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 {

internal/config/config_test.go

@@ -165,3 +165,43 @@ func TestDefaultExpiryMustFitWithinMax(t *testing.T) {
 		t.Error("an unlimited default under a finite maximum was accepted")
 	}
 }
+
+func TestPortOverridesListen(t *testing.T) {
+	cases := []struct {
+		listen string
+		port   int
+		want   string
+	}{
+		{"127.0.0.1:8080", 0, "127.0.0.1:8080"},
+		{"127.0.0.1:8080", 9000, "127.0.0.1:9000"},
+		{"0.0.0.0:8080", 3000, "0.0.0.0:3000"},
+		{"localhost", 3000, "localhost:3000"}, // a bare host is fine with --port
+		{"[::1]:8080", 3000, "[::1]:3000"},
+	}
+	for _, c := range cases {
+		cfg := &Config{
+			Listen: c.listen, Port: c.port, BasePath: "/", DataDir: "d",
+			SweepInterval: time.Minute, MaxConcurrent: 1,
+		}
+		if err := cfg.Normalise(); err != nil {
+			t.Errorf("listen %q port %d: %v", c.listen, c.port, err)
+			continue
+		}
+		if cfg.Listen != c.want {
+			t.Errorf("listen %q port %d => %q, want %q", c.listen, c.port, cfg.Listen, c.want)
+		}
+	}
+
+	for _, c := range []struct {
+		listen string
+		port   int
+	}{{"127.0.0.1:8080", 70000}, {"127.0.0.1:8080", -1}, {"localhost", 0}} {
+		cfg := &Config{
+			Listen: c.listen, Port: c.port, BasePath: "/", DataDir: "d",
+			SweepInterval: time.Minute, MaxConcurrent: 1,
+		}
+		if err := cfg.Normalise(); err == nil {
+			t.Errorf("listen %q port %d was accepted", c.listen, c.port)
+		}
+	}
+}

internal/config/flags.go

@@ -222,7 +222,9 @@ func (s *Set) PrintUsage(w io.Writer, header string) {
 		}
 		fmt.Fprintf(w, "%s\n", name)
 		fmt.Fprintf(w, "        %s", sp.usage)
-		if sp.def != "" && sp.def != "false" {
+		// A zero default means "unset" for the options that have one, and
+		// printing it would read as a real value.
+		if sp.def != "" && sp.def != "false" && sp.def != "0" {
 			fmt.Fprintf(w, " (default %s)", sp.def)
 		}
 		fmt.Fprintf(w, "\n        [%s]\n", s.envName(sp.long))