experimental post-processing filters.

resources/docs/Feed-formats.md

@@ -37,7 +37,7 @@ RSS Guard 3.9.0+ offers extra advanced features which were inspired by [Liferea]
 
 You can select source type of each feed. If you select `URL`, then RSS Guard simply downloads feed file from given location.
 
-However, if you choose `Script` option, then you cannot provide URL of your feed and you rely on custom script to obtain your script and provide its contents to **standard output**. Resulting data written to standard output **MUST** be valid feed file, for example RSS or ATOM XML file.
+However, if you choose `Script` option, then you cannot provide URL of your feed and you rely on custom script to obtain your script and provide its contents to **standard output**. Resulting data written to standard output should be valid feed file, for example RSS or ATOM XML file.
 
 <img src="images/scrape-source-type.png" width="50%">
 
@@ -59,8 +59,12 @@ RSS Guard offers placeholder `%data%` which is automatically replaced with full
 
 Also, working directory of process executing the script is set to RSS Guard's user data folder.
 
-After your source feed data are downloaded either via URL or custom script, you can optionally post-process the data with one more custom script, which will take raw source data as input and must produce processed feed data to **standard output** while printing all error messages to **error output**.
-
-Typical post-processing filter might do things like advanced CSS formatting of feed file entries, removing some ads etc.
+After your source feed data are downloaded either via URL or custom script, you can optionally post-process the data with one more custom script, which will take **raw source data as input** and must produce processed valid feed data to **standard output** while printing all error messages to **error output**.
 
 Format of post-process script execution line is the same as above.
+
+Typical post-processing filter might do things like advanced CSS formatting of feed file entries, removing some ads or simply pretty-printing XML data:
+
+| Command | Explanation |
+|---------|-------------|
+| `bash.exe#-c "xmllint --format -"` | Pretty-print input XML feed data. |

src/librssguard/services/standard/standardfeed.cpp

@@ -474,6 +474,11 @@ QList<Message> StandardFeed::obtainNewMessages(bool* error_during_obtaining) {
   int download_timeout = qApp->settings()->value(GROUP(Feeds), SETTING(Feeds::UpdateTimeout)).toInt();
 
   if (sourceType() == SourceType::Url) {
+    qDebugNN << LOGSEC_CORE
+             << "Downloading URL"
+             << QUOTE_W_SPACE(url())
+             << "to obtain feed data.";
+
     QByteArray feed_contents;
     QList<QPair<QByteArray, QByteArray>> headers;
 
@@ -516,8 +521,45 @@ QList<Message> StandardFeed::obtainNewMessages(bool* error_during_obtaining) {
     }
   }
   else {
+    qDebugNN << LOGSEC_CORE
+             << "Running custom script"
+             << QUOTE_W_SPACE(url())
+             << "to obtain feed data.";
+
     // Use script to generate feed file.
-    formatted_feed_contents = generateFeedFileWithScript(url(), download_timeout);
+    try {
+      formatted_feed_contents = generateFeedFileWithScript(url(), download_timeout);
+    }
+    catch (const ApplicationException& ex) {
+      qCriticalNN << LOGSEC_CORE
+                  << "Custom script for generating feed file failed:"
+                  << QUOTE_W_SPACE_DOT(ex.message());
+
+      setStatus(Status::OtherError);
+      *error_during_obtaining = true;
+      return {};
+    }
+  }
+
+  if (!postProcessScript().simplified().isEmpty()) {
+    qDebugNN << LOGSEC_CORE
+             << "Post-processing obtained feed data with custom script"
+             << QUOTE_W_SPACE_DOT(postProcessScript());
+
+    try {
+      formatted_feed_contents = postProcessFeedFileWithScript(postProcessScript(),
+                                                              formatted_feed_contents,
+                                                              download_timeout);
+    }
+    catch (const ApplicationException& ex) {
+      qCriticalNN << LOGSEC_CORE
+                  << "Post-processing script failed:"
+                  << QUOTE_W_SPACE_DOT(ex.message());
+
+      setStatus(Status::OtherError);
+      *error_during_obtaining = true;
+      return {};
+    }
   }
 
   // Feed data are downloaded and encoded.
@@ -593,6 +635,46 @@ QString StandardFeed::generateFeedFileWithScript(const QString& execution_line,
   }
 }
 
+QString StandardFeed::postProcessFeedFileWithScript(const QString& execution_line, const QString raw_feed_data, int run_timeout) {
+  auto prepared_query = prepareExecutionLine(execution_line);
+  QProcess process;
+
+  process.setInputChannelMode(QProcess::InputChannelMode::ManagedInputChannel);
+  process.setWorkingDirectory(qApp->userDataFolder());
+  process.setProgram(prepared_query.first);
+
+#if defined(Q_OS_WIN)
+  process.setNativeArguments(prepared_query.second);
+#else
+  process.setArguments({ prepared_query.second });
+#endif
+
+  if (!process.open() || process.error() == QProcess::ProcessError::FailedToStart) {
+    throw ApplicationException(QSL("process failed to start"));
+  }
+
+  process.write(raw_feed_data.toUtf8());
+  process.closeWriteChannel();
+
+  if (process.waitForFinished(run_timeout)) {
+    auto raw_output = process.readAllStandardOutput();
+
+    return raw_output;
+  }
+  else {
+    process.kill();
+
+    auto raw_error = process.readAllStandardError();
+
+    if (raw_error.simplified().isEmpty()) {
+      throw ApplicationException(QSL("process failed to finish properly"));
+    }
+    else {
+      throw ApplicationException(QString(raw_error));
+    }
+  }
+}
+
 QNetworkReply::NetworkError StandardFeed::networkError() const {
   return m_networkError;
 }

src/librssguard/services/standard/standardfeed.h

@@ -80,6 +80,7 @@ class StandardFeed : public Feed {
 
     static QPair<QString, QString> prepareExecutionLine(const QString& execution_line);
     static QString generateFeedFileWithScript(const QString& execution_line, int run_timeout);
+    static QString postProcessFeedFileWithScript(const QString& execution_line, const QString raw_feed_data, int run_timeout);
 
     // Tries to guess feed hidden under given URL
     // and uses given credentials.