support handlers returning explicit error codes

Add errors for all the SSH_FXP_STATUS codes to give the developer
implementing request server handlers greater control over the returned
codes. Most helpful in cases where nothing currently would work (eg.
unsupported).

Fixes pkg#223

request-errors.go

@@ -0,0 +1,42 @@
+package sftp
+
+// Error types that match the SFTP's SSH_FXP_STATUS codes. Gives you more
+// direct control of the errors being sent vs. letting the library work them
+// out from the standard os/io errors.
+
+type fxerr uint32
+
+const (
+	ErrSshFxOk               = fxerr(ssh_FX_OK)
+	ErrSshFxEof              = fxerr(ssh_FX_EOF)
+	ErrSshFxNoSuchFile       = fxerr(ssh_FX_NO_SUCH_FILE)
+	ErrSshFxPermissionDenied = fxerr(ssh_FX_PERMISSION_DENIED)
+	ErrSshFxFailure          = fxerr(ssh_FX_FAILURE)
+	ErrSshFxBadMessage       = fxerr(ssh_FX_BAD_MESSAGE)
+	ErrSshFxNoConnection     = fxerr(ssh_FX_NO_CONNECTION)
+	ErrSshFxConnectionLost   = fxerr(ssh_FX_CONNECTION_LOST)
+	ErrSshFxOpUnsupported    = fxerr(ssh_FX_OP_UNSUPPORTED)
+)
+
+func (e fxerr) Error() string {
+	switch e {
+	case ErrSshFxOk:
+		return "OK"
+	case ErrSshFxEof:
+		return "EOF"
+	case ErrSshFxNoSuchFile:
+		return "No Such File"
+	case ErrSshFxPermissionDenied:
+		return "Permission Denied"
+	case ErrSshFxBadMessage:
+		return "Bad Message"
+	case ErrSshFxNoConnection:
+		return "No Connection"
+	case ErrSshFxConnectionLost:
+		return "Connection Lost"
+	case ErrSshFxOpUnsupported:
+		return "Operation Unsupported"
+	default:
+		return "Failure"
+	}
+}

server.go

@@ -564,6 +564,8 @@ func statusFromError(p ider, err error) sshFxpStatusPacket {
 		if errno, ok := e.Err.(syscall.Errno); ok {
 			ret.StatusError.Code = translateErrno(errno)
 		}
+	case fxerr:
+		ret.StatusError.Code = uint32(e)
 	default:
 		switch e {
 		case io.EOF:

server_test.go

@@ -1,12 +1,16 @@
 package sftp
 
 import (
-	"testing"
+	"io"
 	"os"
 	"regexp"
-	"time"
-	"io"
 	"sync"
+	"syscall"
+	"testing"
+	"time"
+
+	"github.com/pkg/errors"
+	"github.com/stretchr/testify/assert"
 )
 
 const (
@@ -61,7 +65,7 @@ func TestRunLsWithLicensesFile(t *testing.T) {
 
    where `id' is the request identifier, and `attrs' is the returned
    file attributes as described in Section ``File Attributes''.
- */
+*/
 func runLsTestHelper(t *testing.T, result, expectedType, path string) {
 	// using regular expressions to make tests work on all systems
 	// a virtual file system (like afero) would be needed to mock valid filesystem checks
@@ -241,3 +245,31 @@ func TestConcurrentRequests(t *testing.T) {
 	}
 	wg.Wait()
 }
+
+// Test error conversion
+func TestStatusFromError(t *testing.T) {
+	type test struct {
+		err error
+		pkt sshFxpStatusPacket
+	}
+	tpkt := func(id, code uint32) sshFxpStatusPacket {
+		return sshFxpStatusPacket{
+			ID:          id,
+			StatusError: StatusError{Code: code},
+		}
+	}
+	test_cases := []test{
+		test{syscall.ENOENT, tpkt(1, ssh_FX_NO_SUCH_FILE)},
+		test{&os.PathError{Err: syscall.ENOENT},
+			tpkt(2, ssh_FX_NO_SUCH_FILE)},
+		test{&os.PathError{Err: errors.New("foo")}, tpkt(3, ssh_FX_FAILURE)},
+		test{ErrSshFxEof, tpkt(4, ssh_FX_EOF)},
+		test{ErrSshFxOpUnsupported, tpkt(5, ssh_FX_OP_UNSUPPORTED)},
+		test{io.EOF, tpkt(6, ssh_FX_EOF)},
+		test{os.ErrNotExist, tpkt(7, ssh_FX_NO_SUCH_FILE)},
+	}
+	for _, tc := range test_cases {
+		tc.pkt.StatusError.msg = tc.err.Error()
+		assert.Equal(t, tc.pkt, statusFromError(tc.pkt, tc.err))
+	}
+}