Make pdfminer Type3 patch conditional on PScript5.dll

It appears that PDFs created by this software have a bug in their BBox
which will cause us to misjudge the space occupied by the font.

Other programs probably work around this by ignoring BBox and reading
each character procedure.

src/ocrmypdf/pdfinfo/__init__.py

@@ -615,9 +615,8 @@ def _pdf_get_pageinfo(pdf, pageno: int, infile, xmltext):
 
     # pageinfo['textinfo'] = _page_get_textblocks(
     #     fspath(infile), pageno, xmltext=xmltext)
-
-    with Path(infile).open('rb') as f:
-        miner = get_page_analysis(f, pageno)
+    pscript5_mode = str(pdf.metadata.get('/Creator')).startswith('PScript5')
+    miner = get_page_analysis(infile, pageno, pscript5_mode)
     pageinfo['textboxes'] = list(simplify_textboxes(miner))
 
     mediabox = [Decimal(d) for d in page.MediaBox.as_list()]

src/ocrmypdf/pdfinfo/layout.py

@@ -16,28 +16,31 @@
 # along with OCRmyPDF.  If not, see <http://www.gnu.org/licenses/>.
 
 import re
+from math import copysign
+from pathlib import Path
+from unittest.mock import patch
 
 import pdfminer.encodingdb
-import pdfminer.pdfinterp
 import pdfminer.pdfdevice
-
+import pdfminer.pdfinterp
 from pdfminer.converter import PDFLayoutAnalyzer
-from pdfminer.pdfdocument import PDFTextExtractionNotAllowed
 from pdfminer.glyphlist import glyphname2unicode
-from pdfminer.layout import (
-    LTChar, LTContainer, LTLayoutContainer, LTPage, LTTextLine, LAParams,
-    LTTextBox
-)
-from pdfminer.pdffont import PDFUnicodeNotDefined, PDFType3Font, PDFFont, PDFCIDFont
+from pdfminer.layout import (LAParams, LTChar, LTContainer, LTLayoutContainer,
+                             LTPage, LTTextBox, LTTextLine)
+from pdfminer.pdfdocument import PDFTextExtractionNotAllowed
+from pdfminer.pdffont import (PDFCIDFont, PDFFont, PDFType3Font,
+                              PDFUnicodeNotDefined)
 from pdfminer.pdfpage import PDFPage
-from pdfminer.utils import matrix2str, bbox2str, fsplit
+from pdfminer.utils import bbox2str, fsplit, matrix2str
 
 from ..exceptions import EncryptedPdfError
 
-
-
 STRIP_NAME = re.compile(r'[0-9]+')
 
+#
+# Unconditional pdfminer patches
+#
+
 def name2unicode(name):
     """Fix pdfminer's regex in name2unicode function
 
@@ -54,27 +57,8 @@ def name2unicode(name):
     if not m:
         raise KeyError(name)
     return chr(int(m.group(0)))
-
 pdfminer.encodingdb.name2unicode = name2unicode
 
-from math import copysign
-def PDFType3Font__get_height(self):
-    h = self.bbox[3]-self.bbox[1]
-    if h == 0:
-        h = self.ascent - self.descent
-    return h * copysign(1.0, self.vscale)
-
-def PDFType3Font__get_descent(self):
-    return self.descent * copysign(1.0, self.vscale)
-
-def PDFType3Font__get_ascent(self):
-    return self.ascent * copysign(1.0, self.vscale)
-
-PDFType3Font.get_height = PDFType3Font__get_height
-PDFType3Font.get_ascent = PDFType3Font__get_ascent
-PDFType3Font.get_descent = PDFType3Font__get_descent
-
-
 original_PDFFont_init = PDFFont.__init__
 def PDFFont__init__(self, descriptor, widths, default_width=None):
     original_PDFFont_init(self, descriptor, widths, default_width)
@@ -85,9 +69,23 @@ def PDFFont__init__(self, descriptor, widths, default_width=None):
     # to misposition text.
     if self.descent > 0:
         self.descent = -self.descent
-
 PDFFont.__init__ = PDFFont__init__
 
+#
+# pdfminer patches when creator is PScript5.dll
+#
+
+def PDFType3Font__PScript5_get_height(self):
+    h = self.bbox[3]-self.bbox[1]
+    if h == 0:
+        h = self.ascent - self.descent
+    return h * copysign(1.0, self.vscale)
+
+def PDFType3Font__PScript5_get_descent(self):
+    return self.descent * copysign(1.0, self.vscale)
+
+def PDFType3Font__PScript5_get_ascent(self):
+    return self.ascent * copysign(1.0, self.vscale)
 
 
 class LTStateAwareChar(LTChar):
@@ -183,17 +181,30 @@ class TextPositionTracker(PDFLayoutAnalyzer):
         return self.result
 
 
-def get_page_analysis(infile, pageno):
+def get_page_analysis(infile, pageno, pscript5_mode):
     rman = pdfminer.pdfinterp.PDFResourceManager(caching=True)
     dev = TextPositionTracker(rman, laparams=LAParams())
     interp = pdfminer.pdfinterp.PDFPageInterpreter(rman, dev)
 
-    page = PDFPage.get_pages(infile, pagenos=[pageno], maxpages=0)
+    if pscript5_mode:
+        patcher = patch.multiple(
+            'pdfminer.pdffont.PDFType3Font',
+            spec=True,
+            get_ascent=PDFType3Font__PScript5_get_ascent,
+            get_descent=PDFType3Font__PScript5_get_descent,
+            get_height=PDFType3Font__PScript5_get_height
+        )
+        patcher.start()
 
-    try:
-        interp.process_page(next(page))
-    except PDFTextExtractionNotAllowed as e:
-        raise EncryptedPdfError()
+    with Path(infile).open('rb') as f:
+        page = PDFPage.get_pages(f, pagenos=[pageno], maxpages=0)
+        try:
+            interp.process_page(next(page))
+        except PDFTextExtractionNotAllowed as e:
+            raise EncryptedPdfError()
+        finally:
+            if pscript5_mode:
+                patcher.stop()
 
     return dev.get_result()