Add --port

internal/config/config.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"net"
 	"net/url"
+	"strconv"
 	"strings"
 	"time"
 )
@@ -13,6 +14,7 @@ import (
 // Config is the fully-resolved server configuration.
 type Config struct {
 	Listen    string
+	Port      int // overrides the port in Listen when set
 	DataDir   string
 	BasePath  string // normalised: always "/" or "/prefix/"
 	PublicURL string // absolute origin+path for generated links; "" => relative
@@ -40,6 +42,8 @@ const EnvPrefix = "SEND_"
 func (c *Config) Register(s *Set) {
 	s.String(&c.Listen, "listen", "l", "127.0.0.1:8080", "ADDR",
 		"address to listen on; keep it on loopback behind a reverse proxy")
+	s.Int(&c.Port, "port", "p", 0,
+		"port to listen on, replacing the one in --listen")
 	s.String(&c.DataDir, "data", "d", "./data", "DIR",
 		"directory holding uploaded objects and their metadata")
 	s.String(&c.BasePath, "base-url", "b", "/", "PATH",
@@ -78,6 +82,23 @@ func (c *Config) Register(s *Set) {
 func (c *Config) Normalise() error {
 	c.BasePath = NormalisePath(c.BasePath)
 
+	// --port is a convenience over --listen: it replaces only the port, so the
+	// host stays wherever --listen (or its default) put it.
+	if c.Port != 0 {
+		if c.Port < 1 || c.Port > 65535 {
+			return fmt.Errorf("--port: %d is not a port number", c.Port)
+		}
+		host, _, err := net.SplitHostPort(c.Listen)
+		if err != nil {
+			// --listen held a bare host, which is fine once a port is supplied.
+			host = strings.TrimSpace(c.Listen)
+		}
+		c.Listen = net.JoinHostPort(host, strconv.Itoa(c.Port))
+	}
+	if _, _, err := net.SplitHostPort(c.Listen); err != nil {
+		return fmt.Errorf("--listen: %q is not an address:port (use --port to set just the port)", c.Listen)
+	}
+
 	if c.PublicURL != "" {
 		u, err := url.Parse(c.PublicURL)
 		if err != nil {