为七牛iOS SDK添加ALAsset上传支持

本blog除部分译文外，所有内容均为原创，如有雷同，算我抄你:-)

Update:七牛官方SDK已经加入了对ALAsset的支持。

问题描述

七牛iOS SDK的上传API只有两个

objc@interface QNUploadManager : NSObject

- (void)putData:(NSData *)data
            key:(NSString *)key
          token:(NSString *)token
       complete:(QNUpCompletionHandler)completionHandler
         option:(QNUploadOption *)option;

- (void)putFile:(NSString *)filePath
            key:(NSString *)key
          token:(NSString *)token
       complete:(QNUpCompletionHandler)completionHandler
         option:(QNUploadOption *)option;

@end

其中putFileXXX是针对文件上传的，这个方法内部是依赖NSFileManager来获取文件信息的

objcNSError *error = nil;
NSDictionary *fileAttr = [[NSFileManager defaultManager] attributesOfItemAtPath:filePath error:&error];

NSNumber *fileSizeNumber = fileAttr[NSFileSize];
UInt32 fileSize = [fileSizeNumber intValue];
NSData *data = [NSData dataWithContentsOfFile:filePath options:NSDataReadingMappedIfSafe error:&error];

那么问题来了，对于ALAsset，即系统相册中的图片或视频，获取到的assetURL是类似于如下形式的：

shassets-library://asset/asset.MOV?id=A16D4A3B-664E-4A75-90E8-37EA3F04FF2E&ext=MOV

NSFileManager无法处理，因而无法正确获取文件大小等信息，更不用说上传了。

解决方案

为便于说明，假定有ALAsset实例asset。
首先，通过asset.defaultRepresentation.size能够获取到对应文件的大小。为QNUploadManager创建一个category，如下

objc@interface QNUploadManager (ALAssetSupport)

- (void)putALasset:(ALAsset *)asset
               key:(NSString *)key
             token:(NSString *)token
          complete:(QNUpCompletionHandler)completionHandler
            option:(QNUploadOption *)option;


@end

具体实现如下

objc- (void)putALasset:(ALAsset *)asset
               key:(NSString *)key
             token:(NSString *)token
          complete:(QNUpCompletionHandler)completionHandler
            option:(QNUploadOption *)option
{
    //other code...


        QNResumeUpload *up = [[QNResumeUpload alloc]
                              initWithData:nil
                              withSize:(UInt32)asset.defaultRepresentation.size
                              withKey:key
                              withToken:token
                              withCompletionHandler:complete
                              withOption:option
                              withModifyTime:modifyTime
                              withRecorder:recorder
                              withRecorderKey:recorderKey
                              withHttpManager:[self getHttpManagerProperty]];
        up.asset = asset;
    }
}

从上面的代码可以看到，QNUploadManager实际上只是获取文件信息，做一些预处理，而真正的上传过程是由QNResumeUpload完成的。QNResumeUpload的初始化入参很多，需要注意的是data和size，一个简化版的initXXX如下

objc- (instancetype)initWithData:(NSData *)data
                    withSize:(UInt32)size
                     withOtherParameters:(XXX *)XXX;

其中data是文件句柄打开后的二进制数据，size是数据长度。
你一定已经发现我在putALassetXXX里很弱智地在data这个入参上传入了nil，这是有原因的。
打开QNResumeUpload.m，搜索data后发现，data本身只在2个获取分块数据的方法里涉及到

objc- (void)makeBlock:(NSString *)uphost
           offset:(UInt32)offset
        blockSize:(UInt32)blockSize
        chunkSize:(UInt32)chunkSize
         progress:(QNInternalProgressBlock)progressBlock
         complete:(QNCompleteBlock)complete;

- (void)putChunk:(NSString *)uphost
          offset:(UInt32)offset
            size:(UInt32)size
         context:(NSString *)context
        progress:(QNInternalProgressBlock)progressBlock
        complete:(QNCompleteBlock)complete; 
}

只要override它们，让它们支持ALAsset即可。
首先为QNResumeUpload添加property

objc@class ALAsset;

@interface QNResumeUpload (ALAssetSupport)
@property (nonatomic, strong) ALAsset *asset;

@end

在putALasset方法里会为此属性赋值。
接着写一个获取指定offset和length的data的方法

objc- (NSData *)dataFromALAssetAtOffset:(NSInteger)offset size:(NSInteger)size
{
    ALAssetRepresentation *rep = [self.asset defaultRepresentation];
    Byte *buffer = (Byte *)malloc(size);
    NSUInteger buffered = [rep getBytes:buffer fromOffset:offset length:size error:nil];

    return [NSData dataWithBytesNoCopy:buffer length:buffered freeWhenDone:YES];
}

最后在makeBlock和putChunk里调用此方法即可，以makeBlock为例

objc- (void)makeBlock:(NSString *)uphost
           offset:(UInt32)offset
        blockSize:(UInt32)blockSize
        chunkSize:(UInt32)chunkSize
         progress:(QNInternalProgressBlock)progressBlock
         complete:(QNCompleteBlock)complete
{
    NSData *data = [self dataFromALAssetAtOffset:offset size:chunkSize];//[self.data subdataWithRange:NSMakeRange(offset, (unsigned int)chunkSize)];
    NSString *url = [[NSString alloc] initWithFormat:@"http://%@/mkblk/%u", uphost, (unsigned int)blockSize];

    UInt32 crc = [QNCrc32 data:data];
    [self setChunkCrcValue:crc];

#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wundeclared-selector"
    SEL selector = @selector(post:withData:withCompleteBlock:withProgressBlock:);
#pragma clang diagnostic pop
    void (*typed_msgSend)(id, SEL, NSString *, NSData *, QNCompleteBlock, QNInternalProgressBlock) = (void *)objc_msgSend;
    typed_msgSend(self, selector, url, data, complete, progressBlock);
}