introduce structure BadIPError and BadHostError

client.go

@@ -14,6 +14,32 @@ import (
 // DefaultClient is the default Client whose setting is the same as http.DefaultClient.
 var DefaultClient *http.Client
 
+// BadIPError is returned when requested address is not permitted by paranoidhttp.
+type BadIPError struct {
+	IP net.IP
+}
+
+func (e *BadIPError) Error() string {
+	return fmt.Sprintf("bad ip is detected: %v", e.IP)
+}
+
+// BadHostError is returned when requested hostname is not permitted by paranoidhttp.
+type BadHostError struct {
+	hostname string
+}
+
+func (e *BadHostError) Error() string {
+	return fmt.Sprintf("bad host is detected: %v", e.hostname)
+}
+
+func newBadIPError(ip net.IP) error {
+	return &BadIPError{ip}
+}
+
+func newBadHostError(hostname string) error {
+	return &BadHostError{hostname}
+}
+
 func mustParseCIDR(addr string) *net.IPNet {
 	_, ipnet, err := net.ParseCIDR(addr)
 	if err != nil {
@@ -43,13 +69,13 @@ func safeAddr(ctx context.Context, resolver *net.Resolver, hostport string) (str
 	ip := net.ParseIP(host)
 	if ip != nil {
 		if ip.To4() != nil && isBadIPv4(ip) {
-			return "", fmt.Errorf("bad ip is detected: %v", ip)
+			return "", newBadIPError(ip)
 		}
 		return net.JoinHostPort(ip.String(), port), nil
 	}
 
 	if isBadHost(host) {
-		return "", fmt.Errorf("bad host is detected: %v", host)
+		return "", newBadHostError(host)
 	}
 
 	r := resolver
@@ -62,7 +88,7 @@ func safeAddr(ctx context.Context, resolver *net.Resolver, hostport string) (str
 	}
 	for _, addr := range addrs {
 		if addr.IP.To4() != nil && isBadIPv4(addr.IP) {
-			return "", fmt.Errorf("bad ip is detected: %v", addr.IP)
+			return "", newBadIPError(addr.IP)
 		}
 	}
 	return net.JoinHostPort(addrs[0].IP.String(), port), nil