trmnl_server_cpp/main.cpp

// Start using chrono when C++20 becomes available
// #include <chrono>
#include <filesystem>
#include <iostream>
#include <list>
#include <map>
#include <memory>
#include <random>
#include <set>
#include <string>
#include <utility>
#include <vector>

#include <stdio.h>
#include <stdint.h>
#include <time.h>

// Stop using these when C++20 becomes available
#include <fcntl.h>
#include <sys/stat.h>

#include "httplib.h"
#include "json.hpp"

#include "helpers.h"
#include "TRMNL.h"

using nlohmann::json;

using namespace std;
namespace fs = std::filesystem;

constexpr int API_KEY_LENGHT = 16;
constexpr char DEFAULT_IMAGE_URL[] = "https://trmnl.com/images/setup/setup-logo.bmp";
constexpr char DEFAULT_IMAGE_FNAME[] = "2024-09-20T00:00:00";

string generate_api_key(int len = API_KEY_LENGHT)
{
	string result = "";
	std::random_device rand;
	std::uniform_int_distribution distribution(0, 63);
	int single;
	char symbol;

	if (len < 0)
	{
		len = API_KEY_LENGHT;
	}

	for (int i = 0; i < len; ++i)
	{
		single = distribution(rand);
		if (single <= 9)
		{
			symbol = '0' + single;
		}
		else if ((single >= 10) && (single <= 35))
		{
			symbol = 'A' + single - 10;
		}
		else if ((single >= 36) && (single <= 61))
		{
			symbol = 'a' + single - 36;
		}
		else if (62 == single)
		{
			symbol = '+';
		}
		else if (63 == single)
		{
			symbol = '/';
		}
		// This should never happen
		else
		{
			symbol = '?';
		}

		result += symbol;
	}

	return result;
}

bool reload_container(TRMNLContainer& container, const string& filename)
{
	json j;
	bool ok = read_file_json(j, filename, &cout);
	if (!ok)
	{
		return false;
	}
	container.clear();
	if (j.is_array())
	{
		for (int i = 0; i < j.size(); ++i)
		{
			container.add_device(j[i]);
		}
	}

	return true;
}

string get_timestamp_from_filename(const string& filepath)
{
	char result[128] = "";

	struct stat status;
	stat(filepath.c_str(), &status);

	// Time of last modification
	time_t file_time = status.st_mtim.tv_sec;

	tm* file_tm;
	file_tm = gmtime(&file_time);

	snprintf(result, sizeof(result) - 1, "%04d-%02d-%02dT%02d:%02d:%02d",
		file_tm->tm_year + 1900,
		file_tm->tm_mon + 1,
		file_tm->tm_mday,
		file_tm->tm_hour,
		file_tm->tm_min,
		file_tm->tm_sec
	);

	return result;
}

// Use this when C++20 becomes available
#if 0
string get_timestamp_from_file_time(const fs::file_time_type& ftime)
{
	char result[128] = "";
	time_t file_time = std::chrono::system_clock::to_time_t(std::chrono::file_clock::to_sys(ftime));

	tm* file_tm;
	file_tm = gmtime(&file_time);

	snprintf(result, sizeof(result) - 1, "%04d-%02d-%02dT%02d:%02d:%02d",
		file_tm->tm_year + 1900,
		file_tm->tm_mon + 1,
		file_tm->tm_mday,
		file_tm->tm_hour,
		file_tm->tm_min,
		file_tm->tm_sec
	);

	return result;
}
#endif

// First string is image filename for URL
// Second string is timestamp for TRMNL filename
pair<string, string> find_image_for_friendly(const string& folder_images, const string& friendly_id)
{
	pair<string, string> result = {"", ""};
	set<string> permitted_extensions = { ".bmp", ".png" };

	if (!fs::is_directory(folder_images))
	{
		return result;
	}

	for (const fs::directory_entry& entry : fs::directory_iterator(folder_images))
	{
		if ((entry.path().stem() == friendly_id) &&
			(0 != permitted_extensions.count(entry.path().extension())))
		{
			result.first = entry.path().filename();
			result.second = get_timestamp_from_filename(entry.path());
			// Change to this when C++20 becomes available
			// result.second = get_timestamp_from_file_time(entry.last_write_time());
		}
	}

	return result;
}

int main(int argc, char **argv)
{
	string config_filename = "config.json";
	string devices_filename = "devices.json";
	string folder_images = "images";

	string host = "";
	uint16_t port = 0;
	string base_url = "";

	string cert_file = "";
	string key_file = "";

	shared_ptr<httplib::Server> server = nullptr;

	bool ok;
	json cfg;
	json devs;
	TRMNLContainer container;

	if (argc > 2)
	{
		config_filename = argv[1];
	}

	ok = read_file_json(cfg, config_filename, &cout);
	if (!ok)
	{
		return -1;
	}

	json_extract(cfg, "host", host);
	json_extract(cfg, "port", port);
	json_extract(cfg, "base_url", base_url);

	json_extract(cfg, "devices_filename", devices_filename);
	json_extract(cfg, "folder_images", folder_images);

	// TODO: Extract when SSL is ready
	// json_extract(cfg, "cert_file", cert_file);
	// json_extract(cfg, "key_file", cert_file);

	if (host.empty())
	{
		cout << "host not provided" << endl;
		return -1;
	}

	if (0 == port)
	{
		cout << "port number not provided" << endl;
		return -1;
	}

	if (base_url.empty())
	{
		cout << "base url not provided" << endl;
		return -1;
	}

	if (folder_images.empty())
	{
		cout << "folder for images is empty" << endl;
		return -1;
	}

	if (!fs::is_directory(folder_images))
	{
		cout << "filepath for images is not a folder" << endl;
		return -1;
	}

	if (!cert_file.empty() && !key_file.empty())
	{
		// TODO: Implement SSL Server Properly
	}
	else
	{
		server = make_shared<httplib::Server>();
	}

	ok = reload_container(container, devices_filename);
	if (!ok)
	{
		cout << "Could not read devices file" << endl;
		return -1;
	}

	auto setup_handler = [&container, &devices_filename](const httplib::Request& req, httplib::Response& res)
	{
		json response;

		if (!req.has_header("ID"))
		{
			// Bad Request - No ID header
			res.status = 400;

			response["status"] = 400;
			response["error"] = "No ID header";

			res.set_header("Content-Type", "application/json");
			res.body = response.dump();

			return;
		}

		// Refresh data from file
		// Someone might have put a new device in
		reload_container(container, devices_filename);

		string id = req.get_header_value("ID");
		TRMNL* trmnl = container.get_device_by_id(id);

		if (nullptr == trmnl)
		{
			res.status = 404;

			response["status"] = 404;
			response["api_key"] = nullptr;
			response["friendly_id"] = nullptr;
			response["image_url"] = nullptr;
			response["filename"] = nullptr;

			res.set_header("Content-Type", "application/json");
			res.body = response.dump();
			return;
		}

		bool should_dump = false;

		res.status = 200;
		if (trmnl->friendly_id().empty())
		{
			should_dump = true;
			trmnl->friendly_id(TRMNL::friendly_from_id(id));
		}

		if (trmnl->api_key().empty())
		{
			should_dump = true;
			trmnl->api_key(generate_api_key());
		}

		response["status"] = 200;
		response["api_key"] = trmnl->api_key();
		response["friendly_id"] = trmnl->friendly_id();
		response["image_url"] = DEFAULT_IMAGE_URL;
		response["filename"] = DEFAULT_IMAGE_FNAME;

		res.set_header("Content-Type", "application/json");
		res.body = response.dump();

		if (should_dump)
		{
			write_file_json(container, devices_filename, &cout);
		}
	};

	auto display_handler = [&container, &devices_filename, &folder_images, &base_url]
		(const httplib::Request& req, httplib::Response& res)
	{
		json response;

		if (!req.has_header("ID") || !req.has_header("Access-Token"))
		{
			// Bad Request
			res.status = 400;

			response["status"] = 400;
			response["error"] = "No ID and Access-Token headers set";

			res.body = response.dump();
			res.set_header("Content-Type", "application/json");
			return;
		}

		// Refresh data from file
		// Someone might have put a new device in
		reload_container(container, devices_filename);

		string id = req.get_header_value("ID");
		string api_key = req.get_header_value("Access-Token");
		TRMNL* trmnl = container.get_device_by_id(id);

		if (nullptr == trmnl)
		{
			// Not Found
			res.status = 404;

			response["status"] = 404;
			response["error"] = "Device not found";

			res.set_header("Content-Type", "application/json");
			res.body = response.dump();
			return;
		}

		if (trmnl->api_key() != api_key)
		{
			// Forbidden
			res.status = 403;

			response["status"] = 403;
			response["error"] = "Wrong credentials for this device";

			res.set_header("Content-Type", "application/json");
			res.body = response.dump();
			return;
		}

		string image_fname;
		string image_timestamp;
		tie(image_fname, image_timestamp) = find_image_for_friendly(folder_images, trmnl->friendly_id());

		// The ID and api_key match here
		res.status = 200;

		// From docs: will be 202 if no user_id is attached to device
		response["status"] = 0;

		if (image_fname.empty())
		{
			response["image_url"] = DEFAULT_IMAGE_URL;
			response["filename"] = DEFAULT_IMAGE_FNAME;
		}
		else
		{
			string full_url = base_url;
			full_url += "/images/";
			full_url += image_fname;
			response["image_url"] = full_url;
			response["filename"] = image_timestamp;
		}

		response["refresh_rate"] = to_string(trmnl->refresh_rate());

		// TODO: Handle firmware updating
		response["update_firmware"] = false;
		response["firmware_url"] = nullptr;
		response["reset_firmware"] = false;

		res.set_header("Content-Type", "application/json");
		res.body = response.dump();
	};

	auto log_handler = [](const httplib::Request& req, httplib::Response& res)
	{
		try
		{
			json j = json::parse(req.body);
			cout << j.dump(4) << endl;
		}
		catch (const exception& e)
		{
			cout << req.body << endl;
		}
		res.status = 200;
	};


	server->Get("/api/setup/*", setup_handler);
	server->Get("/api/display/*", display_handler);
	server->Post("/api/log/*", log_handler);

	ok = server->set_mount_point("/images", folder_images);
	if (!ok)
	{
		cout << "Could not mount images folder" << endl;
		return -1;
	}

	cout << "Server listening on " << host << ":" << port << endl;
	server->listen(host, port);

	return 0;
}