POST提交的时候，+号变成空格了。刚开始以为是服务器端有问题，加密出现问题，后端说不用想，接口绝对没问题。我说我也没问题，我用方法把base64转了一下的，但后面发现还是有+号变空格了，我默默的走开了。
改换用提交表单的方法转base64。

- (void)postFormData:(NSString *)url parameters:(NSDictionary *)params complete:(void(^)(id info,NSError *error))complete
{
    NSURL *nsurl = [NSURL URLWithString:url];
    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:nsurl];
    request.HTTPMethod = @"POST";

    [request setValue:@"multipart/form-data;boundary=boundary" forHTTPHeaderField:@"Content-Type"];
    
    [request setTimeoutInterval:30];
    
    [body appendData:[self getDataWithString:@"--BOUNDARY\r\n" ]];
        
    NSDictionary *dicData = params;
    NSMutableString *bodyContent = [NSMutableString string];
    
    for(NSString *key in dicData.allKeys)
    {
        id value = [dicData objectForKey:key];
        [bodyContent appendFormat:@"--BOUNDARY\r\n"];
        [bodyContent appendFormat:@"Content-Disposition: form-data; name=\"%@\"\r\n\r\n",key];
        [bodyContent appendFormat:@"%@\r\n",value];
    }
        
    NSData *bodyData=[bodyContent dataUsingEncoding:NSUTF8StringEncoding];
        
    request.HTTPBody = bodyData;
    
    [request setValue:[NSString stringWithFormat:@"%lu",(unsigned long)body.length] forHTTPHeaderField:@"Content-Length"];
    [request setValue:@"multipart/form-data; boundary=BOUNDARY" forHTTPHeaderField:@"Content-Type"];
        
    NSURLSessionConfiguration *config = [NSURLSessionConfiguration defaultSessionConfiguration];
    
    NSURLSession *session = [NSURLSession sessionWithConfiguration:config delegate:self delegateQueue:[NSOperationQueue currentQueue]];
    
    NSURLSessionDataTask *dataTask = [session dataTaskWithRequest:request completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error)
    {
        [session finishTasksAndInvalidate];
        if (error)
        {
            
        }
        else
        {
            
        }
    }];
    [dataTask resume];
}

-(NSData *)getDataWithString:(NSString *)string
{
    NSData *data = [string dataUsingEncoding:NSUTF8StringEncoding];
    return data;
}