Analysis of breakpoint continuation and download principle

Interview the candidate the day before yesterday , I just saw him doing file upload and download , The question is suddenly asked without any intention , As a result, the candidate was confused , A little stunned , Maybe he never thought about it , Most uploads and downloads are interfaces , Without a deep understanding of this principle , Or not debug What happened .

First of all, let's talk. HTTP Agreement , You can add Range paragraph , To indicate where the client wants to continue downloading . In previous versions HTTP The protocol does not support breakpoints , HTTP/1.1 From the beginning （ This is also the realization of sub fast transmission ）. It is generally used when downloading breakpoints  Range and Content-Range  Entity head .

Breakpoint continuation is the core of large file data transmission . Especially multithreading technology ,socket technology ,TCP and UDP technology , In addition, the distribution process of the version package will be combined with p2p technology , For example, we often use Thunder download , Baidu SkyDrive , If upload or download is interrupted , Next time you start uploading and downloading again , Definitely not from a new start to download , Instead, start work from the point where it has been interrupted .

Basically realize the idea

The key of breakpoint continuation is breakpoint , So we should design the transmission protocol well , Pictured above , I customized an interaction protocol , Every download request will bring the starting point of the download , In this way, we can support downloading from breakpoints , Actually HTTP This is also the principle of breakpoint continuation in , stay HTTP There is an optional field in the header RANGE, Indicates the scope of the download , Here is what I use JAVA Download breakpoint continuation example implemented in language .

One 、 Files to be renewed

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