ios http POST(数据和图像): Image not getting posted

Question

我使用以下代码将图像和数据推送到服务器中。正在发送数据，但服务器未接收到图像。如果我使用的以下代码有错误，有人能发现我吗:

NSString *urlString = [[NSString alloc]initWithString:[NSString stringWithFormat:@"%@action=savesign",MainURL]];

// set up the form keys and values (revise using 1 NSDictionary at some point - neater than 2 arrays)
NSArray *keys = [[NSArray alloc] initWithObjects:@"user",@"poll",nil];
NSArray *vals = [[NSArray alloc] initWithObjects:user,pollid,nil];

// set up the request object
NSMutableURLRequest *request = [[NSMutableURLRequest alloc] init];
[request setURL:[NSURL URLWithString:urlString]];
[request setHTTPMethod:@"POST"];

//Add content-type to Header. Need to use a string boundary for data uploading.
NSString *boundary = @"0xKhTmLbOuNdArY";
NSString *contentType = [NSString stringWithFormat:@"multipart/form-data; boundary=%@",boundary];
[request addValue:contentType forHTTPHeaderField: @"Content-Type"];

//create the post body
NSMutableData *body = [NSMutableData data];
[body appendData:[[NSString stringWithFormat:@"--%@\r\n",boundary] dataUsingEncoding:NSASCIIStringEncoding]];

//add (key,value) pairs (no idea why all the \r's and \n's are necessary ... but everyone seems to have them)
for (int i=0; i<[keys count]; i++) {
    [body appendData:[[NSString stringWithFormat:@"Content-Disposition: form-data; name=\"%@\"\r\n\r\n",[keys objectAtIndex:i]] dataUsingEncoding:NSASCIIStringEncoding]];
    [body appendData:[[NSString stringWithFormat:@"%@",[vals objectAtIndex:i]] dataUsingEncoding:NSASCIIStringEncoding]];
    [body appendData:[[NSString stringWithFormat:@"\r\n--%@\r\n",boundary] dataUsingEncoding:NSASCIIStringEncoding]];
}
[body appendData:[@"Content-Disposition: form-data; name=\"image\"\r\n" dataUsingEncoding:NSASCIIStringEncoding]];
[body appendData:[@"Content-Type: application/octet-stream\r\n\r\n" dataUsingEncoding:NSASCIIStringEncoding]];
[body appendData:[NSData dataWithContentsOfFile:pngFilePath]];
[body appendData:[[NSString stringWithFormat:@"\r\n--%@--\r\n",boundary] dataUsingEncoding:NSASCIIStringEncoding]];


NSData *imageData = UIImagePNGRepresentation(_Signfield.image);
    [body appendData:[[NSString stringWithFormat:@"--%@\r\n", boundary] dataUsingEncoding:NSUTF8StringEncoding]];
    [body appendData:[[NSString stringWithFormat:@"Content-Disposition: form-data; name=\"%@\"; filename=\"myPngFile.png\"\r\n", _Signfield.image] 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]];

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

// make the connection to the web
NSData *returnData = [NSURLConnection sendSynchronousRequest:request returningResponse:nil error:nil];
NSString *returnString = [[NSString alloc] initWithData:returnData encoding:NSUTF8StringEncoding];

NSLog(returnString);

这是服务器的响应

{"status":"failure","error":[],"user":0}

当我登录并检查数据存在但图像不存在时。

Answer 1

当您通过 HTTP POST 执行文件上传时，通过网络传输的数据如下所示:

POST /upload HTTP/1.1
Accept: */*
Accept-Encoding: gzip, deflate, compress
Content-Length: 17918
Content-Type: multipart/form-data; boundary=0xKhTmLbOuNdArY
Host: example.com
User-Agent: HTTPie/0.7.2

--0xKhTmLbOuNdArY
Content-Disposition: form-data; name="user"

Diphin-Das
--0xKhTmLbOuNdArY
Content-Disposition: form-data; name="poll"

1
--0xKhTmLbOuNdArY
Content-Disposition: form-data; name="image"; filename="myPNGFile.png"
Content-Type: image/png

[Binary PNG image data not shown]
--0xKhTmLbOuNdArY--

前七行是描述向服务器请求的HTTP头，包括:

• HTTP请求方式(POST)
• 请求的资源(/upload)
• HTTP协议(protocol)版本(HTTP/1.1)
• 请求正文的长度(Content-Length: 17918)
• 请求正文中包含的数据类型(Content-Type: multipart/form-data; boundary=0xKhTmLbOuNdArY)

最后一个很有趣。通过将内容类型设置为 multipart/form-data，我们可以在请求正文中包含不同数据类型的组合。 boundary 告诉服务器如何在请求正文中分隔每个表单值。

请求正文中的表单值使用简单结构描述:

--[boundary marker]
Content-Disposition: form-data; name="[parameter name]"
Content-Type: [parameter value MIME type]

[parameter value]

如果参数值为字母数字，则 Content-Type header 是可选的，但对于其他数据类型(图像、视频、文档等)，它是必需的。请求正文的结尾由一个终止边界标记表示，它是一个以双连字符为后缀的标准边界标记，例如--0xKhTmLbOuNdArY--。换行符 (\r\n) 用于分隔内容部分的各个元素。

多部分 POST 请求中的表单值可以有其他元素。如果您有兴趣，可以在 RFC 2388 中阅读它们。 .

为了从 Objective-C 上传文件，您需要根据上述规范制作请求正文。我已经从你的问题中提取代码并重构它以使其正常运行并在此过程中添加了一些解释性注释。

NSDictionary *params = @{ @"user": user, @"poll": pollid };
NSData *imageData = UIImagePNGRepresentation(_Signfield.image);

NSString *urlString = [[NSString alloc]initWithString:[NSString stringWithFormat:@"%@action=savesign",MainURL]];

NSMutableURLRequest *request = [[NSMutableURLRequest alloc] init];
[request setURL:[NSURL URLWithString:urlString]];
[request setHTTPMethod:@"POST"];

NSString *boundary = @"0xKhTmLbOuNdArY";
NSString *kNewLine = @"\r\n";

// Note that setValue is used so as to override any existing Content-Type header.
// addValue appends to the Content-Type header
NSString *contentType = [NSString stringWithFormat:@"multipart/form-data; boundary=%@",boundary];
[request setValue:contentType forHTTPHeaderField: @"Content-Type"];

NSMutableData *body = [NSMutableData data];

// Add the parameters from the dictionary to the request body
for (NSString *name in params.allKeys) {
    NSData *value = [[NSString stringWithFormat:@"%@", params[name]] dataUsingEncoding:NSUTF8StringEncoding];

    [body appendData:[[NSString stringWithFormat:@"--%@%@", boundary, kNewLine] dataUsingEncoding:NSUTF8StringEncoding]];
    [body appendData:[[NSString stringWithFormat:@"Content-Disposition: form-data; name=\"%@\"", name] dataUsingEncoding:NSUTF8StringEncoding]];
    // For simple data types, such as text or numbers, there's no need to set the content type
    [body appendData:[[NSString stringWithFormat:@"%@%@", kNewLine, kNewLine] dataUsingEncoding:NSUTF8StringEncoding]];
    [body appendData:value];
    [body appendData:[kNewLine dataUsingEncoding:NSUTF8StringEncoding]];
}

// Add the image to the request body
[body appendData:[[NSString stringWithFormat:@"--%@%@", boundary, kNewLine] dataUsingEncoding:NSUTF8StringEncoding]];
[body appendData:[[NSString stringWithFormat:@"Content-Disposition: form-data; name=\"%@\"; filename=\"myPngFile.png\"%@", @"image", kNewLine] dataUsingEncoding:NSUTF8StringEncoding]];
[body appendData:[[NSString stringWithFormat:@"Content-Type: image/png"] dataUsingEncoding:NSUTF8StringEncoding]];
[body appendData:[[NSString stringWithFormat:@"%@%@", kNewLine, kNewLine] dataUsingEncoding:NSUTF8StringEncoding]];
[body appendData:imageData];
[body appendData:[kNewLine dataUsingEncoding:NSUTF8StringEncoding]];

// Add the terminating boundary marker to signal that we're at the end of the request body
[body appendData:[[NSString stringWithFormat:@"--%@--", boundary] dataUsingEncoding:NSUTF8StringEncoding]];

[request setHTTPBody:body];

NSData *returnData = [NSURLConnection sendSynchronousRequest:request returningResponse:nil error:nil];
NSString *returnString = [[NSString alloc] initWithData:returnData encoding:NSUTF8StringEncoding];

NSLog(@"%@", returnString);