chore: move runeutil and memoization into internal

internal/runeutil/runeutil.go

@@ -0,0 +1,102 @@
+// Package runeutil provides utility functions for tidying up incoming runes
+// from Key messages.
+package runeutil
+
+import (
+	"unicode"
+	"unicode/utf8"
+)
+
+// Sanitizer is a helper for bubble widgets that want to process
+// Runes from input key messages.
+type Sanitizer interface {
+	// Sanitize removes control characters from runes in a KeyRunes
+	// message, and optionally replaces newline/carriage return/tabs by a
+	// specified character.
+	//
+	// The rune array is modified in-place if possible. In that case, the
+	// returned slice is the original slice shortened after the control
+	// characters have been removed/translated.
+	Sanitize(runes []rune) []rune
+}
+
+// NewSanitizer constructs a rune sanitizer.
+func NewSanitizer(opts ...Option) Sanitizer {
+	s := sanitizer{
+		replaceNewLine: []rune("\n"),
+		replaceTab:     []rune("    "),
+	}
+	for _, o := range opts {
+		s = o(s)
+	}
+	return &s
+}
+
+// Option is the type of option that can be passed to Sanitize().
+type Option func(sanitizer) sanitizer
+
+// ReplaceTabs replaces tabs by the specified string.
+func ReplaceTabs(tabRepl string) Option {
+	return func(s sanitizer) sanitizer {
+		s.replaceTab = []rune(tabRepl)
+		return s
+	}
+}
+
+// ReplaceNewlines replaces newline characters by the specified string.
+func ReplaceNewlines(nlRepl string) Option {
+	return func(s sanitizer) sanitizer {
+		s.replaceNewLine = []rune(nlRepl)
+		return s
+	}
+}
+
+func (s *sanitizer) Sanitize(runes []rune) []rune {
+	// dstrunes are where we are storing the result.
+	dstrunes := runes[:0:len(runes)]
+	// copied indicates whether dstrunes is an alias of runes
+	// or a copy. We need a copy when dst moves past src.
+	// We use this as an optimization to avoid allocating
+	// a new rune slice in the common case where the output
+	// is smaller or equal to the input.
+	copied := false
+
+	for src := 0; src < len(runes); src++ {
+		r := runes[src]
+		switch {
+		case r == utf8.RuneError:
+			// skip
+
+		case r == '\r' || r == '\n':
+			if len(dstrunes)+len(s.replaceNewLine) > src && !copied {
+				dst := len(dstrunes)
+				dstrunes = make([]rune, dst, len(runes)+len(s.replaceNewLine))
+				copy(dstrunes, runes[:dst])
+				copied = true
+			}
+			dstrunes = append(dstrunes, s.replaceNewLine...)
+
+		case r == '\t':
+			if len(dstrunes)+len(s.replaceTab) > src && !copied {
+				dst := len(dstrunes)
+				dstrunes = make([]rune, dst, len(runes)+len(s.replaceTab))
+				copy(dstrunes, runes[:dst])
+				copied = true
+			}
+			dstrunes = append(dstrunes, s.replaceTab...)
+
+		case unicode.IsControl(r):
+			// Other control characters: skip.
+
+		default:
+			// Keep the character.
+			dstrunes = append(dstrunes, runes[src])
+		}
+	}
+	return dstrunes
+}
+
+type sanitizer struct {
+	replaceNewLine []rune
+	replaceTab     []rune
+}

internal/runeutil/runeutil_test.go

@@ -0,0 +1,44 @@
+package runeutil
+
+import (
+	"testing"
+	"unicode/utf8"
+)
+
+func TestSanitize(t *testing.T) {
+	td := []struct {
+		input, output string
+	}{
+		{"", ""},
+		{"x", "x"},
+		{"\n", "XX"},
+		{"\na\n", "XXaXX"},
+		{"\n\n", "XXXX"},
+		{"\t", ""},
+		{"hello", "hello"},
+		{"hel\nlo", "helXXlo"},
+		{"hel\rlo", "helXXlo"},
+		{"hel\tlo", "hello"},
+		{"he\n\nl\tlo", "heXXXXllo"},
+		{"he\tl\n\nlo", "helXXXXlo"},
+		{"hel\x1blo", "hello"},
+		{"hello\xc2", "hello"}, // invalid utf8
+	}
+
+	for _, tc := range td {
+		runes := make([]rune, 0, len(tc.input))
+		b := []byte(tc.input)
+		for i, w := 0, 0; i < len(b); i += w {
+			var r rune
+			r, w = utf8.DecodeRune(b[i:])
+			runes = append(runes, r)
+		}
+		t.Logf("input runes: %+v", runes)
+		s := NewSanitizer(ReplaceNewlines("XX"), ReplaceTabs(""))
+		result := s.Sanitize(runes)
+		rs := string(result)
+		if tc.output != rs {
+			t.Errorf("%q: expected %q, got %q (%+v)", tc.input, tc.output, rs, result)
+		}
+	}
+}