[PDFBOX-4033] KerningSubtable should skip zero-length kerning subtables

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Incomplete
• Affects Version/s: 2.0.8
• Component/s: FontBox
• Labels: easyfix
• Environment: Any
• Flags: Patch
• Assignee: Unassigned
• Reporter: Max Gilead
• Created: 11/Dec/17 10:56
• Updated: 14/Jan/18 16:54
• Resolved: 14/Jan/18 16:54

Description

DejaVuSansLight has a zero-length kerning subtable. This currently triggers an IOException but it seems to be safe to ignore such tables.

The simple fix below (the BLOCK ADDED block) makes PDFBox work with fonts like that.

We must use a locally-patched PDFBox fork as it is paramount to us that it works uninterrupted as much as possible, even with less-than-ideal data.

private void readSubtable0(TTFDataStream data) throws IOException
    {
        int version = data.readUnsignedShort();
        if (version != 0)
        {
            LOG.info("Unsupported kerning sub-table version: " + version);
            return;
        }
        int length = data.readUnsignedShort();
        if (length < 6)
        {
            if (length == 0) // BLOCK ADDED
            {
                LOG.info("Kerning sub-table empty, skipping.");
                return;
            }
            throw new IOException("Kerning sub-table too short, got " + length
                    + " bytes, expect 6 or more.");
        }