parser: Fix handling of JSON front matter with escaped quotes

Fixes #3661

parser/page.go

@@ -305,6 +305,7 @@ func extractFrontMatterDelims(r *bufio.Reader, left, right []byte) (fm []byte, e
 		level     int
 		sameDelim = bytes.Equal(left, right)
 		inQuote   bool
+		escaped   bool
 	)
 	// Frontmatter must start with a delimiter. To check it first,
 	// pre-reads beginning delimiter length - 1 bytes from Reader
@@ -333,7 +334,12 @@ func extractFrontMatterDelims(r *bufio.Reader, left, right []byte) (fm []byte, e
 
 		switch c {
 		case '"':
-			inQuote = !inQuote
+			if !escaped {
+				inQuote = !inQuote
+			}
+			escaped = false
+		case '\\':
+			escaped = true
 		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') {
@@ -396,6 +402,7 @@ func extractFrontMatterDelims(r *bufio.Reader, left, right []byte) (fm []byte, e
 
 			return buf.Bytes(), nil
 		}
+
 	}
 }
 

parser/parse_frontmatter_test.go

@@ -299,6 +299,11 @@ func TestExtractFrontMatterDelim(t *testing.T) {
 		// Issue #3511
 		{`{ "title": "{" }`, `{ "title": "{" }`, noErrExpected},
 		{`{ "title": "{}" }`, `{ "title": "{}" }`, noErrExpected},
+		// Issue #3661
+		{`{ "title": "\"" }`, `{ "title": "\"" }`, noErrExpected},
+		{`{ "title": "\"{", "other": "\"{}" }`, `{ "title": "\"{", "other": "\"{}" }`, noErrExpected},
+		{`{ "title": "\"Foo\"" }`, `{ "title": "\"Foo\"" }`, noErrExpected},
+		{`{ "title": "\"Foo\"\"" }`, `{ "title": "\"Foo\"\"" }`, noErrExpected},
 	}
 
 	for i, test := range tests {
@@ -310,7 +315,7 @@ func TestExtractFrontMatterDelim(t *testing.T) {
 		}
 		if !bytes.Equal(fm, []byte(test.extracted)) {
 			t.Logf("\n%q\n", string(test.frontmatter))
-			t.Errorf("[%d] Frontmatter did not match:\nexp: %q\ngot: %q", i, string(test.extracted), fm)
+			t.Errorf("[%d] Frontmatter did not match:\nexp: %q\ngot:  %q", i, string(test.extracted), fm)
 		}
 	}
 }