[FLINK-9357][tests][yarn] Add margins to exception excerpts

This closes apache#6009.

flink-yarn-tests/src/test/java/org/apache/flink/yarn/YarnTestBase.java

@@ -336,7 +336,7 @@ public boolean accept(File dir, String name) {
  // scan each file for prohibited strings.
  File f = new File(dir.getAbsolutePath() + "/" + name);
  try {
- Scanner scanner = new Scanner(f);
+ BufferingScanner scanner = new BufferingScanner(new Scanner(f), 10);
  while (scanner.hasNextLine()) {
  final String lineFromFile = scanner.nextLine();
  for (String aProhibited : prohibited) {
@@ -358,15 +358,26 @@ public boolean accept(File dir, String name) {
  StringBuilder logExcerpt = new StringBuilder();
 
  logExcerpt.append(System.lineSeparator());
+
+ // include some previous lines in case of irregular formatting
+ for (String previousLine : scanner.getPreviousLines()) {
+ logExcerpt.append(previousLine);
+ logExcerpt.append(System.lineSeparator());
+ }
+
  logExcerpt.append(lineFromFile);
  logExcerpt.append(System.lineSeparator());
  // extract potential stack trace from log
  while (scanner.hasNextLine()) {
  String line = scanner.nextLine();
- if (!line.isEmpty() && (Character.isWhitespace(line.charAt(0)) || line.startsWith("Caused by"))) {
- logExcerpt.append(line);
- logExcerpt.append(System.lineSeparator());
- } else {
+ logExcerpt.append(line);
+ logExcerpt.append(System.lineSeparator());
+ if (line.isEmpty() || (!Character.isWhitespace(line.charAt(0)) && !line.startsWith("Caused by"))) {
+ // the cause has been printed, now add a few more lines in case of irregular formatting
+ for (int x = 0; x < 10 && scanner.hasNextLine(); x++) {
+ logExcerpt.append(scanner.nextLine());
+ logExcerpt.append(System.lineSeparator());
+ }
  break;
  }
  }
@@ -868,4 +879,37 @@ public static void teardown() throws Exception {
  public static boolean isOnTravis() {
  return System.getenv("TRAVIS") != null && System.getenv("TRAVIS").equals("true");
  }
+
+ /**
+ * Wrapper around a {@link Scanner} that buffers the last N lines read.
+ */
+ private static class BufferingScanner {
+
+ private final Scanner scanner;
+ private final int numLinesBuffered;
+ private final List<String> bufferedLines;
+
+ BufferingScanner(Scanner scanner, int numLinesBuffered) {
+ this.scanner = scanner;
+ this.numLinesBuffered = numLinesBuffered;
+ this.bufferedLines = new ArrayList<>(numLinesBuffered);
+ }
+
+ public boolean hasNextLine() {
+ return scanner.hasNextLine();
+ }
+
+ public String nextLine() {
+ if (bufferedLines.size() == numLinesBuffered) {
+ bufferedLines.remove(0);
+ }
+ String line = scanner.nextLine();
+ bufferedLines.add(line);
+ return line;
+ }
+
+ public List<String> getPreviousLines() {
+ return new ArrayList<>(bufferedLines);
+ }
+ }
 }