Initialize module and dependencies

vendor/github.com/emersion/go-message/charset/charset.go

@@ -0,0 +1,64 @@
+// Package charset provides functions to decode and encode charsets.
+//
+// It imports all supported charsets, which adds about 1MiB to binaries size.
+// Importing the package automatically sets message.CharsetReader.
+package charset
+
+import (
+	"fmt"
+	"io"
+	"strings"
+
+	"github.com/emersion/go-message"
+	"golang.org/x/text/encoding"
+	"golang.org/x/text/encoding/charmap"
+	"golang.org/x/text/encoding/htmlindex"
+	"golang.org/x/text/encoding/ianaindex"
+	"golang.org/x/text/encoding/unicode"
+)
+
+// Quirks table for charsets not handled by ianaindex
+//
+// A nil entry disables the charset.
+//
+// For aliases, see
+// https://www.iana.org/assignments/character-sets/character-sets.xhtml
+var charsets = map[string]encoding.Encoding{
+	"ansi_x3.110-1983": charmap.ISO8859_1, // see RFC 1345 page 62, mostly superset of ISO 8859-1
+	"x-utf_8j":         unicode.UTF8,      // alias for UTF-8, see https://icu4c-demos.unicode.org/icu-bin/convexp?s=ALL
+}
+
+func init() {
+	message.CharsetReader = Reader
+}
+
+// Reader returns an io.Reader that converts the provided charset to UTF-8.
+func Reader(charset string, input io.Reader) (io.Reader, error) {
+	var err error
+	enc, ok := charsets[strings.ToLower(charset)]
+	if ok && enc == nil {
+		return nil, fmt.Errorf("charset %q: charset is disabled", charset)
+	} else if !ok {
+		enc, err = ianaindex.MIME.Encoding(charset)
+	}
+	if enc == nil {
+		enc, err = ianaindex.MIME.Encoding("cs" + charset)
+	}
+	if enc == nil {
+		enc, err = htmlindex.Get(charset)
+	}
+	if err != nil {
+		return nil, fmt.Errorf("charset %q: %v", charset, err)
+	}
+	// See https://github.com/golang/go/issues/19421
+	if enc == nil {
+		return nil, fmt.Errorf("charset %q: unsupported charset", charset)
+	}
+	return enc.NewDecoder().Reader(input), nil
+}
+
+// RegisterEncoding registers an encoding. This is intended to be called from
+// the init function in packages that want to support additional charsets.
+func RegisterEncoding(name string, enc encoding.Encoding) {
+	charsets[name] = enc
+}