Django incorrectly restricts HTTP header values to ASCII
|Reported by:||aaugustin||Owned by:||aaugustin|
|Has patch:||yes||Needs documentation:||no|
|Needs tests:||no||Patch needs improvement:||no|
Whenever a HTTP header is set for an HttpResponse, Django raises an exception if its key or value contains non-ASCII characters.
However, RFC2616 defines message headers in section 4.2 as:
message-header = field-name ":" [ field-value ] field-name = token field-value = *( field-content | LWS ) field-content = <the OCTETs making up the field-value and consisting of either *TEXT or combinations of token, separators, and quoted-string>
The TEXT rule is only used for descriptive field contents and values that are not intended to be interpreted by the message parser. Words of *TEXT MAY contain characters from character sets other than ISO- 8859-1  only when encoded according to the rules of RFC 2047 . TEXT = <any OCTET except CTLs, but including LWS>
This indicates that an arbitrary bytestring is acceptable as a value.
I hit this issue while setting a X-SendFile header pointing to a non-ASCII file name. It seems to me that Django should:
- at least accept any bytes content (since any bytestring can be interpreted as latin-1) and attempt converting text content to latin-1, raising an error if that isn't possible
- even better, use MIME encoding for text values that don't fit in the latin-1 charset.
The header keys must stay restricted to ASCII: RFC 2616 says they're of the token type, defined by:
token = 1*<any CHAR except CTLs or separators>
CHAR = <any US-ASCII character (octets 0 - 127)>
Finally, PEP 3333 says:
Note also that strings passed to start_response() as a status or as response headers must follow RFC 2616 with respect to encoding. That is, they must either be ISO-8859-1 characters, or use RFC 2047 MIME encoding.
On Python platforms where the str or StringType type is in fact Unicode-based (e.g. Jython, IronPython, Python 3, etc.), all "strings" referred to in this specification must contain only code points representable in ISO-8859-1 encoding (\u0000 through \u00FF, inclusive).
PS: RFC 2616 points to RFC 822, where section 3.1.2. restricts headers to ASCII. This may explain why Django has this restriction.