listeners: Add support for named socket activation (#7243)

Author: Siomachkin

listeners.go

@@ -38,6 +38,10 @@ import (
 	"github.com/caddyserver/caddy/v2/internal"
 )
 
+// listenFdsStart is the first file descriptor number for systemd socket activation.
+// File descriptors 0, 1, 2 are reserved for stdin, stdout, stderr.
+const listenFdsStart = 3
+
 // NetworkAddress represents one or more network addresses.
 // It contains the individual components for a parsed network
 // address of the form accepted by ParseNetworkAddress().
@@ -305,6 +309,64 @@ func IsFdNetwork(netw string) bool {
 	return strings.HasPrefix(netw, "fd")
 }
 
+// getFdByName returns the file descriptor number for the given
+// socket name from systemd's LISTEN_FDNAMES environment variable.
+// Socket names are provided by systemd via socket activation.
+//
+// The name can optionally include an index to handle multiple sockets
+// with the same name: "web:0" for first, "web:1" for second, etc.
+// If no index is specified, defaults to index 0 (first occurrence).
+func getFdByName(nameWithIndex string) (int, error) {
+	if nameWithIndex == "" {
+		return 0, fmt.Errorf("socket name cannot be empty")
+	}
+
+	fdNamesStr := os.Getenv("LISTEN_FDNAMES")
+	if fdNamesStr == "" {
+		return 0, fmt.Errorf("LISTEN_FDNAMES environment variable not set")
+	}
+
+	// Parse name and optional index
+	parts := strings.Split(nameWithIndex, ":")
+	if len(parts) > 2 {
+		return 0, fmt.Errorf("invalid socket name format '%s': too many colons", nameWithIndex)
+	}
+
+	name := parts[0]
+	targetIndex := 0
+
+	if len(parts) > 1 {
+		var err error
+		targetIndex, err = strconv.Atoi(parts[1])
+		if err != nil {
+			return 0, fmt.Errorf("invalid socket index '%s': %v", parts[1], err)
+		}
+		if targetIndex < 0 {
+			return 0, fmt.Errorf("socket index cannot be negative: %d", targetIndex)
+		}
+	}
+
+	// Parse the socket names
+	names := strings.Split(fdNamesStr, ":")
+
+	// Find the Nth occurrence of the requested name
+	matchCount := 0
+	for i, fdName := range names {
+		if fdName == name {
+			if matchCount == targetIndex {
+				return listenFdsStart + i, nil
+			}
+			matchCount++
+		}
+	}
+
+	if matchCount == 0 {
+		return 0, fmt.Errorf("socket name '%s' not found in LISTEN_FDNAMES", name)
+	}
+
+	return 0, fmt.Errorf("socket name '%s' found %d times, but index %d requested", name, matchCount, targetIndex)
+}
+
 // ParseNetworkAddress parses addr into its individual
 // components. The input string is expected to be of
 // the form "network/host:port-range" where any part is
@@ -336,9 +398,27 @@ func ParseNetworkAddressWithDefaults(addr, defaultNetwork string, defaultPort ui
 		}, err
 	}
 	if IsFdNetwork(network) {
+		fdAddr := host
+
+		// Handle named socket activation (fdname/name, fdgramname/name)
+		if strings.HasPrefix(network, "fdname") || strings.HasPrefix(network, "fdgramname") {
+			fdNum, err := getFdByName(host)
+			if err != nil {
+				return NetworkAddress{}, fmt.Errorf("named socket activation: %v", err)
+			}
+			fdAddr = strconv.Itoa(fdNum)
+
+			// Normalize network to standard fd/fdgram
+			if strings.HasPrefix(network, "fdname") {
+				network = "fd"
+			} else {
+				network = "fdgram"
+			}
+		}
+
 		return NetworkAddress{
 			Network: network,
-			Host:    host,
+			Host:    fdAddr,
 		}, nil
 	}
 	var start, end uint64

listeners_test.go

@@ -15,6 +15,7 @@
 package caddy
 
 import (
+	"os"
 	"reflect"
 	"testing"
 
@@ -652,3 +653,286 @@ func TestSplitUnixSocketPermissionsBits(t *testing.T) {
 		}
 	}
 }
+
+// TestGetFdByName tests the getFdByName function for systemd socket activation.
+func TestGetFdByName(t *testing.T) {
+	// Save original environment
+	originalFdNames := os.Getenv("LISTEN_FDNAMES")
+
+	// Restore environment after test
+	defer func() {
+		if originalFdNames != "" {
+			os.Setenv("LISTEN_FDNAMES", originalFdNames)
+		} else {
+			os.Unsetenv("LISTEN_FDNAMES")
+		}
+	}()
+
+	tests := []struct {
+		name        string
+		fdNames     string
+		socketName  string
+		expectedFd  int
+		expectError bool
+	}{
+		{
+			name:       "simple http socket",
+			fdNames:    "http",
+			socketName: "http",
+			expectedFd: 3,
+		},
+		{
+			name:       "multiple different sockets - first",
+			fdNames:    "http:https:dns",
+			socketName: "http",
+			expectedFd: 3,
+		},
+		{
+			name:       "multiple different sockets - second",
+			fdNames:    "http:https:dns",
+			socketName: "https",
+			expectedFd: 4,
+		},
+		{
+			name:       "multiple different sockets - third",
+			fdNames:    "http:https:dns",
+			socketName: "dns",
+			expectedFd: 5,
+		},
+		{
+			name:       "duplicate names - first occurrence (no index)",
+			fdNames:    "web:web:api",
+			socketName: "web",
+			expectedFd: 3,
+		},
+		{
+			name:       "duplicate names - first occurrence (explicit index 0)",
+			fdNames:    "web:web:api",
+			socketName: "web:0",
+			expectedFd: 3,
+		},
+		{
+			name:       "duplicate names - second occurrence (index 1)",
+			fdNames:    "web:web:api",
+			socketName: "web:1",
+			expectedFd: 4,
+		},
+		{
+			name:       "complex duplicates - first api",
+			fdNames:    "web:api:web:api:dns",
+			socketName: "api:0",
+			expectedFd: 4,
+		},
+		{
+			name:       "complex duplicates - second api",
+			fdNames:    "web:api:web:api:dns",
+			socketName: "api:1",
+			expectedFd: 6,
+		},
+		{
+			name:       "complex duplicates - first web",
+			fdNames:    "web:api:web:api:dns",
+			socketName: "web:0",
+			expectedFd: 3,
+		},
+		{
+			name:       "complex duplicates - second web",
+			fdNames:    "web:api:web:api:dns",
+			socketName: "web:1",
+			expectedFd: 5,
+		},
+		{
+			name:        "socket not found",
+			fdNames:     "http:https",
+			socketName:  "missing",
+			expectError: true,
+		},
+		{
+			name:        "empty socket name",
+			fdNames:     "http",
+			socketName:  "",
+			expectError: true,
+		},
+		{
+			name:        "missing LISTEN_FDNAMES",
+			fdNames:     "",
+			socketName:  "http",
+			expectError: true,
+		},
+		{
+			name:        "index out of range",
+			fdNames:     "web:web",
+			socketName:  "web:2",
+			expectError: true,
+		},
+		{
+			name:        "negative index",
+			fdNames:     "web",
+			socketName:  "web:-1",
+			expectError: true,
+		},
+		{
+			name:        "invalid index format",
+			fdNames:     "web",
+			socketName:  "web:abc",
+			expectError: true,
+		},
+		{
+			name:        "too many colons",
+			fdNames:     "web",
+			socketName:  "web:0:extra",
+			expectError: true,
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			// Set up environment
+			if tc.fdNames != "" {
+				os.Setenv("LISTEN_FDNAMES", tc.fdNames)
+			} else {
+				os.Unsetenv("LISTEN_FDNAMES")
+			}
+
+			// Test the function
+			fd, err := getFdByName(tc.socketName)
+
+			if tc.expectError {
+				if err == nil {
+					t.Errorf("Expected error but got none")
+				}
+			} else {
+				if err != nil {
+					t.Errorf("Expected no error but got: %v", err)
+				}
+				if fd != tc.expectedFd {
+					t.Errorf("Expected FD %d but got %d", tc.expectedFd, fd)
+				}
+			}
+		})
+	}
+}
+
+// TestParseNetworkAddressFdName tests parsing of fdname and fdgramname addresses.
+func TestParseNetworkAddressFdName(t *testing.T) {
+	// Save and restore environment
+	originalFdNames := os.Getenv("LISTEN_FDNAMES")
+	defer func() {
+		if originalFdNames != "" {
+			os.Setenv("LISTEN_FDNAMES", originalFdNames)
+		} else {
+			os.Unsetenv("LISTEN_FDNAMES")
+		}
+	}()
+
+	// Set up test environment
+	os.Setenv("LISTEN_FDNAMES", "http:https:dns")
+
+	tests := []struct {
+		input      string
+		expectAddr NetworkAddress
+		expectErr  bool
+	}{
+		{
+			input: "fdname/http",
+			expectAddr: NetworkAddress{
+				Network: "fd",
+				Host:    "3",
+			},
+		},
+		{
+			input: "fdname/https",
+			expectAddr: NetworkAddress{
+				Network: "fd",
+				Host:    "4",
+			},
+		},
+		{
+			input: "fdname/dns",
+			expectAddr: NetworkAddress{
+				Network: "fd",
+				Host:    "5",
+			},
+		},
+		{
+			input: "fdname/http:0",
+			expectAddr: NetworkAddress{
+				Network: "fd",
+				Host:    "3",
+			},
+		},
+		{
+			input: "fdname/https:0",
+			expectAddr: NetworkAddress{
+				Network: "fd",
+				Host:    "4",
+			},
+		},
+		{
+			input: "fdgramname/http",
+			expectAddr: NetworkAddress{
+				Network: "fdgram",
+				Host:    "3",
+			},
+		},
+		{
+			input: "fdgramname/https",
+			expectAddr: NetworkAddress{
+				Network: "fdgram",
+				Host:    "4",
+			},
+		},
+		{
+			input: "fdgramname/http:0",
+			expectAddr: NetworkAddress{
+				Network: "fdgram",
+				Host:    "3",
+			},
+		},
+		{
+			input:     "fdname/nonexistent",
+			expectErr: true,
+		},
+		{
+			input:     "fdgramname/nonexistent",
+			expectErr: true,
+		},
+		{
+			input:     "fdname/http:99",
+			expectErr: true,
+		},
+		{
+			input:     "fdname/invalid:abc",
+			expectErr: true,
+		},
+		// Test that old fd/N syntax still works
+		{
+			input: "fd/7",
+			expectAddr: NetworkAddress{
+				Network: "fd",
+				Host:    "7",
+			},
+		},
+		{
+			input: "fdgram/8",
+			expectAddr: NetworkAddress{
+				Network: "fdgram",
+				Host:    "8",
+			},
+		},
+	}
+
+	for i, tc := range tests {
+		actualAddr, err := ParseNetworkAddress(tc.input)
+
+		if tc.expectErr && err == nil {
+			t.Errorf("Test %d (%s): Expected error but got none", i, tc.input)
+		}
+		if !tc.expectErr && err != nil {
+			t.Errorf("Test %d (%s): Expected no error but got: %v", i, tc.input, err)
+		}
+		if !tc.expectErr && !reflect.DeepEqual(tc.expectAddr, actualAddr) {
+			t.Errorf("Test %d (%s): Expected %+v but got %+v", i, tc.input, tc.expectAddr, actualAddr)
+		}
+	}
+}