/*
 *  Phusion Passenger - http://www.modrails.com/
 *  Copyright (c) 2010 Phusion
 *
 *  "Phusion Passenger" is a trademark of Hongli Lai & Ninh Bui.
 *
 *  Permission is hereby granted, free of charge, to any person obtaining a copy
 *  of this software and associated documentation files (the "Software"), to deal
 *  in the Software without restriction, including without limitation the rights
 *  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 *  copies of the Software, and to permit persons to whom the Software is
 *  furnished to do so, subject to the following conditions:
 *
 *  The above copyright notice and this permission notice shall be included in
 *  all copies or substantial portions of the Software.
 *
 *  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 *  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 *  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 *  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 *  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 *  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 *  THE SOFTWARE.
 */
#ifndef _PASSENGER_AGENTS_STARTER_HPP_
#define _PASSENGER_AGENTS_STARTER_HPP_

#include <boost/function.hpp>
#include <oxt/system_calls.hpp>
#include <oxt/backtrace.hpp>
#include <string>
#include <vector>
#include <set>

#include <sys/types.h>
#include <unistd.h>
#include <signal.h>

#include "Constants.h"
#include "FileDescriptor.h"
#include "MessageChannel.h"
#include "MessageClient.h"
#include "ServerInstanceDir.h"
#include "Exceptions.h"
#include "ResourceLocator.h"
#include "Utils.h"
#include "Utils/IOUtils.h"
#include "Utils/Base64.h"
#include "Utils/Timer.h"
#include "Utils/ScopeGuard.h"
#include "Utils/VariantMap.h"

namespace Passenger {

using namespace std;
using namespace boost;
using namespace oxt;

/**
 * Utility class for starting various Phusion Passenger agents through the watchdog.
 */
class AgentsStarter {
public:
	enum Type {
		APACHE,
		NGINX
	};
	
private:
	/** The watchdog's PID. Equals 0 if the watchdog hasn't been started yet
	 * or if detach() is called. */
	pid_t pid;
	
	Type type;
	
	/** The watchdog's feedback file descriptor. Only valid if pid != 0. */
	FileDescriptor feedbackFd;
	
	/**
	 * The helper agent's request socket filename. This socket only exists
	 * for the Nginx helper agent, and it's for serving SCGI requests.
	 *
	 * Only valid if pid != 0.
	 */
	string requestSocketFilename;
	
	/**
	 * A password for connecting to the request socket. Only valid if pid != 0.
	 */
	string requestSocketPassword;
	
	/**
	 * The helper agent's message server socket filename, on which e.g. the
	 * application pool server is listening. Only valid if pid != 0.
	 *
	 * The application pool server is available through the account "_web_server".
	 */
	string messageSocketFilename;
	
	/**
	 * A password for the message server socket. The associated username is "_web_server".
	 *
	 * Only valid if pid != 0.
	 */
	string messageSocketPassword;
	
	bool loggingAgentRunningLocally;
	string loggingSocketAddress;
	string loggingSocketPassword;
	
	/**
	 * The server instance dir of the agents. Only valid if pid != 0.
	 */
	ServerInstanceDirPtr serverInstanceDir;
	
	/**
	 * The generation dir of the agents. Only valid if pid != 0.
	 */
	ServerInstanceDir::GenerationPtr generation;
	
	/**
	 * Safely dup2() the given file descriptor to 3 (FEEDBACK_FD).
	 */
	void installFeedbackFd(const FileDescriptor &fd) {
		if (fd != FEEDBACK_FD && syscalls::dup2(fd, FEEDBACK_FD) == -1) {
			int e = errno;
			try {
				MessageChannel channel(fd);
				channel.write("system error",
					"dup2() failed",
					toString(e).c_str(),
					NULL);
				_exit(1);
			} catch (...) {
				fprintf(stderr, "Passenger AgentsStarter: dup2() failed: %s (%d)\n",
					strerror(e), e);
				fflush(stderr);
				_exit(1);
			}
		}
	}
	
	/**
	 * Call this if the watchdog seems to have crashed. This function will try
	 * to determine whether the watchdog is still running, whether it crashed
	 * with a signal, etc. If it has detected that the watchdog is no longer running
	 * then it will set <em>pid</em> to -1.
	 */
	void inspectWatchdogCrashReason(pid_t &pid) {
		this_thread::disable_interruption di;
		this_thread::disable_syscall_interruption dsi;
		int ret, status;
		
		/* Upon noticing that something went wrong, the watchdog
		 * or its subprocesses might still be writing out an error
		 * report, so we wait a while before killing the watchdog.
		 */
		ret = timedWaitPid(pid, &status, 5000);
		if (ret == 0) {
			/* Looks like the watchdog didn't crash and is still running. */
			throw RuntimeException(
				"Unable to start the Phusion Passenger watchdog: "
				"it froze during startup and reported an unknown error");
		} else if (ret != -1 && WIFSIGNALED(status)) {
			/* Looks like a crash which caused a signal. */
			pid = -1;
			throw RuntimeException(
				"Unable to start the Phusion Passenger watchdog: "
				"it seems to have been killed with signal " +
				getSignalName(WTERMSIG(status)) + " during startup");
		} else if (ret == -1) {
			/* Looks like it exited for a different reason and has no exit code. */
			pid = -1;
			throw RuntimeException(
				"Unable to start the Phusion Passenger watchdog: "
				"it seems to have crashed during startup for an unknown reason");
		} else {
			/* Looks like it exited for a different reason, but has an exit code. */
			pid = -1;
			throw RuntimeException(
				"Unable to start the Phusion Passenger watchdog: "
				"it seems to have crashed during startup for an unknown reason, "
				"with exit code " + toString(WEXITSTATUS(status)));
		}
	}
	
	static void killProcessGroupAndWait(pid_t *pid, unsigned long long timeout = 0) {
		if (*pid != -1 && (timeout == 0 || timedWaitPid(*pid, NULL, timeout) <= 0)) {
			this_thread::disable_syscall_interruption dsi;
			syscalls::killpg(*pid, SIGKILL);
			syscalls::waitpid(*pid, NULL, 0);
			*pid = -1;
		}
	}
	
	/**
	 * Behaves like <tt>waitpid(pid, status, WNOHANG)</tt>, but waits at most
	 * <em>timeout</em> miliseconds for the process to exit.
	 */
	static int timedWaitPid(pid_t pid, int *status, unsigned long long timeout) {
		Timer timer;
		int ret;
		
		do {
			ret = syscalls::waitpid(pid, status, WNOHANG);
			if (ret > 0 || ret == -1) {
				return ret;
			} else {
				syscalls::usleep(10000);
			}
		} while (timer.elapsed() < timeout);
		return 0; // timed out
	}
	
	/**
	 * Gracefully shutdown an agent process by sending an exit command to its socket.
	 * Returns whether the agent has successfully processed the exit command.
	 * Any exceptions are caught and will cause false to be returned.
	 */
	bool gracefullyShutdownAgent(const string &socketFilename, const string &username,
	                             const string &password
	) {
		try {
			MessageClient client;
			vector<string> args;
			
			client.connect("unix:" + socketFilename, username, password);
			client.write("exit", NULL);
			return client.read(args) && args[0] == "Passed security" &&
			       client.read(args) && args[0] == "exit command received";
		} catch (const SystemException &) {
		} catch (const IOException &) {
		} catch (const SecurityException &) {
		}
		return false;
	}
	
	string serializePrestartURLs(const set<string> &prestartURLs) const {
		set<string>::const_iterator it;
		string result;
		
		for (it = prestartURLs.begin(); it != prestartURLs.end(); it++) {
			result.append(*it);
			result.append(1, '\0');
		}
		return Base64::encode(result);
	}
	
public:
	/**
	 * Construct a AgentsStarter object. The watchdog and the agents
	 * aren't started yet until you call start().
	 *
	 * @param type Whether one wants to start the Apache or the Nginx helper agent.
	 */
	AgentsStarter(Type type) {
		pid = 0;
		loggingAgentRunningLocally = false;
		this->type = type;
	}
	
	~AgentsStarter() {
		if (pid != 0) {
			this_thread::disable_syscall_interruption dsi;
			bool cleanShutdown = gracefullyShutdownAgent(messageSocketFilename,
				"_web_server", messageSocketPassword);
			if (loggingAgentRunningLocally) {
				string filename = parseUnixSocketAddress(loggingSocketAddress);
				cleanShutdown = cleanShutdown &&
					gracefullyShutdownAgent(filename,
						"logging", loggingSocketPassword);
			}
			
			/* Send a message down the feedback fd to tell the watchdog
			 * Whether this is a clean shutdown. Closing the fd without
			 * sending anything also indicates an unclean shutdown,
			 * but we send a byte anyway in case there are other processes
			 * who have the fd open.
			 */
			if (cleanShutdown) {
				syscalls::write(feedbackFd, "c", 1);
			} else {
				syscalls::write(feedbackFd, "u", 1);
			}
			
			/* If we failed to send an exit command to one of the agents then we have
			 * to forcefully kill all agents now because otherwise one of them might
			 * never exit. We do this by closing the feedback fd without sending a
			 * random byte, to indicate that this is an abnormal shutdown. The watchdog
			 * will then kill all agents.
			 */
			
			feedbackFd.close();
			syscalls::waitpid(pid, NULL, 0);
		}
	}
	
	/**
	 * Returns the type as was passed to the constructor.
	 */
	Type getType() const {
		return type;
	}
	
	/**
	 * Returns the watchdog's PID. Equals 0 if the watchdog hasn't been started yet
	 * or if detach() is called.
	 */
	pid_t getPid() const {
		return pid;
	}
	
	/**
	 * The helper agent's request socket filename, on which it's listening
	 * for SCGI requests.
	 *
	 * @pre getPid() != 0 && getType() == NGINX
	 */
	string getRequestSocketFilename() const {
		return requestSocketFilename;
	}
	
	/**
	 * Returns the password for connecting to the request socket.
	 *
	 * @pre getPid() != 0 && getType() == NGINX
	 */
	string getRequestSocketPassword() const {
		return requestSocketPassword;
	}
	
	string getMessageSocketFilename() const {
		return messageSocketFilename;
	}
	
	string getMessageSocketPassword() const {
		return messageSocketPassword;
	}
	
	string getLoggingSocketAddress() const {
		return loggingSocketAddress;
	}
	
	string getLoggingSocketPassword() const {
		return loggingSocketPassword;
	}
	
	/**
	 * Returns the server instance dir of the agents.
	 *
	 * @pre getPid() != 0
	 */
	ServerInstanceDirPtr getServerInstanceDir() const {
		return serverInstanceDir;
	}
	
	/**
	 * Returns the generation dir of the agents.
	 *
	 * @pre getPid() != 0
	 */
	ServerInstanceDir::GenerationPtr getGeneration() const {
		return generation;
	}
	
	/**
	 * Start the agents through the watchdog, with the given parameters.
	 *
	 * @throws SystemException Something went wrong.
	 * @throws IOException Something went wrong while communicating with one
	 *                     of the agents during its initialization phase.
	 * @throws RuntimeException Something went wrong.
	 */
	void start(int logLevel, const string &debugLogFile,
	           pid_t webServerPid, const string &tempDir,
	           bool userSwitching, const string &defaultUser, const string &defaultGroup,
	           uid_t webServerWorkerUid, gid_t webServerWorkerGid,
	           const string &passengerRoot, const string &rubyCommand,
	           unsigned int maxPoolSize, unsigned int maxInstancesPerApp,
	           unsigned int poolIdleTime,
	           const string &analyticsServer,
	           const string &analyticsLogDir, const string &analyticsLogUser,
	           const string &analyticsLogGroup, const string &analyticsLogPermissions,
	           const string &unionStationGatewayAddress,
	           unsigned short unionStationGatewayPort,
	           const string &unionStationGatewayCert,
	           const set<string> &prestartURLs,
	           const function<void ()> &afterFork = function<void ()>())
	{
		TRACE_POINT();
		this_thread::disable_interruption di;
		this_thread::disable_syscall_interruption dsi;
		ResourceLocator locator(passengerRoot);
		
		string realUnionStationGatewayCert;
		if (unionStationGatewayCert.empty()) {
			realUnionStationGatewayCert = locator.getResourcesDir() + "/union_station_gateway.crt";
		} else if (unionStationGatewayCert != "-") {
			realUnionStationGatewayCert = unionStationGatewayCert;
		}
		string watchdogFilename = locator.getAgentsDir() + "/PassengerWatchdog";
		
		VariantMap watchdogArgs;
		watchdogArgs
			.set    ("web_server_type", type == APACHE ? "apache" : "nginx")
			.setInt ("log_level",       logLevel)
			.set    ("debug_log_file",  debugLogFile)
			.setPid ("web_server_pid",  webServerPid)
			.set    ("temp_dir",        tempDir.empty() ? getSystemTempDir() : tempDir)
			.setBool("user_switching",  userSwitching)
			.set    ("default_user",    defaultUser)
			.set    ("default_group",   defaultGroup)
			.setUid ("web_server_worker_uid", webServerWorkerUid)
			.setGid ("web_server_worker_gid", webServerWorkerGid)
			.set    ("passenger_root",  passengerRoot)
			.set    ("ruby",            rubyCommand)
			.setInt ("max_pool_size",   maxPoolSize)
			.setInt ("max_instances_per_app",     maxInstancesPerApp)
			.setInt ("pool_idle_time",            poolIdleTime)
			.set    ("analytics_server",          analyticsServer)
			.set    ("analytics_log_dir",         analyticsLogDir)
			.set    ("analytics_log_user",        analyticsLogUser)
			.set    ("analytics_log_group",       analyticsLogGroup)
			.set    ("analytics_log_permissions", analyticsLogPermissions)
			.set    ("union_station_gateway_address",  unionStationGatewayAddress)
			.setInt ("union_station_gateway_port", unionStationGatewayPort)
			.set    ("union_station_gateway_cert", realUnionStationGatewayCert)
			.set    ("prestart_urls",   serializePrestartURLs(prestartURLs));
		
		SocketPair fds;
		int e;
		pid_t pid;
		
		fds = createUnixSocketPair();
		pid = syscalls::fork();
		if (pid == 0) {
			// Child
			
			/* Become the session leader so that Apache can't kill the
			 * watchdog with killpg() during shutdown, so that a
			 * Ctrl-C only affects the web server, and so that
			 * we can kill all of our subprocesses in a single killpg().
			 */
			setsid();
			
			// Make sure the feedback fd is 3 and close all file descriptors
			// except stdin, stdout, stderr and 3.
			syscalls::close(fds[0]);
			installFeedbackFd(fds[1]);
			closeAllFileDescriptors(FEEDBACK_FD);
			
			/* We don't know how the web server or the environment affect
			 * signal handlers and the signal mask, so reset this stuff
			 * just in case.
			 */
			resetSignalHandlersAndMask();
			
			if (afterFork) {
				afterFork();
			}
			
			execl(watchdogFilename.c_str(), "PassengerWatchdog", (char *) 0);
			e = errno;
			try {
				MessageChannel channel(FEEDBACK_FD);
				channel.write("exec error", toString(e).c_str(), NULL);
				_exit(1);
			} catch (...) {
				fprintf(stderr, "Passenger AgentsStarter: could not execute %s: %s (%d)\n",
					watchdogFilename.c_str(), strerror(e), e);
				fflush(stderr);
				_exit(1);
			}
		} else if (pid == -1) {
			// Error
			e = errno;
			throw SystemException("Cannot fork a new process", e);
		} else {
			// Parent
			UPDATE_TRACE_POINT();
			FileDescriptor feedbackFd = fds[0];
			MessageChannel feedbackChannel(fds[0]);
			vector<string> args;
			bool result, allAgentsStarted;
			
			ServerInstanceDirPtr serverInstanceDir;
			ServerInstanceDir::GenerationPtr generation;
			ScopeGuard guard(boost::bind(&AgentsStarter::killProcessGroupAndWait, &pid, 0));
			fds[1].close();
			
			
			/****** Send arguments to watchdog through the feedback channel ******/
			
			UPDATE_TRACE_POINT();
			/* Here we don't care about EPIPE and ECONNRESET errors. The watchdog
			 * could have sent an error message over the feedback fd without
			 * reading the arguments. We'll notice that later.
			 */
			try {
				watchdogArgs.writeToChannel(feedbackChannel);
			} catch (const SystemException &e) {
				if (e.code() != EPIPE && e.code() != ECONNRESET) {
					inspectWatchdogCrashReason(pid);
				}
			}
			
			
			/****** Read basic startup information ******/
			
			this_thread::restore_interruption ri(di);
			this_thread::restore_syscall_interruption rsi(dsi);
			UPDATE_TRACE_POINT();
			
			try {
				result = feedbackChannel.read(args);
			} catch (const SystemException &ex) {
				if (ex.code() == ECONNRESET) {
					inspectWatchdogCrashReason(pid);
				} else {
					killProcessGroupAndWait(&pid, 5000);
					guard.clear();
					throw SystemException("Unable to start the Phusion Passenger watchdog: "
						"unable to read its startup information",
						ex.code());
				}
			}
			if (!result) {
				UPDATE_TRACE_POINT();
				inspectWatchdogCrashReason(pid);
			}
			
			UPDATE_TRACE_POINT();
			if (args[0] == "Basic startup info") {
				if (args.size() == 3) {
					serverInstanceDir.reset(new ServerInstanceDir(args[1], false));
					generation = serverInstanceDir->getGeneration(atoi(args[2]));
				} else {
					throw IOException("Unable to start the Phusion Passenger watchdog: "
						"it returned an invalid basic startup information message");
				}
			} else if (args[0] == "Watchdog startup error") {
				killProcessGroupAndWait(&pid, 5000);
				guard.clear();
				throw RuntimeException("Unable to start the Phusion Passenger watchdog "
					"because it encountered the following error during startup: " +
					args[1]);
			} else if (args[0] == "system error") {
				killProcessGroupAndWait(&pid, 5000);
				guard.clear();
				throw SystemException(args[1], atoi(args[2]));
			} else if (args[0] == "exec error") {
				e = atoi(args[1]);
				killProcessGroupAndWait(&pid, 5000);
				guard.clear();
				if (e == ENOENT) {
					string passengerRootConfig;
					if (type == APACHE) {
						passengerRootConfig = "PassengerRoot";
					} else {
						passengerRootConfig = "passenger_root";
					}
					throw RuntimeException("Unable to start the Phusion Passenger watchdog "
						"because its executable (" + watchdogFilename + ") does "
						"not exist. This probably means that your Phusion Passenger "
						"installation is broken or incomplete, or that your '" +
						passengerRootConfig + "' directive is set to the wrong value. "
						"Please reinstall Phusion Passenger or fix your '" +
						passengerRootConfig + "' directive, whichever is applicable.");
				} else {
					throw SystemException("Unable to start the Phusion Passenger watchdog (" +
						watchdogFilename + ")", e);
				}
			}
			
			
			/****** Read agents startup information ******/
			
			UPDATE_TRACE_POINT();
			allAgentsStarted = false;
			
			while (!allAgentsStarted) {
				try {
					UPDATE_TRACE_POINT();
					result = feedbackChannel.read(args);
				} catch (const SystemException &ex) {
					killProcessGroupAndWait(&pid, 5000);
					guard.clear();
					throw SystemException("Unable to start the Phusion Passenger watchdog: "
						"unable to read all agent startup information",
						ex.code());
				}
				if (!result) {
					UPDATE_TRACE_POINT();
					inspectWatchdogCrashReason(pid);
				}
				
				if (args[0] == "HelperAgent info") {
					UPDATE_TRACE_POINT();
					if (args.size() == 5) {
						this->pid = pid;
						this->feedbackFd = feedbackFd;
						requestSocketFilename   = args[1];
						requestSocketPassword   = Base64::decode(args[2]);
						messageSocketFilename   = args[3];
						messageSocketPassword   = Base64::decode(args[4]);
						this->serverInstanceDir = serverInstanceDir;
						this->generation        = generation;
					} else {
						killProcessGroupAndWait(&pid, 5000);
						guard.clear();
						throw IOException("Unable to start the Phusion Passenger watchdog: "
							"it returned an invalid initialization feedback message");
					}
				} else if (args[0] == "LoggingServer info") {
					UPDATE_TRACE_POINT();
					if (args.size() == 3) {
						loggingAgentRunningLocally = true;
						loggingSocketAddress  = args[1];
						loggingSocketPassword = args[2];
					} else {
						killProcessGroupAndWait(&pid, 5000);
						guard.clear();
						throw IOException("Unable to start the Phusion Passenger watchdog: "
							"it returned an invalid initialization feedback message");
					}
				} else if (args[0] == "All agents started") {
					allAgentsStarted = true;
				} else {
					UPDATE_TRACE_POINT();
					killProcessGroupAndWait(&pid, 5000);
					guard.clear();
					throw RuntimeException("One of the Passenger agents sent an unknown feedback message '" + args[0] + "'");
				}
			}
			
			guard.clear();
		}
	}
	
	/**
	 * Close any file descriptors that this object has, and make it so that the destructor
	 * doesn't try to shut down the agents.
	 *
	 * @post getPid() == 0
	 */
	void detach() {
		feedbackFd.close();
		pid = 0;
	}
};

} // namespace Passenger

#endif /* _PASSENGER_AGENTS_STARTER_HPP_ */