Application Octet Stream
These OCTET-STREAM files may be opened by renaming the extension of the attached file to a specific file extension, and then by using an application with support for opening such files. For example, an.octet-stream file may be renamed to a.txt file (if it is indeed a.txt file), and Notepad may then be used to open the file. An octect-stream is a binary byte file. Typically they are base64 encoded, but need to be. Even though it may be a xml text stream, the server does not know the encoding (u8 or u16). The caller should use the proper contenttype.
The HTTP standard says:
If this header [Content-Disposition: attachment] is used in a response with the application/octet-stream content-type, the implied suggestion is that the user agent should not display the response, but directly enter a `save response as...' dialog.
I read that as
But I would have thought that Content-Type would be application/pdf, image/png, etc.
Should I have Content-Type: application/octet-stream if I want browsers to download the file?
1 Answer
No.
The content-type should be whatever it is known to be, if you know it. application/octet-stream is defined as 'arbitrary binary data' in RFC 2046, and there's a definite overlap here of it being appropriate for entities whose sole intended purpose is to be saved to disk, and from that point on be outside of anything 'webby'. Or to look at it from another direction; the only thing one can safely do with application/octet-stream is to save it to file and hope someone else knows what it's for.
You can combine the use of Content-Disposition with other content-types, such as image/png or even text/html to indicate you want saving rather than display. It used to be the case that some browsers would ignore it in the case of text/html but I think this was some long time ago at this point (and I'm going to bed soon so I'm not going to start testing a whole bunch of browsers right now; maybe later).
RFC 2616 also mentions the possibility of extension tokens, and these days most browsers recognise inline to mean you do want the entity displayed if possible (that is, if it's a type the browser knows how to display, otherwise it's got no choice in the matter). This is of course the default behaviour anyway, but it means that you can include the filename part of the header, which browsers will use (perhaps with some adjustment so file-extensions match local system norms for the content-type in question, perhaps not) as the suggestion if the user tries to save.
Hence:
Means 'I don't know what the hell this is. Please save it as a file, preferably named picture.png'.
Means 'This is a PNG image. Please save it as a file, preferably named picture.png'.
Means 'This is a PNG image. Please display it unless you don't know how to display PNG images. Otherwise, or if the user chooses to save it, we recommend the name picture.png for the file you save it as'.
Of those browsers that recognise inline some would always use it, while others would use it if the user had selected 'save link as' but not if they'd selected 'save' while viewing (or at least IE used to be like that, it may have changed some years ago).
protected by Rachel GallenMar 15 at 8:50
Thank you for your interest in this question. Because it has attracted low-quality or spam answers that had to be removed, posting an answer now requires 10 reputation on this site (the association bonus does not count).
Would you like to answer one of these unanswered questions instead?