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:155Please respect copyright.PENANAivXR6UUvzE
----------http range request-------155Please respect copyright.PENANA1OHs1FmiHR
GET /zen.iso HTTP/1.1155Please respect copyright.PENANAx9b3LeT6gq
Range: bytes=100-1023155Please respect copyright.PENANAk1SIkoML78
If-Match: "534231200_1732277116"155Please respect copyright.PENANATtHLKRrDek
......155Please respect copyright.PENANA0WgmSYUx4r
-----------------------------------155Please respect copyright.PENANAzNauxIsU8V
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:155Please respect copyright.PENANAJ28rNJJe1B
----------------html-----------------155Please respect copyright.PENANAi7D0OMcCpe
<a href="/zen.iso">zen.iso</a>155Please respect copyright.PENANAqnOUJcVQoZ
-------------------------------------155Please respect copyright.PENANAoN9RFGP2HQ
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:155Please respect copyright.PENANAWhOzBwNmPT
----------get request------------155Please respect copyright.PENANAMRGQD2uteA
GET /zen.iso HTTP/1.1155Please respect copyright.PENANAokUYtzYfd8
......155Please respect copyright.PENANAq92eBM2DXA
---------------------------------
155Please respect copyright.PENANAPb4ieSukbp
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:155Please respect copyright.PENANAQ5PVIcXM34
----------------server response--------------155Please respect copyright.PENANA3kGcZJLAeE
HTTP/1.1 200 OK155Please respect copyright.PENANAv87XtND4Ni
Date: Sat, 23 Nov 2024 06:29:19 GMT155Please respect copyright.PENANASAGs0J4jOG
accept-ranges: bytes155Please respect copyright.PENANAnkmb6l2UJw
content-range: bytes 0-534231199/534231200155Please respect copyright.PENANAl7EVIdGoMH
ETag: "534231200_1732277116"155Please respect copyright.PENANA12eRmFqxQ8
Content-Disposition: attachment; filename="zen.iso"155Please respect copyright.PENANAJYOhcPQvCF
Content-Length: 534231200155Please respect copyright.PENANAt4uQox5aPf
Content-Type: application/octet-stream
(http response body is the whole file content)155Please respect copyright.PENANAk6mBXjvpFD
-------------------------------------------
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:155Please respect copyright.PENANA8pL4QomsZi
---------------http server send big file content by multiple times--------------155Please respect copyright.PENANAHt7kKq0qMz
const int buf_size=20000000; // buf size is about 20M155Please respect copyright.PENANAtISHiwmwqa
int client_socket; char send_buf[buf_size]; FILE *file;
// first send http response headers155Please respect copyright.PENANAUXgJcWFoHp
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 big155Please respect copyright.PENANACY3G92IQJD
while(there_is_remain_file_content_to_send)155Please respect copyright.PENANASnAO2n6udJ
{ 155Please respect copyright.PENANAiYYauwBHeY
read_remain_file_content_to_send_buf(file, send_buf);155Please respect copyright.PENANAYUXgty7WIc
send_result = send(client_socket, send_buf);155Please respect copyright.PENANA12TFfB7VsX
if(send_result == fail) return; else continue;155Please respect copyright.PENANAzfO6cLjtlI
}
// a way to make etag for a file using its file size and last modifed time155Please respect copyright.PENANA0hK8qBDgZJ
const char *file_etag(const char *path) 155Please respect copyright.PENANAjd5wBcMWdc
{155Please respect copyright.PENANA04JGPWQErB
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;155Please respect copyright.PENANAszyj1NpXrO
}155Please respect copyright.PENANAzRJn8UcTzg
-------------------------------------------------155Please respect copyright.PENANAcTjMw5Zm3M
"accept-ranges: bytes" tells client web browser that the http server support range.155Please respect copyright.PENANAAjrzfocDHi
"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).155Please respect copyright.PENANAVGrVXO5nlO
'ETag: "534231200_1732277116"' tells client web browser the file version.155Please respect copyright.PENANALoplOXVX0R
'Content-Disposition: attachment; filename="zen.iso"' tells client web browser to download the file as attachment, and its file name.155Please respect copyright.PENANANCU12ysRKS
"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.155Please respect copyright.PENANAcUTFNSO1Pr
"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.155Please respect copyright.PENANAYVxQNzfCuV
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.)155Please respect copyright.PENANAdPr0fcj0hl
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:155Please respect copyright.PENANAHy60Vly3Xn
---------resume range request---------155Please respect copyright.PENANAFYDj2ZSvg0
GET /zen.iso HTTP/1.1155Please respect copyright.PENANAlgDuPJec51
Range: bytes=243220480-155Please respect copyright.PENANAX5ZS1dtuCT
If-Match: "534231200_1732277116"155Please respect copyright.PENANAPzpxqJNcCR
......155Please respect copyright.PENANAL7kdH4BbeE
-------------------------------------155Please respect copyright.PENANAAtYk1xMZsZ
"Range: bytes=243220480-" tells the http server to send content from byte 243220480 to end.155Please respect copyright.PENANApO7aj1soYG
'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:155Please respect copyright.PENANA2aqudXnMVd
-------response content from resume point-------155Please respect copyright.PENANAy0mJqQ69Fn
HTTP/1.1 206 Partial Content155Please respect copyright.PENANARgM07OuBb6
Date: Sat, 23 Nov 2024 06:56:17 GMT155Please respect copyright.PENANAfDI2EeeKnw
accept-ranges: bytes155Please respect copyright.PENANA2wPhQtnz5T
content-range: bytes 243220480-534231199/534231200155Please respect copyright.PENANAbe2uCkygFR
Content-Length: 291010720155Please respect copyright.PENANAdCKDGU3nqJ
Content-Type: application/octet-stream155Please respect copyright.PENANARw7mADwGL0
Content-Disposition: attachment; filename="zen.iso"155Please respect copyright.PENANAJtGLDL83Yj
ETag: "534231200_1732277116"
(http response body is the file content from resume point to end)155Please respect copyright.PENANADcaikPINMv
------------------------------------------------155Please respect copyright.PENANAjphiz4Sjxl
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:155Please respect copyright.PENANApS6yMbcv5d
-------response content from resume point-------155Please respect copyright.PENANA8ZEqOx3TE1
HTTP/1.1 200 OK155Please respect copyright.PENANAJFTEaROMk4
Date: Sat, 23 Nov 2024 06:29:19 GMT155Please respect copyright.PENANA04xJdSnNI6
accept-ranges: bytes155Please respect copyright.PENANAVj9YxxZlr0
content-range: bytes 0-634231201/634231202155Please respect copyright.PENANAA12p7F85vr
ETag: "634231202_2732277118"155Please respect copyright.PENANAQxt7SmquWq
Content-Disposition: attachment; filename="zen.iso"155Please respect copyright.PENANAIbFs0tpi5N
Content-Length: 634231202155Please respect copyright.PENANAvu1Fd3Cxo1
Content-Type: application/octet-stream
(http response body is the whole file content)155Please respect copyright.PENANAvUC9VGGVk0
------------------------------------------------155Please respect copyright.PENANAO7YC9k6A1M
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:155Please respect copyright.PENANAn65KfaJTNg
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155Please respect copyright.PENANAXmpl65cKar
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155Please respect copyright.PENANAsMvx7ksuYt
https://gemini.google.com/
感谢互联网上无私奉献的参考资155Please respect copyright.PENANAEJsdxEUKU6
https://developer.mozilla.org/en-US/docs/Web/HTTP/Range_requests155Please respect copyright.PENANAFOp4In9Jen
https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/If-Range155Please respect copyright.PENANAWmQlLR8JIG
https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/ETag155Please respect copyright.PENANAj6i2qmz8A2
https://www.rfc-editor.org/rfc/rfc7233155Please respect copyright.PENANAN8I13l675b
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]155Please respect copyright.PENANAJ9ZENsSHRX
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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