Article 4: multipart/form-data details

Reprinted please indicate the source http://blog.csdn.net/yankai0219/article/details/8159701

Main Content 1. What is multipart/form-data? 2. Upload steps: 3. multipart/form-Data Format 1) Overview 2) Details

1. What is multipart/form-data?Multipart/form-data is a method for uploading files. Multipart/form-data is actually the way the browser uploads files using forms. The most common situation is: when writing an email, add attachments to the email. attachments are usually added using forms, that is, uploaded to the server in the multipart/form-data format.
2. Upload steps:First, the client and the server establish a connection (TCP protocol ).
Second, the client can send data to the server. Because the Upload File actually sends a request to the server.
Third, the client sends data to the server in the format of multipart/form-data. (This is important ).
3. multipart/form-Data Format1) OverviewIn fact, there are multiple Representation Methods for multipart/form-data formats, but I think the most authoritative one is as follows:

First, there are some basics you need to understand about multipart/formdata posts. each part consists of at least a name and a contents part. if the part is made for file upload, there are also a stored Content-Type And a filename. below, we'll discuss what options you use to set these properties in the parts you want to add to your post. first, you need to understand some basic knowledge about multipart/formdata post. Each part contains at least one name and one content part. If this part is used to upload files, you can also have Content-Type and filename information. (From http://curl.haxx.se/libcurl/c/curl_formadd.html)

I like to capture packets through Wireshark and fully understand its content. Packet Capture Website: Fast-loading network disk. Packet capture content: the POST request when the file is uploaded. The field indicating multipart/form-data in the captured packet: MIME multipart media encapsulation.
2) Details:First, we will introduce the correspondence between fields in Wireshark and multipart/form-data: MIME multipart media encapsulation: represents the data in the entire multipart/form-data upload file. Encapsulated multipart part: represents the data of different parts of the form. Boundary: used to separate data from different parts of a form. Secondly, details: 1) Mime multipart media encapsulation, type: multipart/form-data, boundary: "---------- ei4ij5i5ef1gl6km7ef1ch2ae0ei4"This line indicates that the request is in the multipart/form-data format, and boundary is the string "---------- ei4ij5i5ef1gl6km7ef1ch2ae0ei4. 2) Boundary: boundary: used to separate data of different parts of a form. In fact, each part of the data starts with "--" + boundary (this is the standard content described in the MIME standard ). 3) encapsulated multipart part: the description of this part of data that follows boundary: Content-dispostion: Form-data; name = "FILENAME" \ r \ nEach part must have at least one name and one content part.