Add QPDFWriter::getFinalVersion (fixes #266)

ChangeLog

@@ -1,5 +1,10 @@
 2019-01-04  Jay Berkenbilt  <ejb@ql.org>
 
+	* Add new method QPDFWriter::getFinalVersion, which returns the
+	PDF version that will ultimately be written to the final file. See
+	comments in QPDFWriter.hh for some restrictions on its use. Fixes
+	#266.
+
 	* When unexpected errors are found while checking linearization
 	data, print an error message instead of calling assert, which
 	cause the program to crash. Fixes #209, #231.

include/qpdf/QPDFWriter.hh

@@ -404,6 +404,18 @@ class QPDFWriter
     QPDF_DLL
     void registerProgressReporter(PointerHolder<ProgressReporter>);
 
+    // Return the PDF version that will be written into the header.
+    // Calling this method does all the preparation for writing, so it
+    // is an error to call any methods that may cause a change to the
+    // version. Adding new objects to the original file after calling
+    // this may also cause problems. It is safe to update existing
+    // objects or stream contents after calling this method, e.g., to
+    // include the final version number in metadata.
+    QPDF_DLL
+    std::string getFinalVersion();
+
+    // Write the final file. There is no expectation of being able to
+    // call write() more than once.
     QPDF_DLL
     void write();
 
@@ -473,6 +485,7 @@ class QPDFWriter
     void writeLinearized();
     void enqueuePart(std::vector<QPDFObjectHandle>& part);
     void writeEncryptionDictionary();
+    void doWriteSetup();
     void writeHeader();
     void writeHintStream(int hint_id);
     qpdf_offset_t writeXRefTable(
@@ -598,6 +611,7 @@ class QPDFWriter
         bool deterministic_id;
         Pl_MD5* md5_pipeline;
         std::string deterministic_id_data;
+        bool did_write_setup;
 
         // For linearization only
         std::string lin_pass1_filename;

libqpdf/QPDFWriter.cc

@@ -63,6 +63,7 @@ QPDFWriter::Members::Members(QPDF& pdf) :
     max_ostream_index(0),
     deterministic_id(false),
     md5_pipeline(0),
+    did_write_setup(false),
     events_expected(0),
     events_seen(0),
     next_progress_report(0)
@@ -2358,8 +2359,14 @@ QPDFWriter::prepareFileForWrite()
 }
 
 void
-QPDFWriter::write()
+QPDFWriter::doWriteSetup()
 {
+    if (this->m->did_write_setup)
+    {
+        return;
+    }
+    this->m->did_write_setup = true;
+
     // Do preliminary setup
 
     if (this->m->linearized)
@@ -2507,6 +2514,23 @@ QPDFWriter::write()
 	setMinimumPDFVersion("1.5");
     }
 
+    setMinimumPDFVersion(this->m->pdf.getPDFVersion(),
+                         this->m->pdf.getExtensionLevel());
+    this->m->final_pdf_version = this->m->min_pdf_version;
+    this->m->final_extension_level = this->m->min_extension_level;
+    if (! this->m->forced_pdf_version.empty())
+    {
+	QTC::TC("qpdf", "QPDFWriter using forced PDF version");
+	this->m->final_pdf_version = this->m->forced_pdf_version;
+        this->m->final_extension_level = this->m->forced_extension_level;
+    }
+}
+
+void
+QPDFWriter::write()
+{
+    doWriteSetup();
+
     // Set up progress reporting. We spent about equal amounts of time
     // preparing and writing one pass. To get a rough estimate of
     // progress, we track handling of indirect objects. For linearized
@@ -2569,20 +2593,16 @@ QPDFWriter::writeEncryptionDictionary()
     closeObject(this->m->encryption_dict_objid);
 }
 
+std::string
+QPDFWriter::getFinalVersion()
+{
+    doWriteSetup();
+    return this->m->final_pdf_version;
+}
+
 void
 QPDFWriter::writeHeader()
 {
-    setMinimumPDFVersion(this->m->pdf.getPDFVersion(),
-                         this->m->pdf.getExtensionLevel());
-    this->m->final_pdf_version = this->m->min_pdf_version;
-    this->m->final_extension_level = this->m->min_extension_level;
-    if (! this->m->forced_pdf_version.empty())
-    {
-	QTC::TC("qpdf", "QPDFWriter using forced PDF version");
-	this->m->final_pdf_version = this->m->forced_pdf_version;
-        this->m->final_extension_level = this->m->forced_extension_level;
-    }
-
     writeString("%PDF-");
     writeString(this->m->final_pdf_version);
     if (this->m->pclm)

qpdf/qtest/qpdf.test

@@ -173,6 +173,16 @@ $td->runtest("\@file exists and file doesn't",
              {$td->FILE => "check-at-file.out", $td->EXIT_STATUS => 0},
              $td->NORMALIZE_NEWLINES);
 
+show_ntests();
+# ----------
+$td->notify("--- Final Version ---");
+$n_tests += 1;
+
+$td->runtest("check final version",
+             {$td->COMMAND => "test_driver 54 minimal.pdf"},
+             {$td->STRING => "test 54 done\n", $td->EXIT_STATUS => 0},
+             $td->NORMALIZE_NEWLINES);
+
 show_ntests();
 # ----------
 $td->notify("--- Dangling Refs ---");

qpdf/test_driver.cc

@@ -1865,6 +1865,18 @@ void runtest(int n, char const* filename1, char const* arg2)
         w.setStaticID(true);
         w.write();
     }
+    else if (n == 54)
+    {
+        // Test getFinalVersion. This must be invoked with a file
+        // whose final version is not 1.5.
+        QPDFWriter w(pdf, "a.pdf");
+        assert(pdf.getPDFVersion() != "1.5");
+        w.setObjectStreamMode(qpdf_o_generate);
+        if (w.getFinalVersion() != "1.5")
+        {
+            std::cout << "oops: " << w.getFinalVersion() << std::endl;
+        }
+    }
     else
     {
 	throw std::runtime_error(std::string("invalid test ") +