feat: add support for systemd listener activation sockets

To support starting a network service on demand and to
support a "least privilege-approach" with regards to the
permission a network service process needs to have, systemd
supports opening a network socket on behalf of the service
and passing it as an open file descriptor.

The service gets notified about open file descriptors for
this purpose as well as metadata such as named listeners
via environment variables.

This patch adds support for prefixing the listen address
passed with --address with "sd-listen-fd:" to access these
file descriptors, taking either a listener name passed using
the `LISTEN_FDNAMES` environment variable or `LISTEN_FD_$n`
for unnamed file descriptiors where `n` is the id of the
descriptor starting at 3 (LISTEN_FD_3).

See sd_listen_fds(3)

README.md

@@ -86,9 +86,21 @@ directory: .
 # permissions. For example, to allow to read and create, set "RC". Default is "R".
 permissions: R
 
-# The default permissions rules for users. Default is none.
+# The default permissions rules for users. Default is none. Rules are applied
+# from last to first, that is, the first rule that matches the request, starting
+# from the end, will be applied to the request.
 rules: []
 
+# The behavior of redefining the rules for users. It can be:
+# - overwrite: when a user has rules defined, these will overwrite any global
+#   rules already defined. That is, the global rules are not applicable to the
+#   user.
+# - append: when a user has rules defined, these will be appended to the global
+#   rules already defined. That is, for this user, their own specific rules will
+#   be checked first, and then the global rules.
+# Default is 'overwrite'.
+rulesBehavior: overwrite
+
 # Logging configuration
 log:
   # Logging format ('console', 'json'). Default is 'console'.

cmd/root.go

@@ -10,6 +10,7 @@ import (
 	"strings"
 	"syscall"
 
+	"github.com/coreos/go-systemd/v22/activation"
 	"github.com/hacdias/webdav/v5/lib"
 	"github.com/spf13/cobra"
 	"go.uber.org/zap"
@@ -115,7 +116,21 @@ func getListener(cfg *lib.Config) (net.Listener, error) {
 		network string
 	)
 
-	if strings.HasPrefix(cfg.Address, "unix:") {
+	if strings.HasPrefix(cfg.Address, "sd-listen-fd:") {
+		listeners, err := activation.ListenersWithNames()
+		if err != nil {
+			return nil, err
+		}
+
+		address := cfg.Address[13:]
+		listener, ok := listeners[address]
+
+		if !ok || len(listener) < 1 {
+			return nil, errors.New("unknown sd-listen-fd address '" + address + "'")
+		}
+
+		return listener[0], nil
+	} else if strings.HasPrefix(cfg.Address, "unix:") {
 		address = cfg.Address[5:]
 		network = "unix"
 	} else {

go.mod

@@ -3,6 +3,7 @@ module github.com/hacdias/webdav/v5
 go 1.23
 
 require (
+	github.com/coreos/go-systemd/v22 v22.3.2
 	github.com/go-viper/mapstructure/v2 v2.2.1
 	github.com/rs/cors v1.11.1
 	github.com/spf13/cobra v1.8.1

go.sum

@@ -1,3 +1,5 @@
+github.com/coreos/go-systemd/v22 v22.3.2 h1:D9/bQk5vlXQFZ6Kwuu6zaiXJ9oTPe68++AzAJc1DzSI=
+github.com/coreos/go-systemd/v22 v22.3.2/go.mod h1:Y58oyj3AT4RCenI/lSvhwexgC+NSVTIJ3seZv2GcEnc=
 github.com/cpuguy83/go-md2man/v2 v2.0.4/go.mod h1:tgQtvFlXSQOSOSIRvRPT7W67SCa46tRHOmNcaadrF8o=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.2-0.20180830191138-d8f796af33cc h1:U9qPSI2PIWSS1VwoXQT9A3Wy9MM3WgvqSxFWenqJduM=
@@ -8,6 +10,7 @@ github.com/fsnotify/fsnotify v1.8.0 h1:dAwr6QBTBZIkG8roQaJjGof0pp0EeF+tNV7YBP3F/
 github.com/fsnotify/fsnotify v1.8.0/go.mod h1:8jBTzvmWwFyi3Pb8djgCCO5IBqzKJ/Jwo8TRcHyHii0=
 github.com/go-viper/mapstructure/v2 v2.2.1 h1:ZAaOCxANMuZx5RCeg0mBdEZk7DZasvvZIxtHqx8aGss=
 github.com/go-viper/mapstructure/v2 v2.2.1/go.mod h1:oJDH3BJKyqBA2TXFhDsKDGDTlndYOZ6rGS0BRZIxGhM=
+github.com/godbus/dbus/v5 v5.0.4/go.mod h1:xhWf0FNVPg57R7Z0UbKHbJfkEywrmjJnf7w5xrFpKfA=
 github.com/google/go-cmp v0.6.0 h1:ofyhxvXcZhMsU5ulbFiLKl/XBFqE1GSq7atu8tAmTRI=
 github.com/google/go-cmp v0.6.0/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=
 github.com/hashicorp/hcl v1.0.0 h1:0Anlzjpi4vEasTeNFn2mLJgTSwt0+6sfsiTG8qcWGx4=

lib/config.go

@@ -75,6 +75,7 @@ func ParseConfig(filename string, flags *pflag.FlagSet) (*Config, error) {
 	v.SetDefault("Prefix", DefaultPrefix)
 
 	// Other defaults
+	v.SetDefault("RulesBehavior", RulesOverwrite)
 	v.SetDefault("Directory", ".")
 	v.SetDefault("Permissions", "R")
 	v.SetDefault("Debug", false)
@@ -115,7 +116,21 @@ func ParseConfig(filename string, flags *pflag.FlagSet) (*Config, error) {
 			cfg.Users[i].Permissions = cfg.Permissions
 		}
 
-		if !v.IsSet(fmt.Sprintf("Users.%d.Rules", i)) {
+		if !v.IsSet(fmt.Sprintf("Users.%d.RulesBehavior", i)) {
+			cfg.Users[i].RulesBehavior = cfg.RulesBehavior
+		}
+
+		if v.IsSet(fmt.Sprintf("Users.%d.Rules", i)) {
+			switch cfg.Users[i].RulesBehavior {
+			case RulesOverwrite:
+				// Do nothing
+			case RulesAppend:
+				rules := append([]*Rule{}, cfg.Rules...)
+				rules = append(rules, cfg.Users[i].Rules...)
+
+				cfg.Users[i].Rules = rules
+			}
+		} else {
 			cfg.Users[i].Rules = cfg.Rules
 		}
 	}

lib/config_test.go

@@ -232,6 +232,71 @@ rules:
 		require.Nil(t, cfg.Rules[1].Regex)
 	})
 
+	t.Run("Rules Behavior (Default: Overwrite)", func(t *testing.T) {
+		content := `
+directory: /
+rules:
+  - regex: '^.+\.js$'
+  - path: /public/access/
+
+users:
+  - username: foo
+    password: bar
+    rules:
+    - path: /private/access/`
+
+		cfg := writeAndParseConfig(t, content, ".yaml")
+		require.NoError(t, cfg.Validate())
+
+		require.Len(t, cfg.Rules, 2)
+
+		require.Empty(t, cfg.Rules[0].Path)
+		require.NotNil(t, cfg.Rules[0].Regex)
+		require.True(t, cfg.Rules[0].Regex.MatchString("/my/path/to/file.js"))
+		require.False(t, cfg.Rules[0].Regex.MatchString("/my/path/to/file.ts"))
+
+		require.EqualValues(t, "/public/access/", cfg.Rules[1].Path)
+		require.Nil(t, cfg.Rules[1].Regex)
+
+		require.Len(t, cfg.Users, 1)
+		require.Len(t, cfg.Users[0].Rules, 1)
+		require.EqualValues(t, "/private/access/", cfg.Users[0].Rules[0].Path)
+	})
+
+	t.Run("Rules Behavior (Append)", func(t *testing.T) {
+		content := `
+directory: /
+rules:
+  - regex: '^.+\.js$'
+  - path: /public/access/
+rulesBehavior: append
+
+users:
+  - username: foo
+    password: bar
+    rules:
+    - path: /private/access/`
+
+		cfg := writeAndParseConfig(t, content, ".yaml")
+		require.NoError(t, cfg.Validate())
+
+		require.Len(t, cfg.Rules, 2)
+
+		require.Empty(t, cfg.Rules[0].Path)
+		require.NotNil(t, cfg.Rules[0].Regex)
+		require.True(t, cfg.Rules[0].Regex.MatchString("/my/path/to/file.js"))
+		require.False(t, cfg.Rules[0].Regex.MatchString("/my/path/to/file.ts"))
+
+		require.EqualValues(t, "/public/access/", cfg.Rules[1].Path)
+		require.Nil(t, cfg.Rules[1].Regex)
+
+		require.Len(t, cfg.Users, 1)
+		require.Len(t, cfg.Users[0].Rules, 3)
+
+		require.EqualValues(t, cfg.Rules[0], cfg.Users[0].Rules[0])
+		require.EqualValues(t, cfg.Rules[1], cfg.Users[0].Rules[1])
+		require.EqualValues(t, "/private/access/", cfg.Users[0].Rules[2].Path)
+	})
 }
 
 func TestConfigEnv(t *testing.T) {

lib/permissions.go

@@ -36,10 +36,18 @@ func (r *Rule) Matches(path string) bool {
 	return strings.HasPrefix(path, r.Path)
 }
 
+type RulesBehavior string
+
+const (
+	RulesOverwrite RulesBehavior = "overwrite"
+	RulesAppend    RulesBehavior = "append"
+)
+
 type UserPermissions struct {
-	Directory   string
-	Permissions Permissions
-	Rules       []*Rule
+	Directory     string
+	Permissions   Permissions
+	Rules         []*Rule
+	RulesBehavior RulesBehavior
 }
 
 // Allowed checks if the user has permission to access a directory/file
@@ -91,6 +99,13 @@ func (p *UserPermissions) Validate() error {
 		}
 	}
 
+	switch p.RulesBehavior {
+	case RulesAppend, RulesOverwrite:
+		// Good to go
+	default:
+		return fmt.Errorf("invalid rule behavior: %s", p.RulesBehavior)
+	}
+
 	return nil
 }