Experiment: TLS detection

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

@@ -101,6 +101,8 @@ public class ConnectionHelper {
 
     public static native int jni_socket_get_send_buffer(int fd);
 
+    public static native boolean jni_is_numeric_address(String _ip);
+
     static class NetworkState {
         private Boolean connected = null;
         private Boolean suitable = null;

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

@@ -3738,6 +3738,9 @@ class Core {
             if (received == null)
                 received = 0L;
 
+            if (BuildConfig.DEBUG)
+                Log.i("--- TLS=" + helper.getTLS());
+
             String[] authentication = helper.getAuthentication();
             MessageHelper.MessageParts parts = helper.getMessageParts();
 

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

@@ -66,7 +66,9 @@ import java.io.InputStream;
 import java.io.OutputStream;
 import java.io.UnsupportedEncodingException;
 import java.net.IDN;
+import java.net.InetAddress;
 import java.net.URLDecoder;
+import java.net.UnknownHostException;
 import java.nio.charset.Charset;
 import java.nio.charset.StandardCharsets;
 import java.nio.charset.UnsupportedCharsetException;
@@ -1914,6 +1916,95 @@ public class MessageHelper {
         return null;
     }
 
+    Boolean getTLS() throws MessagingException {
+        // https://datatracker.ietf.org/doc/html/rfc2821#section-4.4
+
+        // Time-stamp-line = "Received:" FWS Stamp <CRLF>
+        // Stamp = From-domain By-domain Opt-info ";"  FWS date-time
+        // From-domain = "FROM" FWS Extended-Domain CFWS
+        // By-domain = "BY" FWS Extended-Domain CFWS
+        // Opt-info = [Via] [With] [ID] [For]
+        // Via = "VIA" FWS Link CFWS
+        // With = "WITH" FWS Protocol CFWS
+        // ID = "ID" FWS String / msg-id CFWS
+        // For = "FOR" FWS 1*( Path / Mailbox ) CFWS
+
+        // Extended-Domain = Domain / ( Domain FWS "(" TCP-info ")" ) / ( Address-literal FWS "(" TCP-info ")" )
+        // TCP-info = Address-literal / ( Domain FWS Address-literal )
+        // Link = "TCP" / Addtl-Link
+        // Addtl-Link = Atom
+        // Protocol = "ESMTP" / "SMTP" / Attdl-Protocol
+        // Attdl-Protocol = Atom
+
+        String[] received = imessage.getHeader("Received");
+        if (received == null || received.length == 0)
+            return null;
+
+        final List<String> words = Collections.unmodifiableList(Arrays.asList(
+                "from", "by", "via", "with", "id", "for"));
+
+        // First header is last added header
+        for (String r : received) {
+            String header = MimeUtility.unfold(r);
+
+            int s, e;
+            do {
+                s = header.indexOf('(');
+                e = header.indexOf(')', s);
+                if (s > 0 && e > 0)
+                    header = header.substring(0, s) + header.substring((e + 1));
+            } while (s > 0 && e > 0);
+
+            int semi = header.lastIndexOf(';');
+            if (semi > 0)
+                header = header.substring(0, semi);
+
+            header = header.replaceAll("\\s+", " ");
+
+            Log.i("--- header=" + header);
+
+            String[] parts = header.split(" ");
+            boolean hasFrom = false;
+            boolean hasWith = false;
+            for (int j = 0; j < parts.length - 1; j++) {
+                Log.i("--- part " + j + " " + parts[j] + "=" + parts[j + 1]);
+                if ("from".equalsIgnoreCase(parts[j])) {
+                    hasFrom = true;
+                    String from = parts[j + 1].toLowerCase(Locale.ROOT);
+                    boolean numeric = ConnectionHelper.jni_is_numeric_address(from);
+                    Log.i("--- numeric=" + numeric);
+                    if (numeric)
+                        try {
+                            InetAddress addr = InetAddress.getByName(from);
+                            if (addr.isSiteLocalAddress())
+                                break;
+                            Log.i("--- remote");
+                        } catch (UnknownHostException ex) {
+                            Log.e(ex);
+                        }
+                } else if ("with".equalsIgnoreCase(parts[j])) {
+                    hasWith = true;
+                    if (hasFrom) {
+                        String with = parts[j + 1].toUpperCase(Locale.ROOT);
+                        Log.i("--- MTP=" + with.contains("MTP") + " MTPS=" + with.contains("MTPS"));
+                        // https://www.iana.org/assignments/mail-parameters/mail-parameters.txt
+                        if (!with.contains("MTP"))
+                            return null;
+                        if (!with.contains("MTPS"))
+                            return false;
+                    }
+                    break;
+                }
+                if (words.contains(parts[j]))
+                    j++;
+            }
+            if (hasFrom && !hasWith)
+                return null;
+        }
+
+        return true;
+    }
+
     Long getSent() throws MessagingException {
         ensureEnvelope();
 

app/src/main/jni/fairemail.cc

@@ -157,3 +157,30 @@ Java_eu_faircode_email_ConnectionHelper_jni_1socket_1get_1send_1buffer(
         log_android(ANDROID_LOG_DEBUG, "ioctl(TIOCOUTQ) res=%d queued=%d", res, queued);
     return (res == 0 ? queued : 0);
 }
+
+extern "C"
+JNIEXPORT jboolean JNICALL
+Java_eu_faircode_email_ConnectionHelper_jni_1is_1numeric_1address(
+        JNIEnv *env, jclass clazz,
+        jstring _ip) {
+    jboolean numeric = 0;
+    const char *ip = env->GetStringUTFChars(_ip, 0);
+
+    // https://linux.die.net/man/3/getaddrinfo
+    struct addrinfo hints;
+    memset(&hints, 0, sizeof(struct addrinfo));
+    hints.ai_family = AF_UNSPEC;
+    hints.ai_flags = AI_NUMERICHOST; // suppresses any potentially lengthy network host address lookups
+    struct addrinfo *result;
+    int err = getaddrinfo(ip, nullptr, &hints, &result);
+    if (err)
+        log_android(ANDROID_LOG_DEBUG, "getaddrinfo(%s) error %d: %s", ip, err, gai_strerror(err));
+    else
+        numeric = (jboolean) (result != nullptr);
+
+    if (result != nullptr)
+        freeaddrinfo(result);
+
+    env->ReleaseStringUTFChars(_ip, ip);
+    return numeric;
+}