Improve compatibility with JSON in config parser

The configuration format from the server is almost already a superset
of JSON with exception of two cases:

1) trailing commas from values at the top level (although they are
   supported inside of maps)

2) initial and final brackets on the top level section.

This change relaxes the two cases above to just skip those tokens so
that the config syntax can also support valid JSON objects for
configuring the server which might be helpful when generating it
programmatically.

conf/lex.go

@@ -73,6 +73,9 @@ const (
 	sqStringStart     = '\''
 	sqStringEnd       = '\''
 	optValTerm        = ';'
+	topOptStart       = '{'
+	topOptValTerm     = ','
+	topOptTerm        = '}'
 	blockStart        = '('
 	blockEnd          = ')'
 )
@@ -234,6 +237,8 @@ func lexTop(lx *lexer) stateFn {
 	}
 
 	switch r {
+	case topOptStart:
+		return lexSkip(lx, lexTop)
 	case commentHashStart:
 		lx.push(lexTop)
 		return lexCommentStart
@@ -280,7 +285,7 @@ func lexTopValueEnd(lx *lexer) stateFn {
 		fallthrough
 	case isWhitespace(r):
 		return lexTopValueEnd
-	case isNL(r) || r == eof || r == optValTerm:
+	case isNL(r) || r == eof || r == optValTerm || r == topOptValTerm || r == topOptTerm:
 		lx.ignore()
 		return lexTop
 	}

conf/lex_test.go

@@ -1049,3 +1049,152 @@ func TestMapInclude(t *testing.T) {
 	lx = lex("foo { include \"users.conf\"}")
 	expect(t, lx, expectedItems)
 }
+
+func TestJSONCompat(t *testing.T) {
+	for _, test := range []struct {
+		name     string
+		input    string
+		expected []item
+	}{
+		{
+			name: "should omit initial and final brackets at top level with a single item",
+			input: `
+                        {
+                          "http_port": 8223
+                        }
+                        `,
+			expected: []item{
+				{itemKey, "http_port", 3},
+				{itemInteger, "8223", 3},
+			},
+		},
+		{
+			name: "should omit trailing commas at top level with two items",
+			input: `
+                        {
+                          "http_port": 8223,
+                          "port": 4223
+                        }
+                        `,
+			expected: []item{
+				{itemKey, "http_port", 3},
+				{itemInteger, "8223", 3},
+				{itemKey, "port", 4},
+				{itemInteger, "4223", 4},
+			},
+		},
+		{
+			name: "should omit trailing commas at top level with multiple items",
+			input: `
+                        {
+                          "http_port": 8223,
+                          "port": 4223,
+                          "max_payload": "5MB",
+                          "debug": true,
+                          "max_control_line": 1024
+                        }
+                        `,
+			expected: []item{
+				{itemKey, "http_port", 3},
+				{itemInteger, "8223", 3},
+				{itemKey, "port", 4},
+				{itemInteger, "4223", 4},
+				{itemKey, "max_payload", 5},
+				{itemString, "5MB", 5},
+				{itemKey, "debug", 6},
+				{itemBool, "true", 6},
+				{itemKey, "max_control_line", 7},
+				{itemInteger, "1024", 7},
+			},
+		},
+		{
+			name: "should support JSON not prettified",
+			input: `{"http_port": 8224,"port": 4224}
+                        `,
+			expected: []item{
+				{itemKey, "http_port", 1},
+				{itemInteger, "8224", 1},
+				{itemKey, "port", 1},
+				{itemInteger, "4224", 1},
+			},
+		},
+		{
+			name: "should support JSON not prettified with final bracket after newline",
+			input: `{"http_port": 8225,"port": 4225
+                        }
+                        `,
+			expected: []item{
+				{itemKey, "http_port", 1},
+				{itemInteger, "8225", 1},
+				{itemKey, "port", 1},
+				{itemInteger, "4225", 1},
+			},
+		},
+		{
+			name: "should support uglified JSON with inner blocks",
+			input: `{"http_port": 8227,"port": 4227,"write_deadline": "1h","cluster": {"port": 6222,"routes": ["nats://127.0.0.1:4222","nats://127.0.0.1:4223","nats://127.0.0.1:4224"]}}
+                        `,
+			expected: []item{
+				{itemKey, "http_port", 1},
+				{itemInteger, "8227", 1},
+				{itemKey, "port", 1},
+				{itemInteger, "4227", 1},
+				{itemKey, "write_deadline", 1},
+				{itemString, "1h", 1},
+				{itemKey, "cluster", 1},
+				{itemMapStart, "", 1},
+				{itemKey, "port", 1},
+				{itemInteger, "6222", 1},
+				{itemKey, "routes", 1},
+				{itemArrayStart, "", 1},
+				{itemString, "nats://127.0.0.1:4222", 1},
+				{itemString, "nats://127.0.0.1:4223", 1},
+				{itemString, "nats://127.0.0.1:4224", 1},
+				{itemArrayEnd, "", 1},
+				{itemMapEnd, "", 1},
+			},
+		},
+		{
+			name: "should support prettified JSON with inner blocks",
+			input: `
+                        {
+                          "http_port": 8227,
+                          "port": 4227,
+                          "write_deadline": "1h",
+                          "cluster": {
+                            "port": 6222,
+                            "routes": [
+                              "nats://127.0.0.1:4222",
+                              "nats://127.0.0.1:4223",
+                              "nats://127.0.0.1:4224"
+                            ]
+                          }
+                        }
+                        `,
+			expected: []item{
+				{itemKey, "http_port", 3},
+				{itemInteger, "8227", 3},
+				{itemKey, "port", 4},
+				{itemInteger, "4227", 4},
+				{itemKey, "write_deadline", 5},
+				{itemString, "1h", 5},
+				{itemKey, "cluster", 6},
+				{itemMapStart, "", 6},
+				{itemKey, "port", 7},
+				{itemInteger, "6222", 7},
+				{itemKey, "routes", 8},
+				{itemArrayStart, "", 8},
+				{itemString, "nats://127.0.0.1:4222", 9},
+				{itemString, "nats://127.0.0.1:4223", 10},
+				{itemString, "nats://127.0.0.1:4224", 11},
+				{itemArrayEnd, "", 12},
+				{itemMapEnd, "", 13},
+			},
+		},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			lx := lex(test.input)
+			expect(t, lx, test.expected)
+		})
+	}
+}