Thread: How to work with strings containing possibly several NULLs

I am working on a mail environment which requires me to retrieve mails from a POP3 server. For everyone unfamiliar with how the POP works:

You issue CRLF-terminated commands and retrieve answers of unknown physical lengh containing ASCII chars terminated by a CRLF.CRLF

If I now want to work on parts of that retrieve message - say extract information from the mail header - I'd have to use string-dependent functions - like strstr() or some regexing stuff. But, as I mentioned before, the answer may contain every ASCII char - even the '\0'/NULL character.

Hence, how would you propose I should handle this data? Is there a string function which doesn't depend on the NULL-byte rather than on a given length? Or do I have to write some code which will iterate through all the chars of the answer, replace every NULL-byte with a sequence of my choice and later replace that replacement char again so the integrity isn't destroyed?

Sloede

memmove() moves (copies) memory from one place to another, based on the number of bytes.

Where did you find that anything which is not printable will be encoded?

I just found that in RFC 822:

The field-name must be composed of printable ASCII characters (i.e., characters that have values between 33. and 126., decimal, except colon). The field-body may be composed of any ASCII characters, except CR or LF.

[...]

The body is simply a sequence of lines containing ASCII characters.

That means to me that NULLs can very well be part of the header-field-contents or the message body, or am I getting this totally wrong?

Your right, but that is only true for field-names. The field-body may contain _any ASCII char except CR/LF and the message body may contain ALL ASCII chars - and that's the problem I have:

How to work with string functions on ASCII char-data if the data may contain NULL-bytes?

But how would you suggest to rewrite the regexing functions? Go through the source code and change everything which doesn't fit?

Seems like hell of a lot work

But if you state that this is my solution - why not trying it?


Peace,

Sloede

I don't believe that there can be NULL bytes in an email but if there really are just replace them with some non-ascii byte before processing.
Every byte with a value of more then 127 is not an ASCII character. So there can't be any bytes bigger then 127 in an email. That means you can e.g. replace all '\0' with 0xFF.

That makes sense! Especially when there's no obvious reason for a NULL-byte, there shouldn't be a great loss of information by changing it to some other byte. I'll probably choose some non-printable char as well, as that wouldn't even change the appearance of the text (like the ACK byte for example)