Remove invisible characters when parsing feed ids

src/main/java/org/opentripplanner/framework/lang/StringUtils.java

@@ -1,11 +1,20 @@
 package org.opentripplanner.framework.lang;
 
+import java.util.regex.Pattern;
 import javax.annotation.Nonnull;
 
 /**
  * OTP String utils extending the Java lang String...
  */
 public class StringUtils {
+  /**
+   * Regex to find unprintable characters like newlines and 'ZERO WIDTH SPACE' (U+200B).
+   */
+  private static final String INVISIBLE_CHARS_REGEX = "\\p{C}";
+  /**
+   * Patterns are immutable and thread safe.
+   */
+  private static final Pattern INVISIBLE_CHARS_PATTERN = Pattern.compile(INVISIBLE_CHARS_REGEX);
 
   private StringUtils() {}
 
@@ -119,4 +128,15 @@ public static String quoteReplace(@Nonnull String text) {
   public static String kebabCase(String input) {
     return input.toLowerCase().replace('_', '-');
   }
+
+  /**
+   * Removes unprintable control characters like newlines, tabs and invisible whitespace
+   * like 'ZERO WIDTH SPACE' (U+200B) that don't have an immediate visual representation.
+   * <p>
+   * Note that visible whitespace characters like U+0020 and U+2000 are considered visible and
+   * therefore not removed.
+   */
+  public static String removeInvisibleChars(String input) {
+    return INVISIBLE_CHARS_PATTERN.matcher(input).replaceAll("");
+  }
 }

src/main/java/org/opentripplanner/transit/model/framework/FeedScopedId.java

@@ -5,9 +5,9 @@
 import java.io.Serializable;
 import java.util.Arrays;
 import java.util.List;
-import java.util.stream.Collectors;
 import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
+import org.opentripplanner.framework.lang.StringUtils;
 
 public final class FeedScopedId implements Serializable, Comparable<FeedScopedId> {
 
@@ -59,7 +59,12 @@ public static FeedScopedId parse(String value) throws IllegalArgumentException {
    * Parses a string consisting of concatenated FeedScopedIds to a List
    */
   public static List<FeedScopedId> parseList(String s) {
-    return Arrays.stream(s.split(",")).map(FeedScopedId::parse).collect(Collectors.toList());
+    return Arrays
+      .stream(s.split(","))
+      .map(input -> StringUtils.removeInvisibleChars(input).strip())
+      .filter(i -> !i.isBlank())
+      .map(FeedScopedId::parse)
+      .toList();
   }
 
   public static boolean isValidString(String value) throws IllegalArgumentException {

src/test/java/org/opentripplanner/framework/lang/StringUtilsTest.java

@@ -10,6 +10,7 @@
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.ValueSource;
 import org.opentripplanner.test.support.VariableSource;
 
 class StringUtilsTest {
@@ -82,4 +83,16 @@ void padRight() {
   void quoteReplace() {
     assertEquals("\"key\" : \"value\"", StringUtils.quoteReplace("'key' : 'value'"));
   }
+
+  @ParameterizedTest
+  @ValueSource(
+    strings = {
+      "\u200B",
+      "\n",
+      "\t"
+    }
+  )
+  void removeInvisibleChars(String input) {
+    assertEquals("", StringUtils.removeInvisibleChars(input));
+  }
 }

src/test/java/org/opentripplanner/transit/model/framework/FeedScopedIdTest.java

@@ -3,13 +3,37 @@
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertNull;
 
+import java.util.List;
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.ValueSource;
 
 class FeedScopedIdTest {
 
+  private static final List<FeedScopedId> TRIMET_123 = List.of(new FeedScopedId("trimet", "123"));
+
   @Test
   void ofNullable() {
     assertEquals(new FeedScopedId("FEED", "ID"), FeedScopedId.ofNullable("FEED", "ID"));
     assertNull(FeedScopedId.ofNullable("FEED", null));
   }
+
+  @ParameterizedTest
+  @ValueSource(
+    strings = {
+      "trimet:123",
+      "trimet:123 ",
+      "trimet:123, ",
+      ",trimet:123 , ",
+      ",trimet:123 , ,\u200B,",
+      " trimet:123 ",
+      "\u200Btrimet:123",
+      "\u200B\u200Btri\u200Bmet:123\u200B",
+      "\ntrimet:123\t",
+      "\ntri\nmet:123\t",
+    }
+  )
+  void parseList(String input) {
+    assertEquals(TRIMET_123, FeedScopedId.parseList(input));
+  }
 }