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:166Please respect copyright.PENANASECakae65C
----------http range request-------166Please respect copyright.PENANAyqMT6GT26W
GET /zen.iso HTTP/1.1166Please respect copyright.PENANA71uLXNGHED
Range: bytes=100-1023166Please respect copyright.PENANA7ARAKh9abk
If-Match: "534231200_1732277116"166Please respect copyright.PENANAawxQMZoVMf
......166Please respect copyright.PENANAxup5zHoqv7
-----------------------------------166Please respect copyright.PENANAQ2GHX8GK8j
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:166Please respect copyright.PENANAUnWz8dQF4X
----------------html-----------------166Please respect copyright.PENANAu5C6kI92y7
<a href="/zen.iso">zen.iso</a>166Please respect copyright.PENANANe0JCXOG7a
-------------------------------------166Please respect copyright.PENANA73qUUbGWv8
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:166Please respect copyright.PENANAqdOQqsSzIW
----------get request------------166Please respect copyright.PENANAxnXckKIQ1m
GET /zen.iso HTTP/1.1166Please respect copyright.PENANAx5OYbZ2Lqr
......166Please respect copyright.PENANAogwi8coaPA
---------------------------------
166Please respect copyright.PENANAP0GhUKt0jg
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:166Please respect copyright.PENANAQdnrSi0ekP
----------------server response--------------166Please respect copyright.PENANA8Hoi8TOEpf
HTTP/1.1 200 OK166Please respect copyright.PENANAtR7MF9WM82
Date: Sat, 23 Nov 2024 06:29:19 GMT166Please respect copyright.PENANAiK1d6d45fU
accept-ranges: bytes166Please respect copyright.PENANAgFSIGQzw0N
content-range: bytes 0-534231199/534231200166Please respect copyright.PENANANpsX6yRsu0
ETag: "534231200_1732277116"166Please respect copyright.PENANAnYchWFsF3E
Content-Disposition: attachment; filename="zen.iso"166Please respect copyright.PENANAuWu6678Jfw
Content-Length: 534231200166Please respect copyright.PENANAhz7cKcPLHb
Content-Type: application/octet-stream
(http response body is the whole file content)166Please respect copyright.PENANAWLElApMbCD
-------------------------------------------
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:166Please respect copyright.PENANAO2vgkC7a83
---------------http server send big file content by multiple times--------------166Please respect copyright.PENANANHVg6bwxJa
const int buf_size=20000000; // buf size is about 20M166Please respect copyright.PENANA5GT4f8epT5
int client_socket; char send_buf[buf_size]; FILE *file;
// first send http response headers166Please respect copyright.PENANAm3t1slrqu5
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 big166Please respect copyright.PENANAHeX27IHkcM
while(there_is_remain_file_content_to_send)166Please respect copyright.PENANAWPmSPiNEQQ
{ 166Please respect copyright.PENANApyF92oUuAA
read_remain_file_content_to_send_buf(file, send_buf);166Please respect copyright.PENANA3VqKdfqfnL
send_result = send(client_socket, send_buf);166Please respect copyright.PENANAVHfFpTsxN0
if(send_result == fail) return; else continue;166Please respect copyright.PENANAmTu0PE5A8o
}
// a way to make etag for a file using its file size and last modifed time166Please respect copyright.PENANAk4oXQy5OKP
const char *file_etag(const char *path) 166Please respect copyright.PENANAjn2sslPtu0
{166Please respect copyright.PENANArsbcJkYiyq
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;166Please respect copyright.PENANAI86K8Bmb63
}166Please respect copyright.PENANA6Lqxs2Qzpm
-------------------------------------------------166Please respect copyright.PENANAnoVb9zYysH
"accept-ranges: bytes" tells client web browser that the http server support range.166Please respect copyright.PENANAGrK9IaHuHO
"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).166Please respect copyright.PENANAewS3ea5C8I
'ETag: "534231200_1732277116"' tells client web browser the file version.166Please respect copyright.PENANApW0dKHeB3G
'Content-Disposition: attachment; filename="zen.iso"' tells client web browser to download the file as attachment, and its file name.166Please respect copyright.PENANA1L8aQWsp3S
"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.166Please respect copyright.PENANAerg0LdVir2
"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.166Please respect copyright.PENANA7HnUtsJepG
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.)166Please respect copyright.PENANA9brRrYsGc6
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:166Please respect copyright.PENANAgGrgIstVR8
---------resume range request---------166Please respect copyright.PENANA01XxZOiUPe
GET /zen.iso HTTP/1.1166Please respect copyright.PENANAeggaRdc2Cr
Range: bytes=243220480-166Please respect copyright.PENANA74Vif1SF0X
If-Match: "534231200_1732277116"166Please respect copyright.PENANAp4JDeKDbxN
......166Please respect copyright.PENANADS12NqqDuf
-------------------------------------166Please respect copyright.PENANAtLBrWuZONO
"Range: bytes=243220480-" tells the http server to send content from byte 243220480 to end.166Please respect copyright.PENANAatsEeSY9wq
'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:166Please respect copyright.PENANAmorrFQ8ZIt
-------response content from resume point-------166Please respect copyright.PENANA4YJH60ly9a
HTTP/1.1 206 Partial Content166Please respect copyright.PENANAwnmc8FFU71
Date: Sat, 23 Nov 2024 06:56:17 GMT166Please respect copyright.PENANAAdvQYPVopf
accept-ranges: bytes166Please respect copyright.PENANArOEHarr3wb
content-range: bytes 243220480-534231199/534231200166Please respect copyright.PENANAUL3AlI6plQ
Content-Length: 291010720166Please respect copyright.PENANAlza8jSCKyc
Content-Type: application/octet-stream166Please respect copyright.PENANAPo2S0hG6Vb
Content-Disposition: attachment; filename="zen.iso"166Please respect copyright.PENANANVkljCRCHG
ETag: "534231200_1732277116"
(http response body is the file content from resume point to end)166Please respect copyright.PENANAKEA67xQBcj
------------------------------------------------166Please respect copyright.PENANAVmeDCgz3ka
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:166Please respect copyright.PENANAjPqreOd99N
-------response content from resume point-------166Please respect copyright.PENANAhqwQXhfOk8
HTTP/1.1 200 OK166Please respect copyright.PENANAIIGNv6IsQ9
Date: Sat, 23 Nov 2024 06:29:19 GMT166Please respect copyright.PENANAalk41KkBF3
accept-ranges: bytes166Please respect copyright.PENANAA4JRSCm9xe
content-range: bytes 0-634231201/634231202166Please respect copyright.PENANA3mKZ9RixHw
ETag: "634231202_2732277118"166Please respect copyright.PENANATOc45Ee9uC
Content-Disposition: attachment; filename="zen.iso"166Please respect copyright.PENANAbwvh19h4rP
Content-Length: 634231202166Please respect copyright.PENANA8wwOmgRYpc
Content-Type: application/octet-stream
(http response body is the whole file content)166Please respect copyright.PENANAqjZpHMKc2b
------------------------------------------------166Please respect copyright.PENANAZAkDfNwtnV
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:166Please respect copyright.PENANA8IE82OKUDh
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166Please respect copyright.PENANArSLeNP1zXM
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166Please respect copyright.PENANAppFceTtf6n
https://gemini.google.com/
感谢互联网上无私奉献的参考资166Please respect copyright.PENANAE5WfifxQX9
https://developer.mozilla.org/en-US/docs/Web/HTTP/Range_requests166Please respect copyright.PENANANIA3RcVP2w
https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/If-Range166Please respect copyright.PENANAOtnN6REgtE
https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/ETag166Please respect copyright.PENANAXkfDf2aLQO
https://www.rfc-editor.org/rfc/rfc7233166Please respect copyright.PENANA2WfnZ2hbAE
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]166Please respect copyright.PENANAhbmVzdJLfN
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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