ixml parser: character data that no tag follows

[oblomov-dev]

What is wrong

The value branch of the parse loop takes the offset of the next < without
looking at whether there was one, src/ixml/cl_ixml.clas.locals_imp.abap:

* value
FIND FIRST OCCURRENCE OF '<' IN lv_xml MATCH OFFSET lv_offset.
lv_value = lv_xml(lv_offset).

sy-subrc is ignored, so when the document ends in character data the offset
of the previous match still stands. Two ways that goes wrong:

parse( |hello| ).
" no match had been made yet, so the offset is 0: the value is empty, lv_xml
" does not advance, and the WHILE loop runs forever. It ends as an
" out-of-memory abort of the process, not as an error the caller can see

parse( |<root/>trail| ).
parse( |<root><item>A| ).
" the offset of the last tag stands and reads past the end of the rest

None of the three is well-formed XML. But a truncated response, a file that
turns out to be HTML, or an error page where XML was expected all reach a
parser as they stand — and of all the ways to say "this is not a document",
hanging until the process dies is the worst one.

The change

FIND FIRST OCCURRENCE OF '<' IN lv_xml MATCH OFFSET lv_offset.
IF sy-subrc <> 0.
  lv_offset = strlen( lv_xml ).
ENDIF.

When no tag follows, the rest of the document is the value. The loop advances
in every case and ends, and what was read before stays readable: <root/>trail
keeps its root element, <root><item>A keeps the A.

A well-formed document is untouched — its character data always ends at a <,
so the new branch is never reached.

Tests

• parse_text_without_markup — hello is one text node, and the parse
  returns (this is the test that used to hang)
• parse_text_after_root — <root>…</root>tail still has its root element
• parse_unclosed_tag — <root><item>A keeps the value that was read

npm test is green: abaplint: 0 issue(s) found, 735 file(s) analyzed, and
the full unit run passes.

Note

This says nothing about reporting the malformed document — parse( ) still
returns 0 and if_ixml_parser~num_errors is still a todo. That is its own
change; this one is about the loop that does not terminate.