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font/sfnt: fix hmtx table size validation

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The library assumes the hmtx size to be equal to 2*nGlyph + 2*nHm,
which is a simplification of 4*nHm + 2*(nGlyph-nHm) as described
in the spec. However, fonts seen in the wild sometimes omit the
second term (left side bearings), making validation to fail.

CL fixes the validation code by allowing to omit the second term.

Fixes golang/go#28379

Change-Id: I2293e498e72f95e5fe08c2b375ea7b020d06cde3
Reviewed-on: https://go-review.googlesource.com/c/144080
Reviewed-by: Nigel Tao <nigeltao@golang.org>
This commit is contained in:
Denys Smirnov 2018-10-25 03:51:34 +03:00 committed by Nigel Tao
parent 69cc3646b9
commit 63626fb251
1 changed files with 4 additions and 1 deletions
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5
font/sfnt/sfnt.go
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@ -904,7 +904,10 @@ func (f *Font) parseHhea(buf []byte, numGlyphs int32) (buf1 []byte, ascent, desc
func (f *Font) parseHmtx(buf []byte, numGlyphs, numHMetrics int32) (buf1 []byte, err error) { func (f *Font) parseHmtx(buf []byte, numGlyphs, numHMetrics int32) (buf1 []byte, err error) {
// https://www.microsoft.com/typography/OTSPEC/hmtx.htm // https://www.microsoft.com/typography/OTSPEC/hmtx.htm
if f.hmtx.length != uint32(2*numGlyphs+2*numHMetrics) { // The spec says that the hmtx table's length should be
// "4*numHMetrics+2*(numGlyphs-numHMetrics)". However, some fonts seen in the
// wild omit the "2*(nG-nHM)". See https://github.com/golang/go/issues/28379
if f.hmtx.length != uint32(4*numHMetrics) && f.hmtx.length != uint32(4*numHMetrics+2*(numGlyphs-numHMetrics)) {
return nil, errInvalidHmtxTable return nil, errInvalidHmtxTable
} }
return buf, nil return buf, nil