我们项目里使用的是KTVHTTPCache来实现视频缓存,KTVHTTPCache的实现方式就是第二种,项目地址:(https://github.com/ChangbaDevs/KTVHTTPCache)。
具体实现:
KTVHTTPCache的使用比较简单:
NSURL *proxyURL = [KTVHTTPCache proxyURLWithOriginalURL:originalURL];
AVPlayer *player = [AVPlayer playerWithURL:proxyURL];
可以看出,它是将源视频的URL替换成了自己定义格式的URL,这时我们其实请求的就是local服务器了。
核心的流程大概是这样:
几个核心类实现:
1、KTVHCHTTPServer:
用来搭建local server的,内部使用第三方库HTTPServer实现:
创建自己的Connection类继承自HTTPConnection
@interface KTVHCHTTPConnection : HTTPConnection
重写子类方法,返回相应的response类
- (NSObject *)httpResponseForMethod:(NSString *)method URI:(NSString *)path
{
KTVHCLogHTTPConnection(@"%p, Receive request\nmethod : %@\npath : %@\nURL : %@", self, method, path, request.url);
NSDictionary *parameters = [[KTVHCURLTool tool] parseQuery:request.url.query];
NSURL *URL = [NSURL URLWithString:[parameters objectForKey:@"url"]];
KTVHCDataRequest *dataRequest = [[KTVHCDataRequest alloc] initWithURL:URL headers:request.allHeaderFields];
KTVHCHTTPResponse *response = [[KTVHCHTTPResponse alloc] initWithConnection:self dataRequest:dataRequest];
return response;
}
创建response作为Local Server数据返回体,遵循HTTPResponse协议,实现协议方法
@interface KTVHCHTTPResponse : NSObject
实现协议方法
#pragma mark - HTTPResponse
- (NSData *)readDataOfLength:(NSUInteger)length
{
"读取数据最开始的入口"
NSData *data = [self.reader readDataOfLength:length];
KTVHCLogHTTPResponse(@"%p, Read data : %lld", self, (long long)data.length);
if (self.reader.isFinished) {
KTVHCLogHTTPResponse(@"%p, Read data did finished", self);
[self.reader close];
[self.connection responseDidAbort:self];
}
return data;
}
………………(省略,节省篇幅)
这样,当本地发生请求时,就会获取KTVHCHTTPResponse内部方法返回的数据。
2、KTVHCDataReader和KTVHCDataSourceManager
从服务器返回类可以看到,数据的入口是从KTVHCDataReader的readDataOfLength获取的。
#pragma mark - KTVHCDataReader
- (NSData *)readDataOfLength:(NSUInteger)length
{
[self lock];
if (self.isClosed) {
[self unlock];
return nil;
}
if (self.isFinished) {
[self unlock];
return nil;
}
if (self.error) {
[self unlock];
return nil;
}
NSData *data = [self.sourceManager readDataOfLength:length];
if (data.length > 0) {
self->_readedLength += data.length;
if (self.response.contentLength > 0) {
self->_progress = (double)self.readedLength / (double)self.response.contentLength;
}
}
KTVHCLogDataReader(@"%p, Read data : %lld", self, (long long)data.length);
if (self.sourceManager.isFinished) {
KTVHCLogDataReader(@"%p, Read data did finished", self);
self->_finished = YES;
[self close];
}
[self unlock];
return data;
}
从这个方法里我们可以看到,读取数据又走到了KTVHCDataSourceManager中去。
#pragma mark - KTVHCDataReader
- (void)prepareSourceManager
{
"两个数组保存两种数据来源"
NSMutableArray *fileSources = [NSMutableArray array];
NSMutableArray *networkSources = [NSMutableArray array];
long long min = self.request.range.start;
long long max = self.request.range.end;
NSArray *unitItems = self.unit.unitItems;
for (KTVHCDataUnitItem *item in unitItems) {
long long itemMin = item.offset;
long long itemMax = item.offset + item.length - 1;
if (itemMax < min || itemMin > max) {
continue;
}
if (min > itemMin) {
itemMin = min;
}
if (max < itemMax) {
itemMax = max;
}
min = itemMax + 1;
KTVHCRange range = KTVHCMakeRange(item.offset, item.offset + item.length - 1);
KTVHCRange readRange = KTVHCMakeRange(itemMin - item.offset, itemMax - item.offset);
KTVHCDataFileSource *source = [[KTVHCDataFileSource alloc] initWithPath:item.absolutePath range:range readRange:readRange];
[fileSources addObject:source];
}
[fileSources sortUsingComparator:^NSComparisonResult(KTVHCDataFileSource *obj1, KTVHCDataFileSource *obj2) {
if (obj1.range.start < obj2.range.start) {
return NSOrderedAscending;
}
return NSOrderedDescending;
}];
"对比本地已缓存的数据和视频数据量"
"除了本地的如果还有未获取的数据,就需要网络请求获取了"
long long offset = self.request.range.start;
long long length = KTVHCRangeIsFull(self.request.range) ? KTVHCRangeGetLength(self.request.range) : (self.request.range.end - offset + 1);
for (KTVHCDataFileSource *obj in fileSources) {
long long delta = obj.range.start + obj.readRange.start - offset;
if (delta > 0) {
KTVHCRange range = KTVHCMakeRange(offset, offset + delta - 1);
KTVHCDataRequest *request = [self.request newRequestWithRange:range];
KTVHCDataNetworkSource *source = [[KTVHCDataNetworkSource alloc] initWithRequest:request];
[networkSources addObject:source];
offset += delta;
length -= delta;
}
offset += KTVHCRangeGetLength(obj.readRange);
length -= KTVHCRangeGetLength(obj.readRange);
}
if (length > 0) {
KTVHCRange range = KTVHCMakeRange(offset, self.request.range.end);
KTVHCDataRequest *request = [self.request newRequestWithRange:range];
KTVHCDataNetworkSource *source = [[KTVHCDataNetworkSource alloc] initWithRequest:request];
[networkSources addObject:source];
}
NSMutableArray> *sources = [NSMutableArray array];
[sources addObjectsFromArray:fileSources];
[sources addObjectsFromArray:networkSources];
self.sourceManager = [[KTVHCDataSourceManager alloc] initWithSources:sources delegate:self delegateQueue:self.internalDelegateQueue];
[self.sourceManager prepare];
}
看到KTVHCDataSourceManager的初始化过程, 可以看出其实正常获取数据的是KTVHCDataFileSource和KTVHCDataNetworkSource两个类。
再看一下KTVHCDataSourceManager的readDataOfLength方法:
#pragma mark - KTVHCDataSourceManager
- (NSData *)readDataOfLength:(NSUInteger)length
{
[self lock];
if (self.isClosed) {
[self unlock];
return nil;
}
if (self.isFinished) {
[self unlock];
return nil;
}
if (self.error) {
[self unlock];
return nil;
}
"从Source里读取数据"
NSData *data = [self.currentSource readDataOfLength:length];
self->_readedLength += data.length;
KTVHCLogDataSourceManager(@"%p, Read data : %lld", self, (long long)data.length);
if (self.currentSource.isFinished) {
"一个source读完,切换到下一个Source"
self.currentSource = [self nextSource];
if (self.currentSource) {
KTVHCLogDataSourceManager(@"%p, Switch to next source, %@", self, self.currentSource);
if ([self.currentSource isKindOfClass:[KTVHCDataFileSource class]]) {
[self.currentSource prepare];
}
} else {
KTVHCLogDataSourceManager(@"%p, Read data did finished", self);
self->_finished = YES;
}
}
[self unlock];
return data;
}
**KTVHCDataNetworkSource和KTVHCDataFileSource
从名字就可以看出:这两个类,一个是负责从直接从本地文件提供数据,一个是负责从网络读取之后提供数据
KTVHCDataFileSource的readDataOfLength实现比较明显,就是单纯从文件里读取数据。
看下KTVHCDataNetworkSource:
- (void)ktv_download:(KTVHCDownload *)download didReceiveResponse:(KTVHCDataResponse *)response
{
[self lock];
if (self.isClosed || self.error) {
[self unlock];
return;
}
self->_response = response;
NSString *path = [KTVHCPathTool filePathWithURL:self.request.URL offset:self.request.range.start];
self.unitItem = [[KTVHCDataUnitItem alloc] initWithPath:path offset:self.request.range.start];
KTVHCDataUnit *unit = [[KTVHCDataUnitPool pool] unitWithURL:self.request.URL];
[unit insertUnitItem:self.unitItem];
KTVHCLogDataNetworkSource(@"%p, Receive response\nResponse : %@\nUnit : %@\nUnitItem : %@", self, response, unit, self.unitItem);
[unit workingRelease];
"创建了两个文件句柄,读和写。"
self.writingHandle = [NSFileHandle fileHandleForWritingAtPath:self.unitItem.absolutePath];
self.readingHandle = [NSFileHandle fileHandleForReadingAtPath:self.unitItem.absolutePath];
[self callbackForPrepared];
[self unlock];
}
- (void)ktv_download:(KTVHCDownload *)download didReceiveData:(NSData *)data
{
[self lock];
if (self.isClosed || self.error) {
[self unlock];
return;
}
@try {
"接收到数据之后,写入文件。"
[self.writingHandle writeData:data];
self.downloadLength += data.length;
[self.unitItem updateLength:self.downloadLength];
KTVHCLogDataNetworkSource(@"%p, Receive data : %lld, %lld, %lld", self, (long long)data.length, self.downloadLength, self.unitItem.length);
"有可用数据了,需要回调通知。"
[self callbackForHasAvailableData];
} @catch (NSException *exception) {
NSError *error = [KTVHCError errorForException:exception];
KTVHCLogDataNetworkSource(@"%p, write exception\nError : %@", self, error);
[self callbackForFailed:error];
if (!self.downloadCalledComplete) {
KTVHCLogDataNetworkSource(@"%p, Cancel download task when write exception", self);
[self.downlaodTask cancel];
self.downlaodTask = nil;
}
}
[self unlock];
}
可以看出,两个source的实现比较类似,只不过KTVHCDataNetworkSource多了一个从网络获取数据写入文件的步骤,其实最终提供数据还是通过文件读取的方式。
一旦有可用数据,就通过delegate的方式一直回调,通知response类有可用数据。
#pragma mark - KTVHCHTTPResponse
- (void)ktv_readerDidPrepare:(KTVHCDataReader *)reader
{
KTVHCLogHTTPResponse(@"%p, Prepared", self);
if (self.reader.isPrepared && self.waitingResponse == YES) {
KTVHCLogHTTPResponse(@"%p, Call connection did prepared", self);
[self.connection responseHasAvailableData:self];
}
}
"这个回调获取有可用的数据的通知。"
- (void)ktv_readerHasAvailableData:(KTVHCDataReader *)reader
{
KTVHCLogHTTPResponse(@"%p, Has available data", self);
"这个方法就会触发response的readDataOfLength"
[self.connection responseHasAvailableData:self];
}
- (void)ktv_reader:(KTVHCDataReader *)reader didFailWithError:(NSError *)error
{
KTVHCLogHTTPResponse(@"%p, Failed\nError : %@", self, error);
[self.reader close];
[self.connection responseDidAbort:self];
}