Provide qpdf write progress reporting from C API (fixes #487)

ChangeLog

@@ -1,3 +1,8 @@
+2020-12-20  Jay Berkenbilt  <ejb@ql.org>
+
+	* Add qpdf_register_progress_reporter method to C API,
+	corresponding to QPDFWriter::registerProgressReporter. Fixes #487.
+
 2020-11-28  Jay Berkenbilt  <ejb@ql.org>
 
 	* Add new functions to the C API for manipulating

examples/pdf-linearize.c

@@ -15,6 +15,11 @@ static void usage()
     exit(2);
 }
 
+static void write_progress(int percent, void* data)
+{
+    printf("%s progress: %d%%\n", (char const*)(data), percent);
+}
+
 int main(int argc, char* argv[])
 {
     char* infile = NULL;
@@ -55,6 +60,7 @@ int main(int argc, char* argv[])
          * qpdf_set_deterministic_ID. */
 	qpdf_set_static_ID(qpdf, QPDF_TRUE); /* for testing only */
 	qpdf_set_linearization(qpdf, QPDF_TRUE);
+        qpdf_register_progress_reporter(qpdf, write_progress, infile);
 	qpdf_write(qpdf);
     }
     while (qpdf_more_warnings(qpdf))

examples/qtest/linearize.test

@@ -15,7 +15,8 @@ my $qpdf = $ENV{'QPDF_BIN'} or die;
 
 $td->runtest("linearize",
 	     {$td->COMMAND => "pdf-linearize input.pdf '' a.pdf"},
-	     {$td->STRING => "", $td->EXIT_STATUS => 0});
+	     {$td->REGEXP => '(?s).*input\.pdf progress: \d+\%.*',
+                  $td->EXIT_STATUS => 0});
 
 $td->runtest("check",
 	     {$td->COMMAND => "$qpdf --check a.pdf"},

include/qpdf/qpdf-c.h

@@ -467,6 +467,18 @@ extern "C" {
     void qpdf_force_pdf_version_and_extension(
         qpdf_data qpdf, char const* version, int extension_level);
 
+    /* During write, your report_progress function will be called with
+     * a value between 0 and 100 representing the approximate write
+     * progress. The data object you pass to
+     * qpdf_register_progress_reporter will be handed back to your
+     * function.
+     */
+    QPDF_DLL
+    void qpdf_register_progress_reporter(
+        qpdf_data qpdf,
+        void (*report_progress)(int percent, void* data),
+        void* data);
+
     /* Do actual write operation. */
     QPDF_DLL
     QPDF_ERROR_CODE qpdf_write(qpdf_data qpdf);

libqpdf/qpdf-c.cc

@@ -57,6 +57,30 @@ _qpdf_data::~_qpdf_data()
 {
 }
 
+class ProgressReporter: public QPDFWriter::ProgressReporter
+{
+  public:
+    ProgressReporter(void (*handler)(int, void*), void* data);
+    virtual ~ProgressReporter() = default;
+    virtual void reportProgress(int);
+
+  private:
+    void (*handler)(int, void*);
+    void* data;
+};
+
+ProgressReporter::ProgressReporter(void (*handler)(int, void*), void* data) :
+    handler(handler),
+    data(data)
+{
+}
+
+void
+ProgressReporter::reportProgress(int progress)
+{
+    this->handler(progress, this->data);
+}
+
 // must set qpdf->filename and qpdf->password
 static void call_read(qpdf_data qpdf)
 {
@@ -752,6 +776,15 @@ void qpdf_force_pdf_version_and_extension(
     qpdf->qpdf_writer->forcePDFVersion(version, extension_level);
 }
 
+void qpdf_register_progress_reporter(
+    qpdf_data qpdf,
+    void (*report_progress)(int percent, void* data),
+    void* data)
+{
+    qpdf->qpdf_writer->registerProgressReporter(
+        new ProgressReporter(report_progress, data));
+}
+
 QPDF_ERROR_CODE qpdf_write(qpdf_data qpdf)
 {
     QPDF_ERROR_CODE status = QPDF_SUCCESS;