A couple of minor changes to HTTP limiting

- We now error if there are too many websockets, instead of queuing
   them up. As these have a more explicit "lifetime", it could be
   confusing if http.websocket just blocks indefinitely.
 - Fix a CCME when cleaning up resources.

src/main/java/dan200/computercraft/core/apis/HTTPAPI.java

@@ -10,10 +10,7 @@ import dan200.computercraft.ComputerCraft;
 import dan200.computercraft.api.lua.ILuaAPI;
 import dan200.computercraft.api.lua.ILuaContext;
 import dan200.computercraft.api.lua.LuaException;
-import dan200.computercraft.core.apis.http.CheckUrl;
+import dan200.computercraft.core.apis.http.*;
-import dan200.computercraft.core.apis.http.HTTPRequestException;
-import dan200.computercraft.core.apis.http.Resource;
-import dan200.computercraft.core.apis.http.ResourceQueue;
 import dan200.computercraft.core.apis.http.request.HttpRequest;
 import dan200.computercraft.core.apis.http.websocket.Websocket;
 import io.netty.handler.codec.http.DefaultHttpHeaders;
@@ -33,9 +30,9 @@ public class HTTPAPI implements ILuaAPI
 {
     private final IAPIEnvironment m_apiEnvironment;
 
-    private final ResourceQueue<CheckUrl> checkUrls = new ResourceQueue<>();
+    private final ResourceGroup<CheckUrl> checkUrls = new ResourceGroup<>();
-    private final ResourceQueue<HttpRequest> requests = new ResourceQueue<>( () -> ComputerCraft.httpMaxRequests );
+    private final ResourceGroup<HttpRequest> requests = new ResourceQueue<>( () -> ComputerCraft.httpMaxRequests );
-    private final ResourceQueue<Websocket> websockets = new ResourceQueue<>( () -> ComputerCraft.httpMaxWebsockets );
+    private final ResourceGroup<Websocket> websockets = new ResourceGroup<>( () -> ComputerCraft.httpMaxWebsockets );
 
     public HTTPAPI( IAPIEnvironment environment )
     {
@@ -189,7 +186,10 @@ public class HTTPAPI implements ILuaAPI
                 try
                 {
                     URI uri = Websocket.checkUri( address );
-                    new Websocket( websockets, m_apiEnvironment, uri, address, headers ).queue( Websocket::connect );
+                    if( !new Websocket( websockets, m_apiEnvironment, uri, address, headers ).queue( Websocket::connect ) )
+                    {
+                        throw new LuaException( "Too many websockets already open" );
+                    }
 
                     return new Object[] { true };
                 }

src/main/java/dan200/computercraft/core/apis/http/CheckUrl.java

@@ -26,7 +26,7 @@ public class CheckUrl extends Resource<CheckUrl>
     private final String address;
     private final String host;
 
-    public CheckUrl( ResourceQueue<CheckUrl> limiter, IAPIEnvironment environment, String address, URI uri )
+    public CheckUrl( ResourceGroup<CheckUrl> limiter, IAPIEnvironment environment, String address, URI uri )
     {
         super( limiter );
         this.environment = environment;

src/main/java/dan200/computercraft/core/apis/http/Resource.java

@@ -24,9 +24,9 @@ import java.util.function.Consumer;
 public abstract class Resource<T extends Resource<T>> implements Closeable
 {
     private final AtomicBoolean closed = new AtomicBoolean( false );
-    private final ResourceQueue<T> limiter;
+    private final ResourceGroup<T> limiter;
 
-    protected Resource( ResourceQueue<T> limiter )
+    protected Resource( ResourceGroup<T> limiter )
     {
         this.limiter = limiter;
     }
@@ -93,10 +93,10 @@ public abstract class Resource<T extends Resource<T>> implements Closeable
         tryClose();
     }
 
-    public void queue( Consumer<T> task )
+    public boolean queue( Consumer<T> task )
     {
         @SuppressWarnings( "unchecked" ) T thisT = (T) this;
-        limiter.queue( thisT, () -> task.accept( thisT ) );
+        return limiter.queue( thisT, () -> task.accept( thisT ) );
     }
 
     protected static <T extends Closeable> T closeCloseable( T closeable )

src/main/java/dan200/computercraft/core/apis/http/ResourceGroup.java

@@ -0,0 +1,81 @@
+/*
+ * This file is part of ComputerCraft - http://www.computercraft.info
+ * Copyright Daniel Ratcliffe, 2011-2019. Do not distribute without permission.
+ * Send enquiries to dratcliffe@gmail.com
+ */
+
+package dan200.computercraft.core.apis.http;
+
+import java.util.Collections;
+import java.util.Set;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.function.IntSupplier;
+import java.util.function.Supplier;
+
+/**
+ * A collection of {@link Resource}s, with an upper bound on capacity.
+ */
+public class ResourceGroup<T extends Resource<T>>
+{
+    private static final IntSupplier ZERO = () -> 0;
+
+    final IntSupplier limit;
+
+    boolean active = false;
+
+    final Set<T> resources = Collections.newSetFromMap( new ConcurrentHashMap<>() );
+
+    public ResourceGroup( IntSupplier limit )
+    {
+        this.limit = limit;
+    }
+
+    public ResourceGroup()
+    {
+        this.limit = ZERO;
+    }
+
+    public void startup()
+    {
+        active = true;
+    }
+
+    public synchronized void shutdown()
+    {
+        active = false;
+
+        for( T resource : resources ) resource.close();
+        resources.clear();
+
+        Resource.cleanup();
+    }
+
+
+    public final boolean queue( T resource, Runnable setup )
+    {
+        return queue( () -> {
+            setup.run();
+            return resource;
+        } );
+    }
+
+    public synchronized boolean queue( Supplier<T> resource )
+    {
+        Resource.cleanup();
+        if( !active ) return false;
+
+        int limit = this.limit.getAsInt();
+        if( limit <= 0 || resources.size() < limit )
+        {
+            resources.add( resource.get() );
+            return true;
+        }
+
+        return false;
+    }
+
+    public synchronized void release( T resource )
+    {
+        resources.remove( resource );
+    }
+}

src/main/java/dan200/computercraft/core/apis/http/ResourceQueue.java

@@ -7,80 +7,44 @@
 package dan200.computercraft.core.apis.http;
 
 import java.util.ArrayDeque;
-import java.util.HashSet;
-import java.util.Set;
 import java.util.function.IntSupplier;
 import java.util.function.Supplier;
 
 /**
- * A queue for {@link Resource}s, with built-in rate-limiting.
+ * A {@link ResourceGroup} which will queue items when the group at capacity.
  */
-public class ResourceQueue<T extends Resource<T>>
+public class ResourceQueue<T extends Resource<T>> extends ResourceGroup<T>
 {
-    private static final IntSupplier ZERO = () -> 0;
-
-    private final IntSupplier limit;
-
-    private boolean active = false;
-
-    private final Set<T> resources = new HashSet<>();
     private final ArrayDeque<Supplier<T>> pending = new ArrayDeque<>();
 
     public ResourceQueue( IntSupplier limit )
     {
-        this.limit = limit;
+        super( limit );
     }
 
     public ResourceQueue()
     {
-        this.limit = ZERO;
-    }
-
-    public void startup()
-    {
-        active = true;
     }
 
     public synchronized void shutdown()
     {
-        active = false;
+        super.shutdown();
-
         pending.clear();
-        for( T resource : resources ) resource.close();
-        resources.clear();
-
-        Resource.cleanup();
     }
 
-    public void queue( T resource, Runnable setup )
+    public synchronized boolean queue( Supplier<T> resource )
     {
-        queue( () -> {
+        if( !active ) return false;
-            setup.run();
-            return resource;
-        } );
-    }
 
-    public synchronized void queue( Supplier<T> resource )
+        if( !super.queue( resource ) ) pending.add( resource );
-    {
+        return true;
-        Resource.cleanup();
-        if( !active ) return;
-
-        int limit = this.limit.getAsInt();
-        if( limit <= 0 || resources.size() < limit )
-        {
-            resources.add( resource.get() );
-        }
-        else
-        {
-            pending.add( resource );
-        }
     }
 
     public synchronized void release( T resource )
     {
-        if( !active ) return;
+        super.release( resource );
 
-        resources.remove( resource );
+        if( !active ) return;
 
         int limit = this.limit.getAsInt();
         if( limit <= 0 || resources.size() < limit )

src/main/java/dan200/computercraft/core/apis/http/request/HttpRequest.java

@@ -12,7 +12,7 @@ import dan200.computercraft.core.apis.IAPIEnvironment;
 import dan200.computercraft.core.apis.http.HTTPRequestException;
 import dan200.computercraft.core.apis.http.NetworkUtils;
 import dan200.computercraft.core.apis.http.Resource;
-import dan200.computercraft.core.apis.http.ResourceQueue;
+import dan200.computercraft.core.apis.http.ResourceGroup;
 import dan200.computercraft.core.tracking.TrackingField;
 import io.netty.bootstrap.Bootstrap;
 import io.netty.buffer.ByteBuf;
@@ -64,7 +64,7 @@ public class HttpRequest extends Resource<HttpRequest>
 
     final AtomicInteger redirects;
 
-    public HttpRequest( ResourceQueue<HttpRequest> limiter, IAPIEnvironment environment, String address, String postText, HttpHeaders headers, boolean binary, boolean followRedirects )
+    public HttpRequest( ResourceGroup<HttpRequest> limiter, IAPIEnvironment environment, String address, String postText, HttpHeaders headers, boolean binary, boolean followRedirects )
     {
         super( limiter );
         this.environment = environment;

src/main/java/dan200/computercraft/core/apis/http/request/HttpResponseHandle.java

@@ -27,7 +27,7 @@ public class HttpResponseHandle implements ILuaObject
     private final String responseStatus;
     private final Map<String, String> responseHeaders;
 
-    public HttpResponseHandle(@Nonnull ILuaObject reader, int responseCode, String responseStatus, @Nonnull Map<String, String> responseHeaders)
+    public HttpResponseHandle( @Nonnull ILuaObject reader, int responseCode, String responseStatus, @Nonnull Map<String, String> responseHeaders )
     {
         this.reader = reader;
         this.responseCode = responseCode;

src/main/java/dan200/computercraft/core/apis/http/websocket/Websocket.java

@@ -12,7 +12,7 @@ import dan200.computercraft.core.apis.IAPIEnvironment;
 import dan200.computercraft.core.apis.http.HTTPRequestException;
 import dan200.computercraft.core.apis.http.NetworkUtils;
 import dan200.computercraft.core.apis.http.Resource;
-import dan200.computercraft.core.apis.http.ResourceQueue;
+import dan200.computercraft.core.apis.http.ResourceGroup;
 import dan200.computercraft.shared.util.IoUtil;
 import io.netty.bootstrap.Bootstrap;
 import io.netty.channel.Channel;
@@ -57,7 +57,7 @@ public class Websocket extends Resource<Websocket>
     private final String address;
     private final HttpHeaders headers;
 
-    public Websocket( ResourceQueue<Websocket> limiter, IAPIEnvironment environment, URI uri, String address, HttpHeaders headers )
+    public Websocket( ResourceGroup<Websocket> limiter, IAPIEnvironment environment, URI uri, String address, HttpHeaders headers )
     {
         super( limiter );
         this.environment = environment;