NSURLSession和亚马逊S3上传

Question

我有一个应用程序,目前正在上传图像到亚马逊S3.我一直在尝试将它从使用NSURLConnection切换到NSURLSession,以便在应用程序处于后台时上传可以继续!我似乎遇到了一些问题.创建NSURLRequest并将其传递给NSURLSession,但亚马逊发回403禁止响应,如果我将相同的请求传递给NSURLConnection,则它会完美地上传文件.

以下是创建响应的代码:

NSString *requestURLString = [NSString stringWithFormat:@"http://%@.%@/%@/%@", BUCKET_NAME, AWS_HOST, DIRECTORY_NAME, filename];
NSURL *requestURL = [NSURL URLWithString:requestURLString];
NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:requestURL
                                                       cachePolicy:NSURLRequestReloadIgnoringLocalAndRemoteCacheData
                                                   timeoutInterval:60.0];
// Configure request
[request setHTTPMethod:@"PUT"];
[request setValue:[NSString stringWithFormat:@"%@.%@", BUCKET_NAME, AWS_HOST] forHTTPHeaderField:@"Host"];
[request setValue:[self formattedDateString] forHTTPHeaderField:@"Date"];
[request setValue:@"public-read" forHTTPHeaderField:@"x-amz-acl"];
[request setHTTPBody:imageData];

然后这标志着回应(我认为这来自另一个SO回答):

NSString *contentMd5  = [request valueForHTTPHeaderField:@"Content-MD5"];
NSString *contentType = [request valueForHTTPHeaderField:@"Content-Type"];
NSString *timestamp   = [request valueForHTTPHeaderField:@"Date"];

if (nil == contentMd5)  contentMd5  = @"";
if (nil == contentType) contentType = @"";

NSMutableString *canonicalizedAmzHeaders = [NSMutableString string];

NSArray *sortedHeaders = [[[request allHTTPHeaderFields] allKeys] sortedArrayUsingSelector:@selector(caseInsensitiveCompare:)];

for (id key in sortedHeaders)
{
    NSString *keyName = [(NSString *)key lowercaseString];
    if ([keyName hasPrefix:@"x-amz-"]){
        [canonicalizedAmzHeaders appendFormat:@"%@:%@\n", keyName, [request valueForHTTPHeaderField:(NSString *)key]];
    }
}

NSString *bucket = @"";
NSString *path   = request.URL.path;
NSString *query  = request.URL.query;

NSString *host  = [request valueForHTTPHeaderField:@"Host"];

if (![host isEqualToString:@"s3.amazonaws.com"]) {
    bucket = [host substringToIndex:[host rangeOfString:@".s3.amazonaws.com"].location];
}

NSString* canonicalizedResource;

if (nil == path || path.length < 1) {
    if ( nil == bucket || bucket.length < 1 ) {
        canonicalizedResource = @"/";
    }
    else {
        canonicalizedResource = [NSString stringWithFormat:@"/%@/", bucket];
    }
}
else {
    canonicalizedResource = [NSString stringWithFormat:@"/%@%@", bucket, path];
}

if (query != nil && [query length] > 0) {
    canonicalizedResource = [canonicalizedResource stringByAppendingFormat:@"?%@", query];
}

NSString* stringToSign = [NSString stringWithFormat:@"%@\n%@\n%@\n%@\n%@%@", [request HTTPMethod], contentMd5, contentType, timestamp, canonicalizedAmzHeaders, canonicalizedResource];

NSString *signature = [self signatureForString:stringToSign];

[request setValue:[NSString stringWithFormat:@"AWS %@:%@", self.S3AccessKey, signature] forHTTPHeaderField:@"Authorization"];

然后,如果我使用这行代码:

[NSURLConnection connectionWithRequest:request delegate:self];

它工作并上传文件,但如果我使用:

NSURLSessionUploadTask *task = [self.session uploadTaskWithRequest:request fromFile:[NSURL fileURLWithPath:filePath]];
[task resume];

我得到了禁止的错误..!？

有没有人尝试使用此功能上传到S3并遇到类似问题？我想知道它是否与会话暂停和恢复上传的方式有关,或者是对请求做了一些有趣的事情......？

一种可能的解决方案是将文件上传到我控制的临时服务器,并在完成后将其转发到S3 ......但这显然不是理想的解决方案!

任何帮助深表感谢!!

谢谢!

Answer 1

我根据Zeev Vax的答案做了它的工作.我想对我遇到的问题提供一些见解并提供一些小改进.

例如,构建一个普通的PutRequest

S3PutObjectRequest* putRequest = [[S3PutObjectRequest alloc] initWithKey:keyName inBucket:bucketName];

putRequest.credentials = credentials;
putRequest.filename = theFilePath;

现在我们需要做一些S3Client通常为我们做的工作

// set the endpoint, so it is not null
putRequest.endpoint = s3Client.endpoint;

// if you are using session based authentication, otherwise leave it out
putRequest.securityToken = messageTokenDTO.securityToken;

// sign the request (also computes md5 checksums etc.)
NSMutableURLRequest *request = [s3Client signS3Request:putRequest];

现在将所有这些复制到新请求中.亚马逊使用自己的NSUrlRequest类,这会导致异常

NSMutableURLRequest* request2 = [[NSMutableURLRequest alloc]initWithURL:request.URL];
[request2 setHTTPMethod:request.HTTPMethod];
[request2 setAllHTTPHeaderFields:[request allHTTPHeaderFields]];

现在我们可以开始实际转移了

NSURLSession* backgroundSession = [self backgroundSession];
_uploadTask = [backgroundSession uploadTaskWithRequest:request2 fromFile:[NSURL fileURLWithPath:theFilePath]];
[_uploadTask resume];

这是创建后台会话的代码:

- (NSURLSession *)backgroundSession {
    static NSURLSession *session = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{

        NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration backgroundSessionConfiguration:@"com.example.my.unique.id"];
        session = [NSURLSession sessionWithConfiguration:configuration delegate:self delegateQueue:nil];
    });

    return session;
}

我花了一段时间才弄清楚会话/任务委托需要处理auth挑战(我们实际上是对s3的身份验证).所以只需实施

- (void)URLSession:(NSURLSession *)session didReceiveChallenge:(NSURLAuthenticationChallenge *)challenge completionHandler:(void (^)(NSURLSessionAuthChallengeDisposition, NSURLCredential *))completionHandler {
    NSLog(@"session did receive challenge");
    completionHandler(NSURLSessionAuthChallengePerformDefaultHandling, nil);
}

Answer 2

这里的答案有点过时,我花了很多时间试图在Swift和新的AWS SDK中完成这项工作.所以这里是如何使用新的AWSS3PreSignedURLBuilder(在2.0.7+版本中提供)在Swift中完成的:

class S3BackgroundUpload : NSObject {

    // Swift doesn't support static properties yet, so have to use structs to achieve the same thing.
    struct Static {
        static var session : NSURLSession?
    }

    override init() {
        super.init()

        // Note: There are probably safer ways to store the AWS credentials.
        let configPath = NSBundle.mainBundle().pathForResource("appconfig", ofType: "plist")
        let config = NSDictionary(contentsOfFile: configPath!)
        let accessKey = config.objectForKey("awsAccessKeyId") as String?
        let secretKey = config.objectForKey("awsSecretAccessKey") as String?
        let credentialsProvider = AWSStaticCredentialsProvider .credentialsWithAccessKey(accessKey!, secretKey: secretKey!)

        // AWSRegionType.USEast1 is the default S3 endpoint (use it if you don't need specific endpoints such as s3-us-west-2.amazonaws.com)
        let configuration = AWSServiceConfiguration(region: AWSRegionType.USEast1, credentialsProvider: credentialsProvider)

        // This is setting the configuration for all AWS services, you can also pass in this configuration to the AWSS3PreSignedURLBuilder directly.
        AWSServiceManager.defaultServiceManager().setDefaultServiceConfiguration(configuration)

        if Static.session == nil {
            let configIdentifier = "com.example.s3-background-upload"

            var config : NSURLSessionConfiguration
            if NSURLSessionConfiguration.respondsToSelector("backgroundSessionConfigurationWithIdentifier:") {
                // iOS8
                config = NSURLSessionConfiguration.backgroundSessionConfigurationWithIdentifier(configIdentifier)
            } else {
                // iOS7
                config = NSURLSessionConfiguration.backgroundSessionConfiguration(configIdentifier)
            }

            // NSURLSession background sessions *need* to have a delegate.
            Static.session = NSURLSession(configuration: config, delegate: self, delegateQueue: nil)
        }
    }

    func upload() {
        let s3path = "/some/path/some_file.jpg"
        let filePath = "/var/etc/etc/some_file.jpg"

        // Check if the file actually exists to prevent weird uncaught obj-c exceptions.
        if NSFileManager.defaultManager().fileExistsAtPath(filePath) == false {
            NSLog("file does not exist at %@", filePath)
            return
        }

        // NSURLSession needs the filepath in a "file://" NSURL format.
        let fileUrl = NSURL(string: "file://\(filePath)")

        let preSignedReq = AWSS3GetPreSignedURLRequest()
        preSignedReq.bucket = "bucket-name"
        preSignedReq.key = s3path
        preSignedReq.HTTPMethod = AWSHTTPMethod.PUT                   // required
        preSignedReq.contentType = "image/jpeg"                       // required
        preSignedReq.expires = NSDate(timeIntervalSinceNow: 60*60)    // required

        // The defaultS3PreSignedURLBuilder uses the global config, as specified in the init method.
        let urlBuilder = AWSS3PreSignedURLBuilder.defaultS3PreSignedURLBuilder()

        // The new AWS SDK uses BFTasks to chain requests together:
        urlBuilder.getPreSignedURL(preSignedReq).continueWithBlock { (task) -> AnyObject! in

            if task.error != nil {
                NSLog("getPreSignedURL error: %@", task.error)
                return nil
            }

            var preSignedUrl = task.result as NSURL
            NSLog("preSignedUrl: %@", preSignedUrl)

            var request = NSMutableURLRequest(URL: preSignedUrl)
            request.cachePolicy = NSURLRequestCachePolicy.ReloadIgnoringLocalCacheData

            // Make sure the content-type and http method are the same as in preSignedReq
            request.HTTPMethod = "PUT"
            request.setValue(preSignedReq.contentType, forHTTPHeaderField: "Content-Type")

            // NSURLSession background session does *not* support completionHandler, so don't set it.
            let uploadTask = Static.session?.uploadTaskWithRequest(request, fromFile: fileUrl)

            // Start the upload task:
            uploadTask?.resume()

            return nil
        }
    }
}

extension S3BackgroundUpload : NSURLSessionDelegate {

    func URLSession(session: NSURLSession, dataTask: NSURLSessionDataTask, didReceiveData data: NSData) {
        NSLog("did receive data: %@", NSString(data: data, encoding: NSUTF8StringEncoding))
    }

    func URLSession(session: NSURLSession, task: NSURLSessionTask, didCompleteWithError error: NSError?) {
        NSLog("session did complete")
        if error != nil {
            NSLog("error: %@", error!.localizedDescription)
        }
        // Finish up your post-upload tasks.
    }
}

Answer 3

我NSURLSessionUploadTask还不太清楚，但我可以告诉你我将如何调试它。

我会使用Charles之类的工具来查看我的应用程序发出的 HTTP(S) 请求。问题可能是NSURLSessionUploadTask忽略您设置的标头，或者它使用与 Amazon S3 预期的文件上传不同的 HTTP 方法。这可以通过拦截代理轻松验证。

此外，当 Amazon S3 返回 403 等错误时，它实际上会发回一个 XML 文档，其中包含有关该错误的更多信息。也许有一个委托方法NSURLSession可以检索响应正文？如果没有，那么查尔斯肯定会给你更多的见解。