fix(key): invert the control loop

Instead of reading messages in an array and then sending them into a
channel, this version of key.go writes to the channel directly.

key.go

@@ -1,12 +1,11 @@
 package tea
 
 import (
+	"context"
 	"fmt"
 	"io"
 	"regexp"
 	"unicode/utf8"
-
-	"github.com/mattn/go-localereader"
 )
 
 // KeyMsg contains information about a keypress. KeyMsgs are always sent to
@@ -539,27 +538,30 @@ func (u unknownCSISequenceMsg) String() string {
 
 var spaceRunes = []rune{' '}
 
-// readInputs reads keypress and mouse inputs from a TTY and returns messages
+// readInputs reads keypress and mouse inputs from a TTY and produces messages
 // containing information about the key or mouse events accordingly.
-func readInputs(input io.Reader) ([]Msg, error) {
+func readInputs(ctx context.Context, msgs chan<- Msg, input io.Reader) error {
 	var buf [256]byte
 
-	input = localereader.NewReader(input)
-
-	// Read and block
-	numBytes, err := input.Read(buf[:])
-	if err != nil {
-		return nil, err
-	}
-	b := buf[:numBytes]
-
-	var msgs []Msg
-	for i, w := 0, 0; i < len(b); i += w {
-		var msg Msg
-		w, msg = detectOneMsg(b[i:])
-		msgs = append(msgs, msg)
+	for {
+		// Read and block.
+		numBytes, err := input.Read(buf[:])
+		if err != nil {
+			return err
+		}
+		b := buf[:numBytes]
+
+		var i, w int
+		for i, w = 0, 0; i < len(b); i += w {
+			var msg Msg
+			w, msg = detectOneMsg(b[i:])
+			select {
+			case msgs <- msg:
+			case <-ctx.Done():
+				return ctx.Err()
+			}
+		}
 	}
-	return msgs, nil
 }
 
 var unknownCSIRe = regexp.MustCompile(`^\x1b\[[\x30-\x3f]*[\x20-\x2f]*[\x40-\x7e]`)

key_test.go

@@ -2,13 +2,17 @@ package tea
 
 import (
 	"bytes"
+	"context"
+	"errors"
 	"flag"
 	"fmt"
+	"io"
 	"math/rand"
 	"reflect"
 	"runtime"
 	"sort"
 	"strings"
+	"sync"
 	"testing"
 	"time"
 )
@@ -442,12 +446,7 @@ func TestReadInput(t *testing.T) {
 
 	for i, td := range testData {
 		t.Run(fmt.Sprintf("%d: %s", i, td.keyname), func(t *testing.T) {
-			msgs, err := readInputs(bytes.NewReader(td.in))
-			if err != nil {
-				t.Fatalf("unexpected error: %v", err)
-			}
-
-			// Compute the title for the event sequence.
+			msgs := testReadInputs(t, bytes.NewReader(td.in))
 			var buf strings.Builder
 			for i, msg := range msgs {
 				if i > 0 {
@@ -459,6 +458,7 @@ func TestReadInput(t *testing.T) {
 					fmt.Fprintf(&buf, "%#v:%T", msg, msg)
 				}
 			}
+
 			title := buf.String()
 			if title != td.keyname {
 				t.Errorf("expected message titles:\n  %s\ngot:\n  %s", td.keyname, title)
@@ -475,6 +475,49 @@ func TestReadInput(t *testing.T) {
 	}
 }
 
+func testReadInputs(t *testing.T, input io.Reader) []Msg {
+	// We'll check that the input reader finishes at the end
+	// without error.
+	var wg sync.WaitGroup
+	var inputErr error
+	ctx, cancel := context.WithCancel(context.Background())
+	defer func() {
+		cancel()
+		wg.Wait()
+		if inputErr != nil && !errors.Is(inputErr, io.EOF) {
+			t.Fatalf("unexpected input error: %v", inputErr)
+		}
+	}()
+
+	// The messages we're consuming.
+	msgsC := make(chan Msg)
+
+	// Start the reader in the background.
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		inputErr = readInputs(ctx, msgsC, input)
+		msgsC <- nil
+	}()
+
+	var msgs []Msg
+loop:
+	for {
+		select {
+		case msg := <-msgsC:
+			if msg == nil {
+				// end of input marker for the test.
+				break loop
+			}
+			msgs = append(msgs, msg)
+		case <-time.After(2 * time.Second):
+			t.Errorf("timeout waiting for input event")
+			break loop
+		}
+	}
+	return msgs
+}
+
 // randTest defines the test input and expected output for a sequence
 // of interleaved control sequences and control characters.
 type randTest struct {

tty.go

@@ -5,6 +5,7 @@ import (
 	"io"
 	"time"
 
+	localereader "github.com/mattn/go-localereader"
 	"github.com/muesli/cancelreader"
 )
 
@@ -68,23 +69,10 @@ func (p *Program) initCancelReader() error {
 func (p *Program) readLoop() {
 	defer close(p.readLoopDone)
 
-	for {
-		if p.ctx.Err() != nil {
-			return
-		}
-
-		msgs, err := readInputs(p.cancelReader)
-		if err != nil {
-			if !errors.Is(err, io.EOF) && !errors.Is(err, cancelreader.ErrCanceled) {
-				p.errs <- err
-			}
-
-			return
-		}
-
-		for _, msg := range msgs {
-			p.msgs <- msg
-		}
+	input := localereader.NewReader(p.cancelReader)
+	err := readInputs(p.ctx, p.msgs, input)
+	if !errors.Is(err, io.EOF) && !errors.Is(err, cancelreader.ErrCanceled) {
+		p.errs <- err
 	}
 }