1 files changed, 98 insertions, 0 deletions
diff --git a/plugin/pkg/parse/host.go b/plugin/pkg/parse/host.go
new file mode 100644
index 000000000..87177125f
--- /dev/null
+++ b/plugin/pkg/parse/host.go
@@ -0,0 +1,98 @@
+package parse
+
+import (
+	"fmt"
+	"net"
+	"os"
+
+	"github.com/coredns/coredns/plugin/pkg/transport"
+
+	"github.com/miekg/dns"
+)
+
+// HostPortOrFile parses the strings in s, each string can either be a
+// address, [scheme://]address:port or a filename. The address part is checked
+// and in case of filename a resolv.conf like file is (assumed) and parsed and
+// the nameservers found are returned.
+func HostPortOrFile(s ...string) ([]string, error) {
+	var servers []string
+	for _, h := range s {
+
+		trans, host := Transport(h)
+
+		addr, _, err := net.SplitHostPort(host)
+		if err != nil {
+			// Parse didn't work, it is not a addr:port combo
+			if net.ParseIP(host) == nil {
+				// Not an IP address.
+				ss, err := tryFile(host)
+				if err == nil {
+					servers = append(servers, ss...)
+					continue
+				}
+				return servers, fmt.Errorf("not an IP address or file: %q", host)
+			}
+			var ss string
+			switch trans {
+			case transport.DNS:
+				ss = net.JoinHostPort(host, transport.Port)
+			case transport.TLS:
+				ss = transport.TLS + "://" + net.JoinHostPort(host, transport.TLSPort)
+			case transport.GRPC:
+				ss = transport.GRPC + "://" + net.JoinHostPort(host, transport.GRPCPort)
+			case transport.HTTPS:
+				ss = transport.HTTPS + "://" + net.JoinHostPort(host, transport.HTTPSPort)
+			}
+			servers = append(servers, ss)
+			continue
+		}
+
+		if net.ParseIP(addr) == nil {
+			// Not an IP address.
+			ss, err := tryFile(host)
+			if err == nil {
+				servers = append(servers, ss...)
+				continue
+			}
+			return servers, fmt.Errorf("not an IP address or file: %q", host)
+		}
+		servers = append(servers, h)
+	}
+	return servers, nil
+}
+
+// Try to open this is a file first.
+func tryFile(s string) ([]string, error) {
+	c, err := dns.ClientConfigFromFile(s)
+	if err == os.ErrNotExist {
+		return nil, fmt.Errorf("failed to open file %q: %q", s, err)
+	} else if err != nil {
+		return nil, err
+	}
+
+	servers := []string{}
+	for _, s := range c.Servers {
+		servers = append(servers, net.JoinHostPort(s, c.Port))
+	}
+	return servers, nil
+}
+
+// HostPort will check if the host part is a valid IP address, if the
+// IP address is valid, but no port is found, defaultPort is added.
+func HostPort(s, defaultPort string) (string, error) {
+	addr, port, err := net.SplitHostPort(s)
+	if port == "" {
+		port = defaultPort
+	}
+	if err != nil {
+		if net.ParseIP(s) == nil {
+			return "", fmt.Errorf("must specify an IP address: `%s'", s)
+		}
+		return net.JoinHostPort(s, port), nil
+	}
+
+	if net.ParseIP(addr) == nil {
+		return "", fmt.Errorf("must specify an IP address: `%s'", addr)
+	}
+	return net.JoinHostPort(addr, port), nil
+}