parser: Fix handling of quoted brackets in JSON front matter

Also remove a broken JSON test.

Fixes #3511

parser/page.go

@@ -304,8 +304,8 @@ func extractFrontMatterDelims(r *bufio.Reader, left, right []byte) (fm []byte, e
 		buf       bytes.Buffer
 		level     int
 		sameDelim = bytes.Equal(left, right)
+		inQuote   bool
 	)
-
 	// Frontmatter must start with a delimiter. To check it first,
 	// pre-reads beginning delimiter length - 1 bytes from Reader
 	for i := 0; i < len(left)-1; i++ {
@@ -332,6 +332,8 @@ func extractFrontMatterDelims(r *bufio.Reader, left, right []byte) (fm []byte, e
 		}
 
 		switch c {
+		case '"':
+			inQuote = !inQuote
 		case left[len(left)-1]:
 			if sameDelim { // YAML, TOML case
 				if bytes.HasSuffix(buf.Bytes(), left) && (buf.Len() == len(left) || buf.Bytes()[buf.Len()-len(left)-1] == '\n') {
@@ -373,10 +375,14 @@ func extractFrontMatterDelims(r *bufio.Reader, left, right []byte) (fm []byte, e
 					}
 				}
 			} else { // JSON case
-				level++
+				if !inQuote {
+					level++
+				}
 			}
 		case right[len(right)-1]: // JSON case only reaches here
-			level--
+			if !inQuote {
+				level--
+			}
 		}
 
 		if level == 0 {

parser/parse_frontmatter_test.go

@@ -296,18 +296,21 @@ func TestExtractFrontMatterDelim(t *testing.T) {
 		{"{\n{\n}\n}\n", "{\n{\n}\n}", noErrExpected},
 		{"{\n  \"categories\": \"d\",\n  \"tags\": [\n    \"a\", \n    \"b\", \n    \"c\"\n  ]\n}\nJSON Front Matter with tags and categories", "{\n  \"categories\": \"d\",\n  \"tags\": [\n    \"a\", \n    \"b\", \n    \"c\"\n  ]\n}", noErrExpected},
 		{"{\n  \"categories\": \"d\"\n  \"tags\": [\n    \"a\" \n    \"b\" \n    \"c\"\n  ]\n}\nJSON Front Matter with tags and categories", "{\n  \"categories\": \"d\"\n  \"tags\": [\n    \"a\" \n    \"b\" \n    \"c\"\n  ]\n}", noErrExpected},
+		// Issue #3511
+		{`{ "title": "{" }`, `{ "title": "{" }`, noErrExpected},
+		{`{ "title": "{}" }`, `{ "title": "{}" }`, noErrExpected},
 	}
 
-	for _, test := range tests {
+	for i, test := range tests {
 		fm, err := extractFrontMatterDelims(bufio.NewReader(strings.NewReader(test.frontmatter)), []byte("{"), []byte("}"))
 		if (err == nil) != test.errIsNil {
 			t.Logf("\n%q\n", string(test.frontmatter))
-			t.Errorf("Expected err == nil => %t, got: %t. err: %s", test.errIsNil, err == nil, err)
+			t.Errorf("[%d] Expected err == nil => %t, got: %t. err: %s", i, test.errIsNil, err == nil, err)
 			continue
 		}
 		if !bytes.Equal(fm, []byte(test.extracted)) {
 			t.Logf("\n%q\n", string(test.frontmatter))
-			t.Errorf("Frontmatter did not match:\nexp: %q\ngot: %q", string(test.extracted), fm)
+			t.Errorf("[%d] Frontmatter did not match:\nexp: %q\ngot: %q", i, string(test.extracted), fm)
 		}
 	}
 }