registry: create emptyServiceConfig without parsing

emptyServiceConfig is a default service-config for situations where
no config-file is available (e.g. when used in the CLI). If won't
have mirrors configured, but does have the default insecure registry
CIDRs for loopback interfaces configured.

Before this patch, this config was constructeed using the same code
that handled constructing the config with a config present, but this
involved parsing CIDR masks, and much more.

With this patch, the service config is constructed as a literal, making
it more transparent that it does not depend on any config or state.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

registry/config.go

@@ -56,8 +56,38 @@ var (
 		Host:   DefaultRegistryHost,
 	}
 
-	emptyServiceConfig, _ = newServiceConfig(ServiceOptions{})
-	validHostPortRegex    = lazyregexp.New(`^` + reference.DomainRegexp.String() + `$`)
+	// ipv6Loopback is the CIDR for the IPv6 loopback address ("::1"); "::1/128"
+	ipv6Loopback = &net.IPNet{
+		IP:   net.IPv6loopback,
+		Mask: net.CIDRMask(128, 128),
+	}
+
+	// ipv4Loopback is the CIDR for IPv4 loopback addresses ("127.0.0.0/8")
+	ipv4Loopback = &net.IPNet{
+		IP:   net.IPv4(127, 0, 0, 0),
+		Mask: net.CIDRMask(8, 32),
+	}
+
+	// emptyServiceConfig is a default service-config for situations where
+	// no config-file is available (e.g. when used in the CLI). If won't
+	// have mirrors configured, but does have the default insecure registry
+	// CIDRs for loopback interfaces configured.
+	emptyServiceConfig = &serviceConfig{
+		IndexConfigs: map[string]*registry.IndexInfo{
+			IndexName: {
+				Name:     IndexName,
+				Mirrors:  make([]string, 0),
+				Secure:   true,
+				Official: true,
+			},
+		},
+		InsecureRegistryCIDRs: []*registry.NetIPNet{
+			(*registry.NetIPNet)(ipv6Loopback),
+			(*registry.NetIPNet)(ipv4Loopback),
+		},
+	}
+
+	validHostPortRegex = lazyregexp.New(`^` + reference.DomainRegexp.String() + `$`)
 
 	// certsDir is used to override defaultCertsDir.
 	certsDir string