っていう文言読む限り，明らかに blocking-preserving じゃんかよぉ〜．ぶ〜ぶ〜ぶ〜． API の reference 読んでもこれの確証が持てなかったから，（blocking-preserving を保証しようと）わざわざ内部にバッファを持たせてた私の苦労は一体なんだったのかと小1時間……．
The converters write to the target all converted output as far as possible, and then write any remaining output to the internal services buffer. When the conversion routines are called again, the internal buffer is flushed out and written to the target buffer before proceeding with any further conversion.
つーか，逆向きは？
一瞬逆向きはど〜なんだという疑問も湧いたけれど，
っていってるから逆向きも blocking-preserving か．……ホント？
The converters always consume the source buffer as far as possible, and advance the source pointer.
