Allow cancellation of HTTP requests

`NETWORK::HttpRequest()` now returns a HttpRequestFuture with a
`Cancel()` method.

Docs/Luadoc/Lua.xml

@@ -2051,6 +2051,9 @@
 			<Function name='GetHeld'/>
 			<Function name='GetActive'/>
 		</Class>
+		<Class name='HttpRequestFuture'>
+			<Function name='Cancel'/>
+		</Class>
 		<Class base='ActorFrame' name='TextBanner'>
 			<Function name='Load'/>
 			<Function name='SetFromSong'/>
@@ -2498,6 +2501,7 @@
 			<EnumValue name='&apos;HttpErrorCode_TooManyRedirects&apos;' value='13'/>
 			<EnumValue name='&apos;HttpErrorCode_ChunkReadError&apos;' value='14'/>
 			<EnumValue name='&apos;HttpErrorCode_CannotReadBody&apos;' value='15'/>
+			<EnumValue name='&apos;HttpErrorCode_Cancelled&apos;' value='16'/>
 		</Enum>
 		<Enum name='ImageCacheMode'>
 			<EnumValue name='&apos;ImageCacheMode_Off&apos;' value='0'/>

Docs/Luadoc/LuaDocumentation.xml

@@ -3560,7 +3560,7 @@ end
 	<Function name='IsUrlAllowed' return='bool' arguments='string url'>
 		Returns true if access to <code>url</code> is allowed.
 	</Function>
-	<Function name='HttpRequest' return='void' arguments='table params'>
+	<Function name='HttpRequest' return='HttpRequestFuture' arguments='table params'>
 		Performs an HTTP request.<br />
 		Usage example:
 <pre><code>
@@ -6210,6 +6210,12 @@ local spr = Def.Sprite{
 		Returns true if the note was initiated.
 	</Function>
 </Class>
+<Class name='HttpRequestFuture'>
+	<Function name='Cancel' return='void' arguments=''>
+                Cancels the running HTTP request. Does nothing if the request
+                has already completed.
+	</Function>
+</Class>
 <Class name='TextBanner' grouping='Actor'>
 	<Function name='Load' return='void' arguments='string sMetricsGroup'>
 		Loads the TextBanner from the specified metrics group.

src/NetworkManager.cpp

@@ -10,6 +10,7 @@
 #include <ixwebsocket/IXUrlParser.h>
 
 #include <algorithm>
+#include <memory>
 #include <unordered_map>
 #include <vector>
 
@@ -94,7 +95,7 @@ bool NetworkManager::IsUrlAllowed(const std::string& url)
 	return std::find(allowedHosts.begin(), allowedHosts.end(), host) != allowedHosts.end();
 }
 
-void NetworkManager::HttpRequest(const HttpRequestArgs& args)
+HttpRequestFuturePtr NetworkManager::HttpRequest(const HttpRequestArgs& args)
 {
 	ix::HttpRequestArgsPtr req = this->httpClient.createRequest(args.url, args.method);
 	req->body = args.body;
@@ -114,6 +115,8 @@ void NetworkManager::HttpRequest(const HttpRequestArgs& args)
 	}
 
 	this->httpClient.performRequest(req, args.onResponse);
+
+	return std::make_shared<HttpRequestFuture>(req);
 }
 
 std::string NetworkManager::UrlEncode(const std::string& value)
@@ -126,10 +129,43 @@ std::string NetworkManager::EncodeQueryParameters(const std::unordered_map<std::
 	return this->httpClient.serializeHttpParameters(query);
 }
 
+int HttpRequestFuture::gc(lua_State *L)
+{
+	void *udata = luaL_checkudata(L, 1, "HttpRequestFuture");
+	auto futptr = static_cast<HttpRequestFuturePtr*>(udata);
+	futptr->~shared_ptr();
+	return 0;
+}
+
+int HttpRequestFuture::Cancel(lua_State *L)
+{
+	void *udata = luaL_checkudata(L, 1, "HttpRequestFuture");
+	auto fut = *static_cast<HttpRequestFuturePtr*>(udata);
+	fut->args->cancel = true;
+	return 0;
+}
+
 
 // lua start
 #include "LuaBinding.h"
 
+static void registerHttpRequestMetatable(lua_State *L)
+{
+	const luaL_Reg HttpRequest_meta[] = {
+		{"__gc", HttpRequestFuture::gc},
+		{"Cancel", HttpRequestFuture::Cancel},
+		{NULL, NULL},
+	};
+
+	luaL_newmetatable(L, "HttpRequestFuture");
+	luaL_register(L, NULL, HttpRequest_meta);
+	lua_pushvalue(L, -1);
+	lua_setfield(L, -2, "__index");
+	lua_pop(L, 1);
+}
+
+REGISTER_WITH_LUA_FUNCTION(registerHttpRequestMetatable)
+
 /** @brief Allow Lua to have access to the NetworkManager. */
 class LunaNetworkManager: public Luna<NetworkManager>
 {
@@ -302,7 +338,13 @@ public:
 
 		if (p->IsUrlAllowed(args.url))
 		{
-			p->HttpRequest(args);
+			auto fut = p->HttpRequest(args);
+
+			void *vp = lua_newuserdata(L, sizeof(std::shared_ptr<HttpRequestFuture>));
+			new(vp) std::shared_ptr<::HttpRequestFuture>(fut);
+			luaL_getmetatable(L, "HttpRequestFuture");
+			lua_setmetatable(L, -2);
+			return 1;
 		}
 		else
 		{
@@ -311,10 +353,8 @@ public:
 			{
 				handleUrlForbidden(L, args.url, onResponseRef);
 			}
+			return 0;
 		}
-
-		lua_pushnil(L);
-		return 1;
 	}
 
 	static int UrlEncode(T* p, lua_State *L)
@@ -415,6 +455,7 @@ private:
 			case ix::HttpErrorCode::TooManyRedirects:	LuaHelpers::Push(L, HttpErrorCode_TooManyRedirects); break;
 			case ix::HttpErrorCode::ChunkReadError:		LuaHelpers::Push(L, HttpErrorCode_ChunkReadError); break;
 			case ix::HttpErrorCode::CannotReadBody:		LuaHelpers::Push(L, HttpErrorCode_CannotReadBody); break;
+			case ix::HttpErrorCode::Cancelled:		LuaHelpers::Push(L, HttpErrorCode_Cancelled); break;
 			default:					LuaHelpers::Push(L, HttpErrorCode_UnknownError); break;
 		}
 		lua_setfield(L, -2, "error");

src/NetworkManager.h

@@ -5,6 +5,7 @@
 #include "StdString.h"
 
 #include <functional>
+#include <memory>
 #include <string>
 #include <unordered_map>
 
@@ -36,6 +37,7 @@ enum HttpErrorCode
 	HttpErrorCode_TooManyRedirects,
 	HttpErrorCode_ChunkReadError,
 	HttpErrorCode_CannotReadBody,
+	HttpErrorCode_Cancelled,
 
 	NUM_HttpErrorCode,
 	HttpErrorCode_Invalid,
@@ -56,6 +58,20 @@ struct HttpRequestArgs
 	std::function<void(const ix::HttpResponsePtr& response)> onResponse = [](const ix::HttpResponsePtr& response) {};
 };
 
+class HttpRequestFuture
+{
+public:
+	HttpRequestFuture(ix::HttpRequestArgsPtr& args) : args(args) {};
+
+	static int gc(lua_State *L);
+	static int Cancel(lua_State *L);
+
+private:
+	ix::HttpRequestArgsPtr args;
+};
+
+typedef std::shared_ptr<HttpRequestFuture> HttpRequestFuturePtr;
+
 class NetworkManager
 {
 public:
@@ -63,7 +79,7 @@ public:
 	~NetworkManager();
 
 	bool IsUrlAllowed(const std::string& url);
-	void HttpRequest(const HttpRequestArgs& args);
+	HttpRequestFuturePtr HttpRequest(const HttpRequestArgs& args);
 	std::string UrlEncode(const std::string& value);
 	std::string EncodeQueryParameters(const std::unordered_map<std::string, std::string>& query);