LaunchServer: Add the LaunchServer to centralise file associations.

Step one of moving DesktopServices::open handling out of process. This
makes it easier to do things like read in associations for which program
opens which files or protocols. This gives users the ability to modify
the associations without having to rebuild :^)

Services/LaunchServer/Launcher.cpp

@@ -0,0 +1,123 @@
+/*
+ * Copyright (c) 2020, Nicholas Hollett <niax@niax.co.uk>, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "Launcher.h"
+#include <LibCore/ConfigFile.h>
+#include <stdio.h>
+#include <sys/stat.h>
+
+namespace LaunchServer {
+
+static Launcher* s_the;
+static bool spawn(String executable, String argument);
+
+Launcher::Launcher()
+{
+    ASSERT(s_the == nullptr);
+    s_the = this;
+}
+
+Launcher& Launcher::the()
+{
+    ASSERT(s_the);
+    return *s_the;
+}
+
+void Launcher::load_config(const Core::ConfigFile& cfg)
+{
+    for (auto key : cfg.keys("FileType")) {
+        m_file_handlers.set(key.to_lowercase(), cfg.read_entry("FileType", key));
+    }
+
+    for (auto key : cfg.keys("Protocol")) {
+        m_protocol_handlers.set(key.to_lowercase(), cfg.read_entry("Protocol", key));
+    }
+}
+
+bool Launcher::open_url(const URL& url)
+{
+    if (url.protocol() == "file")
+        return open_file_url(url);
+
+    return open_with_handlers(m_protocol_handlers, url.protocol(), url.to_string(), "/bin/Browser");
+}
+
+bool spawn(String executable, String argument)
+{
+    pid_t child_pid = fork();
+    if (child_pid < 0) {
+        perror("fork");
+        return false;
+    }
+    if (child_pid == 0) {
+        if (execl(executable.characters(), executable.characters(), argument.characters(), nullptr) < 0) {
+            perror("execl");
+            return false;
+        }
+        ASSERT_NOT_REACHED();
+    }
+    return true;
+}
+
+bool Launcher::open_with_handlers(const HashMap<String, String>& handlers, const String key, const String argument, const String default_program)
+{
+    auto program_path = handlers.get(key);
+    if (program_path.has_value())
+        return spawn(program_path.value(), argument);
+
+    // There wasn't a handler for this, so try the fallback instead
+    program_path = handlers.get("*");
+    if (program_path.has_value())
+        return spawn(program_path.value(), argument);
+
+    // Absolute worst case, try the provided default
+
+    return spawn(default_program, argument);
+}
+
+bool Launcher::open_file_url(const URL& url)
+{
+    struct stat st;
+    if (stat(url.path().characters(), &st) < 0) {
+        perror("stat");
+        return false;
+    }
+
+    // TODO: Make directory opening configurable
+    if (S_ISDIR(st.st_mode))
+        return spawn("/bin/FileManager", url.path());
+
+    if (st.st_mode & (S_IXUSR | S_IXGRP | S_IXOTH))
+        return spawn(url.path(), {});
+
+    auto extension_parts = url.path().to_lowercase().split('.');
+    String extension = {};
+    if (extension_parts.size() > 1)
+        extension = extension_parts.last();
+    return open_with_handlers(m_file_handlers, extension, url.path(), "/bin/TextEdit");
+}
+
+}