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path: root/pacredir.c
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/*
 * (C) 2013 by Christian Hesse <mail@eworm.de>
 *
 * This software may be used and distributed according to the terms
 * of the GNU General Public License, incorporated herein by reference.
 *
 * This is an example code skeleton provided by vim-skeleton.
 */

#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <signal.h>
#include <time.h>

#include <avahi-client/client.h>
#include <avahi-client/lookup.h>
#include <avahi-common/simple-watch.h>
#include <avahi-common/malloc.h>
#include <avahi-common/error.h>

#include <curl/curl.h>
#include <microhttpd.h>

#define PAGE307 "<html><head><title>307 temporary redirect</title>" \
		"</head><body>307 temporary redirect: " \
		"<a href=\"%s\">%s</a></body></html>"
#define PAGE404 "<html><head><title>404 Not Found</title>" \
		"</head><body>404 Not Found: %s</body></html>"
#define PORT	7077
#define SERVICE	"_pacserve._tcp"
#define BADTIME	60 * 10

/* hosts */
struct hosts {
	/* host name */
	char * host;
	/* http port */
	uint16_t port;
	/* unix timestamp of last bad request */
	__time_t bad;
	/* true if host is offline */
	uint8_t offline;
	/* pointer to next struct element */
	struct hosts * next;
};

/* global variables */
struct hosts * hosts = NULL;
static AvahiSimplePoll *simple_poll = NULL;

/*** resolve_callback_new ***
 * Called whenever a service has been resolved successfully or timed out */
static void resolve_callback_new(AvahiServiceResolver *r, AVAHI_GCC_UNUSED AvahiIfIndex interface, AVAHI_GCC_UNUSED AvahiProtocol protocol,
		AvahiResolverEvent event, const char *name, const char *type, const char *domain, const char *host, const AvahiAddress *address,
		AVAHI_GCC_UNUSED uint16_t port, AVAHI_GCC_UNUSED AvahiStringList *txt, AVAHI_GCC_UNUSED AvahiLookupResultFlags flags,
		AVAHI_GCC_UNUSED void* userdata) {
	struct hosts * tmphosts = hosts;

	assert(r);

	switch (event) {
		case AVAHI_RESOLVER_FAILURE:
			fprintf(stderr, "(Resolver) Failed to resolve service '%s' of type '%s' in domain '%s': %s\n",
				name, type, domain, avahi_strerror(avahi_client_errno(avahi_service_resolver_get_client(r))));
			break;

		case AVAHI_RESOLVER_FOUND: {
			while (tmphosts->host != NULL) {
				if (strcmp(tmphosts->host, host) == 0) {
#					if defined DEBUG
					printf("Host is already in the list: %s\n", host);
#					endif
					tmphosts->offline = 0;
					goto out;
				}
				tmphosts = tmphosts->next;
			}
			printf("Adding host: %s, port %d\n", host, port);
			tmphosts->host = strdup(host);
			tmphosts->port = port;
			tmphosts->bad = 0;
			tmphosts->offline = 0;
			tmphosts->next = realloc(tmphosts->next, sizeof(struct hosts));
			tmphosts = tmphosts->next;
			tmphosts->host = NULL;
			tmphosts->next = NULL;

			break;
		}
	}

out:
	avahi_service_resolver_free(r);
}

/*** resolve_callback_remove ***
 * Called whenever a service has been resolved successfully or timed out */
static void resolve_callback_remove(AvahiServiceResolver *r, AVAHI_GCC_UNUSED AvahiIfIndex interface, AVAHI_GCC_UNUSED AvahiProtocol protocol,
		AvahiResolverEvent event, const char *name, const char *type, const char *domain, const char *host, const AvahiAddress *address,
		AVAHI_GCC_UNUSED uint16_t port, AVAHI_GCC_UNUSED AvahiStringList *txt, AVAHI_GCC_UNUSED AvahiLookupResultFlags flags,
		AVAHI_GCC_UNUSED void* userdata) {
	struct hosts * tmphosts = hosts;

	assert(r);

	switch (event) {
		case AVAHI_RESOLVER_FAILURE:
			fprintf(stderr, "(Resolver) Failed to resolve service '%s' of type '%s' in domain '%s': %s\n",
				name, type, domain, avahi_strerror(avahi_client_errno(avahi_service_resolver_get_client(r))));
			break;

		case AVAHI_RESOLVER_FOUND: {
			while (tmphosts->host != NULL) {
				if (strcmp(tmphosts->host, host) == 0) {
					printf("Marking host offline: %s\n", host);
					tmphosts->offline = 1;
					goto out;
				}
				tmphosts = tmphosts->next;
			}
			break;
		}
	}

out:
	avahi_service_resolver_free(r);
}

/*** browse_callback ***
 * Called whenever a new services becomes available on the LAN or is removed from the LAN */
static void browse_callback(AvahiServiceBrowser *b, AvahiIfIndex interface, AvahiProtocol protocol, AvahiBrowserEvent event, const char *name,
		const char *type, const char *domain, AVAHI_GCC_UNUSED AvahiLookupResultFlags flags, void* userdata) {
	AvahiClient *c = userdata;

	assert(b);

	switch (event) {
		case AVAHI_BROWSER_FAILURE:

			fprintf(stderr, "(Browser) %s\n", avahi_strerror(avahi_client_errno(avahi_service_browser_get_client(b))));
			avahi_simple_poll_quit(simple_poll);
			return;

		case AVAHI_BROWSER_NEW:
#			if defined DEBUG
			fprintf(stderr, "(Browser) NEW: service '%s' of type '%s' in domain '%s'\n", name, type, domain);
#			endif

			/* We ignore the returned resolver object. In the callback
			 * function we free it. If the server is terminated before
			 * the callback function is called the server will free
			 * the resolver for us. */

			if (avahi_service_resolver_new(c, interface, protocol, name, type, domain, AVAHI_PROTO_UNSPEC, 0, resolve_callback_new, c) == NULL)
				fprintf(stderr, "Failed to resolve service '%s': %s\n", name, avahi_strerror(avahi_client_errno(c)));

			break;

		case AVAHI_BROWSER_REMOVE:
#			if defined DEBUG
			fprintf(stderr, "(Browser) REMOVE: service '%s' of type '%s' in domain '%s'\n", name, type, domain);
#			endif

			if (avahi_service_resolver_new(c, interface, protocol, name, type, domain, AVAHI_PROTO_UNSPEC, 0, resolve_callback_remove, c) == NULL)
				fprintf(stderr, "Failed to resolve service '%s': %s\n", name, avahi_strerror(avahi_client_errno(c)));

			break;

		case AVAHI_BROWSER_ALL_FOR_NOW:
		case AVAHI_BROWSER_CACHE_EXHAUSTED:
			break;
	}
}

/*** client_callback ***/
static void client_callback(AvahiClient *c, AvahiClientState state, AVAHI_GCC_UNUSED void * userdata) {
	assert(c);

	if (state == AVAHI_CLIENT_FAILURE) {
		fprintf(stderr, "Server connection failure: %s\n", avahi_strerror(avahi_client_errno(c)));
		avahi_simple_poll_quit(simple_poll);
	}
}

/*** get_http_code ***/
int get_http_code(const char * host, const uint16_t port, const char * url) {
	CURL *curl;
	CURLcode res;
	unsigned int http_code;

	curl_global_init(CURL_GLOBAL_ALL);

	if ((curl = curl_easy_init()) != NULL) {
		curl_easy_setopt(curl, CURLOPT_URL, url);
		/* example.com is redirected, so we tell libcurl to follow redirection */ 
		curl_easy_setopt(curl, CURLOPT_FOLLOWLOCATION, 1L);
		/* set user agent */
		curl_easy_setopt(curl, CURLOPT_USERAGENT, "pacredir/" VERSION);
		/* do not receive body */
		curl_easy_setopt(curl, CURLOPT_NOBODY, 1);
		/* set connection timeout to 2 seconds
		 * if the host needs longer we do not want to use it anyway ;) */
		curl_easy_setopt(curl, CURLOPT_CONNECTTIMEOUT, 2);

		/* get it! */
		if (curl_easy_perform(curl) != CURLE_OK) {
			fprintf(stderr, "Could not connect to server %s on port %d.\n", host, port);
			return -1;
		}

		if ((res = curl_easy_getinfo(curl, CURLINFO_RESPONSE_CODE, &http_code)) != CURLE_OK) {
			fprintf(stderr, "curl_easy_getinfo() failed: %s\n", curl_easy_strerror(res));
			return -1;
		}

		/* always cleanup */ 
		curl_easy_cleanup(curl);
	}

	/* we're done with libcurl, so clean it up */
	curl_global_cleanup();

	return http_code;
}

/*** ahc_echo ***
 * called whenever a http request is received */
static int ahc_echo(void * cls, struct MHD_Connection * connection, const char * uri, const char * method,
		const char * version, const char * upload_data, size_t * upload_data_size, void ** ptr) {
	static int dummy;
	struct MHD_Response * response;
	int ret;
	struct hosts * tmphosts = hosts;

	char * url = NULL, * page;
	const char * basename;
	int http_code = 0;
	struct timeval tv;

	/* we want to filename, not the path */
	basename = uri;
	while (strstr(basename, "/") != NULL)
		basename = strstr(basename, "/") + 1;

	if (strcmp(method, "GET") != 0)
		return MHD_NO; /* unexpected method */
	if (&dummy != *ptr) {
		/* The first time only the headers are valid,
		 * do not respond in the first round... */
		*ptr = &dummy;
		return MHD_YES;
	}
	if (*upload_data_size != 0)
		return MHD_NO; /* upload data in a GET!? */

	/* clear context pointer */
	*ptr = NULL;

	/* do not process db requests */
	/* TODO: do some timestamp magic to find suitable db files */
	if (strcmp(basename + strlen(basename) - 3, ".db") == 0) {
#		if defined DEBUG
		printf("Not precessing db file request for %s\n", basename);
#		endif
	} else {
		/* try to find a server */
		while (tmphosts->host != NULL) {
			gettimeofday(&tv, NULL);

			/* skip host if offline or had a bad request within last BADTIME seconds */
			if (tmphosts->offline == 1 || tmphosts->bad + BADTIME > tv.tv_sec) {
				tmphosts = tmphosts->next;
				continue;
			}

			url = malloc(10 + strlen(tmphosts->host) + 5 + strlen(basename));
			sprintf(url, "http://%s:%d/%s", tmphosts->host, tmphosts->port, basename);

			printf("Trying %s\n", url);
			if ((http_code = get_http_code(tmphosts->host, tmphosts->port, url)) == MHD_HTTP_OK)
				break;
			else if (http_code == -1)
				tmphosts->bad = tv.tv_sec;

			tmphosts = tmphosts->next;
		}
	}

	/* give response */
	if (http_code == MHD_HTTP_OK) {
		printf("Redirecting to %s\n", url);
		page = malloc(strlen(PAGE307) + strlen(url) + strlen(basename) + 1);
		sprintf(page, PAGE307, url, basename);
		response = MHD_create_response_from_data(strlen(url), (void*) url, MHD_NO, MHD_NO);
		ret =  MHD_add_response_header(response, "Location", url);
		ret = MHD_queue_response(connection, MHD_HTTP_TEMPORARY_REDIRECT, response);
	} else {
		printf("File %s not found, giving up.\n", basename);
		page = malloc(strlen(PAGE404) + strlen(basename) + 1);
		sprintf(page, PAGE404, basename);
		response = MHD_create_response_from_data(strlen(page), (void*) page, MHD_NO, MHD_NO);
		ret = MHD_queue_response(connection, MHD_HTTP_NOT_FOUND, response);
	}
	MHD_destroy_response(response);

	free(page);
	if (url != NULL)
		free(url);

	return ret;
}

/*** sigterm_callback ***/
void sigterm_callback(int signal) {
	avahi_simple_poll_quit(simple_poll);
}

/*** sighup_callback ***/
void sighup_callback(int signal) {
	struct hosts * tmphosts = hosts;
	
	printf("Received SIGHUP, marking all hosts offline.\n");

	while (tmphosts->host != NULL) {
		tmphosts->offline = 1;
		tmphosts = tmphosts->next;
	}
}

/*** main ***/
int main(int argc, char ** argv) {
	AvahiClient *client = NULL;
	AvahiServiceBrowser *sb = NULL;
	int error;
	int ret = 1;
	struct MHD_Daemon * mhd;
	struct hosts * tmphosts;

	printf("Starting pacredir/" VERSION "\n");

	/* allocate first struct element as dummy */
	hosts = malloc(sizeof(struct hosts));
	hosts->host = NULL;
	hosts->port = 0;
	hosts->bad = 0;
	hosts->offline = 0;
	hosts->next = NULL;

	/* allocate main loop object */
	if (!(simple_poll = avahi_simple_poll_new())) {
		fprintf(stderr, "Failed to create simple poll object.\n");
		goto fail;
	}

	/* allocate a new client */
	client = avahi_client_new(avahi_simple_poll_get(simple_poll), 0, client_callback, NULL, &error);

	/* check wether creating the client object succeeded */
	if (!client) {
		fprintf(stderr, "Failed to create client: %s\n", avahi_strerror(error));
		goto fail;
	}

	/* create the service browser */
	if (!(sb = avahi_service_browser_new(client, AVAHI_IF_UNSPEC, AVAHI_PROTO_UNSPEC, SERVICE, NULL, 0, browse_callback, client))) {
		fprintf(stderr, "Failed to create service browser: %s\n", avahi_strerror(avahi_client_errno(client)));
		goto fail;
	}

	if ((mhd = MHD_start_daemon(MHD_USE_THREAD_PER_CONNECTION, PORT, NULL, NULL, &ahc_echo, NULL, MHD_OPTION_END)) == NULL) {
		fprintf(stderr, "Could not start daemon on port %d.\n", PORT);
		return EXIT_FAILURE;
	}

	/* register signal callbacks */
	signal(SIGTERM, sigterm_callback);
	signal(SIGHUP, sighup_callback);
	
	/* run the main loop */
	avahi_simple_poll_loop(simple_poll);

	MHD_stop_daemon(mhd);

	ret = EXIT_SUCCESS;

fail:

	/* Cleanup things */
	while(hosts->host != NULL) {
		free(hosts->host);
		tmphosts = hosts->next;
		free(hosts);
		hosts = tmphosts;
	}

	if (sb)
		avahi_service_browser_free(sb);

	if (client)
		avahi_client_free(client);

	if (simple_poll)
		avahi_simple_poll_free(simple_poll);

	return ret;
}

// vim: set syntax=c: