AFNetworking 2.0 多部分请求正文空白

如同这个问题 https://stackoverflow.com/questions/20774692/afnetworking-multipart-request-body-is-nil.

使用 AFNetworking 2.0.3 并尝试使用 AFHTTPSessionManager 的 POST + ConstructionBodyWithBlock 上传图像。由于未知的原因，当向服务器发出请求时，HTTP 帖子正文似乎始终为空。

我在下面继承了 AFHTTPSessionManager （因此使用[self POST ...].

我尝试过以两种方式构建请求。

Method 1：我只是尝试传递参数，然后仅添加图像数据（如果存在）。

- (void) createNewAccount:(NSString *)nickname accountType:(NSInteger)accountType primaryPhoto:(UIImage *)primaryPhoto
{
    NSString *accessToken = self.accessToken;

    // Ensure none of the params are nil, otherwise it'll mess up our dictionary
    if (!nickname) nickname = @"";
    if (!accessToken) accessToken = @"";

    NSDictionary *params = @{@"nickname": nickname,
                             @"type": [[NSNumber alloc] initWithInteger:accountType],
                             @"access_token": accessToken};
    NSLog(@"Creating new account %@", params);

    [self POST:@"accounts" parameters:params constructingBodyWithBlock:^(id<AFMultipartFormData> formData) {
        if (primaryPhoto) {
            [formData appendPartWithFileData:UIImageJPEGRepresentation(primaryPhoto, 1.0)
                                        name:@"primary_photo"
                                    fileName:@"image.jpg"
                                    mimeType:@"image/jpeg"];
        }
    } success:^(NSURLSessionDataTask *task, id responseObject) {
        NSLog(@"Created new account successfully");
    } failure:^(NSURLSessionDataTask *task, NSError *error) {
        NSLog(@"Error: couldn't create new account: %@", error);
    }];
}

Method 2：尝试在块本身中构建表单数据：

- (void) createNewAccount:(NSString *)nickname accountType:(NSInteger)accountType primaryPhoto:(UIImage *)primaryPhoto
{
    // Ensure none of the params are nil, otherwise it'll mess up our dictionary
    if (!nickname) nickname = @"";
    NSLog(@"Creating new account %@", params);

    [self POST:@"accounts" parameters:nil constructingBodyWithBlock:^(id<AFMultipartFormData> formData) {
        [formData appendPartWithFormData:[nickname dataUsingEncoding:NSUTF8StringEncoding] name:@"nickname"];
        [formData appendPartWithFormData:[NSData dataWithBytes:&accountType length:sizeof(accountType)] name:@"type"];
        if (self.accessToken)
            [formData appendPartWithFormData:[self.accessToken dataUsingEncoding:NSUTF8StringEncoding] name:@"access_token"];
        if (primaryPhoto) {
            [formData appendPartWithFileData:UIImageJPEGRepresentation(primaryPhoto, 1.0)
                                        name:@"primary_photo"
                                    fileName:@"image.jpg"
                                    mimeType:@"image/jpeg"];
        }
    } success:^(NSURLSessionDataTask *task, id responseObject) {
        NSLog(@"Created new account successfully");
    } failure:^(NSURLSessionDataTask *task, NSError *error) {
        NSLog(@"Error: couldn't create new account: %@", error);
    }];
}

无论使用哪种方法，当 HTTP 请求到达服务器时，都没有 POST 数据或查询字符串参数，只有 HTTP 标头。

Transfer-Encoding: Chunked
Content-Length: 
User-Agent: MyApp/1.0 (iPhone Simulator; iOS 7.0.3; Scale/2.00)
Connection: keep-alive
Host: 127.0.0.1:5000
Accept: */*
Accept-Language: en;q=1, fr;q=0.9, de;q=0.8, zh-Hans;q=0.7, zh-Hant;q=0.6, ja;q=0.5
Content-Type: multipart/form-data; boundary=Boundary+0xAbCdEfGbOuNdArY
Accept-Encoding: gzip, deflate

有什么想法吗？还发布了一个错误AFNetworking 的 github 存储库 https://github.com/AFNetworking/AFNetworking/issues/1732.

罗布是绝对正确的，你看到的问题与（现已关闭）有关第1398期 https://github.com/AFNetworking/AFNetworking/issues/1398。然而，我想提供一个快速的tl；dr，以防其他人在寻找。

首先，这是由github 上的 gberginc https://github.com/gberginc您可以根据以下方式对文件上传进行建模：

NSString* apiUrl = @"http://example.com/upload";

// Prepare a temporary file to store the multipart request prior to sending it to the server due to an alleged
// bug in NSURLSessionTask.
NSString* tmpFilename = [NSString stringWithFormat:@"%f", [NSDate timeIntervalSinceReferenceDate]];
NSURL* tmpFileUrl = [NSURL fileURLWithPath:[NSTemporaryDirectory() stringByAppendingPathComponent:tmpFilename]];

// Create a multipart form request.
NSMutableURLRequest *multipartRequest = [[AFHTTPRequestSerializer serializer] multipartFormRequestWithMethod:@"POST"
                                                                                                   URLString:apiUrl
                                                                                                  parameters:nil constructingBodyWithBlock:^(id<AFMultipartFormData> formData)
                                         {
                                             [formData appendPartWithFileURL:[NSURL fileURLWithPath:filePath]
                                                                        name:@"file"
                                                                    fileName:fileName
                                                                    mimeType:@"image/jpeg" error:nil];
                                         } error:nil];

// Dump multipart request into the temporary file.
[[AFHTTPRequestSerializer serializer] requestWithMultipartFormRequest:multipartRequest
                                          writingStreamContentsToFile:tmpFileUrl
                                                    completionHandler:^(NSError *error) {
                                                        // Once the multipart form is serialized into a temporary file, we can initialize
                                                        // the actual HTTP request using session manager.

                                                        // Create default session manager.
                                                        AFURLSessionManager *manager = [[AFURLSessionManager alloc] initWithSessionConfiguration:[NSURLSessionConfiguration defaultSessionConfiguration]];

                                                        // Show progress.
                                                        NSProgress *progress = nil;
                                                        // Here note that we are submitting the initial multipart request. We are, however,
                                                        // forcing the body stream to be read from the temporary file.
                                                        NSURLSessionUploadTask *uploadTask = [manager uploadTaskWithRequest:multipartRequest
                                                                                                                   fromFile:tmpFileUrl
                                                                                                                   progress:&progress
                                                                                                          completionHandler:^(NSURLResponse *response, id responseObject, NSError *error)
                                                                                              {
                                                                                                  // Cleanup: remove temporary file.
                                                                                                  [[NSFileManager defaultManager] removeItemAtURL:tmpFileUrl error:nil];

                                                                                                  // Do something with the result.
                                                                                                  if (error) {
                                                                                                      NSLog(@"Error: %@", error);
                                                                                                  } else {
                                                                                                      NSLog(@"Success: %@", responseObject);
                                                                                                  }
                                                                                              }];

                                                        // Add the observer monitoring the upload progress.
                                                        [progress addObserver:self
                                                                   forKeyPath:@"fractionCompleted"
                                                                      options:NSKeyValueObservingOptionNew
                                                                      context:NULL];

                                                        // Start the file upload.
                                                        [uploadTask resume];
                                                    }];

其次，总结一下问题（以及为什么必须使用临时文件作为解决方法），它确实有两个方面。

1. Apple 认为内容长度标头在其控制之下，并且当为某个内容设置 HTTP 主体流时NSURLRequestApple 的库会将编码设置为 Chunked，然后放弃该标头（从而清除 AFNetworking 设置的任何内容长度值）
2. 上传的服务器不支持Transfer-Encoding: Chunked（例如S3）

但事实证明，如果您从文件上传请求（因为提前知道总请求大小），Apple 的库将正确设置内容长度标头。疯狂吧？