HTTP Protocol Message Structure and Data Transmission

In the HTTP protocol, requests and responses are transmitted using ASCII characters. If binary data needs to be transmitted, it must be encoded using methods such as Base64 or MIME. This is because protocols like POP3 and SMTP are designed for text-based communication, whereas FTP supports the transmission of binary data without requiring encoding into character data.

If binary data is transmitted directly via HTTP without encoding (e.g., Base64), several issues may arise:

1. The specific length of the transmitted bytes cannot be determined.
2. For certain numbers, the server may not be able to process the binary transmission correctly.

HTTP request headers and response headers are transmitted in ASCII text format, but the content bodies (request/response payloads) can take various forms. When processing data, the receiver relies on the Content-Type attribute within the request or response headers. For example, Content-Type: image/gif indicates that an image object (binary data) is being transmitted, specifically in GIF format. The Content-Length: 91 header specifies that the size of the transmitted data is 91 bytes. If the response header does not include a Transfer-Encoding field, it implies that the transmitted data has undergone no form of encoding conversion and represents the raw content of the source file.