Ensure skin servers have a valid address (or gateway in the case of legacy)

src/hdskins/java/com/voxelmodpack/hdskins/HDSkinManager.java

@@ -242,6 +242,8 @@ public final class HDSkinManager implements IResourceManagerReloadListener {
     }
 
     public void addSkinServer(SkinServer skinServer) {
+        skinServer.validate();
+
         skinServers.add(skinServer);
     }
 

src/hdskins/java/com/voxelmodpack/hdskins/skins/AbstractSkinServer.java

@@ -9,6 +9,11 @@ import java.util.concurrent.CompletableFuture;
 
 import javax.annotation.Nullable;
 
+import org.apache.commons.lang3.builder.ToStringBuilder;
+import org.apache.logging.log4j.util.Strings;
+
+import com.google.gson.JsonParseException;
+import com.google.gson.annotations.Expose;
 import com.mojang.authlib.GameProfile;
 import com.mojang.authlib.exceptions.AuthenticationException;
 import com.mojang.authlib.minecraft.MinecraftProfileTexture;
@@ -20,6 +25,12 @@ import net.minecraft.util.Session;
 
 public abstract class AbstractSkinServer implements SkinServer {
 
+    @Expose
+    protected final String address;
+
+    public AbstractSkinServer(String address) {
+        this.address = address;
+    }
 
     @Override
     public final Optional<MinecraftTexturesPayload> loadProfileData(GameProfile profile) {
@@ -40,8 +51,21 @@ public abstract class AbstractSkinServer implements SkinServer {
         }, HDSkinManager.skinUploadExecutor);
     }
 
+    @Override
+    public void validate() throws JsonParseException {
+        if (Strings.isBlank(address)) {
+            throw new JsonParseException("Address was not specified.");
+        }
+    }
+
     protected abstract MinecraftTexturesPayload getProfileData(GameProfile profile);
 
     protected abstract SkinUploadResponse doUpload(Session session, URI image, Type type, Map<String, String> metadata) throws AuthenticationException, IOException;
 
+    @Override
+    public String toString() {
+        return new ToStringBuilder(this, IndentedToStringStyle.INSTANCE)
+                .append("address", address)
+                .build();
+    }
 }

src/hdskins/java/com/voxelmodpack/hdskins/skins/BethlehemSkinServer.java

@@ -9,7 +9,6 @@ import org.apache.http.HttpStatus;
 
 import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.ImmutableMap.Builder;
-import com.google.gson.annotations.Expose;
 import com.mojang.authlib.GameProfile;
 import com.mojang.authlib.exceptions.AuthenticationException;
 import com.mojang.authlib.minecraft.MinecraftProfileTexture.Type;
@@ -23,11 +22,8 @@ public class BethlehemSkinServer extends AbstractSkinServer {
 
     private static final String SERVER_ID = "7853dfddc358333843ad55a2c7485c4aa0380a51";
 
-    @Expose
+    public BethlehemSkinServer(String address) {
-    private final String address;
+        super(address);
-
-    private BethlehemSkinServer(String address) {
-        this.address = address;
     }
 
     @Override

src/hdskins/java/com/voxelmodpack/hdskins/skins/LegacySkinServer.java

@@ -1,6 +1,5 @@
 package com.voxelmodpack.hdskins.skins;
 
-import com.google.common.base.Strings;
 import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.ImmutableMap.Builder;
 import com.google.gson.annotations.Expose;
@@ -16,10 +15,10 @@ import org.apache.commons.lang3.builder.ToStringBuilder;
 import org.apache.http.HttpStatus;
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
+import org.apache.logging.log4j.util.Strings;
 
 import java.io.IOException;
 import java.net.URI;
-import java.util.Collections;
 import java.util.EnumMap;
 import java.util.Locale;
 import java.util.Map;
@@ -32,23 +31,16 @@ public class LegacySkinServer extends AbstractSkinServer {
 
     private static final Logger logger = LogManager.getLogger();
 
-    @Expose
-    private final String address;
-
     @Expose
     private final String gateway;
 
     public LegacySkinServer(String address, @Nullable String gateway) {
-        this.address = address;
+        super(address);
-        this.gateway = gateway;
+        this.gateway = Strings.isBlank(gateway) ? address : gateway;
     }
 
     @Override
     public Map<Type, MinecraftProfileTexture> getPreviewTextures(GameProfile profile) {
-        if (Strings.isNullOrEmpty(gateway)) {
-            return Collections.emptyMap();
-        }
-
         Map<Type, MinecraftProfileTexture> map = new EnumMap<>(Type.class);
 
         for (Type type : Type.values()) {
@@ -105,8 +97,10 @@ public class LegacySkinServer extends AbstractSkinServer {
                 response = response.substring(7);
             }
 
-            if (!response.equalsIgnoreCase("OK") && !response.endsWith("OK"))
+            if (!response.equalsIgnoreCase("OK") && !response.endsWith("OK")) {
                 throw new IOException(response);
+            }
+
             return new SkinUploadResponse(response);
         }
     }

src/hdskins/java/com/voxelmodpack/hdskins/skins/SkinServer.java

@@ -3,6 +3,7 @@ package com.voxelmodpack.hdskins.skins;
 import com.google.common.collect.Lists;
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
+import com.google.gson.JsonParseException;
 import com.mojang.authlib.GameProfile;
 import com.mojang.authlib.exceptions.AuthenticationException;
 import com.mojang.authlib.minecraft.MinecraftProfileTexture;
@@ -39,6 +40,8 @@ public interface SkinServer extends Exposable {
 
     CompletableFuture<SkinUploadResponse> uploadSkin(Session session, @Nullable URI image, MinecraftProfileTexture.Type type, Map<String, String> metadata);
 
+    void validate() throws JsonParseException;
+
     public static void verifyServerConnection(Session session, String serverId) throws AuthenticationException {
         MinecraftSessionService service = Minecraft.getMinecraft().getSessionService();
         service.joinServer(session.getProfile(), session.getToken(), serverId);

src/hdskins/java/com/voxelmodpack/hdskins/skins/SkinServerSerializer.java

@@ -32,6 +32,10 @@ public class SkinServerSerializer implements JsonSerializer<SkinServer>, JsonDes
     public SkinServer deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
         String type = json.getAsJsonObject().get("type").getAsString();
 
-        return context.deserialize(json, HDSkinManager.INSTANCE.getSkinServerClass(type));
+        SkinServer server = context.deserialize(json, HDSkinManager.INSTANCE.getSkinServerClass(type));
+
+        server.validate();
+
+        return server;
     }
 }

src/hdskins/java/com/voxelmodpack/hdskins/skins/ValhallaSkinServer.java

@@ -2,7 +2,6 @@ package com.voxelmodpack.hdskins.skins;
 
 import com.google.common.base.Preconditions;
 import com.google.gson.JsonObject;
-import com.google.gson.annotations.Expose;
 import com.mojang.authlib.GameProfile;
 import com.mojang.authlib.exceptions.AuthenticationException;
 import com.mojang.authlib.minecraft.MinecraftProfileTexture;
@@ -14,7 +13,6 @@ import javax.annotation.Nullable;
 
 import net.minecraft.client.Minecraft;
 import net.minecraft.util.Session;
-import org.apache.commons.lang3.builder.ToStringBuilder;
 import org.apache.http.HttpHeaders;
 import org.apache.http.HttpResponse;
 import org.apache.http.HttpStatus;
@@ -42,13 +40,10 @@ import java.util.UUID;
 @ServerType("valhalla")
 public class ValhallaSkinServer extends AbstractSkinServer {
 
-    @Expose
-    private final String address;
-
     private transient String accessToken;
 
     public ValhallaSkinServer(String address) {
-        this.address = address;
+        super(address);
     }
 
     @Override
@@ -222,13 +217,6 @@ public class ValhallaSkinServer extends AbstractSkinServer {
         return URI.create(String.format("%s/auth/response", address));
     }
 
-    @Override
-    public String toString() {
-        return new ToStringBuilder(this, IndentedToStringStyle.INSTANCE)
-                .append("address", address)
-                .build();
-    }
-
     @SuppressWarnings("WeakerAccess")
     private static class AuthHandshake {