Only pass encoded headers to MimeHeader

Remove code to encode header values from from MimeHeader.writeTo()

app/core/src/main/java/com/fsck/k9/message/MessageBuilder.java

@@ -26,6 +26,7 @@ import com.fsck.k9.mail.MessagingException;
 import com.fsck.k9.mail.internet.MessageIdGenerator;
 import com.fsck.k9.mail.internet.MimeBodyPart;
 import com.fsck.k9.mail.internet.MimeHeader;
+import com.fsck.k9.mail.internet.MimeHeaderEncoder;
 import com.fsck.k9.mail.internet.MimeMessage;
 import com.fsck.k9.mail.internet.MimeMessageHelper;
 import com.fsck.k9.mail.internet.MimeMultipart;
@@ -108,7 +109,8 @@ public abstract class MessageBuilder {
         }
 
         if (!K9.isHideUserAgent()) {
-            message.setHeader("User-Agent", resourceProvider.userAgent());
+            String encodedUserAgent = MimeHeaderEncoder.encode("User-Agent", resourceProvider.userAgent());
+            message.setHeader("User-Agent", encodedUserAgent);
         }
 
         final String replyTo = identity.getReplyTo();

app/core/src/main/java/com/fsck/k9/message/PgpMessageBuilder.java

@@ -27,6 +27,7 @@ import com.fsck.k9.mail.Message.RecipientType;
 import com.fsck.k9.mail.MessagingException;
 import com.fsck.k9.mail.filter.EOLConvertingOutputStream;
 import com.fsck.k9.mail.internet.BinaryTempFileBody;
+import com.fsck.k9.mail.internet.Headers;
 import com.fsck.k9.mail.internet.MessageIdGenerator;
 import com.fsck.k9.mail.internet.MimeBodyPart;
 import com.fsck.k9.mail.internet.MimeHeader;
@@ -219,7 +220,7 @@ public class PgpMessageBuilder extends MessageBuilder {
             messageContentBodyPart.setHeader(MimeHeader.HEADER_CONTENT_TYPE,
                     messageContentBodyPart.getContentType() + "; protected-headers=\"v1\"");
             messageContentBodyPart.setHeader(MimeHeader.SUBJECT, subjects[0]);
-            currentProcessedMimeMessage.setHeader(MimeHeader.SUBJECT, resourceProvider.encryptedSubject());
+            currentProcessedMimeMessage.setSubject(resourceProvider.encryptedSubject());
         }
     }
 

mail/common/src/main/java/com/fsck/k9/mail/internet/MimeHeader.kt

@@ -76,21 +76,9 @@ class MimeHeader {
     }
 
     private fun Appendable.appendNameValueField(field: Field) {
-        val value = field.value
-        val encodedValue = if (hasToBeEncoded(value)) {
-            EncoderUtil.encodeEncodedWord(value)
-        } else {
-            value
-        }
-
         append(field.name)
         append(": ")
-        append(encodedValue)
+        append(field.value)
-    }
-
-    // encode non printable characters except LF/CR/TAB codes.
-    private fun hasToBeEncoded(text: String): Boolean {
-        return text.any { !it.isVChar() && !it.isWspOrCrlf() }
     }
 
     companion object {

mail/common/src/main/java/com/fsck/k9/mail/internet/MimeHeaderEncoder.kt

@@ -0,0 +1,26 @@
+package com.fsck.k9.mail.internet
+
+object MimeHeaderEncoder {
+    @JvmStatic
+    fun encode(name: String, value: String): String {
+        // TODO: Fold long text that provides enough opportunities for folding and doesn't contain any characters that
+        //  need to be encoded.
+        return if (hasToBeEncoded(name, value)) {
+            EncoderUtil.encodeEncodedWord(value)
+        } else {
+            value
+        }
+    }
+
+    private fun hasToBeEncoded(name: String, value: String): Boolean {
+        return exceedsRecommendedLineLength(name, value) || charactersNeedEncoding(value)
+    }
+
+    private fun exceedsRecommendedLineLength(name: String, value: String): Boolean {
+        return name.length + 2 /* colon + space */ + value.length > RECOMMENDED_MAX_LINE_LENGTH
+    }
+
+    private fun charactersNeedEncoding(text: String): Boolean {
+        return text.any { !it.isVChar() && !it.isWspOrCrlf() }
+    }
+}

mail/common/src/main/java/com/fsck/k9/mail/internet/MimeMessage.java

@@ -261,12 +261,13 @@ public class MimeMessage extends Message {
      */
     @Override
     public String getSubject() {
-        return MimeUtility.unfoldAndDecode(getFirstHeader("Subject"), this);
+        return MimeUtility.unfoldAndDecode(getFirstHeader(MimeHeader.SUBJECT), this);
     }
 
     @Override
     public void setSubject(String subject) {
-        setHeader("Subject", subject);
+        String encodedSubject = MimeHeaderEncoder.encode(MimeHeader.SUBJECT, subject);
+        setHeader(MimeHeader.SUBJECT, encodedSubject);
     }
 
     @Override