Support delimiters(_-.~) as start or end characters for a segment. (#336)

Support delimiters(_-.~) as start or end characters for a segment if the segment does not contain complex resource names.

A segment can start with a delimiter, as long as there is no { right after it.
A segment can end with a delimiter, as long as there is no } right before it.
A segment like .{well}-{known} or {well}-{known}. is invalid.
A segment like .well-known, .well-{known} or .-~{well-known} is considered a literal hence is valid.

Author: blakeli0

api-common-java/src/main/java/com/google/api/pathtemplate/PathTemplate.java

@@ -887,9 +887,7 @@ private static ImmutableList<Segment> parseTemplate(String template) {
 
       boolean isLastSegment = (template.indexOf(seg) + seg.length()) == template.length();
       boolean isCollectionWildcard = !isLastSegment && (seg.equals("-") || seg.equals("-}"));
-      if (!isCollectionWildcard
-          && (COMPLEX_DELIMITER_PATTERN.matcher(seg.substring(0, 1)).find()
-              || COMPLEX_DELIMITER_PATTERN.matcher(seg.substring(seg.length() - 1)).find())) {
+      if (!isCollectionWildcard && isSegmentBeginOrEndInvalid(seg)) {
         throw new ValidationException("parse error: invalid begin or end character in '%s'", seg);
       }
       // Disallow zero or multiple delimiters between variable names.
@@ -1015,6 +1013,20 @@ private static ImmutableList<Segment> parseTemplate(String template) {
     return builder.build();
   }
 
+  private static boolean isSegmentBeginOrEndInvalid(String seg) {
+    // A segment is invalid if it contains only one character and the character is a delimiter
+    if (seg.length() == 1 && COMPLEX_DELIMITER_PATTERN.matcher(seg).find()) {
+      return true;
+    }
+    // A segment can start with a delimiter, as long as there is no { right after it.
+    // A segment can end with a delimiter, as long as there is no } right before it.
+    // e.g. Invalid: .{well}-{known}, {well}-{known}-
+    // Valid: .well-known, .well-{known}, .-~{well-known}, these segments are all considered as literals for matching
+    return (COMPLEX_DELIMITER_PATTERN.matcher(seg.substring(0, 1)).find() && seg.charAt(1) == '{')
+        || (COMPLEX_DELIMITER_PATTERN.matcher(seg.substring(seg.length() - 1)).find()
+            && seg.charAt(seg.length() - 2) == '}');
+  }
+
   private static List<Segment> parseComplexResourceId(String seg) {
     List<Segment> segments = new ArrayList<>();
     List<String> separatorIndices = new ArrayList<>();

api-common-java/src/test/java/com/google/api/pathtemplate/PathTemplateTest.java

@@ -487,9 +487,6 @@ public void complexResourceBasicInvalidIds() {
   @Test
   public void complexResourceMultipleDelimiters() {
     thrown.expect(ValidationException.class);
-    PathTemplate.create("projects/*/zones/.-~{zone_a}");
-    thrown.expectMessage(
-        String.format("parse error: invalid begin or end character in '%s'", ".-~{zone_a}"));
 
     PathTemplate.create("projects/*/zones/{zone_a}~.{zone_b}");
     thrown.expectMessage(
@@ -717,6 +714,80 @@ public void instantiateWithCustomVerbs() {
     Truth.assertThat(template.matches(templateInstance)).isTrue();
   }
 
+  @Test
+  public void instantiateWithASegmentStartsWithADelimiter() {
+    PathTemplate pathTemplate =
+        PathTemplate.create(
+            "v1beta1/{parent=projects/*/locations/*/clusters/*}/.well-known/openid-configuration");
+    String pattern =
+        "v1beta1/projects/abc/locations/def/clusters/yte/.well-known/openid-configuration";
+    Truth.assertThat(pathTemplate.matches(pattern)).isTrue();
+  }
+
+  @Test
+  public void instantiateWithASegmentContainingComplexResourceNamesAndStartsWithADelimiter() {
+    thrown.expect(ValidationException.class);
+    PathTemplate.create(
+        "v1beta1/{parent=projects/*/locations/*/clusters/*}/.{well}-{known}/openid-configuration");
+    thrown.expectMessage(
+        String.format("parse error: invalid begin or end character in '%s'", ".{well}-{known}"));
+  }
+
+  @Test
+  public void
+      instantiateWithASegmentContainingNoComplexResourceNamesAndStartsWithMultipleDelimiters() {
+    PathTemplate pathTemplate =
+        PathTemplate.create(
+            "v1beta1/{parent=projects/*/locations/*/clusters/*}/.-~well-known/openid-configuration");
+    String pattern =
+        "v1beta1/projects/abc/locations/def/clusters/yte/.-~well-known/openid-configuration";
+    Truth.assertThat(pathTemplate.matches(pattern)).isTrue();
+  }
+
+  @Test
+  public void instantiateWithASegmentOnlyContainingOneDelimiter() {
+    thrown.expect(ValidationException.class);
+    PathTemplate.create("v1/publishers/{publisher}/books/.");
+    thrown.expectMessage(String.format("parse error: invalid begin or end character in '%s'", "."));
+  }
+
+  @Test
+  public void instantiateWithASegmentOnlyContainingOneCharacter() {
+    PathTemplate pathTemplate = PathTemplate.create("v1/publishers/{publisher}/books/a");
+    String pattern = "v1/publishers/o'reilly/books/a";
+    Truth.assertThat(pathTemplate.matches(pattern)).isTrue();
+  }
+
+  @Test
+  public void instantiateWithASegmentEndsWithADelimiter() {
+    PathTemplate pathTemplate =
+        PathTemplate.create(
+            "v1beta1/{parent=projects/*/locations/*/clusters/*}/well-known./openid-configuration");
+    String pattern =
+        "v1beta1/projects/abc/locations/def/clusters/yte/well-known./openid-configuration";
+    Truth.assertThat(pathTemplate.matches(pattern)).isTrue();
+  }
+
+  @Test
+  public void instantiateWithASegmentContainingComplexResourceNamesAndEndsWithADelimiter() {
+    thrown.expect(ValidationException.class);
+    PathTemplate.create(
+        "v1beta1/{parent=projects/*/locations/*/clusters/*}/{well}-{known}./openid-configuration");
+    thrown.expectMessage(
+        String.format("parse error: invalid begin or end character in '%s'", "{well}-{known}."));
+  }
+
+  @Test
+  public void
+      instantiateWithASegmentContainingNoComplexResourceNamesAndEndsWithMultipleDelimiters() {
+    PathTemplate pathTemplate =
+        PathTemplate.create(
+            "v1beta1/{parent=projects/*/locations/*/clusters/*}/well-known.-~/openid-configuration");
+    String pattern =
+        "v1beta1/projects/abc/locations/def/clusters/yte/well-known.-~/openid-configuration";
+    Truth.assertThat(pathTemplate.matches(pattern)).isTrue();
+  }
+
   // Other
   // =====