ip/resolver/http/service.go: refactor default decoder function into its own module

ip/resolver/decoder/text.go

@@ -0,0 +1,19 @@
+package decoder
+
+import (
+	"bufio"
+	"io"
+	"strings"
+)
+
+// Text decoder that expects the IP address
+// to be on the first line of the response.
+// The decoder will only trim trailing and leading whitespace.
+func Text(r io.Reader) (string, error) {
+	line, err := bufio.NewReader(r).ReadString('\n')
+	if err == nil || err == io.EOF {
+		line = strings.TrimRight(line, "\r\n")
+		line = strings.TrimSpace(line)
+	}
+	return line, err
+}