feat: configure multiple host key options

client.go

@@ -17,13 +17,10 @@ import (
 	"sync"
 	"time"
 
-	"github.com/moov-io/base/log"
-	"github.com/moov-io/go-sftp/pkg/sshx"
-
 	"github.com/go-kit/kit/metrics/prometheus"
+	"github.com/moov-io/base/log"
 	"github.com/pkg/sftp"
 	stdprometheus "github.com/prometheus/client_golang/prometheus"
-
 	"golang.org/x/crypto/ssh"
 )
 
@@ -39,25 +36,6 @@ var (
 	}, []string{"hostname"})
 )
 
-type ClientConfig struct {
-	Hostname string
-	Username string
-	Password string
-
-	Timeout        time.Duration
-	MaxConnections int
-	PacketSize     int
-
-	HostPublicKey string
-
-	// ClientPrivateKey must be a base64 encoded string
-	ClientPrivateKey         string
-	ClientPrivateKeyPassword string // not base64 encoded
-
-	SkipChmodAfterUpload  bool
-	SkipDirectoryCreation bool
-}
-
 type Client interface {
 	Ping() error
 	Close() error
@@ -186,7 +164,7 @@ func (c *client) clearConnectionOnError(err error) error {
 var (
 	hostKeyCallbackOnce sync.Once
 	hostKeyCallback     = func(logger log.Logger) {
-		msg := "sftp: WARNING!!! Insecure default of skipping SFTP host key validation. Please set HostPublicKey"
+		msg := "sftp: WARNING!!! Insecure default of skipping SFTP host key validation. Please set HostPublicKey(s)"
 		if logger != nil {
 			logger.Warn().Log(msg)
 		}
@@ -200,12 +178,12 @@ func sftpConnect(logger log.Logger, cfg ClientConfig) (*ssh.Client, io.WriteClos
 	}
 	conf.SetDefaults()
 
-	if cfg.HostPublicKey != "" {
-		pubKey, err := sshx.ReadPubKey([]byte(cfg.HostPublicKey))
+	if hostKeys := cfg.HostKeys(); len(hostKeys) > 0 {
+		callback, err := NewMultiKeyCallback(hostKeys)
 		if err != nil {
-			return nil, nil, nil, fmt.Errorf("problem parsing ssh public key: %w", err)
+			return nil, nil, nil, err
 		}
-		conf.HostKeyCallback = ssh.FixedHostKey(pubKey)
+		conf.HostKeyCallback = callback
 	} else {
 		hostKeyCallbackOnce.Do(func() {
 			hostKeyCallback(logger)

client_config.go

@@ -0,0 +1,51 @@
+package go_sftp
+
+import "time"
+
+type ClientConfig struct {
+	Hostname string
+	Username string
+	Password string
+
+	Timeout        time.Duration
+	MaxConnections int
+	PacketSize     int
+
+	// HostPublicKey configures an SSH public key to validate the remote server's host key.
+	// If provided, this key will be merged into HostPublicKeys.
+	// Deprecated: Use HostPublicKeys instead.
+	HostPublicKey string
+
+	// HostPublicKeys configures multiple SSH public keys to validate the remote server's host key.
+	// Any key provided in HostPublicKey will be appended to this list.
+	HostPublicKeys []string
+
+	// ClientPrivateKey must be a base64 encoded string
+	ClientPrivateKey         string
+	ClientPrivateKeyPassword string // not base64 encoded
+
+	SkipChmodAfterUpload  bool
+	SkipDirectoryCreation bool
+}
+
+// HostKeys returns the list of configured public keys to use for host key verification.
+func (cfg ClientConfig) HostKeys() []string {
+	if cfg.HostPublicKey != "" {
+		cfg.HostPublicKeys = append(cfg.HostPublicKeys, cfg.HostPublicKey)
+	}
+
+	return dedupe(cfg.HostPublicKeys)
+}
+
+func dedupe[T comparable](vals []T) []T {
+	seen := make(map[T]struct{})
+	var out []T
+	for i := range vals {
+		if _, ok := seen[vals[i]]; ok {
+			continue
+		}
+		seen[vals[i]] = struct{}{}
+		out = append(out, vals[i])
+	}
+	return out
+}

client_config_test.go

@@ -0,0 +1,58 @@
+package go_sftp_test
+
+import (
+	"testing"
+
+	sftp "github.com/moov-io/go-sftp"
+	"github.com/stretchr/testify/require"
+)
+
+func TestClientConfig_HostKeys(t *testing.T) {
+	tests := []struct {
+		name string
+		cfg  sftp.ClientConfig
+		want []string
+	}{
+		{
+			name: "no host keys",
+			cfg:  sftp.ClientConfig{},
+			want: nil,
+		},
+		{
+			name: "only HostPublicKey",
+			cfg: sftp.ClientConfig{
+				HostPublicKey: "public-key",
+			},
+			want: []string{"public-key"},
+		},
+		{
+			name: "only HostPublicKeys",
+			cfg: sftp.ClientConfig{
+				HostPublicKeys: []string{
+					"public-key-1",
+					"public-key-2",
+				},
+			},
+			want: []string{"public-key-1", "public-key-2"},
+		},
+		{
+			name: "combined and unique",
+			cfg: sftp.ClientConfig{
+				HostPublicKey: "public-key",
+				HostPublicKeys: []string{
+					"public-key",
+					"public-key-1",
+					"public-key-1",
+				},
+			},
+			want: []string{"public-key", "public-key-1"},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := tt.cfg.HostKeys()
+			require.Equal(t, tt.want, got)
+		})
+	}
+}

hostkeys.go

@@ -0,0 +1,36 @@
+package go_sftp
+
+import (
+	"bytes"
+	"fmt"
+	"net"
+
+	"github.com/moov-io/go-sftp/pkg/sshx"
+	"golang.org/x/crypto/ssh"
+)
+
+type MultiKeyCallback struct {
+	hostKeys []ssh.PublicKey
+}
+
+func NewMultiKeyCallback(keys []string) (ssh.HostKeyCallback, error) {
+	m := &MultiKeyCallback{}
+	for i := range keys {
+		pubKey, err := sshx.ReadPubKey([]byte(keys[i]))
+		if err != nil {
+			return nil, fmt.Errorf("sftp: reading host key at index %d: %w", i, err)
+		}
+		m.hostKeys = append(m.hostKeys, pubKey)
+	}
+	return m.check, nil
+}
+
+// check is an ssh.HostKeyCallback based on ssh.FixedHostKey, running the equality check against each configured key.
+func (m *MultiKeyCallback) check(_ string, _ net.Addr, key ssh.PublicKey) error {
+	for _, mKey := range m.hostKeys {
+		if bytes.Equal(key.Marshal(), mKey.Marshal()) {
+			return nil
+		}
+	}
+	return fmt.Errorf("sftp: no matching host keys")
+}

hostkeys_test.go

@@ -0,0 +1,67 @@
+package go_sftp_test
+
+import (
+	"testing"
+
+	sftp "github.com/moov-io/go-sftp"
+	"github.com/stretchr/testify/require"
+	"golang.org/x/crypto/ssh"
+)
+
+const (
+	rsaKey     = "ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQD1MU4KKe56DW+cnEomhmk0JMp5dS5LUDvrNM8cRE8i/JxPRsEbrHsta7/1Bj6jutAVTvHVSDrCZ5c+TIXlhSGQEfbjlXMiu9vP4vewdFTfm1xUdryv8MO5+Tas0HlbO9h92aV/SBpBxMLCIBVM9U+zKxmskxR1QMQZ7tzRGMnYMhQD74V6ANnwndDAlWspF+LcaUaDQqjeMDTv86q+ki4uDID5dwvx4eX11exfT+LwCvTMpCKhPJawA7QwnXNVvSEu/4p9EkNKr1xNIoiJdIwOnWrX8kAmlVkwL1cKCQF7wOfneYjKxJUMKwKtPZ9qtMmeOlhO7pLxhbtjcwvfIg69"
+	ecdsaKey   = "ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBEQFGqHGgr0e0jyq2ojt1TJgsFdLrn9w6iYXn1oWvuiOQgVAUL/6vrwQQ7ncbqM7/ZOaonx3C2Kr2IZHIXRmVXc="
+	ed25519Key = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIPZ3WQItO2r2wfGrjedz9LGwlLFgIUM6GbIpBKvaxiSz"
+
+	mismatchKey = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAINnH6Geq7YNlClxNhCMN0IVt1f0XsPyMYqlW5htNYLpy"
+)
+
+func TestMultiKeyCallback_Check(t *testing.T) {
+	tests := []struct {
+		name    string
+		key     string
+		wantErr bool
+	}{
+		{
+			name:    "host key mismatch",
+			key:     mismatchKey,
+			wantErr: true,
+		},
+		{
+			name:    "rsa match",
+			key:     rsaKey,
+			wantErr: false,
+		},
+		{
+			name:    "ecdsa match",
+			key:     "example.io " + ecdsaKey,
+			wantErr: false,
+		},
+		{
+			name:    "ed25519 match",
+			key:     ed25519Key,
+			wantErr: false,
+		},
+	}
+
+	callback, err := sftp.NewMultiKeyCallback([]string{
+		rsaKey,
+		ecdsaKey,
+		ed25519Key,
+	})
+	require.NoError(t, err)
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			hostKey, _, _, _, err := ssh.ParseAuthorizedKey([]byte(tt.key))
+			require.NoError(t, err)
+
+			err = callback("", nil, hostKey)
+			if tt.wantErr {
+				require.Error(t, err)
+			} else {
+				require.NoError(t, err)
+			}
+		})
+	}
+}