Implement page manipulation APIs

Jay Berkenbilt
1 parent e01ae196
Showing 4 changed files with 175 additions and 103 deletions
include/qpdf/Constants.h
include/qpdf/QPDF.hh
libqpdf/QPDF_pages.cc
qpdf/qpdf.testcov
@@ -22,7 +22,8 @@ enum qpdf_error_code_e
     qpdf_e_system,		/* I/O error, memory error, etc. */
     qpdf_e_unsupported,		/* PDF feature not (yet) supported by qpdf */
     qpdf_e_password,		/* incorrect password for encrypted file */
-    qpdf_e_damaged_pdf		/* syntax errors or other damage in PDF */
+    qpdf_e_damaged_pdf,		/* syntax errors or other damage in PDF */
+    qpdf_e_pages,               /* erroneous or unsupported pages structure */
 };
  
 /* Write Parameters */
@@ -340,14 +340,26 @@ class QPDF
     // Convenience routines for common functions.  See also
     // QPDFObjectHandle.hh for additional convenience routines.
  
-    // Traverse page tree return all /Page objects.
+    // Page handling API
+
+    // Traverse page tree return all /Page objects.  Note that calls
+    // to page manipulation APIs will change the internal vector that
+    // this routine returns a pointer to.  If you don't want that,
+    // assign this to a regular vector rather than a const reference.
     QPDF_DLL
     std::vector<QPDFObjectHandle> const& getAllPages();
  
-    // QPDF internally caches the /Pages tree.  This method will clear
-    // the cache when e.g. direct modifications have been made.
+    // This method synchronizes QPDF's cache of the page structure
+    // with the actual /Pages tree.  If you restrict changes to the
+    // /Pages tree, including addition, removal, or replacement of
+    // pages or changes to any /Pages objects, to calls to these page
+    // handling APIs, you never need to call this method.  If you
+    // modify /Pages structures directly, you must call this method
+    // afterwards.  This method updates the internal list of pages, so
+    // after calling this method, any previous references returned by
+    // getAllPages() will be valid again.
     QPDF_DLL
-    void clearPagesCache();
+    void updateAllPagesCache();
  
     // Add new page at the beginning or the end of the current pdf
     QPDF_DLL
@@ -356,11 +368,11 @@ class QPDF
     // Add new page before or after refpage
     QPDF_DLL
     void addPageAt(QPDFObjectHandle newpage, bool before,
-                   QPDFObjectHandle const& refpage);
+                   QPDFObjectHandle refpage);
  
-    // Remove pageoh from the pdf.
+    // Remove page from the pdf.
     QPDF_DLL
-    void removePage(QPDFObjectHandle const& pageoh);
+    void removePage(QPDFObjectHandle page);
  
     // Resolver class is restricted to QPDFObjectHandle so that only
     // it can resolve indirect references.
@@ -541,12 +553,12 @@ class QPDF
  
     void getAllPagesInternal(QPDFObjectHandle cur_pages,
 			     std::vector<QPDFObjectHandle>& result);
-    // creates pageobj_to_pages_pos if necessary
-    // returns position, or -1 if not found
+    void insertPage(QPDFObjectHandle newpage, int pos);
     int findPage(int objid, int generation);
-    int findPage(QPDFObjectHandle const& pageoh); // convenience
-
+    int findPage(QPDFObjectHandle& page);
     void flattenPagesTree();
+    void insertPageobjToPage(QPDFObjectHandle const& obj, int pos,
+                             bool check_duplicate);
  
     // methods to support encryption -- implemented in QPDF_encryption.cc
     encryption_method_e interpretCF(QPDFObjectHandle);
@@ -6,6 +6,40 @@
 #include <qpdf/QUtil.hh>
 #include <qpdf/QPDFExc.hh>
  
+// In support of page manipulation APIs, these methods internally
+// maintain state about pages in a pair of data structures: all_pages,
+// which is a vector of page objects, and pageobj_to_pages_pos, which
+// maps a page object to its position in the all_pages array.
+// Unfortunately, the getAllPages() method returns a const reference
+// to all_pages and has been in the public API long before the
+// introduction of mutation APIs, so we're pretty much stuck with it.
+// Anyway, there are lots of calls to it in the library, so the
+// efficiency of having it cached is probably worth keeping it.
+
+// The goal of this code is to ensure that the all_pages vector, which
+// users may have a reference to, and the pageobj_to_pages_pos map,
+// which users will not have access to, remain consistent outside of
+// any call to the library.  As long as users only touch the /Pages
+// structure through page-specific API calls, they never have to worry
+// about anything, and this will also stay consistent.  If a user
+// touches anything about the /Pages structure outside of these calls
+// (such as by directly looking up and manipulating the underlying
+// objects), they can call updatePagesCache() to bring things back in
+// sync.
+
+// If the user doesn't ever use the page manipulation APIs, then qpdf
+// leaves the /Pages structure alone.  If the user does use the APIs,
+// then we push all inheritable objects down and flatten the /Pages
+// tree.  This makes it easier for us to keep /Pages, all_pages, and
+// pageobj_to_pages_pos internally consistent at all times.
+
+// Responsibility for keeping all_pages, pageobj_to_pages_pos, and the
+// Pages structure consistent should remain in as few places as
+// possible.  As of initial writing, only flattenPagesTree,
+// insertPage, and removePage, along with methods they call, are
+// concerned with it.  Everything else goes through one of those
+// methods.
+
 std::vector<QPDFObjectHandle> const&
 QPDF::getAllPages()
 {
@@ -44,152 +78,173 @@ QPDF::getAllPagesInternal(QPDFObjectHandle cur_pages,
     }
 }
  
-// FIXXX here down
-
 void
-QPDF::clearPagesCache()
+QPDF::updateAllPagesCache()
 {
+    // Force regeneration of the pages cache.  We force immediate
+    // recalculation of all_pages since users may have references to
+    // it that they got from calls to getAllPages().  We can defer
+    // recalculation of pageobj_to_pages_pos until needed.
+    QTC::TC("qpdf", "QPDF updateAllPagesCache");
     this->all_pages.clear();
     this->pageobj_to_pages_pos.clear();
+    getAllPages();
 }
  
 void
 QPDF::flattenPagesTree()
 {
-    clearPagesCache();
+    // If not already done, flatten the /Pages structure and
+    // initialize pageobj_to_pages_pos.
  
-    // FIXME: more specific method, we don't want to generate the extra stuff.
-    // We also need cheap fixup after addPage/removePage.
+    if (! this->pageobj_to_pages_pos.empty())
+    {
+        return;
+    }
  
-    // no compressed objects to be produced here...
-    std::map<int, int> object_stream_data;
-    optimize(object_stream_data); // push down inheritance
+    // Push inherited objects down to the /Page level
+    optimizePagesTree(true);
+    getAllPages();
  
-    std::vector<QPDFObjectHandle> kids = this->getAllPages();
     QPDFObjectHandle pages = this->trailer.getKey("/Root").getKey("/Pages");
  
-    const int len = kids.size();
+    int const len = (int)this->all_pages.size();
     for (int pos = 0; pos < len; ++pos)
     {
-        // populate pageobj_to_pages_pos
-        ObjGen og(kids[pos].getObjectID(), kids[pos].getGeneration());
-        if (! this->pageobj_to_pages_pos.insert(std::make_pair(og, pos)).second)
-        {
-            // insert failed: duplicate entry found
-            *out_stream << "WARNING: duplicate page reference found, "
-                        << "but currently not fully supported." << std::endl;
-        }
-
-        // fix parent links
-        kids[pos].replaceKey("/Parent", pages);
+        // populate pageobj_to_pages_pos and fix parent pointer
+        insertPageobjToPage(this->all_pages[pos], pos, true);
+        this->all_pages[pos].replaceKey("/Parent", pages);
     }
  
-    pages.replaceKey("/Kids", QPDFObjectHandle::newArray(kids));
+    pages.replaceKey("/Kids", QPDFObjectHandle::newArray(this->all_pages));
     // /Count has not changed
     assert(pages.getKey("/Count").getIntValue() == len);
 }
  
-int
-QPDF::findPage(int objid, int generation)
-{
-    if (this->pageobj_to_pages_pos.empty())
-    {
-        flattenPagesTree();
-    }
-    std::map<ObjGen, int>::iterator it =
-        this->pageobj_to_pages_pos.find(ObjGen(objid, generation));
-    if (it != this->pageobj_to_pages_pos.end())
-    {
-        return (*it).second;
-    }
-    return -1; // throw?
-}
-
-int
-QPDF::findPage(QPDFObjectHandle const& pageoh)
+void
+QPDF::insertPageobjToPage(QPDFObjectHandle const& obj, int pos,
+                          bool check_duplicate)
 {
-    if (!pageoh.isInitialized())
+    ObjGen og(obj.getObjectID(), obj.getGeneration());
+    bool duplicate =
+        (! this->pageobj_to_pages_pos.insert(std::make_pair(og, pos)).second);
+    if (duplicate && check_duplicate)
     {
-        return -1;
-        // TODO? throw
+        QTC::TC("qpdf", "QPDF duplicate page reference");
+        setLastObjectDescription("page " + QUtil::int_to_string(pos) +
+                                 " (numbered from zero)",
+                                 og.obj, og.gen);
+        throw QPDFExc(qpdf_e_pages, this->file->getName(),
+                      this->last_object_description, 0,
+                      "duplicate page reference found;"
+                      " this would cause loss of data");
     }
-    return findPage(pageoh.getObjectID(), pageoh.getGeneration());
 }
  
 void
-QPDF::addPage(QPDFObjectHandle newpage, bool first)
+QPDF::insertPage(QPDFObjectHandle newpage, int pos)
 {
-    if (this->pageobj_to_pages_pos.empty())
-    {
-        flattenPagesTree();
-    }
+    // pos is numbered from 0, so pos = 0 inserts at the begining and
+    // pos = npages adds to the end.
  
-    newpage.assertPageObject(); // FIXME: currently private
+    flattenPagesTree();
+    newpage.assertPageObject();
+
+    QTC::TC("qpdf", "QPDF insert page",
+            (pos == 0) ? 0 :                      // insert at beginning
+            (pos == ((int)this->all_pages.size())) ? 1 : // insert at end
+            2);                                   // insert in middle
  
     QPDFObjectHandle pages = this->trailer.getKey("/Root").getKey("/Pages");
     QPDFObjectHandle kids = pages.getKey("/Kids");
+    assert ((pos >= 0) && (pos <= (int)this->all_pages.size()));
  
     newpage.replaceKey("/Parent", pages);
-    if (first)
-    {
-        kids.insertItem(0, newpage);
-    }
-    else
+    kids.insertItem(pos, newpage);
+    int npages = kids.getArrayNItems();
+    pages.replaceKey("/Count", QPDFObjectHandle::newInteger(npages));
+    this->all_pages.insert(this->all_pages.begin() + pos, newpage);
+    assert((int)this->all_pages.size() == npages);
+    for (int i = pos + 1; i < npages; ++i)
     {
-        kids.appendItem(newpage);
+        insertPageobjToPage(this->all_pages[i], i, false);
     }
-    pages.replaceKey("/Count",
-                     QPDFObjectHandle::newInteger(kids.getArrayNItems()));
-
-    // FIXME: this is overkill, but cache is now stale
-    clearPagesCache();
+    insertPageobjToPage(newpage, pos, true);
+    assert((int)this->pageobj_to_pages_pos.size() == npages);
 }
  
 void
-QPDF::addPageAt(QPDFObjectHandle newpage, bool before,
-                QPDFObjectHandle const &refpage)
+QPDF::removePage(QPDFObjectHandle page)
 {
-    int refpos = findPage(refpage); // also ensures flat /Pages
-    if (refpos == -1)
-    {
-        throw "Could not find refpage";
-    }
-
-    newpage.assertPageObject();
+    int pos = findPage(page); // also ensures flat /Pages
+    QTC::TC("qpdf", "QPDF remove page",
+            (pos == 0) ? 0 :                          // remove at beginning
+            (pos == ((int)this->all_pages.size() - 1)) ? 1 : // remove at end
+            2);                                       // remove in middle
  
     QPDFObjectHandle pages = this->trailer.getKey("/Root").getKey("/Pages");
     QPDFObjectHandle kids = pages.getKey("/Kids");
  
+    kids.eraseItem(pos);
+    int npages = kids.getArrayNItems();
+    pages.replaceKey("/Count", QPDFObjectHandle::newInteger(npages));
+    this->all_pages.erase(this->all_pages.begin() + pos);
+    assert((int)this->all_pages.size() == npages);
+    this->pageobj_to_pages_pos.erase(
+        ObjGen(page.getObjectID(), page.getGeneration()));
+    assert((int)this->pageobj_to_pages_pos.size() == npages);
+    for (int i = pos; i < npages; ++i)
+    {
+        insertPageobjToPage(this->all_pages[i], i, false);
+    }
+}
+
+void
+QPDF::addPageAt(QPDFObjectHandle newpage, bool before,
+                QPDFObjectHandle refpage)
+{
+    int refpos = findPage(refpage);
     if (! before)
     {
         ++refpos;
     }
-
-    newpage.replaceKey("/Parent", pages);
-    kids.insertItem(refpos, newpage);
-    pages.replaceKey("/Count",
-                     QPDFObjectHandle::newInteger(kids.getArrayNItems()));
-
-    // FIXME: this is overkill, but cache is now stale
-    clearPagesCache();
+    insertPage(newpage, refpos);
 }
  
+
 void
-QPDF::removePage(QPDFObjectHandle const& pageoh)
+QPDF::addPage(QPDFObjectHandle newpage, bool first)
 {
-    int pos = findPage(pageoh); // also ensures flat /Pages
-    if (pos == -1)
+    getAllPages();
+    if (first)
     {
-        throw "Can't remove non-existing page";
+        insertPage(newpage, 0);
     }
+    else
+    {
+        insertPage(newpage, (int)this->all_pages.size());
+    }
+}
  
-    QPDFObjectHandle pages = this->trailer.getKey("/Root").getKey("/Pages");
-    QPDFObjectHandle kids = pages.getKey("/Kids");
-
-    kids.eraseItem(pos);
-    pages.replaceKey("/Count",
-                     QPDFObjectHandle::newInteger(kids.getArrayNItems()));
+int
+QPDF::findPage(QPDFObjectHandle& page)
+{
+    page.assertPageObject();
+    return findPage(page.getObjectID(), page.getGeneration());
+}
  
-    // FIXME: this is overkill, but cache is now stale
-    clearPagesCache();
+int
+QPDF::findPage(int objid, int generation)
+{
+    flattenPagesTree();
+    std::map<ObjGen, int>::iterator it =
+        this->pageobj_to_pages_pos.find(ObjGen(objid, generation));
+    if (it == this->pageobj_to_pages_pos.end())
+    {
+        setLastObjectDescription("page object", objid, generation);
+        QPDFExc(qpdf_e_pages, this->file->getName(),
+                this->last_object_description, 0,
+                "page object not referenced in /Pages tree");
+    }
+    return (*it).second;
 }
@@ -203,3 +203,7 @@ qpdf-c called qpdf_init_write_memory 0
 exercise processFile(name) 0
 exercise processFile(FILE*) 0
 exercise processMemoryFile 0
+QPDF duplicate page reference 0
+QPDF remove page 2
+QPDF insert page 2
+QPDF updateAllPagesCache 0