README child-mnemonic vector and host-key note; ssh install refuses a ~/.ssh it cannot enter (closes #51)

The README now gives the child mnemonic keyfunc prints for the abandon ... about test mnemonic at index 0, checked by the README vectors test; the BIP-85 specification vector stays, marked as starting from a master key keyfunc cannot take. It also says ssh install needs the host key in known_hosts already, and how to get round that. ssh install now also lists ~/.ssh/. on its first connection and refuses, before any upload, a ~/.ssh it can read but not enter, which sftp shows as empty; a file where ~/.ssh belongs is refused the same way.

Model: opus-5-5
Co-authored-by: clawbot <sneak+clawbot@sneak.cloud>

internal/cli/ssh_test.go

@@ -52,7 +52,7 @@ const (
 )
 
 // notADirectory is what a test puts where the .ssh directory belongs
-// to make a step of the write session fail.
+// to make a .ssh that is listed but cannot be entered.
 const notADirectory = "a file where the directory belongs\n"
 
 // missingIdentity is a path with no file at it, handed to sftp after
@@ -106,9 +106,11 @@ const marker = "KEYFUNC_TEST_MARKER"
 // another for a file that is there and cannot be read, which is a
 // failure. A directory shut to the user is stood in for by mode 000,
 // which the listing reads off the mode itself so that the test does not
-// turn on the user it runs as. An -i naming a file that is not here
-// draws the warning ssh writes for it, which carries the wording of a
-// missing file into a session that goes on to authenticate.
+// turn on the user it runs as, and one the user can enter but not write
+// to by mode 500, which the put reads off the same way. An -i naming a
+// file that is not here draws the warning ssh writes for it, which
+// carries the wording of a missing file into a session that goes on to
+// authenticate.
 const installer = `
 [ -n "$KEYFUNC_TEST_ENVIRONMENT" ] && env > "$KEYFUNC_TEST_ENVIRONMENT"
 previous=
@@ -160,7 +162,13 @@ while IFS= read -r line; do
 			printf 'remote open "%s": Permission denied\n' "$home/$2" >&2
 		fi
 		;;
-	put) cp "$2" "$home/$3" 2>/dev/null || worked=no ;;
+	put)
+		if [ "$(stat -c '%a' "$(dirname "$home/$3")")" = 500 ]; then
+			worked=no
+		else
+			cp "$2" "$home/$3" 2>/dev/null || worked=no
+		fi
+		;;
 	mkdir) mkdir "$home/$2" 2>/dev/null || worked=no ;;
 	chmod) chmod "$2" "$home/$3" 2>/dev/null || worked=no ;;
 	rename) mv "$home/$2" "$home/$3" 2>/dev/null || worked=no ;;
@@ -329,6 +337,29 @@ func TestAnUnreadableDirectoryIsNotWrittenInto(t *testing.T) {
 	require.Equal(t, 1, connections(t, pretend))
 }
 
+func TestADirectoryThatCannotBeEnteredIsRefusedBeforeAnyUpload(t *testing.T) {
+	t.Setenv(mnemonic.Variable, example())
+
+	pretend := pretendHost(t)
+
+	// A file where .ssh belongs is listed and cannot be entered, which is
+	// how sftp sees a directory that can be read but not entered: the
+	// listing of .ssh comes up and the listing of .ssh/. finds nothing.
+	inTheWay := filepath.Join(pretend.home, keptUnder)
+	require.NoError(t,
+		os.WriteFile(inTheWay, []byte(notADirectory), fileMode),
+	)
+
+	printed, _, err := attempt(t, host)
+	require.ErrorIs(t, err, ssh.ErrCannotEnter)
+	require.Empty(t, printed)
+
+	// The read and nothing after it: no upload was tried, and what was
+	// on the host is still what is on the host.
+	require.Equal(t, 1, connections(t, pretend))
+	require.Equal(t, notADirectory, read(t, inTheWay))
+}
+
 func TestAnExistingDirectoryKeepsItsModeAndIsNotRemade(t *testing.T) {
 	t.Setenv(mnemonic.Variable, example())
 
@@ -392,27 +423,30 @@ func TestAFailedStepNamesTheUploadedFileAndChangesNothing(t *testing.T) {
 
 	pretend := pretendHost(t)
 
-	// A file where the .ssh directory belongs: the listing shows it and
-	// so the directory reads as already there, but then the put has
-	// nowhere to put anything, so the write session ends at the put.
-	inTheWay := filepath.Join(pretend.home, keptUnder)
-	require.NoError(t,
-		os.WriteFile(inTheWay, []byte(notADirectory), fileMode),
-	)
+	// A .ssh that can be listed and entered but not written to: the
+	// fetch finds no file in it, and then the put has nowhere to put
+	// anything, so the write session ends at the put.
+	const unwritable = 0o500
+
+	directory := filepath.Join(pretend.home, keptUnder)
+	require.NoError(t, os.Mkdir(directory, unwritable))
 
 	printed, said, err := attempt(t, host)
 	require.Error(t, err)
 	require.Empty(t, printed)
 	require.Contains(t, said, "put failed")
 
-	// The put is the first and last command the write session got to,
-	// and the file it was uploading is the one the message names.
+	// The put, after the three commands of the fetch, is the first and
+	// last command the write session got to, and the file it was
+	// uploading is the one the message names.
 	sent := recorded(t, pretend.batch)
-	require.Len(t, sent, 3)
-	require.Equal(t, "put", strings.Fields(sent[2])[0])
-	require.Contains(t, err.Error(), strings.Fields(sent[2])[2])
+	require.Len(t, sent, 4)
+	require.Equal(t, "put", strings.Fields(sent[3])[0])
+	require.Contains(t, err.Error(), strings.Fields(sent[3])[2])
 
-	require.Equal(t, notADirectory, read(t, inTheWay))
+	left, err := os.ReadDir(directory)
+	require.NoError(t, err)
+	require.Empty(t, left)
 
 	// The same run again, this way for the status it ends with.
 	given := os.Args