feat: add $IPFS_PATH/gateway file

The file contains the gateway your node is hosting in the http://<host>:<port> RFC 3986 format.
Structurally it works exactly the same as the API file.

cmd/ipfs/daemon.go

@@ -806,6 +806,12 @@ func serveHTTPGateway(req *cmds.Request, cctx *oldcmds.Context) (<-chan error, e
 		return nil, fmt.Errorf("serveHTTPGateway: ConstructNode() failed: %s", err)
 	}
 
+	if len(listeners) > 0 {
+		if err := node.Repo.SetGatewayAddr(listeners[0].Addr()); err != nil {
+			return nil, fmt.Errorf("serveHTTPGateway: SetGatewayAddr() failed: %w", err)
+		}
+	}
+
 	errc := make(chan error)
 	var wg sync.WaitGroup
 	for _, lis := range listeners {

repo/fsrepo/fsrepo.go

@@ -5,6 +5,7 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"net"
 	"os"
 	"path/filepath"
 	"strings"
@@ -63,6 +64,7 @@ func (err NoRepoError) Error() string {
 }
 
 const apiFile = "api"
+const gatewayFile = "gateway"
 const swarmKeyFile = "swarm.key"
 
 const specFn = "datastore_spec"
@@ -387,6 +389,44 @@ func (r *FSRepo) SetAPIAddr(addr ma.Multiaddr) error {
 	return err
 }
 
+// SetGatewayAddr writes the Gateway Addr to the /gateway file.
+func (r *FSRepo) SetGatewayAddr(addr net.Addr) error {
+	// Create a temp file to write the address, so that we don't leave empty file when the
+	// program crashes after creating the file.
+	tmpPath := filepath.Join(r.path, "."+gatewayFile+".tmp")
+	f, err := os.Create(tmpPath)
+	if err != nil {
+		return err
+	}
+	var good bool
+	// Silently remove as worst last case with defers.
+	defer func() {
+		if !good {
+			os.Remove(tmpPath)
+		}
+	}()
+	defer f.Close()
+
+	if _, err := fmt.Fprintf(f, "http://%s", addr.String()); err != nil {
+		return err
+	}
+	if err := f.Close(); err != nil {
+		return err
+	}
+
+	// Atomically rename the temp file to the correct file name.
+	err = os.Rename(tmpPath, filepath.Join(r.path, gatewayFile))
+	good = err == nil
+	if good {
+		return nil
+	}
+	// Remove the temp file when rename return error
+	if err1 := os.Remove(tmpPath); err1 != nil {
+		return fmt.Errorf("File Rename error: %w, File remove error: %s", err, err1.Error())
+	}
+	return err
+}
+
 // openConfig returns an error if the config file is not present.
 func (r *FSRepo) openConfig() error {
 	conf, err := serialize.Load(r.configFilePath)
@@ -474,6 +514,11 @@ func (r *FSRepo) Close() error {
 		log.Warn("error removing api file: ", err)
 	}
 
+	err = os.Remove(filepath.Join(r.path, gatewayFile))
+	if err != nil && !os.IsNotExist(err) {
+		log.Warn("error removing gateway file: ", err)
+	}
+
 	if err := r.ds.Close(); err != nil {
 		return err
 	}

repo/mock.go

@@ -3,6 +3,7 @@ package repo
 import (
 	"context"
 	"errors"
+	"net"
 
 	filestore "github.com/ipfs/go-filestore"
 	keystore "github.com/ipfs/go-ipfs-keystore"
@@ -50,6 +51,8 @@ func (m *Mock) Close() error { return m.D.Close() }
 
 func (m *Mock) SetAPIAddr(addr ma.Multiaddr) error { return errTODO }
 
+func (m *Mock) SetGatewayAddr(addr net.Addr) error { return errTODO }
+
 func (m *Mock) Keystore() keystore.Keystore { return m.K }
 
 func (m *Mock) SwarmKey() ([]byte, error) {

repo/repo.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"errors"
 	"io"
+	"net"
 
 	filestore "github.com/ipfs/go-filestore"
 	keystore "github.com/ipfs/go-ipfs-keystore"
@@ -51,6 +52,9 @@ type Repo interface {
 	// SetAPIAddr sets the API address in the repo.
 	SetAPIAddr(addr ma.Multiaddr) error
 
+	// SetGatewayAddr sets the Gateway address in the repo.
+	SetGatewayAddr(addr net.Addr) error
+
 	// SwarmKey returns the configured shared symmetric key for the private networks feature.
 	SwarmKey() ([]byte, error)
 

test/sharness/t0110-gateway.sh

@@ -287,6 +287,12 @@ test_expect_success "GET compact blocks succeeds" '
   test_cmp expected actual
 '
 
+test_expect_success "Verify gateway file" '
+  cat "$IPFS_PATH/gateway" >> gateway_file_actual &&
+  echo -n "http://$GWAY_ADDR" >> gateway_daemon_actual &&
+  test_cmp gateway_daemon_actual gateway_file_actual
+'
+
 test_kill_ipfs_daemon