Added new escaper for already percent encoded inputs

Author: alexander-asenov

google-http-client/src/main/java/com/google/api/client/util/escape/PercentEncodedEscaper.java

@@ -0,0 +1,57 @@
+package com.google.api.client.util.escape;
+
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+/**
+ * An {@link Escaper} implementation that preserves percent-encoded sequences in the input string.
+ *
+ * <p>This escaper applies the provided {@link Escaper} to all parts of the input string except for
+ * valid percent-encoded sequences (e.g., <code>%20</code>), which are left unchanged.
+ */
+public class PercentEncodedEscaper extends Escaper {
+
+  /** Pattern to match valid percent-encoded sequences (e.g., %20). */
+  static final Pattern PCT_ENCODE_PATTERN = Pattern.compile("%[0-9A-Fa-f]{2}");
+
+  private final Escaper escaper;
+
+  public PercentEncodedEscaper(Escaper escaper) {
+    if (escaper == null) {
+      throw new NullPointerException("Escaper cannot be null");
+    }
+    this.escaper = escaper;
+  }
+
+  /**
+   * Escapes the input string using the provided {@link Escaper}, preserving valid percent-encoded
+   * sequences.
+   *
+   * @param string the input string to escape
+   * @return the escaped string with percent-encoded sequences left unchanged
+   */
+  @Override
+  public String escape(String string) {
+    if (string == null || string.isEmpty()) {
+      return string;
+    }
+
+    Matcher matcher = PCT_ENCODE_PATTERN.matcher(string);
+    StringBuilder sb = new StringBuilder();
+
+    int lastEnd = 0;
+    while (matcher.find()) {
+      sb.append(escaper.escape(string.substring(lastEnd, matcher.start())));
+
+      sb.append(string.substring(matcher.start(), matcher.end()));
+
+      lastEnd = matcher.end();
+    }
+
+    if (lastEnd < string.length()) {
+      sb.append(escaper.escape(string.substring(lastEnd)));
+    }
+
+    return sb.toString();
+  }
+}

google-http-client/src/test/java/com/google/api/client/util/escape/PercentEncodedEscaperTest.java

@@ -0,0 +1,32 @@
+package com.google.api.client.util.escape;
+
+import junit.framework.TestCase;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+@RunWith(JUnit4.class)
+public class PercentEncodedEscaperTest extends TestCase {
+  @Test
+  public void testEscape() {
+    PercentEncodedEscaper escaper =
+        new PercentEncodedEscaper(
+            new PercentEscaper(PercentEscaper.SAFE_PLUS_RESERVED_CHARS_URLENCODER));
+    String input = "Hello%20World+/?#[]";
+
+    String actual = escaper.escape(input);
+    assertEquals(input, actual); // No change expected since it's already percent-encoded
+  }
+
+  @Test
+  public void testEscapeEncode() {
+    PercentEncodedEscaper escaper =
+        new PercentEncodedEscaper(
+            new PercentEscaper(PercentEscaper.SAFE_PLUS_RESERVED_CHARS_URLENCODER));
+    String input = "Hello World%";
+    String expected = "Hello%20World%25";
+
+    String actual = escaper.escape(input);
+    assertEquals(expected, actual);
+  }
+}