Adds custom migration source and process plugins.

src/Plugin/migrate/process/ExtractFileContents.php

@@ -0,0 +1,54 @@
+<?php
+
+namespace Drupal\cdesai_migrate\Plugin\migrate\process;
+
+use Drupal\migrate\MigrateSkipRowException;
+use Drupal\migrate\Row;
+use Drupal\migrate\ProcessPluginBase;
+use Drupal\migrate\MigrateExecutableInterface;
+use Drush\Drush;
+
+/**
+ * Provides a 'Extract File Contents' migrate process plugin.
+ *
+ * Extracts contents of a file.
+ *
+ * @MigrateProcessPlugin(
+ *  id = "extract_file_contents"
+ * )
+ */
+class ExtractFileContents extends ProcessPluginBase {
+
+  /**
+   * {@inheritdoc}
+   *
+   * @throws \Drupal\migrate\MigrateSkipRowException
+   */
+  public function transform($value, MigrateExecutableInterface $migrate_executable, Row $row, $destination_property) {
+    $error = FALSE;
+    $page = $row->get('page');
+
+    if (is_null($value) || trim($value) === '') {
+      $error = "Skipping because content filepath is empty for {$page}.";
+    }
+    elseif (!is_file($value)) {
+      $error = "Skipping because content file is missing for {$page}.";
+    }
+    else {
+      $contents = file_get_contents($value);
+      if ($contents !== FALSE) {
+        return $contents;
+      }
+
+      $error = "Skipping because content file is unreadable for {$page}.";
+    }
+
+    if ($error) {
+      Drush::output()->writeln($error);
+      throw new MigrateSkipRowException($error);
+    }
+
+    return '';
+  }
+
+}