Use custom deserialization to handle list extensions

src/io/calidog/certstream/CertStream.java

@@ -1,6 +1,7 @@
 package io.calidog.certstream;
 
 import com.google.gson.Gson;
+import com.google.gson.GsonBuilder;
 import com.google.gson.JsonSyntaxException;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -60,13 +61,13 @@ public static void onMessage(CertStreamMessageHandler handler)
             CertStreamMessagePOJO msg;
             try
             {
-                msg = new Gson().fromJson(string, CertStreamMessagePOJO.class);
+                msg = certStreamGson.fromJson(string, CertStreamMessagePOJO.class);
 
                 if (msg.messageType.equalsIgnoreCase("heartbeat"))
                 {
                     return;
                 }
-            }catch (JsonSyntaxException e)
+            } catch (JsonSyntaxException e)
             {
                 System.out.println(e.getMessage());
                 logger.warn("onMessage had an exception parsing some json", e);
@@ -87,6 +88,15 @@ public static void onMessage(CertStreamMessageHandler handler)
         });
     }
 
+    private static Gson certStreamGson =
+            new GsonBuilder()
+                    .registerTypeAdapter
+                    (
+                        CertStreamCertificatePOJO.class,
+                        new CertStreamCertificatePOJODeserializer()
+                    )
+                    .create();
+
     /**
      * @param handler A {@link Consumer<CertStreamMessage>} that we'll
      *                run in a Thread that stays alive as long
@@ -99,7 +109,7 @@ public static void onMessageAlternativeServer (CertStreamMessageHandler handler,
             CertStreamMessagePOJO msg;
 
             try {
-                msg = new Gson().fromJson(string, CertStreamMessagePOJO.class);
+                msg = certStreamGson.fromJson(string, CertStreamMessagePOJO.class);
 
                 if (msg.messageType.equalsIgnoreCase("heartbeat")) {
                     return;

src/io/calidog/certstream/CertStreamCertificate.java

@@ -16,7 +16,7 @@
  */
 public class CertStreamCertificate extends X509Certificate {
     private HashMap<String, String> subject;
-    private HashMap<String, String> extensions;
+    private HashMap<String, String[]> extensions;
 
     private double notBefore;
     private double notAfter;
@@ -257,7 +257,7 @@ public byte[] getExtensionValue(String s) {
      * passed-in oid String. The oid string is represented
      * by whatever CertStream passes us.
      */
-    public String getStringExtensionValue(String key)
+    public String[] getStringExtensionValue(String key)
     {
         return extensions.get(key);
     }

src/io/calidog/certstream/CertStreamCertificatePOJO.java

@@ -12,7 +12,9 @@ public class CertStreamCertificatePOJO {
 
     HashMap<String, String> subject;
 
-    HashMap<String, String> extensions;
+    // values can be either strings or lists of strings, so we use a a custom deserializer
+    // that converts strings into singleton arrays
+    HashMap<String, String[]> extensions;
 
     @SerializedName("not_before")
     double notBefore;

src/io/calidog/certstream/CertStreamCertificatePOJODeserializer.java

@@ -0,0 +1,62 @@
+package io.calidog.certstream;
+
+import com.google.gson.*;
+
+import java.lang.reflect.Type;
+import java.util.HashMap;
+
+public class CertStreamCertificatePOJODeserializer implements JsonDeserializer<CertStreamCertificatePOJO> {
+
+    @Override
+    public CertStreamCertificatePOJO deserialize(
+            JsonElement jsonElement,
+            Type type,
+            JsonDeserializationContext jsonDeserializationContext
+    ) throws JsonParseException {
+        JsonObject jsonObj = jsonElement.getAsJsonObject();
+
+        JsonObject jsonExtensions;
+
+        HashMap<String, String[]> extensionMap = null;
+
+        if (jsonObj.has("extensions"))
+        {
+            jsonExtensions = jsonObj.remove("extensions").getAsJsonObject();
+
+            final HashMap<String, String[]> finalExtensionMap = new HashMap<>(jsonExtensions.size());
+
+            jsonExtensions
+                    .entrySet()
+                    .forEach
+                    (
+                            (java.util.Map.Entry<String, JsonElement> entry) ->
+                            {
+                                String key = entry.getKey();
+                                JsonElement value = entry.getValue();
+                                String[] extensionValueList;
+                                try {
+                                    extensionValueList = new String[] { value.getAsString() };
+                                } catch (IllegalStateException | UnsupportedOperationException e) {
+                                    JsonArray extensionJsonArray = value.getAsJsonArray();
+                                    extensionValueList = new String[extensionJsonArray.size()];
+
+                                    for (int i = 0; i < extensionJsonArray.size(); i++) {
+                                        extensionValueList[i] = extensionJsonArray.get(i).getAsString();
+                                    }
+                                }
+
+                                finalExtensionMap.put(key, extensionValueList);
+                            }
+                    );
+
+            extensionMap = finalExtensionMap;
+        }
+
+        CertStreamCertificatePOJO retVal =
+                jsonDeserializationContext.deserialize(jsonElement, type);
+
+        retVal.extensions = extensionMap;
+
+        return retVal;
+    }
+}