mime: do not perform more than one read in a row

Input buffer filling may delay the data sending if data reads are slow.
To overcome this problem, file and callback data reads do not accumulate
in buffer anymore. All other data (memory data and mime framing) are
considered as fast and still concatenated in buffer.
As this may highly impact performance in terms of data overhead, an early
end of part data check is added to spare a read call.
When encoding a part's data, an encoder may require more bytes than made
available by a single read. In this case, the above rule does not apply
and reads are performed until the encoder is able to deliver some data.

Tests 643, 644, 645, 650 and 654 have been adapted to the output data
changes, with test data size reduced to avoid the boredom of long lists of
1-byte chunks in verification data.
New test 667 checks mimepost using single-byte read callback with encoder.
New test 668 checks the end of part data early detection.

Fixes #4826
Reported-by: MrdUkk on github

1 files changed, 1 insertions, 1 deletions

diff --git a/tests/data/Makefile.inc b/tests/data/Makefile.inc
index 99052007f..4cb7a8e74 100644
--- a/tests/data/Makefile.inc
+++ b/tests/data/Makefile.inc
@@ -85,7 +85,7 @@ test626 test627 test628 test629 test630 test631 test632 test633 test634 \
 test635 test636 test637 test638 test639 test640 test641 test642 \
 test643 test644 test645 test646 test647 test648 test649 test650 test651 \
 test652 test653 test654 test655 test656 test658 test659 test660 test661 \
-test662 test663 test664 test665 \
+test662 test663 test664 test665 test667 test668 \
 test670 test671 test672 test673 \
 \
 test700 test701 test702 test703 test704 test705 test706 test707 test708 \