Experimental: block list support

app/src/main/java/eu/faircode/email/Core.java

@@ -69,6 +69,9 @@ import java.io.FileOutputStream;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;
+import java.net.Inet4Address;
+import java.net.Inet6Address;
+import java.net.InetAddress;
 import java.net.SocketException;
 import java.net.UnknownHostException;
 import java.text.DateFormat;
@@ -2148,6 +2151,47 @@ class Core {
                     message.warning = Log.formatThrowable(ex, false);
                 }
 
+            boolean check_spam = prefs.getBoolean("check_spam", BuildConfig.DEBUG);
+            if (check_spam)
+                try {
+                    String host = helper.getReceivedFromHost();
+                    if (host != null) {
+                        InetAddress addr = InetAddress.getByName(host);
+                        Log.i("Received from " + host + "=" + addr);
+
+                        StringBuilder lookup = new StringBuilder();
+                        if (addr instanceof Inet4Address) {
+                            List<String> a = Arrays.asList(addr.getHostAddress().split("\\."));
+                            Collections.reverse(a);
+                            lookup.append(TextUtils.join(".", a)).append('.');
+                        } else if (addr instanceof Inet6Address) {
+                            StringBuilder sb = new StringBuilder();
+                            byte[] a = addr.getAddress();
+                            for (int i = 0; i < 8; i++)
+                                sb.append(String.format("%02x",
+                                        ((a[i << 1] << 8) & 0xff00) | (a[(i << 1) + 1] & 0xff)));
+                            sb.reverse();
+                            for (char kar : sb.toString().toCharArray())
+                                lookup.append(kar).append('.');
+                        }
+
+                        lookup.append("zen.spamhaus.org");
+
+                        try {
+                            InetAddress.getByName(lookup.toString());
+                            if (message.warning == null)
+                                message.warning = lookup.toString();
+                            else
+                                message.warning += ", " + lookup;
+                        } catch (UnknownHostException ignore) {
+                        }
+                    }
+                } catch (UnknownHostException ex) {
+
+                } catch (Throwable ex) {
+                    Log.w(folder.name, ex);
+                }
+
             boolean check_reply = prefs.getBoolean("check_reply", false);
             if (check_reply &&
                     message.from != null && message.from.length > 0 &&

app/src/main/java/eu/faircode/email/MessageHelper.java

@@ -96,6 +96,8 @@ public class MessageHelper {
     static final int DEFAULT_ATTACHMENT_DOWNLOAD_SIZE = 256 * 1024; // bytes
     static final long ATTACHMENT_PROGRESS_UPDATE = 1500L; // milliseconds
 
+    // https://tools.ietf.org/html/rfc4021
+
     static void setSystemProperties(Context context) {
         System.setProperty("mail.mime.decodetext.strict", "false");
 
@@ -835,6 +837,18 @@ public class MessageHelper {
         return result;
     }
 
+    String getReceivedFromHost() throws MessagingException {
+        String[] received = imessage.getHeader("Received");
+        if (received == null || received.length == 0)
+            return null;
+
+        String[] h = MimeUtility.unfold(received[received.length - 1]).split("\\s+");
+        if (h.length > 1 && h[0].equalsIgnoreCase("from"))
+            return h[1];
+
+        return null;
+    }
+
     private Address[] getAddressHeader(String name) throws MessagingException {
         String header = imessage.getHeader(name, ",");
         if (header == null)