[tx] cffread CFF2 fails with extra names in post 2.0

[blueshade7]

tx -cff2 fails with the attached CFF2 font.

% tx -cff2  SourceSansPro-Regular-cff2-A.otf
tx: --- SourceSansPro-Regular-cff2-A.otf
tx: (cfr) post 2.0: string data didn't reach end of table
tx: (cfr) client failed glyph parse

ots-sanitize reports no problem about the font.

The font contains only one glyph other than .notdef but the post table version 2.0 contains extra unused glyph names. This appears to be confusing cffread.

% spot -tpost SourceSansPro-Regular-cff2-A.otf
### [post] (00000420)
version           =2.0 (00020000)
italicAngle       =0.000 (00000000)
underlinePosition =-50
underlineThickness=50
isFixedPitch      =0
minMemType42      =0
maxMemType42      =0
minMemType1       =0
maxMemType1       =0
--- format 2.0
numberGlyphs=2
--- glyphNameIndex[glyphId]=value
[0]=0 [1]=259 
--- names[index]={len,<name>}
[0]={6,<Abreve>} [1]={11,<Abreveacute>} [2]={14,<Abrevedotbelow>} [3]={11,<Abrevegrave>} [4]={15,<Abrevehookabove>} [5]={11,<Abrevetilde>} [6]={6,<Acaron>} [7]={16,<Acircumflexacute>} [8]={19,<Acircumflexdotbelow>} [9]={16,<Acircumflexgrave>} 

SourceSansPro-Regular-cff2-A.otf.zip

[blueshade7]

postReadcounts the number of names used by all glyphs in post 2.0 in variable strCount.

afdko/c/public/lib/source/cffread/cffread.c

Lines 2003 to 2011 in 7648029

	for (i = 0; i < numGlyphs; i++) {
	unsigned short nid = read2(h);
	h->post.fmt2.glyphNameIndex.array[i] = nid;
	if (nid > 32767) {
	message(h, "post 2.0: invalid name id (table ignored)");
	goto parseError;
	} else if (nid > 257)
	strCount++;
	}

Then copies this many strings from the beginning of the string area in the post table.

afdko/c/public/lib/source/cffread/cffread.c

Lines 2019 to 2031 in 7648029

	dnaSET_CNT(h->post.fmt2.strings, strCount);
	p = h->post.fmt2.buf.array;
	end = p + length;
	for (i = 0; i < h->post.fmt2.strings.cnt; i++) {
	length = *(uint8_t *)p;
	*p++ = '\0';
	h->post.fmt2.strings.array[i] = p;
	p += length;
	if (p > end) {
	message(h, "post 2.0: invalid strings");
	goto parseError;
	}
	}

If any unused names are included, used names that follow cannot be correctly looked up by post2GetName.

afdko/c/public/lib/source/cffread/cffread.c

Lines 1847 to 1848 in 7648029

	else if (nid - 258 >= h->post.fmt2.strings.cnt) {
	return NULL; /* Out of bounds; .notdef */