After having downloaded a big files from HTTP how to check if it's ok?

Question

Are there any way to send an http request to know for example the md5 of a file?

I need it because I have a php script that downloads a remote file from http and then writes it locally.

I would like to check if it was transfered right.

Thanks

There's a [`Content-MD5`](http://www.faqs.org/rfcs/rfc1864.html) header supposed to be in HTTP responses, but few webservers send it. For Apache it depends on the `ContentDigest On` directive. — mario, Feb 15 '11 at 21:57

score 1 · Accepted Answer · answered Feb 15 '11 at 21:59

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HTTP (in reality TCP) has internal error checking, so everything you download ist correct. The only problem you can have is an incomplete download, so check for filesize.

answered Feb 15 '11 at 21:59

Tobias P.

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score -1 · Answer 2 · answered Feb 15 '11 at 21:56

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Without checksum at original server, either external or inside file (like .exe), you can't. HTTP provides no such functionality.

answered Feb 15 '11 at 21:56

Teson

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score -1 · Answer 3 · answered Feb 15 '11 at 22:04

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This isn't efficient, but you could download it twice and checksum each (with md5 or sha). If the two match, and the size matches the content-length header, it's probably correct.

answered Feb 15 '11 at 22:04

jcomeau_ictx

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or you have two copies of a corrupt file – Matthew Feb 15 '11 at 22:07
yes, but then it's probably corrupt on the server as well, if both checksums match. it was still *transferred* "right". – jcomeau_ictx Feb 15 '11 at 22:09

After having downloaded a big files from HTTP how to check if it's ok?

3 Answers3