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:204Please respect copyright.PENANAtvPsbz8cmx
----------http range request-------204Please respect copyright.PENANArpyahdvrQM
GET /zen.iso HTTP/1.1204Please respect copyright.PENANACeOTsQCKgv
Range: bytes=100-1023204Please respect copyright.PENANAJ9ojJtmLh5
If-Match: "534231200_1732277116"204Please respect copyright.PENANAiacDrbgAiv
......204Please respect copyright.PENANABKtngb4sX7
-----------------------------------204Please respect copyright.PENANAEPDlhUM2sU
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:204Please respect copyright.PENANAedm2GwtJY8
----------------html-----------------204Please respect copyright.PENANAcN8JLU407u
<a href="/zen.iso">zen.iso</a>204Please respect copyright.PENANAzHQncHTP74
-------------------------------------204Please respect copyright.PENANA9py27j62rk
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:204Please respect copyright.PENANAMxcgZdh1qQ
----------get request------------204Please respect copyright.PENANAgj7rDaNbV5
GET /zen.iso HTTP/1.1204Please respect copyright.PENANAIjHEibeyIp
......204Please respect copyright.PENANAQnj4Hc5Vzl
---------------------------------
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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:204Please respect copyright.PENANAHUnehqO097
----------------server response--------------204Please respect copyright.PENANAmk36snrjnm
HTTP/1.1 200 OK204Please respect copyright.PENANABPeUxI8rCY
Date: Sat, 23 Nov 2024 06:29:19 GMT204Please respect copyright.PENANASR0tVW7amr
accept-ranges: bytes204Please respect copyright.PENANAeK8KLXHZjZ
content-range: bytes 0-534231199/534231200204Please respect copyright.PENANAy3PTBt4ZiX
ETag: "534231200_1732277116"204Please respect copyright.PENANAaI7wBqCFXO
Content-Disposition: attachment; filename="zen.iso"204Please respect copyright.PENANAHrchtxBrkO
Content-Length: 534231200204Please respect copyright.PENANATLbPVl8hqh
Content-Type: application/octet-stream
(http response body is the whole file content)204Please respect copyright.PENANAqusLFQnJrV
-------------------------------------------
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:204Please respect copyright.PENANAsQQgegQUYc
---------------http server send big file content by multiple times--------------204Please respect copyright.PENANANyeOzXNC8d
const int buf_size=20000000; // buf size is about 20M204Please respect copyright.PENANAQ7yh9rHMM8
int client_socket; char send_buf[buf_size]; FILE *file;
// first send http response headers204Please respect copyright.PENANA3il6TPGmmR
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 big204Please respect copyright.PENANAlH9jLpwKPl
while(there_is_remain_file_content_to_send)204Please respect copyright.PENANAgf9ei538Ea
{ 204Please respect copyright.PENANAiABpruPjHc
read_remain_file_content_to_send_buf(file, send_buf);204Please respect copyright.PENANAiNRRDybqFY
send_result = send(client_socket, send_buf);204Please respect copyright.PENANAs0G9ovwvBB
if(send_result == fail) return; else continue;204Please respect copyright.PENANARww4dH6reF
}
// a way to make etag for a file using its file size and last modifed time204Please respect copyright.PENANA4iuhbr1f3k
const char *file_etag(const char *path) 204Please respect copyright.PENANAADAyMYGkHt
{204Please respect copyright.PENANAfgeI7MxexF
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;204Please respect copyright.PENANA8ZOltw03br
}204Please respect copyright.PENANALvAwfVWXqf
-------------------------------------------------204Please respect copyright.PENANAq2Dhgacg9n
"accept-ranges: bytes" tells client web browser that the http server support range.204Please respect copyright.PENANABxKEKWPeN5
"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).204Please respect copyright.PENANAUsLQhumOak
'ETag: "534231200_1732277116"' tells client web browser the file version.204Please respect copyright.PENANACDw96tjBYb
'Content-Disposition: attachment; filename="zen.iso"' tells client web browser to download the file as attachment, and its file name.204Please respect copyright.PENANAoQNvrwHTVK
"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.204Please respect copyright.PENANAsVagEssNnO
"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.204Please respect copyright.PENANArem8bEd5vI
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.)204Please respect copyright.PENANALuIZkQK3QF
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:204Please respect copyright.PENANAIvIRRgDVcZ
---------resume range request---------204Please respect copyright.PENANAQoXCTRRTab
GET /zen.iso HTTP/1.1204Please respect copyright.PENANANX12TN6HYi
Range: bytes=243220480-204Please respect copyright.PENANAbPNooYBEq7
If-Match: "534231200_1732277116"204Please respect copyright.PENANA3iEqhG7Kdb
......204Please respect copyright.PENANAO9vr4KZjsN
-------------------------------------204Please respect copyright.PENANAOpdhdreEuc
"Range: bytes=243220480-" tells the http server to send content from byte 243220480 to end.204Please respect copyright.PENANADd4x7yXxfz
'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:204Please respect copyright.PENANAjCj5Ld2iHL
-------response content from resume point-------204Please respect copyright.PENANA8gUC0UOnbg
HTTP/1.1 206 Partial Content204Please respect copyright.PENANAat4z4svcsp
Date: Sat, 23 Nov 2024 06:56:17 GMT204Please respect copyright.PENANAXedJhVXm7f
accept-ranges: bytes204Please respect copyright.PENANAgzgkZs1644
content-range: bytes 243220480-534231199/534231200204Please respect copyright.PENANAWOVxIUfeMF
Content-Length: 291010720204Please respect copyright.PENANACyxwrqdyyS
Content-Type: application/octet-stream204Please respect copyright.PENANAvv0M72MWaa
Content-Disposition: attachment; filename="zen.iso"204Please respect copyright.PENANAcSRNFitd4F
ETag: "534231200_1732277116"
(http response body is the file content from resume point to end)204Please respect copyright.PENANAs1XWQR71gN
------------------------------------------------204Please respect copyright.PENANAbZqd4yEJJy
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:204Please respect copyright.PENANAUTWHkHxOsL
-------response content from resume point-------204Please respect copyright.PENANAifPH4ZshDg
HTTP/1.1 200 OK204Please respect copyright.PENANA6cBYqKLH6V
Date: Sat, 23 Nov 2024 06:29:19 GMT204Please respect copyright.PENANARCRrDaH0Zl
accept-ranges: bytes204Please respect copyright.PENANAmMCs383LHq
content-range: bytes 0-634231201/634231202204Please respect copyright.PENANACy67Wz7GTf
ETag: "634231202_2732277118"204Please respect copyright.PENANAdhVelcv7IU
Content-Disposition: attachment; filename="zen.iso"204Please respect copyright.PENANAuCV9nk3wp8
Content-Length: 634231202204Please respect copyright.PENANA2b2BGJwAbE
Content-Type: application/octet-stream
(http response body is the whole file content)204Please respect copyright.PENANAuFFNQ03i3Z
------------------------------------------------204Please respect copyright.PENANAcmfLGPVVaG
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:204Please respect copyright.PENANADbAntRio5R
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204Please respect copyright.PENANAdfNYgCSDSQ
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204Please respect copyright.PENANA8AU0TigHkj
https://gemini.google.com/
感谢互联网上无私奉献的参考资204Please respect copyright.PENANADMiOv35Zv6
https://developer.mozilla.org/en-US/docs/Web/HTTP/Range_requests204Please respect copyright.PENANAv7AIIPk0Sp
https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/If-Range204Please respect copyright.PENANAMUb7sqneur
https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/ETag204Please respect copyright.PENANAOnY9ooGNaz
https://www.rfc-editor.org/rfc/rfc7233204Please respect copyright.PENANAl5BfUyptiY
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]204Please respect copyright.PENANAU2MO6UgHV2
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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