How to download a file and save it to the documents directory with AFNetworking?

I am using the AFNetworking library. I can't figure out how to download a file and save it to the documents directory.

NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:@"..."]];
AFHTTPRequestOperation *operation = [[[AFHTTPRequestOperation alloc] initWithRequest:request] autorelease];

NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *path = [[paths objectAtIndex:0] stringByAppendingPathComponent:@"filename"];
operation.outputStream = [NSOutputStream outputStreamToFileAtPath:path append:NO];

[operation setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) {
    NSLog(@"Successfully downloaded file to %@", path);
} failure:^(AFHTTPRequestOperation *operation, NSError *error) {
    NSLog(@"Error: %@", error);
}];

[operation start];

I'm gonna bounce off @mattt's answer and post a version for AFNetworking 2.0 using AFHTTPRequestOperationManager.

NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *path = [[paths objectAtIndex:0] stringByAppendingPathComponent:@"filename"];

AFHTTPRequestOperationManager *manager = [AFHTTPRequestOperationManager manager];
AFHTTPRequestOperation *op = [manager GET:@"http://example.com/file/to/download" 
                               parameters:nil
    success:^(AFHTTPRequestOperation *operation, id responseObject) {
         NSLog(@"successful download to %@", path);
    } failure:^(AFHTTPRequestOperation *operation, NSError *error) {
         NSLog(@"Error: %@", error);
    }];
op.outputStream = [NSOutputStream outputStreamToFileAtPath:path append:NO];

I'm talking about AFNetworking 2.0

[AFHTTPRequestOperationManager manager] creates manager object with default AFJSONResponseSerializer, and it performs content types restriction. Take a look at this

- (BOOL)validateResponse:(NSHTTPURLResponse *)response
                    data:(NSData *)data
                   error:(NSError * __autoreleasing *)error

So we need to create a none response serializer and use AFHTTPRequestOperationManager as normal.

Here is the AFNoneResponseSerializer

@interface AFNoneResponseSerializer : AFHTTPResponseSerializer

+ (instancetype)serializer;

@end

@implementation AFNoneResponseSerializer

#pragma mark - Initialization
+ (instancetype)serializer
{
    return [[self alloc] init];
}

- (instancetype)init
{
    self = [super init];

    return self;
}

#pragma mark - AFURLResponseSerializer
- (id)responseObjectForResponse:(NSURLResponse *)response
                           data:(NSData *)data
                          error:(NSError *__autoreleasing *)error

{
    return data;
}

@end

Usage

self.manager = [AFHTTPRequestOperationManager manager];
self.manager.responseSerializer = [AFNoneResponseSerializer serializer];

[self.manager GET:@"https://sites.google.com/site/iphonesdktutorials/xml/Books.xml"
           parameters:parameters
              success:^(AFHTTPRequestOperation *operation, id responseObject)
    {
        if (success) {
            success(responseObject);
        }
    } failure:^(AFHTTPRequestOperation *operation, NSError *error) {
        if (failure) {
            failure(error);
        }
    }];

so that we can get the whole file without any serialization

Documentation page has example with section 'Creating a Download Task':

NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration defaultSessionConfiguration];
AFURLSessionManager *manager = [[AFURLSessionManager alloc] initWithSessionConfiguration:configuration];

NSURL *URL = [NSURL URLWithString:@"http://example.com/download.zip"];
NSURLRequest *request = [NSURLRequest requestWithURL:URL];

NSURLSessionDownloadTask *downloadTask = [manager downloadTaskWithRequest:request progress:nil destination:^NSURL *(NSURL *targetPath, NSURLResponse *response) {
    NSURL *documentsDirectoryURL = [[NSFileManager defaultManager] URLForDirectory:NSDocumentDirectory inDomain:NSUserDomainMask appropriateForURL:nil create:NO error:nil];
    return [documentsDirectoryURL URLByAppendingPathComponent:[response suggestedFilename]];
} completionHandler:^(NSURLResponse *response, NSURL *filePath, NSError *error) {
    NSLog(@"File downloaded to: %@", filePath);
}];
[downloadTask resume];

NB! Code work with iOS 7+ (tested with AFNetworking 2.5.1)

From AFNetworking docs. Save to loaded file to your documents. AFNetworking 3.0

NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration defaultSessionConfiguration];
AFURLSessionManager *manager = [[AFURLSessionManager alloc] initWithSessionConfiguration:configuration];

NSURL *URL = [NSURL URLWithString:@"http://example.com/download.zip"];
NSURLRequest *request = [NSURLRequest requestWithURL:URL];

NSURLSessionDownloadTask *downloadTask = [manager downloadTaskWithRequest:request progress:nil destination:^NSURL *(NSURL *targetPath, NSURLResponse *response) {
    NSURL *documentsDirectoryURL = [[NSFileManager defaultManager] URLForDirectory:NSDocumentDirectory inDomain:NSUserDomainMask appropriateForURL:nil create:NO error:nil];
    return [documentsDirectoryURL URLByAppendingPathComponent:[response suggestedFilename]];
} completionHandler:^(NSURLResponse *response, NSURL *filePath, NSError *error) {
    NSLog(@"File downloaded to: %@", filePath);
}];
[downloadTask resume];