Require { or [ for JSON detection

fuzz_test.go

@@ -54,15 +54,16 @@ func FuzzDetect(f *testing.F) {
 		}
 		assertResultInvariants(t, first, false, len(data))
 		binary, _ := binaryFormat(data)
-		expectJSON := binary == "" && json.Valid(data) && utf8.Valid(data)
+		container := hasJSONContainerPrefix(data)
+		expectJSON := binary == "" && container && json.Valid(data) && utf8.Valid(data)
 		if got := first.Format == FormatJSON; got != expectJSON {
 			t.Fatalf("Detect JSON match = %v, want %v for %x", got, expectJSON, data)
 		}
 
 		prefix := DetectPrefix(data)
 		if len(data) > 0 {
 			expectedPrefix := first
-			if parseJSON(data) == jsonIncomplete {
+			if container && parseJSON(data) == jsonIncomplete {
 				expectedPrefix.Format = FormatJSON
 				expectedPrefix.MIME = mimeJSON
 			}

json.go

@@ -43,10 +43,21 @@ type jsonParser struct {
 }
 
 func isJSON(data []byte, prefix bool) bool {
+	if !hasJSONContainerPrefix(data) {
+		return false
+	}
 	result := parseJSON(data)
 	return result == jsonComplete || prefix && result == jsonIncomplete
 }
 
+func hasJSONContainerPrefix(data []byte) bool {
+	i := 0
+	for i < len(data) && isJSONWhitespace(data[i]) {
+		i++
+	}
+	return i < len(data) && (data[i] == '{' || data[i] == '[')
+}
+
 func parseJSON(data []byte) jsonParseResult {
 	parser := jsonParser{data: data}
 	parser.skipWhitespace()

json_test.go

@@ -14,11 +14,6 @@ func TestJSONDetection(t *testing.T) {
 	}{
 		{name: "object", input: `{"schemaVersion": 2}`},
 		{name: "array", input: `[1, "two", false, null]`},
-		{name: "string", input: `"hello"`},
-		{name: "number", input: `-12.5e+2`},
-		{name: "true", input: `true`},
-		{name: "false", input: `false`},
-		{name: "null", input: `null`},
 		{name: "surrounding whitespace", input: " \t\r\n{\"key\": \"value\"}\n"},
 		{name: "Unicode", input: `{"message":"héllo, 世界","escaped":"\uD834\uDD1E"}`},
 		{name: "escaped characters", input: `["\b\f\n\r\t\/\\\""]`},
@@ -44,6 +39,12 @@ func TestInvalidJSONRetainsExistingClassification(t *testing.T) {
 		name  string
 		input string
 	}{
+		{name: "bare string", input: `"hello"`},
+		{name: "bare number", input: `-12.5e+2`},
+		{name: "bare integer", input: `12345`},
+		{name: "bare true", input: `true`},
+		{name: "bare false", input: `false`},
+		{name: "bare null", input: `null`},
 		{name: "mismatched delimiters", input: `{]`},
 		{name: "whitespace only", input: " \t\r\n"},
 		{name: "missing value", input: `{"key":}`},
@@ -144,16 +145,16 @@ func TestJSONPrefixDetection(t *testing.T) {
 		{name: "truncated object value", input: `{"key":`},
 		{name: "truncated array", input: `[`},
 		{name: "truncated array value", input: `[1,`},
-		{name: "truncated string", input: `"value`},
-		{name: "truncated escape", input: `"value\`},
-		{name: "truncated Unicode escape", input: `"value\u12`},
-		{name: "truncated negative number", input: `-`},
-		{name: "truncated fraction", input: `1.`},
-		{name: "truncated exponent", input: `1e`},
-		{name: "truncated signed exponent", input: `1e+`},
-		{name: "truncated true", input: `tru`},
-		{name: "truncated false", input: `fals`},
-		{name: "truncated null", input: `nul`},
+		{name: "truncated array string", input: `["value`},
+		{name: "truncated array escape", input: `["value\`},
+		{name: "truncated array Unicode escape", input: `["value\u12`},
+		{name: "truncated array number", input: `[-`},
+		{name: "truncated array fraction", input: `[1.`},
+		{name: "truncated array exponent", input: `[1e`},
+		{name: "truncated array signed exponent", input: `[1e+`},
+		{name: "truncated array true", input: `[tru`},
+		{name: "truncated array false", input: `[fals`},
+		{name: "truncated array null", input: `[nul`},
 		{name: "leading whitespace", input: " \n{"},
 	}
 
@@ -179,6 +180,9 @@ func TestInvalidJSONPrefixRetainsExistingClassification(t *testing.T) {
 		input string
 	}{
 		{name: "plain text", input: `package`},
+		{name: "bare number", input: `123`},
+		{name: "bare string", input: `"value`},
+		{name: "bare literal", input: `tru`},
 		{name: "whitespace only", input: " \t\r\n"},
 		{name: "mismatched delimiters", input: `{]`},
 		{name: "trailing comma", input: `[1,]`},