本文描述了Http服务器使用http range支持浏览器的下载管理器下载大文件时可暂停和继续的实现方法,后面用英文写,但我的英文不太好,如有错误之处,希望大家帮我纠正,我的联系方式在后面。
Section A. Summary
I'm making a http server in C, in order to support big file download, I have to support Http Range in my server, as the usual way for web browsers to download big files is to use its download manager, where we can pause and resume the download progress. For the pause and resume functions of download manager to work, the http server must support Http Range requests.
Besides file download, http range is also needed for <video> element to play videos on web page, when the user click a random position of the video time line, the browser use http range requests to get the corresponding file content of the video file.
Http range is imported into http protocol from http 1.1. A http range request is like this:198Please respect copyright.PENANAhycKfNFqBZ
----------http range request-------198Please respect copyright.PENANAQ0Qu9HLmar
GET /zen.iso HTTP/1.1198Please respect copyright.PENANATVsKrsK1g3
Range: bytes=100-1023198Please respect copyright.PENANAXNhtYlejKw
If-Match: "534231200_1732277116"198Please respect copyright.PENANA4iyT7KDNNB
......198Please respect copyright.PENANA1K7NQExwtD
-----------------------------------198Please respect copyright.PENANACdLoZJyfmU
It means to get the content from byte 100 to byte 1023, totally 924 bytes, and it tells the http server the etag value of already downloaded part is "534231200_1732277116", the etag value is used for the web browser to determine if the requested content has been modified, it's necessory for some browsers like chrome and edge to resume the download of a file. If http server do not provide etag for range content, the resume function of web browser download manager will not work.
Section B. Detailed Steps
The following is the steps for serving file download, support pause and resume functions of web browser download manager.
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Step 1. make a link for file to download, for example:198Please respect copyright.PENANAaFJhw4SZWz
----------------html-----------------198Please respect copyright.PENANAIELDgTGCvt
<a href="/zen.iso">zen.iso</a>198Please respect copyright.PENANALDvVaGVYNF
-------------------------------------198Please respect copyright.PENANAbDlzPoPiXi
When user click the link, web browser download manager will take care of the file download immediately. We cannot use javascript fetch(url) to start downloading, as in this way javascript code will take care of the download instead of download manager.
When the link is clicked, the http request sent to server is like this:198Please respect copyright.PENANAtyKsEg7Y0l
----------get request------------198Please respect copyright.PENANAFU6gaxDJbz
GET /zen.iso HTTP/1.1198Please respect copyright.PENANA1LAWYnTnWo
......198Please respect copyright.PENANA83wTPFINEs
---------------------------------
198Please respect copyright.PENANAwOmsWgrs3d
Step 2. when http server receives above request, it sends the whole file content as response body back as usual, and indicates support of http range in the response headers, like this:198Please respect copyright.PENANAFE7ofGKKvg
----------------server response--------------198Please respect copyright.PENANAoSm5b52AVL
HTTP/1.1 200 OK198Please respect copyright.PENANAjTnLiazW3X
Date: Sat, 23 Nov 2024 06:29:19 GMT198Please respect copyright.PENANAaV0ejBgIE7
accept-ranges: bytes198Please respect copyright.PENANAreWuiFALyv
content-range: bytes 0-534231199/534231200198Please respect copyright.PENANAyg2qOEgfp1
ETag: "534231200_1732277116"198Please respect copyright.PENANAQzDLPRnbdf
Content-Disposition: attachment; filename="zen.iso"198Please respect copyright.PENANANrlyxW8acg
Content-Length: 534231200198Please respect copyright.PENANABMnq1HzBak
Content-Type: application/octet-stream
(http response body is the whole file content)198Please respect copyright.PENANAo0cfoROHis
-------------------------------------------
Http server usually use a small buf to send the whole file content by multiple times if the file size is bigger than it, like this:198Please respect copyright.PENANAJWLTJUOnQa
---------------http server send big file content by multiple times--------------198Please respect copyright.PENANAVGNIenC1yu
const int buf_size=20000000; // buf size is about 20M198Please respect copyright.PENANA5AMoCFUuc6
int client_socket; char send_buf[buf_size]; FILE *file;
// first send http response headers198Please respect copyright.PENANAVWJqi00iXh
send_http_response_headers(client_socket, http_response_headers);
// then send the whole file content as response body by multiple times if the file is big198Please respect copyright.PENANAUNtEsdKQWn
while(there_is_remain_file_content_to_send)198Please respect copyright.PENANAfxff5iOk95
{ 198Please respect copyright.PENANAhWBLNNFHoZ
read_remain_file_content_to_send_buf(file, send_buf);198Please respect copyright.PENANAhGjXsjvkry
send_result = send(client_socket, send_buf);198Please respect copyright.PENANAuH7nbtuZ1C
if(send_result == fail) return; else continue;198Please respect copyright.PENANAMHMkcUTMSh
}
// a way to make etag for a file using its file size and last modifed time198Please respect copyright.PENANAoKmrm1ufqw
const char *file_etag(const char *path) 198Please respect copyright.PENANAHjK59ON1lL
{198Please respect copyright.PENANAlLKzNQHeWz
struct stat st; if (stat(path, &st) < 0) return NULL; char* data=malloc(64); snprintf(data, 63, "%ld_%ld", (long)st.st_size, (long)st.st_mtime); return data;198Please respect copyright.PENANA2lWh3mzdSa
}198Please respect copyright.PENANAvPKRE2SzIT
-------------------------------------------------198Please respect copyright.PENANAn0bfyihUux
"accept-ranges: bytes" tells client web browser that the http server support range.198Please respect copyright.PENANAeDXahiJnZL
"content-range: bytes 0-534231199/534231200" tells client web browser the content range(0-534231199) of the response body and the total file size(534231200).198Please respect copyright.PENANAOvNV0MzR1V
'ETag: "534231200_1732277116"' tells client web browser the file version.198Please respect copyright.PENANA7izWW070oG
'Content-Disposition: attachment; filename="zen.iso"' tells client web browser to download the file as attachment, and its file name.198Please respect copyright.PENANAvi0TdaiUvC
"Content-Length: 534231200" tells client web browser the total size of the response body, which is the size of the whole file in this example.198Please respect copyright.PENANAGYXeEMgcWK
"Content-Type: application/octet-stream" tells client web browser to treat the response body as binary stream.
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step 3. When the web browser receives above response, it knows the server support http range, and knows the total file size by "content-range: bytes 0-534231199/534231200", it also saves the etag for later comparation.198Please respect copyright.PENANAdfNyIk3hFt
If the file is big, the above sends may take several minutes, during this time, the user can click pause in the download manager of web browser(for firefox, you have to press ctrl and right click the file to show the pause command.)198Please respect copyright.PENANA01aFgKLJ6A
When pause is pressed, the web browser disconnects with http server, and the "send_result = send(client_socket, send_buf);" of http server will be fail, then the http server stops sending anymore.
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step 4. Later the user can click resume to continue the download in download manager, and the download manager will send a http range request to tell the server the resume start point, like this:198Please respect copyright.PENANAzdiT4ZNBj2
---------resume range request---------198Please respect copyright.PENANA1afS9aqYjO
GET /zen.iso HTTP/1.1198Please respect copyright.PENANAuA4qxmbD8b
Range: bytes=243220480-198Please respect copyright.PENANAijih1uMNAP
If-Match: "534231200_1732277116"198Please respect copyright.PENANAw6xZBEtOT0
......198Please respect copyright.PENANASTtAVcERu7
-------------------------------------198Please respect copyright.PENANA37QtuZY50Z
"Range: bytes=243220480-" tells the http server to send content from byte 243220480 to end.198Please respect copyright.PENANAUxbmz0U6qX
'If-Match: "534231200_1732277116"' tells the http server to check the file etag.
If the etag remains the same, it means the file is not changed, so the server can send from the resume point 243220480, and its response status should be 206 partial content, like this:198Please respect copyright.PENANABSK2FJ5egW
-------response content from resume point-------198Please respect copyright.PENANAhEgp6IEEwG
HTTP/1.1 206 Partial Content198Please respect copyright.PENANApur7pGcqKX
Date: Sat, 23 Nov 2024 06:56:17 GMT198Please respect copyright.PENANAmad7P4zCac
accept-ranges: bytes198Please respect copyright.PENANAvv3Shs7TP8
content-range: bytes 243220480-534231199/534231200198Please respect copyright.PENANAJuZ19aWZlS
Content-Length: 291010720198Please respect copyright.PENANA1O9fsnvTHv
Content-Type: application/octet-stream198Please respect copyright.PENANAsX0ZxC0yop
Content-Disposition: attachment; filename="zen.iso"198Please respect copyright.PENANAKNJlYVeTee
ETag: "534231200_1732277116"
(http response body is the file content from resume point to end)198Please respect copyright.PENANA7Yu6wJFeQe
------------------------------------------------198Please respect copyright.PENANA5ZxTcJI16X
When client download manager receives this response, it will keep the already downloaded content and append the new respone body content to it.
If the etag diffs, it means the file has been changed, then the server should send the file content from beginning to end, with a 200 OK response status, like this:198Please respect copyright.PENANAEgQaIhlloh
-------response content from resume point-------198Please respect copyright.PENANA85VajyzzXc
HTTP/1.1 200 OK198Please respect copyright.PENANAhzAqCMzcx0
Date: Sat, 23 Nov 2024 06:29:19 GMT198Please respect copyright.PENANA0DHmmK4IGB
accept-ranges: bytes198Please respect copyright.PENANAa5Av9HntY4
content-range: bytes 0-634231201/634231202198Please respect copyright.PENANAwWtjfVo5pt
ETag: "634231202_2732277118"198Please respect copyright.PENANAiP9925e3ky
Content-Disposition: attachment; filename="zen.iso"198Please respect copyright.PENANAPDVaAfBxaN
Content-Length: 634231202198Please respect copyright.PENANAjBKWUgWcB8
Content-Type: application/octet-stream
(http response body is the whole file content)198Please respect copyright.PENANAOyuMOrUKvw
------------------------------------------------198Please respect copyright.PENANA2LACr6FGFI
When client download manager receives this response, it will clear the already downloaded content and start download from beginning.
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step 5. when a <video src="/video_file.mp4"> is used to play videos on web page, the browser also used http range requests, as Zeng Xu's article describes:198Please respect copyright.PENANAaxjVZQbuVc
https://www.zeng.dev/post/2023-http-range-and-play-mp4-in-browser/?
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Section C. Thanks
感謝曾旭的幫助,曾旭的文章对http range有非常好的描述。
感谢stackoverflow对使用etag的提示198Please respect copyright.PENANACRHiYzBguY
https://stackoverflow.com/questions/66998172/does-google-chrome-and-similar-browsers-support-range-headers-for-standard-downl
感谢gemini等ai对写代码的辅助198Please respect copyright.PENANA32oV2CAtvH
https://gemini.google.com/
感谢互联网上无私奉献的参考资198Please respect copyright.PENANA6Z64AXKFc9
https://developer.mozilla.org/en-US/docs/Web/HTTP/Range_requests198Please respect copyright.PENANAqesuuloRGa
https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/If-Range198Please respect copyright.PENANAaDSar7pBlk
https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/ETag198Please respect copyright.PENANA9AOPvD1cpx
https://www.rfc-editor.org/rfc/rfc7233198Please respect copyright.PENANAMPA3LvDe1v
https://mirrors.tuna.tsinghua.edu.cn/ubuntu-releases/24.10/
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Section D. Contacts Me
If you found any errors or have any suggestions for this article, please let me know, my wechat: si_jinmin, my email: [email protected]198Please respect copyright.PENANAhDdaHkRf0z
如果您发现本文有任何错误,或者对本文有好的建议,欢迎与我联系探讨,我的微信: si_jinmin, 我的email: [email protected]
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