关键代码记录

    NSDictionary *params = @{@"type" : @"1"};
    GODebugLog(@"path : %@", path);

/// ********************************************************************************
    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString: path] cachePolicy:NSURLRequestReloadIgnoringLocalCacheData timeoutInterval:10];
    // 1、组装 http body ===================
    // ①定义分界线（boundary）
    NSString *boundaryID = [[NSString stringWithFormat:@"boundary_cba_cfrdce_%@_%@", @(arc4random()), @(arc4random())] md5]; // 分界线标识符
    NSString *boundary = [NSString stringWithFormat:@"--%@", boundaryID]; // 分界线
    NSString *boundaryEnding = [NSString stringWithFormat:@"--%@--", boundaryID]; // 分界线结束
    
    // ②图片data
    NSData *imgData = UIImageJPEGRepresentation(pic, 0.5);
    
    // ③http body的字符串
    NSMutableString *bodyString = [NSMutableString string];
    // 遍历keys，组装文本类型参数
    NSArray *keys = [params allKeys];
    for (NSString *key in keys) {
        // 添加分界线，换行
        [bodyString appendFormat:@"%@\r\n", boundary];
        // 添加参数名称，换2行
        [bodyString appendFormat:@"Content-Disposition: form-data; name=\"%@\"\r\n\r\n", key];
        // 添加参数的值,换行
        [bodyString appendFormat:@"%@\r\n", [params objectForKey:key]];
    }
    // 添加分界线，换行
    [bodyString appendFormat:@"%@\r\n", boundary];
    // 组装文件类型参数, 换行
    NSString *fileParamName = @"file"; // 文件参数名
    NSString *filename = @"avatar.jpg"; // 文件名
    [bodyString appendFormat:@"Content-Disposition: form-data; name=\"%@\"; filename=\"%@\"\r\n", fileParamName, filename];
    // 声明上传文件的格式，换2行
    NSString *fileType = @"image/jpeg";
    [bodyString appendFormat:@"Content-Type: %@\r\n\r\n", fileType];
    
    // 声明 http body data
    NSMutableData *bodyData = [NSMutableData data];
    // 将 body 字符串 bodyString 转化为UTF8格式的二进制数据
    NSData *bodyParamData = [bodyString dataUsingEncoding:NSUTF8StringEncoding];
    [bodyData appendData:bodyParamData];
    // 将 image 的 data 加入
    [bodyData appendData:imgData];
    
    [bodyData appendData:[@"\r\n" dataUsingEncoding:NSUTF8StringEncoding]]; // image数据添加完后 加一个换行
    
    // 分界线结束符加入（以 NSData 形式）
    NSString *boundryEndingWithReturn = [NSString stringWithFormat:@"%@\r\n", boundaryEnding]; // 分界线结束符加换行
    NSData *boundryEndingData = [boundryEndingWithReturn dataUsingEncoding:NSUTF8StringEncoding];
    [bodyData appendData:boundryEndingData];
    // 设置 http body data
    request.HTTPBody = bodyData;
    // 组装 http body 结束 ===================
    
    // 设置 http header 中的 Content-Type 的值
    NSString *content = [NSString stringWithFormat:@"multipart/form-data; boundary=%@", boundaryID];
    [request setValue:content forHTTPHeaderField:@"Content-Type"];
    // 设置 Content-Length
    [request setValue:[NSString stringWithFormat:@"%@", @(bodyData.length)] forHTTPHeaderField:@"Content-Length"];
    // 设置请求方式 POST
    request.HTTPMethod = @"POST";
    
// 三种方式都可以发起请求

   #if 0 // NSURLConnection
    [NSURLConnection sendAsynchronousRequest:request queue:[NSOperationQueue mainQueue] completionHandler:^(NSURLResponse * _Nullable response, NSData * _Nullable data, NSError * _Nullable connectionError) {
        GODebugLog(@"response : %@", response);
        GODebugLog(@"data : %@", data);
        GODebugLog(@"connectionError : %@", connectionError);
        
        NSDictionary *dic = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingMutableContainers error:nil];
        NSLog(@"dic : %@", dic);
        success(dic);
    }];
    
#elif 1 // NSURLSessionUploadTask
    
    NSURLSessionUploadTask *uploadTask = [[NSURLSession sharedSession] uploadTaskWithRequest:request fromData:bodyData completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) {
        GODebugLog(@"data : %@", data);
        GODebugLog(@"response : %@", response);
        GODebugLog(@"error : %@", error);
        
        NSDictionary *dic = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingMutableContainers error:nil];
        NSLog(@"dic : %@", dic);
        
        success(dic);
        
    }];
    [uploadTask resume];
#else // NSURLSessionDataTask
    NSURLSessionConfiguration *config = [NSURLSessionConfiguration defaultSessionConfiguration];
    NSURLSession *session = [NSURLSession sessionWithConfiguration:config];
    NSURLSessionDataTask *dataTask = [session dataTaskWithRequest:request completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) {
        GODebugLog(@"data : %@", data);
        GODebugLog(@"response : %@", response);
        GODebugLog(@"error : %@", error);
        
        NSDictionary *dic = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingMutableContainers error:nil];
        NSLog(@"dic : %@", dic);
        
        success(dic);

    }];
    [dataTask resume];
#endif

前一种方式拼接方式为将所有参数及参数的值（除去文件参数）拼接成一个NSString，然后再一起转换为NSData，也可以将每一个参数和参数值分别转换为NSData，逐个将NSData拼接到一起，两种方式结果是一致的。

    NSMutableURLRequest *request = [[NSMutableURLRequest alloc] init];
    [request setCachePolicy:NSURLRequestReloadIgnoringLocalCacheData];
    [request setHTTPShouldHandleCookies:NO];
    [request setTimeoutInterval:30];
    [request setHTTPMethod:@"POST"];

    NSString *boundaryID = [[NSString stringWithFormat:@"boundary_cba_cfrdce_%@_%@", @(arc4random()), @(arc4random())] md5]; // 分界线标识符

    // set Content-Type in HTTP header
    NSString *contentType = [NSString stringWithFormat:@"multipart/form-data; boundary=%@", boundaryID];
    [request setValue:contentType forHTTPHeaderField: @"Content-Type"];

    // post body
    NSMutableData *body = [NSMutableData data];

    // add params (all params are strings)
    for (NSString *param in params) {
        [body appendData:[[NSString stringWithFormat:@"--%@\r\n", boundaryID] dataUsingEncoding:NSUTF8StringEncoding]];
        [body appendData:[[NSString stringWithFormat:@"Content-Disposition: form-data; name=\"%@\"\r\n\r\n", param] dataUsingEncoding:NSUTF8StringEncoding]];
        [body appendData:[[NSString stringWithFormat:@"%@\r\n", [params objectForKey:param]] dataUsingEncoding:NSUTF8StringEncoding]];
    }
    
    if (imageData) {
        [body appendData:[[NSString stringWithFormat:@"--%@\r\n", boundaryID] dataUsingEncoding:NSUTF8StringEncoding]];
        [body appendData:[[NSString stringWithFormat:@"Content-Disposition: form-data; name=\"%@\"; filename=\"image.jpg\"\r\n", @"file"] dataUsingEncoding:NSUTF8StringEncoding]];
        [body appendData:[@"Content-Type: image/jpeg\r\n\r\n" dataUsingEncoding:NSUTF8StringEncoding]];
        [body appendData:imageData];
        [body appendData:[[NSString stringWithFormat:@"\r\n"] dataUsingEncoding:NSUTF8StringEncoding]];
    }

    [body appendData:[[NSString stringWithFormat:@"--%@--\r\n", boundaryID] dataUsingEncoding:NSUTF8StringEncoding]];

    // setting the body of the post to the reqeust
    [request setHTTPBody:body];

    // set the content-length
    NSString *postLength = [NSString stringWithFormat:@"%lu", (unsigned long)[body length]];
    [request setValue:postLength forHTTPHeaderField:@"Content-Length"];

    // set URL
    [request setURL:[NSURL URLWithString: path]];

    // 三种方式都可以发起请求

   #if 0 // NSURLConnection
    [NSURLConnection sendAsynchronousRequest:request queue:[NSOperationQueue mainQueue] completionHandler:^(NSURLResponse * _Nullable response, NSData * _Nullable data, NSError * _Nullable connectionError) {
        GODebugLog(@"response : %@", response);
        GODebugLog(@"data : %@", data);
        GODebugLog(@"connectionError : %@", connectionError);
        
        NSDictionary *dic = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingMutableContainers error:nil];
        NSLog(@"dic : %@", dic);
        success(dic);
    }];
    
#elif 1 // NSURLSessionUploadTask
    
    NSURLSessionUploadTask *uploadTask = [[NSURLSession sharedSession] uploadTaskWithRequest:request fromData:bodyData completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) {
        GODebugLog(@"data : %@", data);
        GODebugLog(@"response : %@", response);
        GODebugLog(@"error : %@", error);
        
        NSDictionary *dic = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingMutableContainers error:nil];
        NSLog(@"dic : %@", dic);
        
        success(dic);
        
    }];
    [uploadTask resume];
#else // NSURLSessionDataTask
    NSURLSessionConfiguration *config = [NSURLSessionConfiguration defaultSessionConfiguration];
    NSURLSession *session = [NSURLSession sessionWithConfiguration:config];
    NSURLSessionDataTask *dataTask = [session dataTaskWithRequest:request completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) {
        GODebugLog(@"data : %@", data);
        GODebugLog(@"response : %@", response);
        GODebugLog(@"error : %@", error);
        
        NSDictionary *dic = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingMutableContainers error:nil];
        NSLog(@"dic : %@", dic);
        
        success(dic);

    }];
    [dataTask resume];
#endif