Add util

util/net/net.go

@@ -0,0 +1,63 @@
+package net
+
+import (
+	"errors"
+	"fmt"
+	"net"
+	"strconv"
+	"strings"
+)
+
+// Listen takes addr:portmin-portmax and binds to the first available port
+// Example: Listen("localhost:5000-6000", fn)
+func Listen(addr string, fn func(string) (net.Listener, error)) (net.Listener, error) {
+	// host:port || host:min-max
+	parts := strings.Split(addr, ":")
+
+	//
+	if len(parts) < 2 {
+		return fn(addr)
+	}
+
+	// try to extract port range
+	ports := strings.Split(parts[len(parts)-1], "-")
+
+	// single port
+	if len(ports) < 2 {
+		return fn(addr)
+	}
+
+	// we have a port range
+
+	// extract min port
+	min, err := strconv.Atoi(ports[0])
+	if err != nil {
+		return nil, errors.New("unable to extract port range")
+	}
+
+	// extract max port
+	max, err := strconv.Atoi(ports[1])
+	if err != nil {
+		return nil, errors.New("unable to extract port range")
+	}
+
+	// set host
+	host := parts[:len(parts)-1]
+
+	// range the ports
+	for port := min; port <= max; port++ {
+		// try bind to host:port
+		ln, err := fn(fmt.Sprintf("%s:%d", host, port))
+		if err == nil {
+			return ln, nil
+		}
+
+		// hit max port
+		if port == max {
+			return nil, err
+		}
+	}
+
+	// why are we here?
+	return nil, fmt.Errorf("unable to bind to %s", addr)
+}