Improve option parsing

The existing code did not provide for escaping characters, which made
certain option values impossible to represent, for example:

 password='spaces and ' a quote'

In addition, ParseUrl would not allow even a single space in any value.

Add standard backslash escaping, matching libpq's own conninfo_parse.

Apply this escaping to special characters in ParseURL.

conn.go

@@ -308,9 +308,12 @@ func parseOpts(name string, o values) error {
 
 		if r != '\'' {
 			for !unicode.IsSpace(r) {
-				if r != '\\' {
-					valRunes = append(valRunes, r)
+				if r == '\\' {
+					if r, ok = s.Next(); !ok {
+						return fmt.Errorf(`missing character after backslash`)
+					}
 				}
+				valRunes = append(valRunes, r)
 
 				if r, ok = s.Next(); !ok {
 					break
@@ -323,10 +326,11 @@ func parseOpts(name string, o values) error {
 					return fmt.Errorf(`unterminated quoted string literal in connection string`)
 				}
 				switch r {
-				case '\\':
-					continue
 				case '\'':
 					break quote
+				case '\\':
+					r, _ = s.Next()
+					fallthrough
 				default:
 					valRunes = append(valRunes, r)
 				}

conn_test.go

@@ -935,6 +935,13 @@ func TestParseOpts(t *testing.T) {
 		// The parser ignores spaces after = and interprets the next set of non-whitespace characters as the value.
 		{"user= password=foo", values{"user": "password=foo"}, true},
 
+		// Backslash escapes next char
+		{`user=a\ \'\\b`, values{"user": `a '\b`}, true},
+		{`user='a \'b'`, values{"user": `a 'b`}, true},
+
+		// Incomplete escape
+		{`user=x\`, values{}, false},
+
 		// No '=' after the key
 		{"postgre://marko@internet", values{}, false},
 		{"dbname user=goodbye", values{}, false},

doc.go

@@ -61,6 +61,10 @@ Use single quotes for values that contain whitespace:
 
     "user=pqgotest password='with spaces'"
 
+A backslash will escape the next character in values:
+
+    "user=space\ man password='it\'s valid'
+
 Note that the connection parameter client_encoding (which sets the
 text encoding for the connection) may be set but must be "UTF8",
 matching with the same rules as Postgres. It is an error to provide

url.go

@@ -39,9 +39,10 @@ func ParseURL(url string) (string, error) {
 	}
 
 	var kvs []string
+	escaper := strings.NewReplacer(` `, `\ `, `'`, `\'`, `\`, `\\`)
 	accrue := func(k, v string) {
 		if v != "" {
-			kvs = append(kvs, k+"="+v)
+			kvs = append(kvs, k+"="+escaper.Replace(v))
 		}
 	}
 

url_test.go

@@ -17,8 +17,8 @@ func TestSimpleParseURL(t *testing.T) {
 }
 
 func TestFullParseURL(t *testing.T) {
-	expected := "dbname=database host=hostname.remote password=secret port=1234 user=username"
-	str, err := ParseURL("postgres://username:secret@hostname.remote:1234/database")
+	expected := `dbname=database host=hostname.remote password=top\ secret port=1234 user=username`
+	str, err := ParseURL("postgres://username:top%20secret@hostname.remote:1234/database")
 	if err != nil {
 		t.Fatal(err)
 	}