Markus Wiederkehr wrote:
On Tue, Feb 10, 2009 at 8:28 PM, Oleg Kalnichevski <[email protected]> wrote:
Markus Wiederkehr wrote:
I've been investigating the current code a little bit more and I've
come to think that something really goes wrong. Please have a look at
the code.
Class AbstractEntity has a ByteArrayBuffer "linebuf" and a
CharArrayBuffer "fieldbuf". Method fillFieldBuffer() copies bytes from
the underlying stream to "linebuf" (line 146:
instream.readLine(linebuf)). Later on the input bytes are appended to
"fieldbuf" (line 143: fieldbuf.append(linebuf, 0, len)). At this point
bytes are decoded into characters. A closer look at CharArrayBuffer
reveals how this is done:
int ch = b[i1];
if (ch < 0) {
ch = 256 + ch;
}
This is equivalent to ISO-8859-1 conversion because Latin 1 is the
only charset that directly maps byte codes 00 to ff to unicode code
points 0000 to 00ff.
All works well as long as the underlying stream only contains ASCII bytes.
But assume the message contains non-ASCII bytes and a Content-Type
field with a charset parameter is also present. In this case the input
bytes should probably be decoded using that specified charset instead
of Latin 1. This is the opposite situation to the LENIENT writing mode
where we encode header fields using the charset from the Content-Type
field.
To me, parsing of MIME headers using any charset other that US-ASCII never
made any sense of what so ever, but so be it.
Interesting.. I always thought that the lenient writing mode is a
requirement coming from the http world or HC more specifically.
If my memory does not fail me it was the other way around. Prior to 0.4
mime4j only supported what is now called lenient mode.
And if
someone wants to write non-ascii chars using the content-type charset
it seems only natural that a corresponding parsing mode is also
required.
True. This is very reasonable.
So, in the lenient mode, effectively, we would have to do the following: (1)
parse headers (at least partially) in order to locate Content-Type header
and extract the charset attribute from it, if present; (2) parse all headers
again (probably, lazily) using the charset from the Content-Type.
Exactly.
That's quite a bit of extra work.
Well, actually not very much, at least when compared to the current
code. Currently header fields are already parsed twice, by
AbstractEntity and a second time by MessageBuilder. MessageBuilder
would only have to keep the raw fields in a list and defer the Field
creation until endHeader() is invoked..
>
Okay, so now assume we have parsed that message and use the LENIENT
writing mode to write it out again. Clearly we have a serious round
tripping issue now, because Latin 1 was used to decode the fields but
the potentially different Content-Type charset is used to encode them
again.
I think the inherent problem is that AbstractEntity attempts to
convert bytes into characters. This should not happen so early in the
process.
In my opinion it would be better if AbstractEntity treated a header
field as a byte array. It would be better to pass a byte array to a
ContentHandler or a BodyDescriptor. The ContentHandler /
BodyDescriptor implementation can then decide how to decode the bytes.
This would push the responsibility of detecting the charset and correct
parsing of headers to individual ContentHandler implementations and would
make the task of implementing a ContentHandler more complex, but probably is
the most flexible solution to the problem.
A ContentHandler receives everything else as a sequence of bytes; the
message body as well as preamble/epilogue of a multipart. Only the
headers come as string.
This could really help with the goal of complete round tripping..
Class Field could store the original raw field value in a byte array
instead a String.
One drawback would be that duplicate parsing of header fields is maybe
inevitable..
Opinions?
I am in favor of using ByteArrayBuffer at the ContentHandler level, even
though this would make the task of implementing it more difficult.
All right. If there are no objections, I can put together a patch along
the lines outlined above.
Oleg
Oleg
Markus
PS: I don't indent to stop 0.6 but maybe we should keep the note
regarding round trip issues in the release notes.
