Make MTU configurable and implement TCP MSS

debug.html

@@ -147,13 +147,35 @@ <h4>Debugger</h4>
                 </td>
             </tr>
 
+            <tr>
+                <td colspan="2"><hr></td>
+            </tr>
+
             <tr>
                 <td><label for="relay_url">Networking proxy (leave blank to disable)</label></td>
                 <td>
                     <input id="relay_url" type="text" value="wss://relay.widgetry.org/">
                 </td>
             </tr>
 
+            <tr>
+                <td><label for="net_device_type">Network Device Type</label></td>
+                <td>
+                    <select id="net_device_type">
+                        <option value="ne2k">ne2k</option>
+                        <option value="virtio">virtio</option>
+                    </select>
+                 </td>
+            </tr>
+
+            <tr>
+                <td><label for="mtu">Network MTU (only used for virtio)</label></td>
+                <td>
+                    <input id="mtu" type="number" value="1500" min="68" max="65535" step="1"> B<br>
+                 </td>
+            </tr>
+
+
             <tr>
                 <td colspan="2"><hr></td>
             </tr>

docs/networking.md

@@ -62,6 +62,7 @@ Backends `fetch` and `wisp` support a couple of special settings in `config.net_
 | **dns_method** | str  | DNS method to use, either `static` or `doh`. `static`: use built-in DNS server, `doh`: use [DNS-over-HTTPS](https://en.wikipedia.org/wiki/DNS_over_HTTPS) (DoH). Defaults to `static` for `fetch` and to `doh` for `wisp` backend. |
 | **doh_server** | str  | Host name or IP address (and optional port number) of the DoH server if `dns_method` is `doh`. The value is expanded to the URL `https://DOH_SERVER/dns-query`. Default: `cloudflare-dns.com`. |
 | **cors_proxy** | str  | CORS proxy server URL, do not use a proxy if undefined. Default: undefined (`fetch` backend only). |
+| **mtu**        | int  | The MTU used for the virtual network. Increasing it can improve performance. This only works if the NIC type is `virtio`. Default: `1500` |
 
 #### Example `net_device` settings
 

index.html

@@ -247,6 +247,10 @@ <h4 id="setup">Setup</h4>
                 </td>
             </tr>
 
+            <tr>
+                <td colspan="2"><hr></td>
+            </tr>
+
             <tr>
                 <td><label for="relay_url">Networking proxy</label><br>
                     Presets: <a id="network_none">none</a>, <a id="network_inbrowser">inbrowser</a>, <a id="network_relay">public relay</a>, <a id="network_wisp">wisp</a>, <a id="network_fetch">fetch</a></td>
@@ -255,6 +259,23 @@ <h4 id="setup">Setup</h4>
                 </td>
             </tr>
 
+            <tr>
+                <td><label for="net_device_type">Network Device Type</label></td>
+                <td>
+                    <select id="net_device_type">
+                        <option value="ne2k">ne2k</option>
+                        <option value="virtio">virtio</option>
+                    </select>
+                 </td>
+            </tr>
+
+            <tr>
+                <td><label for="mtu">Network MTU (only used for virtio)</label></td>
+                <td>
+                    <input id="mtu" type="number" value="1500" min="68" max="65535" step="1"> B<br>
+                 </td>
+            </tr>
+
             <tr>
                 <td colspan="2"><hr></td>
             </tr>

src/browser/fake_network.js

@@ -45,18 +45,14 @@ const TCP_DYNAMIC_PORT_RANGE = TCP_DYNAMIC_PORT_END - TCP_DYNAMIC_PORT_START;
 
 const ETH_HEADER_SIZE     = 14;
 const ETH_PAYLOAD_OFFSET  = ETH_HEADER_SIZE;
-const ETH_PAYLOAD_SIZE    = 1500;
+const MTU_DEFAULT         = 1500;
 const ETH_TRAILER_SIZE    = 4;
-const ETH_FRAME_SIZE      = ETH_HEADER_SIZE + ETH_PAYLOAD_SIZE + ETH_TRAILER_SIZE;
 const IPV4_HEADER_SIZE    = 20;
 const IPV4_PAYLOAD_OFFSET = ETH_PAYLOAD_OFFSET + IPV4_HEADER_SIZE;
-const IPV4_PAYLOAD_SIZE   = ETH_PAYLOAD_SIZE - IPV4_HEADER_SIZE;
 const UDP_HEADER_SIZE     = 8;
 const UDP_PAYLOAD_OFFSET  = IPV4_PAYLOAD_OFFSET + UDP_HEADER_SIZE;
-const UDP_PAYLOAD_SIZE    = IPV4_PAYLOAD_SIZE - UDP_HEADER_SIZE;
 const TCP_HEADER_SIZE     = 20;
 const TCP_PAYLOAD_OFFSET  = IPV4_PAYLOAD_OFFSET + TCP_HEADER_SIZE;
-const TCP_PAYLOAD_SIZE    = IPV4_PAYLOAD_SIZE - TCP_HEADER_SIZE;
 const ICMP_HEADER_SIZE    = 4;
 
 const DEFAULT_DOH_SERVER = "cloudflare-dns.com";
@@ -161,15 +157,19 @@ class GrowableRingbuffer
     }
 }
 
-export function create_eth_encoder_buf()
+export function create_eth_encoder_buf(mtu = MTU_DEFAULT)
 {
+    const ETH_FRAME_SIZE = ETH_HEADER_SIZE + mtu + ETH_TRAILER_SIZE;
+    const IPV4_PAYLOAD_SIZE = mtu - IPV4_HEADER_SIZE;
+    const UDP_PAYLOAD_SIZE = IPV4_PAYLOAD_SIZE - UDP_HEADER_SIZE;
+
     const eth_frame = new Uint8Array(ETH_FRAME_SIZE);
     const buffer = eth_frame.buffer;
     const offset = eth_frame.byteOffset;
     return {
         eth_frame: eth_frame,
         eth_frame_view: new DataView(buffer),
-        eth_payload_view: new DataView(buffer, offset + ETH_PAYLOAD_OFFSET, ETH_PAYLOAD_SIZE),
+        eth_payload_view: new DataView(buffer, offset + ETH_PAYLOAD_OFFSET, mtu),
         ipv4_payload_view: new DataView(buffer, offset + IPV4_PAYLOAD_OFFSET, IPV4_PAYLOAD_SIZE),
         udp_payload_view: new DataView(buffer, offset + UDP_PAYLOAD_OFFSET, UDP_PAYLOAD_SIZE),
         text_encoder: new TextEncoder()
@@ -190,6 +190,17 @@ function view_set_array(offset, data, view, out)
     return data.length;
 }
 
+/**
+ * Write zeros into the view starting at offset
+ * @param {number} offset
+ * @param {number} length
+ * @param {DataView} view
+ */
+function view_set_zeros(offset, length, view, out)
+{
+    out.eth_frame.fill(0, view.byteOffset + offset, view.byteOffset + offset + length);
+}
+
 /**
  * UTF8-encode given string into view starting at offset, return number of bytes written.
  *
@@ -949,19 +960,31 @@ function write_tcp(spec, out) {
     if(tcp.ece) flags |= 0x40;
     if(tcp.cwr) flags |= 0x80;
 
-    const doff = TCP_HEADER_SIZE >> 2;  // header length in 32-bit words
+    let doff = TCP_HEADER_SIZE;
+    if(tcp.options) {
+        if(tcp.options.mss) {
+            view.setUint8(doff, 0x02); //mss option type
+            view.setUint8(doff + 1, 0x04); //option length
+            view.setUint16(doff + 2, tcp.options.mss);
+            doff += 4;
+        }
+    }
+
+    let total_length = Math.ceil(doff / 4) * 4; // needs to a multiple of 4 bytes
+    if(tcp.options && total_length - doff > 0) {
+        view_set_zeros(doff, total_length - doff, view, out); //write zeros into remaining space for options
+    }
 
     view.setUint16(0, tcp.sport);
     view.setUint16(2, tcp.dport);
     view.setUint32(4, tcp.seq);
     view.setUint32(8, tcp.ackn);
-    view.setUint8(12, doff << 4);
+    view.setUint8(12, (total_length >> 2) << 4); // header length in 32-bit words
     view.setUint8(13, flags);
     view.setUint16(14, tcp.winsize);
     view.setUint16(16, 0); // checksum initially zero before calculation
     view.setUint16(18, tcp.urgent || 0);
 
-    let total_length = TCP_HEADER_SIZE;
     if(spec.tcp_data) {
         total_length += view_set_array(TCP_HEADER_SIZE, spec.tcp_data, view, out);
     }
@@ -991,7 +1014,7 @@ export function fake_tcp_connect(dport, adapter)
         throw new Error("pool of dynamic TCP port numbers exhausted, connection aborted");
     }
 
-    let conn = new TCPConnection();
+    let conn = new TCPConnection(adapter);
 
     conn.tuple = tuple;
     conn.hsrc = adapter.router_mac;
@@ -1000,7 +1023,6 @@ export function fake_tcp_connect(dport, adapter)
     conn.hdest = adapter.vm_mac;
     conn.dport = dport;
     conn.pdest = adapter.vm_ip;
-    conn.net = adapter;
     adapter.tcp_conn[tuple] = conn;
     conn.connect();
     return conn;
@@ -1017,10 +1039,14 @@ export function fake_tcp_probe(dport, adapter) {
 /**
  * @constructor
  */
-export function TCPConnection()
+export function TCPConnection(adapter)
 {
+    this.mtu = (adapter.mtu || MTU_DEFAULT);
+    const IPV4_PAYLOAD_SIZE = this.mtu - IPV4_HEADER_SIZE;
+    const TCP_PAYLOAD_SIZE = IPV4_PAYLOAD_SIZE - TCP_HEADER_SIZE;
+
     this.state = TCP_STATE_CLOSED;
-    this.net = null; // The adapter is stored here
+    this.net = adapter; // The adapter is stored here
     this.send_buffer = new GrowableRingbuffer(2048, 0);
     this.send_chunk_buf = new Uint8Array(TCP_PAYLOAD_SIZE);
     this.in_active_close = false;
@@ -1119,7 +1145,10 @@ TCPConnection.prototype.accept = function(packet) {
         ackn: this.ack,
         winsize: packet.tcp.winsize,
         syn: true,
-        ack: true
+        ack: true,
+        options: {
+            mss: (this.mtu - TCP_HEADER_SIZE - IPV4_HEADER_SIZE)
+        }
     };
     // dbg_log(`TCP[${this.tuple}]: accept(): sending SYN+ACK in state "${this.state}", next "${TCP_STATE_ESTABLISHED}"`, LOG_FETCH);
     this.state = TCP_STATE_ESTABLISHED;

src/browser/fetch_network.js

@@ -33,7 +33,8 @@ export function FetchNetworkAdapter(bus, config)
     this.dns_method = config.dns_method || "static";
     this.doh_server = config.doh_server;
     this.tcp_conn = {};
-    this.eth_encoder_buf = create_eth_encoder_buf();
+    this.mtu = config.mtu;
+    this.eth_encoder_buf = create_eth_encoder_buf(this.mtu);
     this.fetch = (...args) => fetch(...args);
 
     // Ex: 'https://corsproxy.io/?'
@@ -55,9 +56,8 @@ FetchNetworkAdapter.prototype.destroy = function()
 FetchNetworkAdapter.prototype.on_tcp_connection = function(packet, tuple)
 {
     if(packet.tcp.dport === 80) {
-        let conn = new TCPConnection();
+        let conn = new TCPConnection(this);
         conn.state = TCP_STATE_SYN_RECEIVED;
-        conn.net = this;
         conn.on("data", on_data_http);
         conn.tuple = tuple;
         conn.accept(packet);

src/browser/main.js

@@ -12,6 +12,8 @@ const DEFAULT_NETWORKING_PROXIES = ["wss://relay.widgetry.org/", "ws://localhost
 const DEFAULT_MEMORY_SIZE = 128;
 const DEFAULT_VGA_MEMORY_SIZE = 8;
 const DEFAULT_BOOT_ORDER = 0;
+const DEFAULT_MTU = 1500;
+const DEFAULT_NIC_TYPE = "ne2k";
 
 const MAX_ARRAY_BUFFER_SIZE_MB = 2000;
 
@@ -1689,6 +1691,8 @@ function onload()
     if(query_args.has("mute")) $("disable_audio").checked = bool_arg(query_args.get("mute"));
     if(query_args.has("acpi")) $("acpi").checked = bool_arg(query_args.get("acpi"));
     if(query_args.has("boot_order")) $("boot_order").value = query_args.get("boot_order");
+    if(query_args.has("net_device_type")) $("net_device_type").value = query_args.get("net_device_type");
+    if(query_args.has("mtu")) $("mtu").value = query_args.get("mtu");
 
     for(const dev of ["fda", "fdb"])
     {
@@ -2091,6 +2095,7 @@ function start_emulation(profile, query_args)
             settings.acpi = query_args.has("acpi") ? bool_arg(query_args.get("acpi")) : settings.acpi;
             settings.use_bochs_bios = query_args.get("bios") === "bochs";
             settings.net_device_type = query_args.get("net_device_type") || settings.net_device_type;
+            settings.mtu = parseInt(query_args.get("mtu"), 10) || undefined;
         }
 
         settings.relay_url = query_args.get("relay_url");
@@ -2239,6 +2244,21 @@ function start_emulation(profile, query_args)
             settings.bios = { url: BIOSPATH + "bochs-bios.bin" };
             settings.vga_bios = { url: BIOSPATH + "bochs-vgabios.bin" };
         }
+
+        const nic_type = $("net_device_type").value || DEFAULT_NIC_TYPE;
+        if(!settings.net_device_type || nic_type !== DEFAULT_NIC_TYPE)
+        {
+            settings.net_device_type = nic_type;
+        }
+        if(settings.net_device_type !== DEFAULT_NIC_TYPE) new_query_args.set("net_device_type", settings.net_device_type);
+
+        const mtu = parseInt($("mtu").value, 10) || DEFAULT_MTU;
+        if(!settings.mtu || mtu !== DEFAULT_MTU)
+        {
+            settings.mtu = mtu;
+        }
+        if(settings.mtu !== DEFAULT_MTU) new_query_args.set("mtu", settings.mtu.toString());
+
     }
 
     if(!query_args)
@@ -2253,9 +2273,10 @@ function start_emulation(profile, query_args)
             use_graphical_text: false,
         },
         net_device: {
-            type: settings.net_device_type || "ne2k",
+            type: settings.net_device_type || DEFAULT_NIC_TYPE,
             relay_url: settings.relay_url,
-            cors_proxy: settings.cors_proxy
+            cors_proxy: settings.cors_proxy,
+            mtu: settings.mtu
         },
         autostart: true,
 

src/browser/wisp_network.js

@@ -36,7 +36,8 @@ export function WispNetworkAdapter(wisp_url, bus, config)
     this.dns_method = config.dns_method || "doh";
     this.doh_server = config.doh_server;
     this.tcp_conn = {};
-    this.eth_encoder_buf = create_eth_encoder_buf();
+    this.mtu = config.mtu;
+    this.eth_encoder_buf = create_eth_encoder_buf(this.mtu);
 
     this.bus.register("net" + this.id + "-mac", function(mac) {
         this.vm_mac = new Uint8Array(mac.split(":").map(function(x) { return parseInt(x, 16); }));
@@ -93,10 +94,12 @@ WispNetworkAdapter.prototype.process_incoming_wisp_frame = function(frame) {
             }
 
             if(this.connections[stream_id].congested) {
-                for(const packet of this.congested_buffer) {
+                const buffer = this.congested_buffer.slice(0);
+                this.congested_buffer.length = 0;
+                this.connections[stream_id].congested = false;
+                for(const packet of buffer) {
                     this.send_packet(packet.data, packet.type, stream_id);
                 }
-                this.connections[stream_id].congested = false;
             }
             break;
         case 4: // CLOSE
@@ -190,9 +193,8 @@ WispNetworkAdapter.prototype.destroy = function()
  */
 WispNetworkAdapter.prototype.on_tcp_connection = function(packet, tuple)
 {
-    let conn = new TCPConnection();
+    let conn = new TCPConnection(this);
     conn.state = TCP_STATE_SYN_RECEIVED;
-    conn.net = this;
     conn.tuple = tuple;
     conn.stream_id = this.last_stream++;
     this.tcp_conn[tuple] = conn;

src/cpu.js

@@ -1210,7 +1210,7 @@ CPU.prototype.init = function(settings, device_bus)
         }
         else if(settings.net_device.type === "virtio")
         {
-            this.devices.virtio_net = new VirtioNet(this, device_bus, settings.preserve_mac_from_state_image);
+            this.devices.virtio_net = new VirtioNet(this, device_bus, settings.preserve_mac_from_state_image, settings.net_device.mtu);
         }
 
         if(settings.fs9p)

src/virtio_net.js

@@ -9,6 +9,8 @@ import * as marshall from "../lib/marshall.js";
 import { CPU } from "./cpu.js";
 import { BusConnector } from "./bus.js";
 
+const MTU_DEFAULT = 1500;
+
 const VIRTIO_NET_F_MAC = 5;
 const VIRTIO_NET_F_CTRL_VQ = 17;
 const VIRTIO_NET_F_STATUS = 16;
@@ -24,8 +26,9 @@ const VIRTIO_NET_CTRL_MAC_ADDR_SET = 1;
  * @param {CPU} cpu
  * @param {BusConnector} bus
  * @param {Boolean} preserve_mac_from_state_image
+ * @param {number} mtu
  */
-export function VirtioNet(cpu, bus, preserve_mac_from_state_image)
+export function VirtioNet(cpu, bus, preserve_mac_from_state_image, mtu = MTU_DEFAULT)
 {
     /** @const @type {BusConnector} */
     this.bus = bus;
@@ -177,7 +180,7 @@ export function VirtioNet(cpu, bus, preserve_mac_from_state_image)
                 {
                     bytes: 2,
                     name: "mtu",
-                    read: () => 1500,
+                    read: () => mtu,
                     write: data => {},
                 }
            ])

v86.d.ts

@@ -333,6 +333,7 @@ export interface V86Options {
         dns_method?: "static" | "doh";
         doh_server?: string;
         cors_proxy?: string;
+        mtu?: number;
     };
 }