Add QPDFPageLabelDocumentHelper

ChangeLog

@@ -1,5 +1,12 @@
 2018-12-18  Jay Berkenbilt  <ejb@ql.org>
 
+	* Add QPDFPageLabelDocumentHelper class. This is a document helper
+	class that provides useful methods for dealing with page labels.
+	It abstracts the fact that they are stored as number trees and
+	deals with interpolating intermediate values that are not in the
+	tree. It also has helper functions used by the qpdf command line
+	tool to preserve page labels when merging and splitting files.
+
 	* Add QPDFNumberTreeObjectHelper class. This class provides useful
 	methods for dealing with number trees, which are discussed in
 	section 7.9.7 of the PDF spec (ISO-32000). Page label dictionaries

include/qpdf/QPDFPageLabelDocumentHelper.hh

@@ -0,0 +1,100 @@
+// Copyright (c) 2005-2018 Jay Berkenbilt
+//
+// This file is part of qpdf.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// Versions of qpdf prior to version 7 were released under the terms
+// of version 2.0 of the Artistic License. At your option, you may
+// continue to consider qpdf to be licensed under those terms. Please
+// see the manual for additional information.
+
+#ifndef QPDFPAGELABELDOCUMENTHELPER_HH
+#define QPDFPAGELABELDOCUMENTHELPER_HH
+
+#include <qpdf/QPDFDocumentHelper.hh>
+
+#include <qpdf/QPDF.hh>
+#include <qpdf/QPDFNumberTreeObjectHelper.hh>
+#include <vector>
+
+#include <qpdf/DLL.h>
+
+// Page labels are discussed in the PDF spec (ISO-32000) in section
+// 12.4.2.
+//
+// Page labels are implemented as a number tree. Each key is a page
+// index, numbered from 0. The values are dictionaries with the
+// following keys, all optional:
+//
+// * /Type: if present, must be /PageLabel
+// * /S: one of /D, /R, /r, /A, or /a for decimal, upper-case and
+//   lower-case Roman numeral, or upper-case and lower-case alphabetic
+// * /P: if present, a fixed prefix string that is prepended to each
+//   page number
+// * /St: the starting number, or 1 if not specified
+
+class QPDFPageLabelDocumentHelper: public QPDFDocumentHelper
+{
+  public:
+    QPDF_DLL
+    QPDFPageLabelDocumentHelper(QPDF&);
+
+    QPDF_DLL
+    bool hasPageLabels();
+
+    // Return a page label dictionary representing the page label for
+    // the given page. The page does not need to appear explicitly in
+    // the page label dictionary. This method will adjust /St as
+    // needed to produce a label that is suitable for the page.
+    QPDF_DLL
+    QPDFObjectHandle getLabelForPage(long long page_idx);
+
+    // Append to the incoming vector a list of objects suitable for
+    // inclusion in a /PageLabels dictionary's /Nums field. start_idx
+    // and end_idx are the indexes to the starting and ending pages
+    // (inclusive) in the original file, and new_start_idx is the
+    // index to the first page in the new file. For example, if pages
+    // 10 through 12 of one file are being copied to a new file as
+    // pages 6 through 8, you would call getLabelsForPageRange(10, 12,
+    // 6), which would return as many entries as are required to add
+    // to the new file's PageLabels. This method fabricates a suitable
+    // entry even if the original document has no page labels. This
+    // behavior facilitates using this function to incrementally build
+    // up a page labels tree when merging files.
+    QPDF_DLL
+    void
+    getLabelsForPageRange(long long start_idx, long long end_idx,
+                          long long new_start_idx,
+                          std::vector<QPDFObjectHandle>& new_labels);
+
+  private:
+    class Members
+    {
+        friend class QPDFPageLabelDocumentHelper;
+
+      public:
+        QPDF_DLL
+        ~Members();
+
+      private:
+        Members();
+        Members(Members const&);
+
+        PointerHolder<QPDFNumberTreeObjectHelper> labels;
+    };
+
+    PointerHolder<Members> m;
+};
+
+#endif // QPDFPAGELABELDOCUMENTHELPER_HH

libqpdf/QPDFPageLabelDocumentHelper.cc

@@ -0,0 +1,125 @@
+#include <qpdf/QPDFPageLabelDocumentHelper.hh>
+#include <qpdf/QTC.hh>
+
+QPDFPageLabelDocumentHelper::Members::~Members()
+{
+}
+
+QPDFPageLabelDocumentHelper::Members::Members()
+{
+}
+
+QPDFPageLabelDocumentHelper::QPDFPageLabelDocumentHelper(QPDF& qpdf) :
+    QPDFDocumentHelper(qpdf),
+    m(new Members())
+{
+    QPDFObjectHandle root = qpdf.getRoot();
+    if (root.hasKey("/PageLabels"))
+    {
+        this->m->labels = new QPDFNumberTreeObjectHelper(
+            root.getKey("/PageLabels"));
+    }
+}
+
+bool
+QPDFPageLabelDocumentHelper::hasPageLabels()
+{
+    return 0 != this->m->labels.getPointer();
+}
+
+QPDFObjectHandle
+QPDFPageLabelDocumentHelper::getLabelForPage(long long page_idx)
+{
+    QPDFObjectHandle result(QPDFObjectHandle::newNull());
+    if (! hasPageLabels())
+    {
+        return result;
+    }
+    QPDFNumberTreeObjectHelper::numtree_number offset = 0;
+    QPDFObjectHandle label;
+    if (! this->m->labels->findObjectAtOrBelow(page_idx, label, offset))
+    {
+        return result;
+    }
+    if (! label.isDictionary())
+    {
+        return result;
+    }
+    QPDFObjectHandle S = label.getKey("/S");   // type (D, R, r, A, a)
+    QPDFObjectHandle P = label.getKey("/P");   // prefix
+    QPDFObjectHandle St = label.getKey("/St"); // starting number
+    long long start = 1;
+    if (St.isInteger())
+    {
+        start = St.getIntValue();
+    }
+    start += offset;
+    result = QPDFObjectHandle::newDictionary();
+    result.replaceOrRemoveKey("/S", S);
+    result.replaceOrRemoveKey("/P", P);
+    result.replaceOrRemoveKey("/St", QPDFObjectHandle::newInteger(start));
+    return result;
+}
+
+void
+QPDFPageLabelDocumentHelper::getLabelsForPageRange(
+    long long start_idx, long long end_idx, long long new_start_idx,
+    std::vector<QPDFObjectHandle>& new_labels)
+{
+    // Start off with a suitable label for the first page. For every
+    // remaining page, if that page has an explicit entry, copy it.
+    // Otherwise, let the subsequent page just sequence from the prior
+    // entry. If there is no entry for the first page, fabricate one
+    // that would match how the page would look in a new file in which
+    // it also didn't have an explicit label.
+    QPDFObjectHandle label = getLabelForPage(start_idx);
+    if (label.isNull())
+    {
+        label = QPDFObjectHandle::newDictionary();
+        label.replaceKey(
+            "/St", QPDFObjectHandle::newInteger(1 + new_start_idx));
+    }
+    // See if the new label is redundant based on the previous entry
+    // in the vector. If so, don't add it.
+    size_t size = new_labels.size();
+    bool skip_first = false;
+    if (size >= 2)
+    {
+        QPDFObjectHandle last = new_labels[size - 1];
+        QPDFObjectHandle last_idx = new_labels[size - 2];
+        if (last_idx.isInteger() && last.isDictionary() &&
+            (label.getKey("/S").unparse() == last.getKey("/S").unparse()) &&
+            (label.getKey("/P").unparse() == last.getKey("/P").unparse()) &&
+            label.getKey("/St").isInteger() &&
+            last.getKey("/St").isInteger())
+        {
+            long long int st_delta =
+                label.getKey("/St").getIntValue() -
+                last.getKey("/St").getIntValue();
+            long long int idx_delta =
+                new_start_idx - last_idx.getIntValue();
+            if (st_delta == idx_delta)
+            {
+                QTC::TC("qpdf", "QPDFPageLabelDocumentHelper skip first");
+                skip_first = true;
+            }
+        }
+    }
+    if (! skip_first)
+    {
+        new_labels.push_back(QPDFObjectHandle::newInteger(new_start_idx));
+        new_labels.push_back(label);
+    }
+
+    long long int idx_offset = new_start_idx - start_idx;
+    for (long long i = start_idx + 1; i <= end_idx; ++i)
+    {
+        if (this->m->labels->hasIndex(i) &&
+            (label = getLabelForPage(i)).isDictionary())
+        {
+            new_labels.push_back(QPDFObjectHandle::newInteger(i + idx_offset));
+            new_labels.push_back(label);
+        }
+    }
+}
+

libqpdf/build.mk

@@ -45,6 +45,7 @@ SRCS_libqpdf = \
 	libqpdf/QPDFObject.cc \
 	libqpdf/QPDFObjectHandle.cc \
 	libqpdf/QPDFPageDocumentHelper.cc \
+	libqpdf/QPDFPageLabelDocumentHelper.cc \
 	libqpdf/QPDFPageObjectHelper.cc \
 	libqpdf/QPDFSystemError.cc \
 	libqpdf/QPDFTokenizer.cc \

qpdf/qtest/qpdf.test

@@ -234,6 +234,24 @@ $td->runtest("number trees",
 	     {$td->FILE => "number-tree.out", $td->EXIT_STATUS => 0},
 	     $td->NORMALIZE_NEWLINES);
 
+show_ntests();
+# ----------
+$td->notify("--- Page Labels ---");
+$n_tests += 3;
+
+$td->runtest("complex page labels",
+	     {$td->COMMAND => "test_driver 47 page-labels-num-tree.pdf"},
+	     {$td->FILE => "page-labels-num-tree.out", $td->EXIT_STATUS => 0},
+	     $td->NORMALIZE_NEWLINES);
+$td->runtest("no zero entry for page labels",
+	     {$td->COMMAND => "test_driver 47 page-labels-no-zero.pdf"},
+	     {$td->FILE => "page-labels-no-zero.out", $td->EXIT_STATUS => 0},
+	     $td->NORMALIZE_NEWLINES);
+$td->runtest("no page labels",
+	     {$td->COMMAND => "test_driver 47 minimal.pdf"},
+	     {$td->FILE => "no-page-labels.out", $td->EXIT_STATUS => 0},
+	     $td->NORMALIZE_NEWLINES);
+
 show_ntests();
 # ----------
 $td->notify("--- Page API Tests ---");

qpdf/qtest/qpdf/no-page-labels.out

@@ -0,0 +1,2 @@
+1 << /St 2 >>
+test 47 done

qpdf/qtest/qpdf/page-labels-no-zero.out

@@ -0,0 +1,15 @@
+1 << /St 2 >>
+3 << /P (blank) /St 1 >>
+4 << /P (X-) /S /A /St 17 >>
+6 << /P () /St 1 >>
+7 << /S /R /St 3 >>
+10 << /S /D /St 1 >>
+12 << /S /a /St 1 >>
+13 << /S /a /St 3 >>
+16 << /P (q.) /S /D /St 6 >>
+20 << /P (www) /St 1 >>
+21 << /S /D /St 12 >>
+23 << /S /D /St 16059 >>
+24 << /S /R /St 50 >>
+30 << /S /r /St 54 >>
+test 47 done

qpdf/qtest/qpdf/page-labels-num-tree.out

@@ -0,0 +1,15 @@
+1 << /S /r /St 1 >>
+3 << /P (blank) /St 1 >>
+4 << /P (X-) /S /A /St 17 >>
+6 << /P () /St 1 >>
+7 << /S /R /St 3 >>
+10 << /S /D /St 1 >>
+12 << /S /a /St 1 >>
+13 << /S /a /St 3 >>
+16 << /P (q.) /S /D /St 6 >>
+20 << /P (www) /St 1 >>
+21 << /S /D /St 12 >>
+23 << /S /D /St 16059 >>
+24 << /S /R /St 50 >>
+30 << /S /r /St 54 >>
+test 47 done

qpdf/test_driver.cc

@@ -7,6 +7,7 @@
 #include <qpdf/QPDFPageObjectHelper.hh>
 #include <qpdf/QPDFAcroFormDocumentHelper.hh>
 #include <qpdf/QPDFNumberTreeObjectHelper.hh>
+#include <qpdf/QPDFPageLabelDocumentHelper.hh>
 #include <qpdf/QUtil.hh>
 #include <qpdf/QTC.hh>
 #include <qpdf/Pl_StdioFile.hh>
@@ -1690,6 +1691,21 @@ void runtest(int n, char const* filename1, char const* arg2)
         assert("six" == oh.getStringValue());
         assert(2 == offset);
     }
+    else if (n == 47)
+    {
+        // Test page labels.
+        QPDFPageLabelDocumentHelper pldh(pdf);
+        size_t npages = pdf.getRoot().getKey("/Pages").
+            getKey("/Count").getIntValue();
+        std::vector<QPDFObjectHandle> labels;
+        pldh.getLabelsForPageRange(0, npages - 1, 1, labels);
+        assert(labels.size() % 2 == 0);
+        for (size_t i = 0; i < labels.size(); i+= 2)
+        {
+            std::cout << labels.at(i).getIntValue() << " "
+                      << labels.at(i+1).unparse() << std::endl;
+        }
+    }
     else
     {
 	throw std::runtime_error(std::string("invalid test ") +