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fix: use 8bit Content-Transfer-Encoding for non-ASCII text bodies #477

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fix: use 8bit Content-Transfer-Encoding for non-ASCII text bodies #477

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21 changes: 16 additions & 5 deletions internal/cmd/gmail_mime.go
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Original file line number Diff line number Diff line change
Expand Up @@ -136,13 +136,13 @@ func buildRFC822(opts mailOptions, cfg *rfc822Config) ([]byte, error) {
return b.Bytes(), nil
case hasHTML && !hasPlain:
writeHeader(&b, "Content-Type", "text/html; charset=\"utf-8\"")
writeHeader(&b, "Content-Transfer-Encoding", "7bit")
writeHeader(&b, "Content-Transfer-Encoding", transferEncodingForText(htmlBody))
b.WriteString("\r\n")
writeBodyWithTrailingCRLF(&b, htmlBody)
return b.Bytes(), nil
default:
writeHeader(&b, "Content-Type", "text/plain; charset=\"utf-8\"")
writeHeader(&b, "Content-Transfer-Encoding", "7bit")
writeHeader(&b, "Content-Transfer-Encoding", transferEncodingForText(plainBody))
b.WriteString("\r\n")
writeBodyWithTrailingCRLF(&b, plainBody)
return b.Bytes(), nil
Expand Down Expand Up @@ -171,11 +171,11 @@ func buildRFC822(opts mailOptions, cfg *rfc822Config) ([]byte, error) {
fmt.Fprintf(&b, "--%s--\r\n", altBoundary)
case hasHTML && !hasPlain:
b.WriteString("Content-Type: text/html; charset=\"utf-8\"\r\n")
b.WriteString("Content-Transfer-Encoding: 7bit\r\n\r\n")
fmt.Fprintf(&b, "Content-Transfer-Encoding: %s\r\n\r\n", transferEncodingForText(htmlBody))
writeBodyWithTrailingCRLF(&b, htmlBody)
default:
b.WriteString("Content-Type: text/plain; charset=\"utf-8\"\r\n")
b.WriteString("Content-Transfer-Encoding: 7bit\r\n\r\n")
fmt.Fprintf(&b, "Content-Transfer-Encoding: %s\r\n\r\n", transferEncodingForText(plainBody))
writeBodyWithTrailingCRLF(&b, plainBody)
}

Expand Down Expand Up @@ -292,10 +292,21 @@ func writeBodyWithTrailingCRLF(b *bytes.Buffer, body string) {
func writeTextPart(b *bytes.Buffer, boundary string, contentType string, body string) {
_, _ = fmt.Fprintf(b, "--%s\r\n", boundary)
_, _ = fmt.Fprintf(b, "Content-Type: %s\r\n", contentType)
b.WriteString("Content-Transfer-Encoding: 7bit\r\n\r\n")
_, _ = fmt.Fprintf(b, "Content-Transfer-Encoding: %s\r\n\r\n", transferEncodingForText(body))
writeBodyWithTrailingCRLF(b, body)
}

// transferEncodingForText returns "7bit" for pure ASCII text and "8bit" for
// text containing non-ASCII bytes (e.g. UTF-8). Using "7bit" for UTF-8 content
// violates RFC 2045 §2.7 and can cause mail servers to mangle the message or
// strip attachments.
func transferEncodingForText(s string) string {
if isASCII(s) {
return "7bit"
}
return "8bit"
}

func randomBoundary() (string, error) {
var b [18]byte
if _, err := rand.Read(b[:]); err != nil {
Expand Down