Native DKIM improvements

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

@@ -2026,12 +2026,17 @@ public class MessageHelper {
                     String dns = kv.get("s") + "._domainkey." + signer;
                     Log.i("DKIM lookup " + dns);
                     DnsHelper.DnsRecord[] records = DnsHelper.lookup(context, dns, "txt");
-                    if (records.length > 0) {
+                    if (records.length == 0)
+                        continue;
+
                     Log.i("DKIM got " + records[0].name);
                     Map<String, String> dk = getKeyValues(records[0].name);
 
-                        Log.i("DKIM canonicalization=" + kv.get("c"));
+                    String canonic = kv.get("c");
-                        String[] c = kv.get("c").split("/");
+                    Log.i("DKIM canonicalization=" + canonic);
+                    if (canonic == null)
+                        canonic = "simple/simple";
+                    String[] c = canonic.split("/");
 
                     StringBuilder head = new StringBuilder();
 
@@ -2040,6 +2045,7 @@ public class MessageHelper {
 
                     boolean from = false;
                     List<String> _h = new ArrayList<>();
+                    if (hs != null)
                         for (String key : hs.split(":")) {
                             _h.add(key.trim());
                             from = (from || "from".equalsIgnoreCase(key.trim()));
@@ -2057,7 +2063,9 @@ public class MessageHelper {
                         idx = (idx == null ? 1 : idx + 1);
                         index.put(_n, idx);
 
-                            String[] h = ("DKIM-Signature".equals(n) ? new String[]{header} : amessage.getHeader(n));
+                        String[] h = ("DKIM-Signature".equals(n)
+                                ? new String[]{header}
+                                : amessage.getHeader(n));
                         if (h == null || idx > h.length) {
                             // https://datatracker.ietf.org/doc/html/rfc6376/#section-5.4
                             Log.i("DKIM missing header=" + n + "[" + idx + "/" + (h == null ? null : h.length) + "]");
@@ -2128,7 +2136,11 @@ public class MessageHelper {
                     byte[] bh = MessageDigest.getInstance(halgo).digest(body.getBytes());  // TODO: charset
                     Log.i("DKIM bh=" + Base64.encodeToString(bh, Base64.NO_WRAP) + "/" + kv.get("bh"));
 
-                        String p = dk.get("p").replaceAll("\\s+", "");
+                    String pubkey = dk.get("p");
+                    if (pubkey == null)
+                        continue;
+
+                    String p = pubkey.replaceAll("\\s+", "");
                     Log.i("DKIM pubkey=" + p);
 
                     X509EncodedKeySpec pubKeySpec = new X509EncodedKeySpec(Base64.decode(p, Base64.DEFAULT));
@@ -2136,11 +2148,13 @@ public class MessageHelper {
                     PublicKey pubKey = keyFactory.generatePublic(pubKeySpec);
                     Signature sig = Signature.getInstance(salgo); // a=
 
-                        String s = kv.get("b").replaceAll("\\s+", "");
+                    String hash = kv.get("b");
+                    if (hash == null)
+                        continue;
+                    String s = hash.replaceAll("\\s+", "");
                     Log.i("DKIM signature=" + s);
 
                     byte[] signature = Base64.decode(s, Base64.DEFAULT);
-                        // TODO: check signature length
 
                     sig.initVerify(pubKey);
                     sig.update(head.toString().getBytes());
@@ -2153,7 +2167,6 @@ public class MessageHelper {
                     if (verified &&
                             !signers.contains(signer))
                         signers.add(signer);
-                    }
                 } catch (Throwable ex) {
                     Log.e("DKIM", ex);
                 }