Add config options for a global bandwidth limit

This uses Netty's global traffic shaping handlers to limit the rate at
which packets can be sent and received. If the bandwidth limit is hit,
we'll start dropping packets, which will mean remote servers send
traffic to us at a much slower pace.

This isn't perfect, as there is only a global limit, and not a
per-computer one. As a result, its possible for one computer to use
all/most bandwidth, and thus slow down other computers.

This would be something to improve on in the future. However, I've spent
a lot of time reading the netty source code and docs, and the
implementation for that is significantly more complex, and one I'm not
comfortable working on right now.

For the time being, this satisfies the issues in #33 and hopefully
alleviates server owner's concerns about the http API. Remaining
problems can either be solved by moderation (with help of the
//computercraft track` command) or future updates.

Closes #33

src/main/java/dan200/computercraft/shared/Config.java

@@ -12,6 +12,7 @@ import com.google.common.base.CaseFormat;
 import com.google.common.base.Converter;
 import dan200.computercraft.ComputerCraft;
 import dan200.computercraft.api.turtle.event.TurtleAction;
+import dan200.computercraft.core.apis.http.NetworkUtils;
 import dan200.computercraft.core.apis.http.options.Action;
 import dan200.computercraft.core.apis.http.options.AddressRuleConfig;
 import dan200.computercraft.shared.peripheral.monitor.MonitorRenderer;
@@ -56,6 +57,9 @@ public final class Config
     private static final ConfigValue<Integer> httpMaxRequests;
     private static final ConfigValue<Integer> httpMaxWebsockets;
 
+    private static final ConfigValue<Integer> httpDownloadBandwidth;
+    private static final ConfigValue<Integer> httpUploadBandwidth;
+
     private static final ConfigValue<Boolean> commandBlockEnabled;
     private static final ConfigValue<Integer> modemRange;
     private static final ConfigValue<Integer> modemHighAltitudeRange;
@@ -187,6 +191,20 @@ public final class Config
                 .comment( "The number of websockets a computer can have open at one time. Set to 0 for unlimited." )
                 .defineInRange( "max_websockets", ComputerCraft.httpMaxWebsockets, 1, Integer.MAX_VALUE );
 
+            builder
+                .comment( "Limits bandwidth used by computers" )
+                .push( "bandwidth" );
+
+            httpDownloadBandwidth = builder
+                .comment( "The number of bytes which can be downloaded in a second. This is shared across all computers. (bytes/s)" )
+                .defineInRange( "global_download", ComputerCraft.httpDownloadBandwidth, 1, Integer.MAX_VALUE );
+
+            httpUploadBandwidth = builder
+                .comment( "The number of bytes which can be uploaded in a second. This is shared across all computers. (bytes/s)" )
+                .defineInRange( "global_upload", ComputerCraft.httpUploadBandwidth, 1, Integer.MAX_VALUE );
+
+            builder.pop();
+
             builder.pop();
         }
 
@@ -329,6 +347,8 @@ public final class Config
 
         ComputerCraft.httpMaxRequests = httpMaxRequests.get();
         ComputerCraft.httpMaxWebsockets = httpMaxWebsockets.get();
+        ComputerCraft.httpDownloadBandwidth = httpDownloadBandwidth.get();
+        NetworkUtils.reloadConfig();
 
         // Peripheral
         ComputerCraft.enableCommandBlock = commandBlockEnabled.get();