About 'application/octet-stream' MIME attachments. A MIME attachment with the content type 'application/octet-stream' is a binary file.Typically, it will be an.
According to the MIME that you've given, you're reading data that's in non-textual binary format. You cannot convert it with iconv or similar, because it's meant for converting text from one (textual) encoding to another. If your data is not textual, then a conversion to any character encoding is meaningless and will just corrupt the data, but not make it any more readable.
The typical way to present binary as readable text for inspection is. There's an existing answer for implementing it in c.
I receive data every day from a client, but I can't read it. It's an encoded file.
If I open it directly with cat, less or vi, I can't read it. The customer shared the data file as filename.ZIP.zip (120 Mb).
After I extracted the contents I got one more zip file like filename.ZIP.zip (120 Mb) and filename.ZIP (125 mb). Once again extracting I get filename (4-5 GB) with file type application/octet-stream; charset=binary format.
Content Type Application Octet Stream
NOTE: I receive the file in some different formats, like binary, ISO8859, etc. It is inappropriate to use iconv on non-text files. What you can do is use a hex-dump program to view the contents of a binary file.