[cli] Abstract out terminal interactions

Replace direct interaction with the terminal with an abstraction. This
abstraction is tightly constrained to the capabilities needed for the
CLI's display. Using this abstraction allows for straightforward testing
of the interactive renderers.

pkg/backend/display/internal/terminal/info.go

@@ -0,0 +1,79 @@
+package terminal
+
+import (
+	"fmt"
+	"io"
+
+	gotty "github.com/ijc/Gotty"
+)
+
+type Info interface {
+	Parse(attr string, params ...interface{}) (string, error)
+
+	ClearLine(out io.Writer)
+	CursorUp(out io.Writer, count int)
+	CursorDown(out io.Writer, count int)
+}
+
+/* Satisfied by gotty.TermInfo as well as noTermInfo from below */
+type termInfo interface {
+	Parse(attr string, params ...interface{}) (string, error)
+}
+
+type noTermInfo int // canary used when no terminfo.
+
+func (ti noTermInfo) Parse(attr string, params ...interface{}) (string, error) {
+	return "", fmt.Errorf("noTermInfo")
+}
+
+type info struct {
+	termInfo
+}
+
+var _ = Info(info{})
+
+func OpenInfo(terminal string) Info {
+	if i, err := gotty.OpenTermInfo(terminal); err == nil {
+		return info{i}
+	}
+	return info{noTermInfo(0)}
+}
+
+func (i info) ClearLine(out io.Writer) {
+	// el2 (clear whole line) is not exposed by terminfo.
+
+	// First clear line from beginning to cursor
+	if attr, err := i.Parse("el1"); err == nil {
+		fmt.Fprintf(out, "%s", attr)
+	} else {
+		fmt.Fprintf(out, "\x1b[1K")
+	}
+	// Then clear line from cursor to end
+	if attr, err := i.Parse("el"); err == nil {
+		fmt.Fprintf(out, "%s", attr)
+	} else {
+		fmt.Fprintf(out, "\x1b[K")
+	}
+}
+
+func (i info) CursorUp(out io.Writer, count int) {
+	if count == 0 { // Should never be the case, but be tolerant
+		return
+	}
+	if attr, err := i.Parse("cuu", count); err == nil {
+		fmt.Fprintf(out, "%s", attr)
+	} else {
+		fmt.Fprintf(out, "\x1b[%dA", count)
+	}
+}
+
+func (i info) CursorDown(out io.Writer, count int) {
+	if count == 0 { // Should never be the case, but be tolerant
+		return
+	}
+	if attr, err := i.Parse("cud", count); err == nil {
+		fmt.Fprintf(out, "%s", attr)
+	} else {
+		fmt.Fprintf(out, "\x1b[%dB", count)
+	}
+}

pkg/backend/display/internal/terminal/mock.go

@@ -0,0 +1,74 @@
+package terminal
+
+import (
+	"io"
+	"sync"
+)
+
+type MockTerminal struct {
+	m sync.Mutex
+
+	width, height int
+	info          Info
+
+	keys chan string
+
+	dest io.Writer
+}
+
+func NewMockTerminal(dest io.Writer, width, height int) *MockTerminal {
+	return &MockTerminal{
+		width:  width,
+		height: height,
+		info:   info{noTermInfo(0)},
+		keys:   make(chan string),
+		dest:   dest,
+	}
+}
+
+func (t *MockTerminal) Close() error {
+	close(t.keys)
+	return nil
+}
+
+func (t *MockTerminal) Size() (width, height int, err error) {
+	t.m.Lock()
+	defer t.m.Unlock()
+
+	return t.width, t.height, nil
+}
+
+func (t *MockTerminal) Write(b []byte) (int, error) {
+	return t.dest.Write(b)
+}
+
+func (t *MockTerminal) ClearLine() {
+	t.info.ClearLine(t)
+}
+
+func (t *MockTerminal) CursorUp(count int) {
+	t.info.CursorUp(t, count)
+}
+
+func (t *MockTerminal) CursorDown(count int) {
+	t.info.CursorDown(t, count)
+}
+
+func (t *MockTerminal) ReadKey() (string, error) {
+	k, ok := <-t.keys
+	if !ok {
+		return "", io.EOF
+	}
+	return k, nil
+}
+
+func (t *MockTerminal) SetSize(width, height int) {
+	t.m.Lock()
+	defer t.m.Unlock()
+
+	t.width, t.height = width, height
+}
+
+func (t *MockTerminal) SendKey(key string) {
+	t.keys <- key
+}

pkg/backend/display/internal/terminal/term.go

@@ -0,0 +1,183 @@
+package terminal
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"io"
+	"os"
+
+	"github.com/muesli/cancelreader"
+	"golang.org/x/term"
+)
+
+type Terminal interface {
+	io.WriteCloser
+
+	Size() (width, height int, err error)
+
+	ClearLine()
+	CursorUp(count int)
+	CursorDown(count int)
+
+	ReadKey() (string, error)
+}
+
+var ErrNotATerminal = errors.New("not a terminal")
+
+type terminal struct {
+	fd   int
+	info Info
+	save *term.State
+
+	out io.Writer
+	in  cancelreader.CancelReader
+}
+
+func Open(in io.Reader, out io.Writer) (Terminal, error) {
+	type fileLike interface {
+		Fd() uintptr
+	}
+
+	outFile, ok := out.(fileLike)
+	if !ok {
+		return nil, ErrNotATerminal
+	}
+	outFd := int(outFile.Fd())
+
+	inFile, err := cancelreader.NewReader(in)
+	if err != nil {
+		return nil, ErrNotATerminal
+	}
+
+	width, height, err := term.GetSize(outFd)
+	if err != nil {
+		return nil, fmt.Errorf("getting dimensions: %w", err)
+	}
+	if width == 0 || height == 0 {
+		return nil, fmt.Errorf("unusable dimensions (%v x %v)", width, height)
+	}
+
+	termType := os.Getenv("TERM")
+	if termType == "" {
+		termType = "vt102"
+	}
+	info := OpenInfo(termType)
+
+	save, err := term.MakeRaw(outFd)
+	if err != nil {
+		return nil, fmt.Errorf("enabling raw mode: %w", err)
+	}
+
+	return &terminal{
+		fd:   outFd,
+		info: info,
+		save: save,
+		out:  out,
+		in:   inFile,
+	}, nil
+}
+
+func (t *terminal) Close() error {
+	t.in.Cancel()
+	return term.Restore(t.fd, t.save)
+}
+
+func (t *terminal) Size() (width, height int, err error) {
+	return term.GetSize(t.fd)
+}
+
+func (t *terminal) Write(b []byte) (int, error) {
+	written := 0
+	for {
+		newline := bytes.IndexByte(b, '\n')
+		if newline == -1 {
+			w, err := t.out.Write(b)
+			written += w
+			return written, err
+		}
+
+		w, err := t.out.Write(b[:newline])
+		written += w
+		if err != nil {
+			return written, err
+		}
+
+		if _, err = t.out.Write([]byte{'\r', '\n'}); err != nil {
+			return written, err
+		}
+		written++
+
+		b = b[newline+1:]
+	}
+}
+
+func (t *terminal) ClearLine() {
+	t.info.ClearLine(t.out)
+}
+
+func (t *terminal) CursorUp(count int) {
+	t.info.CursorUp(t.out, count)
+}
+
+func (t *terminal) CursorDown(count int) {
+	t.info.CursorDown(t.out, count)
+}
+
+func (t *terminal) ReadKey() (string, error) {
+	type stateFunc func(b byte) (stateFunc, string)
+
+	var stateIntermediate stateFunc
+	stateIntermediate = func(b byte) (stateFunc, string) {
+		if b >= 0x20 && b < 0x30 {
+			return stateIntermediate, ""
+		}
+		switch b {
+		case 'A':
+			return nil, "up"
+		case 'B':
+			return nil, "down"
+		default:
+			return nil, "<control>"
+		}
+	}
+	var stateParameter stateFunc
+	stateParameter = func(b byte) (stateFunc, string) {
+		if b >= 0x30 && b < 0x40 {
+			return stateParameter, ""
+		}
+		return stateIntermediate(b)
+	}
+	stateBracket := func(b byte) (stateFunc, string) {
+		if b == '[' {
+			return stateParameter, ""
+		}
+		return nil, "<control>"
+	}
+	stateEscape := func(b byte) (stateFunc, string) {
+		if b == 0x1b {
+			return stateBracket, ""
+		}
+		if b == 3 {
+			return nil, "ctrl+c"
+		}
+		return nil, string([]byte{b})
+	}
+
+	state := stateEscape
+	for {
+		var b [1]byte
+		if _, err := t.in.Read(b[:]); err != nil {
+			if errors.Is(err, cancelreader.ErrCanceled) {
+				err = io.EOF
+			}
+			return "", err
+		}
+
+		next, key := state(b[0])
+		if next == nil {
+			return key, nil
+		}
+		state = next
+	}
+}