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.
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.
That's quite a bit of extra work.
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.
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.
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.
