watch config file

src/config/config.cpp

@@ -1,21 +1,30 @@
 #include "config/config.hpp"
 #include "common/exception.hpp"
 
-#include <filesystem>
-#include <optional>
+#include <linux/limits.h>
+#include <sys/inotify.h>
 #include <toml11/find.hpp>
 #include <toml11/parser.hpp>
 #include <toml.hpp>
+#include <unistd.h>
 
 #include <unordered_map>
 #include <string_view>
+#include <filesystem>
 #include <exception>
 #include <stdexcept>
+#include <iostream>
+#include <optional>
 #include <cstddef>
 #include <utility>
+#include <cstring>
+#include <chrono>
+#include <thread>
+#include <cerrno>
 #include <atomic>
 #include <memory>
 #include <string>
+#include <array>
 
 using namespace Config;
 
@@ -25,15 +34,17 @@ namespace {
 }
 
 bool Config::loadAndWatchConfig(const std::string& file) {
+    if (!std::filesystem::exists(file))
+        return false;
+
     // parse config file
-    toml::value toml{};
-    if (std::filesystem::exists(file)) {
-        try {
-            toml = toml::parse(file);
-        } catch (const std::exception& e) {
-            throw LSFG::rethrowable_error("Unable to parse configuration file", e);
-        }
+    std::optional<toml::value> parsed;
+    try {
+        parsed.emplace(toml::parse(file));
+    } catch (const std::exception& e) {
+        throw LSFG::rethrowable_error("Unable to parse configuration file", e);
     }
+    auto& toml = *parsed;
 
     // parse global configuration
     auto& global = globalConf;
@@ -81,9 +92,66 @@ bool Config::loadAndWatchConfig(const std::string& file) {
     }
 
     // prepare config watcher
-    // (TODO)
+    std::thread([file = file, valid = global.valid]() {
+        try {
+            const int fd = inotify_init();
+            if (fd < 0)
+                throw std::runtime_error("Failed to initialize inotify\n"
+                    "- " + std::string(strerror(errno)));
 
-    return false;
+            const int wd = inotify_add_watch(fd, file.c_str(), IN_MODIFY | IN_CLOSE_WRITE);
+            if (wd < 0) {
+                close(fd);
+
+                throw std::runtime_error("Failed to add inotify watch for " + file + "\n"
+                    "- " + std::string(strerror(errno)));
+            }
+
+            // watch for changes
+            std::optional<std::chrono::steady_clock::time_point> discard_until;
+
+            std::array<char, (sizeof(inotify_event) + NAME_MAX + 1) * 20> buffer{};
+            while (true) {
+                const ssize_t len = read(fd, buffer.data(), buffer.size());
+                if (len <= 0 && errno != EINTR) {
+                    inotify_rm_watch(fd, wd);
+                    close(fd);
+
+                    throw std::runtime_error("Error reading inotify event\n"
+                        "- " + std::string(strerror(errno)));
+                }
+
+                size_t i{};
+                while (std::cmp_less(i, len)) {
+                    auto* event = reinterpret_cast<inotify_event*>(&buffer.at(i));
+                    i += sizeof(inotify_event) + event->len;
+                    if (event->len <= 0)
+                        continue;
+
+                    // stall a bit, then mark as invalid
+                    discard_until.emplace(std::chrono::steady_clock::now()
+                        + std::chrono::milliseconds(500));
+                }
+
+                auto now = std::chrono::steady_clock::now();
+                if (discard_until.has_value() && now > *discard_until) {
+                    discard_until.reset();
+
+                    // mark config as invalid
+                    valid->store(false, std::memory_order_release);
+
+                    // and wait until it has been marked as valid again
+                    while (!valid->load(std::memory_order_acquire))
+                        std::this_thread::sleep_for(std::chrono::milliseconds(50));
+                }
+            }
+        } catch (const std::exception& e) {
+            std::cerr << "lsfg-vk: Error in config watcher thread:\n";
+            std::cerr << "- " << e.what() << '\n';
+        }
+    }).detach();
+
+    return true;
 }
 
 Configuration Config::getConfig(std::string_view name) {

src/main.cpp

@@ -67,7 +67,7 @@ namespace {
         try {
             Config::loadAndWatchConfig(file);
         } catch (const std::exception& e) {
-            std::cerr << "lsfg-vk: An error occured while trying to parse the configuration, exiting:" << '\n';
+            std::cerr << "lsfg-vk: An error occured while trying to parse the configuration, exiting:\n";
             std::cerr << "- " << e.what() << '\n';
             exit(0);
         }
@@ -77,7 +77,7 @@ namespace {
         try {
             conf = Config::getConfig(name);
         } catch (const std::exception& e) {
-            std::cerr << "lsfg-vk: The configuration for " << name << " is invalid, exiting." << '\n';
+            std::cerr << "lsfg-vk: The configuration for " << name << " is invalid, exiting.\n";
             std::cerr << e.what() << '\n';
             exit(0);
         }