Simple webchat for server (#1998)

* expose simple web interface on root domain

* embed index and add --path for choosing static dir

* allow server to multithread

because web browsers send a lot of garbage requests we want the server
to multithread when serving 404s for favicon's etc. To avoid blowing up
llama we just take a mutex when it's invoked.


* let's try this with the xxd tool instead and see if msvc is happier with that

* enable server in Makefiles

* add /completion.js file to make it easy to use the server from js

* slightly nicer css

* rework state management into session, expose historyTemplate to settings

---------

Co-authored-by: Georgi Gerganov <ggerganov@gmail.com>

examples/server/public/completion.js

@@ -0,0 +1,81 @@
+const paramDefaults = {
+  stream: true,
+  n_predict: 500,
+  temperature: 0.2,
+  stop: ["</s>"]
+};
+
+/**
+ * This function completes the input text using a llama dictionary.
+ * @param {object} params - The parameters for the completion request.
+ * @param {object} controller - an instance of AbortController if you need one, or null.
+ * @param {function} callback - The callback function to call when the completion is done.
+ * @returns {string} the completed text as a string. Ideally ignored, and you get at it via the callback.
+ */
+export const llamaComplete = async (params, controller, callback) => {
+  if (!controller) {
+    controller = new AbortController();
+  }
+  const completionParams = { ...paramDefaults, ...params };
+
+  // we use fetch directly here becasue the built in fetchEventSource does not support POST
+  const response = await fetch("/completion", {
+    method: 'POST',
+    body: JSON.stringify(completionParams),
+    headers: {
+      'Connection': 'keep-alive',
+      'Content-Type': 'application/json',
+      'Accept': 'text/event-stream'
+    },
+    signal: controller.signal,
+  });
+
+  const reader = response.body.getReader();
+  const decoder = new TextDecoder();
+
+  let content = "";
+
+  try {
+
+    let cont = true;
+
+    while (cont) {
+      const result = await reader.read();
+      if (result.done) {
+        break;
+      }
+
+      // sse answers in the form multiple lines of: value\n with data always present as a key. in our case we
+      // mainly care about the data: key here, which we expect as json
+      const text = decoder.decode(result.value);
+
+      // parse all sse events and add them to result
+      const regex = /^(\S+):\s(.*)$/gm;
+      for (const match of text.matchAll(regex)) {
+        result[match[1]] = match[2]
+      }
+
+      // since we know this is llama.cpp, let's just decode the json in data
+      result.data = JSON.parse(result.data);
+      content += result.data.content;
+
+      // callack
+      if (callback) {
+        cont = callback(result) != false;
+      }
+
+      // if we got a stop token from server, we will break here
+      if (result.data.stop) {
+        break;
+      }
+    }
+  } catch (e) {
+    console.error("llama error: ", e);
+    throw e;
+  }
+  finally {
+    controller.abort();
+  }
+
+  return content;
+}