#include <time.h>
#include <sys/random.h>
#include <errno.h>
#include <sys/socket.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <arpa/inet.h>
#include <netinet/ip.h>
#include <limits.h>
#include <search.h>
#define ECB 1
#define AES128 1
#include <aes.c>
#include <bencoding.c>

time_t seconds () {
	struct timespec tp;
	clock_gettime(CLOCK_MONOTONIC, &tp);
	return tp.tv_sec;
}

int family (const char * addr) {
	return memcmp("\0\0\0\0\0\0\0\0\0\0\xFF\xFF", addr, 12) ? AF_INET6 : AF_INET;
}

#define K 8

/**
 * node representation
 */

struct node {
	char id[20];
	struct sockaddr_in6 addr;
	int unanswered; /**< number of packets I've sent since last_received */
	time_t last_received; /**< time when I received the last packet from it */
	time_t last_sent; /**< time when I sent the last packet to it */
	struct node * next;
};

/**
 * creates a new node
 */

struct node * node_init () {
	struct node * n = calloc(1, sizeof *n);
	if (!n)
		return NULL;
	n->last_received = seconds();
	n->last_sent = seconds();
	return n;
}

/**
 * frees a node
 *
 * @param n	[in]	the node to be freed
 */

void node_free (struct node * n) {
	free(n);
}

/**
 * bucket representation
 */

struct bucket {
	char id[20]; /**< bucket spans from id inclusive to next->id exclusive */
	struct node * nodes;
	struct bucket * next;
};

/**
 * creates a new bucket
 */

struct bucket * bucket_init () {
	struct bucket * b = calloc(1, sizeof *b);
	if (!b)
		return NULL;
	return b;
}

/**
 * frees a bucket
 *
 * @param b	[in]	the bucket to be freed
 */

void bucket_free (struct bucket * b) {
	struct node * node = b->nodes;
	while (node) {
		struct node * old = node;
		node = node->next;
		node_free(old);
	}
	free(b);
}

/**
 * peer of a torrent
 */

struct peer {
	struct sockaddr_in6 addr; /**< peer ip address and port */
	struct peer * next;
};

/**
 * free a torrent peer
 */

void peer_free (struct peer * p) {
	free(p);
}

/**
 * reason why a torrent is in our database. 0 just means it is stored as a result of an announce
 */

enum torrent {
	announce = 1 << 0, /**< will announce myself on every work() call with no packet */
	peers = 1 << 1, /**< will get peers on every work() call with no packet */
	info = 1 << 2, /**< download metadata into `dht->dl`/$hash.info */
	dl = 1 << 3 /**< download torrent content into `dht->dl`/$hash.blob TODO */
};

/**
 * torrent we are interested in
 */

struct torrent {
	enum torrent type;
	char hash[20]; /**< infohash */
	struct peer * peers;
	time_t last; /**< last operation on this torrent, so that inactive torrents are purged */
	struct node * nodes; /**< closest DHT nodes to this hash */
	char pieces[]; /**< when checking a torrent, this is filled. every piece is one bit. TODO */
};

/**
 * free a torrent object and it's nodes and peers
 */

void torrent_free (struct torrent * t) {
	struct node * n = t->nodes;
	while (n) {
		struct node * old = n;
		n = n->next;
		node_free(n);
	}
	struct peer * p = t->peers;
	while (p) {
		struct peer * old = p;
		p = p->next;
		peer_free(old);
	}
	free(t);
}

/**
 * compares two torrent objects based on their hash
 */

int torrent_compare (const void * a, const void * b) {
	return memcmp(((const struct torrent *) a)->hash, ((const struct torrent *) b)->hash, 20);
}

/**
 * handle for the library
 */

struct dht {
	char id[20]; /**< own id */
	int socket; /**< v4&v6 UDP socket that is bound on UDP and sends to nodes */
	char secret[16]; /**< for calculating opaque write token, random */
	FILE * log; /**< FILE to log to, defaults to stderr */
	struct bucket * buckets;
	struct bucket * buckets6; /**< IPv6 routing table */
	struct torrent ** torrents; /**< binary tree of torrents for which we want to know peers */
	int dl; /**< dirfd storage directory for download and info torrents */
};

/**
 * creates a handle. you can override log in the result struct.
 *
 * this function does not log, as log fd is not known yet
 *
 * socket must be close()d before being overriden, if the caller wants to use custom binding.
 *
 * binds UDP to all ifaces
 *
 * @param c	[in]	bencoding object containing the persistent config file, generated from a previous run with persistent(). memory ownership is NOT transfered, it's the caller's responsibility to free the object. can be NULL.
 */

struct dht * dht_init (const struct bencoding * c) {
	struct dht * d = calloc(1, sizeof *d);
	d->log = stderr;
	d->dl = -1;
	d->buckets = bucket_init();
	errno = 0;
	if (!d)
		return NULL;
	if (getrandom(d->id, 20, GRND_NONBLOCK) == -1)
		goto e;
	if (getrandom(d->secret, 16, GRND_NONBLOCK) == -1)
		goto e;
	d->socket = socket(AF_INET6, SOCK_DGRAM | SOCK_NONBLOCK | SOCK_CLOEXEC, 0);
	if (d->socket == -1)
		goto e;
	struct sockaddr_in6 a = {
		sin6_family = AF_INET6,
		sin6_addr = in6addr_any
	};
	if (bind(d->socket, &a, sizeof a) == -1)
		goto e;
	if (c) {
		const struct bencoding * id = bpath(c, "id");
		if (id & id->type & string && id->valuelen == 20)
			memcpy(d->id, id->value, 20);
		bforeach (bpath(c, "nodes"), str) {
			struct sockaddr_in6 addr;
			char remote[INET6_ADDRSTRLEN + 7];
			strncpy(remote, str->value, str->valuelen);
			char * port = strchr(remote, ':');
			if (port) {
				if (inet_pton(AF_INET6, remote, &addr) == 1) {
					addr.sin6_port = htons(atoi(++port));
					ping_node(d, &addr);
				}
			}
		}
	}
	return d;
	e:
	free(d);
	return NULL;
}

/**
 * frees a handle. does nothing if handle is NULL. does not fclose log. closes socket. please set socket to -1 before calling if you don't want to close it.
 */

#define L(o, f, ...) do {char t[512]; time_t n = time(NULL); strftime(t, 512, "%c", localtime(&n)); fprintf(o, "[%s] %s()%s:%d: " f "\n", t, __func__, __FILE__, __LINE__ __VA_OPT__(,) __VA_ARGS__)} while (0)

void dht_free (struct dht * d) {
	if (d->socket != -1)
		if (close(d->socket) == -1)
			L(d->log, "close(d->socket) == -1");
	struct bucket * bucket = d->buckets;
	while (bucket) {
		struct bucket * old = bucket;
		bucket = bucket->next;
		bucket_free(old);
	}
	free(d);
}

/**
 * generate a bencoding struct containing the persistent storage config
 *
 * this config contains:
 * 	- nodes from the routing table that can be used to bootstrap into the dht net
 * 	- this node's id
 *
 * please make sure that you do not start two nodes from the same config
 *
 * @param d	[in]	library handle
 * @return bencoding object, whose memory ownership is transfered to the caller, which must call bencoding_free() on it.
 */

struct bencoding * persistent (const struct dht * d) {
	struct bencoding * b = calloc(1, sizeof *b);
	b->type = dict;
	struct bencoding * id = calloc(1, sizeof *id);
	id->type = string;
	id->value = malloc(20);
	id->valuelen = 20;
	memcpy(id->value, d->id);
	id->key = bstr(strdup("id"));
	binsert(b, id);
	struct bencoding * nodes = calloc(1, sizeof *nodes);
	nodes->type = list;
	struct bucket * bucket = d->buckets;
	while (bucket) {
		struct node * node = bucket->nodes;
		while (node) {
			char remote[INET6_ADDRSTRLEN + 7];
			if (inet_ntop(AF_INET6, &node->addr, remote, sizeof node->addr))
				binsert(nodes, bstr(strdup(remote)));
			node = node->next;
		}
		bucket = bucket->next;
	}
	binsert(b, nodes);
	return b;
}

/**
 * generates a 16 byte token for allowing a node to store it's IP addres in our node. verify with valid()
 *
 * @param d	[in]	used to obtain the secret key
 * @param t	[out]	the destination to which to write the 16 bytes
 * @param a	[in]	the node's IP address, from which get_peers was received
 * @param l	[in]	the length of socket address struct a
 */

void token (const struct dht * d, char * t, struct sockaddr_in6 * a) {
	struct AES_ctx aes;
	memcpy(t, a->sin6_addr, 16);
	AES_init_ctx(&aes, dht->secret);
	AES_ECB_encrypt(&aes, t);
}

/**
 * verifies a 16 byte token, if it was really generated with token(), to prevent unsolicited adding of IPs to storage with src ip addr spoofing.
 *
 * @param d	[in]	used to obtain the secret key
 * @param t	[in]	the address from which to obtain the 16 byte token
 * @param a	[in]	the node's IP address, from which announce was received
 * @param l	[in]	the length of socket address struct a
 * @return 1 if the token is valid for this node, 0 otherwise
 */

int valid (const struct dht * d, const char * t, struct sockaddr_in6 * a) {
	char try[16];
	memcpy(try, t, 16);
	token(d, try, a, l);
	return !memcmp(try, t, 16);
}

/**
 * sends a bencoding object to the remote node. does not free the input bencoding. inserts a v key to the input bencoding.
 *
 * @param d	[in]	the dht library handle
 * @param b	[in]	the bencoding to send serialized, m. ownership NOT transfered
 * @param a	[in]	destination address
 */

void sendb (const struct dht * d, struct bencoding * b, struct sockaddr_in6 * a) {
	char remote[INET6_ADDRSTRLEN + 7];
	if (!inet_ntop(a->sa_family, a, remote, sizeof *a))
		snprintf(remote, sizeof remote,  "(inet_ntop: %s)", strerror(errno));
	sprintf(remote+strlen(remote), ":%d", ntohs(((struct sockaddr_in6 *) a)->sin6_port));
	struct bencoding * v = bstr(strdup("TK00"));
	v->key = bstr(strdup("v"));
	binsert(b, v);
	int len = b2json_length(b);
	char json[len+1];
	b2json(json, a);
	json[len] = '\0';
	L(d->log, "sending to %s: %s", remote, json);
	len = bencode_length(b);
	char text[len];
	bencode(text, b);
	if (sendto(dht->socket, text, len, MSG_DONTWAIT | MSG_NOSIGNAL, a, sizeof *a) == -1)
		L(d->log, "sendto(%s): %s", remote, strerror(errno));
}

/**
 * sends an error rpc packet to a node. make sure that this is always similar size to the received packet, otherwise we could get amplification attacks.
 *
 * @param d	[in]	the dht library handle, for logging and for socket fd
 * @param b	[in]	the incoming packet that caused the error, to get key t
 * @param a	[in]	address of the incoming packet to which an error is sent
 * @param num	[in]	error number, as specified by BEP-0005
 * @param text	[in]	error text. memory ownership is transfered and string is freed, so make sure it's allocated on heap and no longer used by the caller - for static strings use strdup()
 */

void send_error (const struct dht * d, const struct bencoding * b, struct sockaddr_in6 * a, int errnum, char * text) {
	struct bencoding * e = calloc(1, sizeof *e);
	e->type = list;
	e->key = bstr(strdup("e"));
	binsert(e, bstr(text));
	binsert(e, bnum(errnum));
	struct bencoding * y = bstr(strdup("e"));
	b->key = bstr(strdup("y"));
	struct bencoding * response = calloc(1, sizeof *response);
	binsert(response, y);
	binsert(response, e);
	binsert(response, bpath(b, "t"));
	sendb(d, response, a);
	free_bencoding(response);
}

/**
 * decides if a node id belongs to a bucket or not. this does not actually check the bucket for it's contents, just the ranges.
 *
 * @param id	[in]	the node id
 * @param b	[in]	the bucket
 * @return 1 if belongs to a bucket, 0 otherwise
 */

int in_bucket (const char * id, const struct bucket * b) {
	return memcmp(id, b->id, 20) >= 0 && (!b->next || memcmp(id, b->next->id, 20) < 0);
}

/**
 * searches for a stored node based on id
 *
 * @param id	[in]	the node id
 * @param b		pointer to a variable containing a pointer to the first bucket in ll. after the call the value at this pointer is overwritten to the bucket that should contain this node. since it's overwritten, do NOT just pass &dht->buckets. do struct bucket * b = dht->buckets and pass &b instead.
 * @param n	[out]	the node directly before the searched for node. NULL is written if this node would be placed at the start of the bucket. NULL may be passed without consequences.
 * @return the pointer to the node or NULL if not found
 */

struct node * find (const char * id, struct bucket ** b, struct ** n) {
	while (!in_bucket(id, *b))
		*b = (*b)->next;
	struct node * node = (*b)->nodes;
	struct prev = NULL;
	while (node && memcmp(node->id, id) < 0) {
		prev = node;
		node = node->next;
	}
	*n = prev;
}

/**
 * informs the library of a successfully received response packet from a node, knowing it's id and ip:port. do not call if the node queried us, if that's the case, use potential_node().
 *
 * if the node is new, it's added in a bucket.
 *
 * if the node is found in a bucket, it's last received time and unanswered are updated
 *
 * @param d	[in]	handle
 * @param id	[in]	node id that was received
 * @param addr	[in]	address from which the id was received
 */

void replied (const struct dht * d, const char * id, const struct sockaddr_in6 * addr) {
	struct bucket * b = d->buckets;
	struct node * n;
	struct node * found = find(id, &b, &n);
	if (found) {
		found->last_received = seconds();
		found->unanswered = 0;
	}

}

/**
 * ping a raw node by sending a get_peers
 *
 * instead of sending a ping query, we send a find_node query. this gets us useful information of peers around our ID instead of just a blank ping reply. infolgedessen we don't have to actively search for our neighbour nodes, since we'll get them through pings anyways
 *
 * instead of sending a find_node for an ID close to ours, we could send a find_node for a random ID far from us. though those buckets will probably quickly be filled by torrent searches.
 *
 * @param d	[in]	library handle
 * @param a	[in]	address of node
 */

void ping_node (const struct dht * d, const struct sockaddr_in6 * a) {
	char target[20];
	memcpy(target, d->id, 20);
	if (target[19] & 1) // flip the last bit, so the other node doesn't just return
		target[19] &= 0xFE;	// our ID but K ids around it
	else
		target[19] |= 1;
	find_node(d, a, target);
}

/**
 * sends a find_node query to a "raw node"
 * 
 * @param d	[in]	handle
 * @param a	[in]	address of the remote node
 * @param query	[in]	20 byte id we are querying
 */

void find_node (const struct dht * d, const struct sockaddr_in6 * a, const char * query) {
	struct bencoding * b = calloc(1, sizeof *b);
	b->type = dict;
	struct bencoding * t = bstr(strdup("t@_a.si"));
	t->key = bstr(strdup("t"));
	t->value[2] = '4';
	t->type = string;
	binsert(b, t);
	struct bencoding * y = bstr(strdup("q"));
	t->key = bstr(strdup("y"));
	t->type = string;
	binsert(b, y);
	struct bencoding * q = bstr(strdup("find_node"));
	q->key = bstr(strdup("q"));
	q->type = string;
	binsert(b, q);
	struct bencoding * a = calloc(1, sizeof *a);
	a->type = dict;
	struct bencoding * id = calloc(1, sizeof *id);
	id->type = string;
	id->valuelen = 20;
	id->key = bstr(strdup("key"));
	memcpy((id->value = malloc(20)), d->id, 20);
	binsert(a, id);
	struct bencoding * want = calloc(1, sizeof *want); // BEP-0032
	want->key = bstr(strdup("want"));
	want->type = list;
	binsert(want, bstr(strdup("n4")));
	binsert(want, bstr(strdup("n6")));
	binsert(a, want);
	struct bencoding * target = calloc(1, sizeof *target);
	target->key = bstr(strdup("target"));
	target->type = string;
	target->valuelen = 20;
	memcpy((id->value = malloc(20)), query, 20);
	binsert(a, id);
	binsert(b, a);
	sendb(d, b, a);
	free_bencoding(b);
}

/**
 * returns a count of nodes in a linked list
 *
 * @param n	[in]	first node in ll
 */

int node_count (const struct node * n) {
	int c = 0;
	while (n) {
		c++;
		n = n->next;
	}
	return c;
}

/**
 * returns the distance between two ids. if it cannot be represented with an unsigned int, UINT_MAX is returned.
 *
 * TODO: test util
 */

unsigned int distance (const char * a, const char * b) {
	char xor[20];
	memcpy(xor, a);
	for (int i = 0; i < 20; i++) {
		xor[i] ^= b[i];
		if (i < 20-sizeof unsigned && xor[i])
			return UINT_MAX;
	}
	unsigned r = 0;
	for (int i = 0; i < sizeof unsigned; i++)
		r |= xor[i] << (sizeof unsigned - 1 - i) * 8;
}

enum node_grade {
	good,
	bad,
	questionable
};

/**
 * determines if node is considered good, bad or questionable
 *
 * @param n	[in]	node
 * @return enum node_grade
 */

enum node_grade node_grade (const struct node * n) {
	if (node->last_received + 15*60 < seconds()) {
		if (node->last_sent + 14*60 < seconds() && node->unanswered > 1)
			return bad;
		return questionable;
	}
	return good;
}

/**
 * returns 1 if bucket is perfect, meaning it is fresh, has K nodes, and all nodes are good. bucket that contains id is almost never perfect, as it can usually be split into smaller buckets, that's why param d is required to get own id
 *
 * if d is NULL, it's not checked whether we fall into the bucket and whether it could be split
 *
 * @param d	[in]	library handle to get own id
 * @param b	[in]	the bucket
 */

int bucket_good (const struct dht * d, const struct bucket * b) {
	if (d) {
		if (!bucket_good(NULL, b))
			return 0;
		if (in_bucket(d->id, b)) {
			struct node * n = b->nodes;
			while (n->next) {
				if (distance(n->id, n->next->id) != 1)
					return 0;
			}
			return 1;
		}
		return 1;
	} else {
		if (node_count(b->nodes) < K)
			return 0;
		struct node * n = b->nodes;
		if (n) {
			if (node_grade(n) != good)
				return 0;
			n = n->next;
		}
	}
}

/**
 * when we are sure that a node exists on a specific ip:port and we know it's port, but we are unsure if the node is already in the routing table, we call this function, which makes a query to this node if it's a candidate for filling the routing table. this doesn't yet add it to the routing table, because we are unsure if it's a good node / can respond to queries. replied() is called if a node replied to our query.
 *
 * @param d	[in]	library handle
 * @param a	[in]	pointer to sockaddr of the node
 * @param id	[in]	id of the node, 20 bytes is read from this address
 */

void potential_node (const struct dht * d, const struct sockaddr_in6 * a, const char * id) {
	struct bucket * bucket = d->buckets;
	if (family(a->sin6_addr.s6_addr) == AF_INET6)
		bucket = b->buckets6;
	if (find(id, &bucket, NULL))
		return;
	if (!bucket_good(bucket));
		ping_node(d, a);
}

/**
 * adds a torrent to a list of torrents
 * 
 * if the torrent already exists in the database flags of this one will be anded with the flags of the old one, meaning this function can be used to set keep, announce, info and dl flags. see @return for important details.
 *
 * @param d	[in]	dht library handler
 * @param t	[in]	torrent object, whose memory ownership is transfered to the library and must be heap allocated
 * @return the new pointer to the torrent. if the torrent is already in the storage, the passed torrent will be freed, so the return value must be checked if you intend to use the torrent weiter
 */

struct torrent * add_torrent (struct dht * d, struct torrent * t) {
	return *(struct torrent **) tsearch(t, &d->torrents, torrent_compare);
}

/**
 * deletes a torrent from storage. if you downloaded a torrent and set keep/announce flags, do not remove_torrent once you're done with it, but instead just clear keep/announce bits. this will remove the torrent when necessary.
 *
 * @param d	[in]	the library handle
 * @param t	[in]	the pointer to the torrent to be deleted. do not craft torrent yourself, it must be stored in dht and that specific instance must be passed
 */

void remove_torrent (struct dht * d, struct torrent * t) {
	tdelete(t, &d->dht->torrents, torrent_compare);
	free(t);
}

/**
 * find a torrent based on hash
 *
 * @param d	[in]	the library handle
 * @param h	[in]	a 20 byte infohash
 */

struct torrent * find_torrent (struct dht * d, const char * h) {
	struct torrent t;
	memcpy(t.hash, h, 20);
	const struct torrent ** t = tfind(&t, &d->torrents, torrent_compare);
	if (t)
		return *t;
}

/**
 * returns a dict containing nodes or nodes6 bencoding list (with a key) with compact nodes in the bucket. if exact node is found, only that one is in the list.
 *
 * @param d	[in]	library handle
 * @param id	[in]	target node id, 20 bytes is read from this location
 * @param f	[in]	address family, AF_INET or AF_INET6
 * @return bencoding object whose memory ownership and free responsibility is transfered to the caller
 */

struct bencoding * nodes (const struct dht * d, const char * id, sa_family_t f) {
	struct bencoding * nodes = calloc(1, sizeof *nodes);
	nodes->type = list;
	nodes->key = bstr(strdup(f == AF_INET ? "nodes" : "nodes6"));
	binsert(r, nodes);
	struct bucket * bucket = f == AF_INET ? d->buckets : d->bucket6;
	struct node * found = find(id, &bucket, NULL);
#define ADDRLEN(f) (f == AF_INET ? 4 : 16)
	if (found) {
		struct bencoding * compact = calloc(1, sizeof *compact);
		compact->type = string;
		compact->value = malloc((compact->valuelen = 20+ADDRLEN(f)+2));
		memcpy(compact->value, found->id, 20);
		memcpy(compact->value+20, found->addr.sin6_addr.s6_addr+(16-ADDRLEN(f)), ADDRLEN(f));
		memcpy(compact->value+20+ADDRLEN(f), found->addr.sin6_port, 2);
		binsert(nodes, compact);
	} else {
		struct node * node = bucket->nodes;
		while (node) {
			struct bencoding * compact = calloc(1, sizeof *compact);
			compact->type = string;
			compact->value = malloc((compact->valuelen = 20+ADDRLEN(f)+2));
			memcpy(compact->value, found->id, 20);
			memcpy(compact->value+20, found->addr.sin6_addr.s6_addr+(16-ADDRLEN(f)), ADDRLEN(f));
			memcpy(compact->value+20+ADDRLEN(f), found->addr.sin6_port, 2);
			binsert(nodes, compact);
			node = node->next;
		}
	}
	return nodes;
}

/**
 * handles an incoming packet
 *
 * @param d	[in]	library handle
 * @param pkt	[in]	incoming UDP packet content
 * @param len	[in]	length of the packet
 * @param addr	[in]	IP address and port of sender
 */

void handle (struct dht * d, char * pkt, int len, struct sockaddr_in6 addr) {
	struct bdecoding * b = bdecode(pkt, len, replace);
	struct bdecoding * v = bpath(b, "v");
	char * node_ver = "";
	char remote[INET_ADDRSTRLEN + INET6_ADDRSTRLEN + 7 + (v && v->type & string) ? v->valuelen : 0];
	if (!inet_ntop(addr.sa_family, &addr, remote, sizeof addr))
		snprintf(remote, sizeof remote,  "(inet_ntop: %s)", strerror(errno));
		sprintf(remote+strlen(remote), ":%d", ntohs(addr.sin6_port));
	}
	if (v && v->type & string) {
		node_ver = v->value;
		sprintf(remote+strlen(remote), "-%s", node_ver);
	}
	struct bdecoding * y = bpath(b, "y");
	char * msg_type = "";
	if (y && y->type & string)
		msg_type = y->value;
	switch (msg_type[0]) {
		case 'Q':
		case 'q':
			struct bencoding * q = bpath(b, "q");
			char * qtype = "";
			if (q && q->type & string)
				qtype = q->value;
			struct bencoding * rid = bpath(b, "a/id");
			if (rid && rid->type & string && rid->valuelen == 20)
				potential_node(d, &addr, rid->value);
			switch (qtype[0]) {
				case 'P': // ping
				case 'p':
					else { // see NOTE01
						int len = b2json_length(b);
						char j[len+1];
						b2json(j, b);
						j[len] = '\0';
						L("%s did not send a valid id in %s", remote, j);
					}
					struct bencoding * id = calloc(1, sizeof *id);
					id->type = string;
					id->key = bstr(strdup("id"));
					memcpy((id->value = malloc((id->valuelen = 20))), d->id, 20);
					struct bencoding * r = calloc(1, sizeof *r);
					r->type = dict;
					r->key = bstr(strdup("r"));
					binsert(r, id);
					struct bencoding * y = bstr(strdup("r"));
					y->key = bstr(strdup("y"));
					struct bencoding * response = calloc(1, sizeof *response);
					response->type = dict;
					binsert(response, y);
					binsert(response, r);
					binsert(response, bclone(bpath(b, "t")));
					sendb(d, response, &addr, addrlen);
					free_bencoding(response);
					break;
				case 'F': // find_node
				case 'f':
					struct bencoding * target = bpath(b, "a/target");
					if (!target || !(target->type & string) || target->valuelen != 20)
						break; // see NOTE01
					struct bencoding * response = calloc(1, sizeof *response);
					response->type = dict;
					struct bencoding * y = bstr(strdup("r"));
					y->key = bstr(strdup("y"));
					binsert(response, y);
					binsert(response, bclone(bpath(b, "r")));
					struct bencoding * r = calloc(1, sizeof *r);
					r->type = dict;
					struct bencoding * id = calloc(1, sizeof *id);
					id->type = string;
					id->key = bstr(strdup("id"));
					memcpy((id->value = malloc((id->valuelen = 20))), d->id, 20);
					binsert(r, id);
					binsert(response, r);
					if (family(addr.sin6_addr.s6_addr) == AF_INET || bval(bpath("a/want"), "v4"))
						binsert(response, nodes(d, target->value, AF_INET));
					if (family(addr.sin6_addr.s6_addr) == AF_INET6 || bval(bpath("a/want"), "v6")) {
						binsert(response, nodes(d, target->value, AF_INET6));
					sendb(d, response, &addr, addrlen);
					break;
				case 'G': // get_peers
				case 'g':
					struct bencoding * hash = bpath(b, "a/info_hash");
					if (!hash || !(hash->type & string) || target->valuelen != 20)
						break; // see NOTE01
					struct bencoding * response = calloc(1, sizeof *response);
					response->type = dict;
					struct benncoding * y = bstr(strdup("r"));
					y->key = bstr(strdup("y"));
					binsert(response, y);
					binsert(response, bclone(bpath(b, "r")));
					struct bencoding * r = calloc(1, sizeof *r);
					r->type = dict;
					struct bencoding * id = calloc(1, sizeof *id);
					id->type = string;
					id->key = bstr(strdup("id"));
					memcpy((id->value = malloc((id->valuelen = 20))), d->id, 20);
					binsert(r, id);
					binsert(response, r);
					if (family(addr.sin6_addr.s6_addr) == AF_INET || bval(bpath("a/want"), "v4"))
						binsert(response, nodes(d, target->value, AF_INET));
					if (family(addr.sin6_addr.s6_addr) == AF_INET6 || bval(bpath("a/want"), "v6")) {
						binsert(response, nodes(d, target->value, AF_INET6));
					// TODO: token, peers
					sendb(d, response, &addr, addrlen);
					break;
				default: // see NOTE01
					int len = b2json_length(b);
					char json[len+1];
					b2json(json, b);
					json[len] = '\0';
					L(dht->log, "%s sent an unknown query type: %s");
					break;
			}
			break;
		case 'R':
		case 'r':
			break;
		case 'E':
		case 'e':
			struct bdecoding * e = bpath(b, "e");
			char * errtype = "Unspecified Error";
			if (e && e->child)
				switch (e->child->intvalue) {
					case 201:
						errtype = "Generic Error";
						break;
					case 202:
						errtype = "Server Error";
						break;
					case 203:
						errtype = "Protocol Error, such as a malformed packet, invalid arguments, or bad token";
						break;
					case 204:
						errtype = "Method Unknown";
						break;
					default:
						errtype = "Unknown Error";
						break;
				}
			char * msg = NULL;
			if (e && e->child && e->child->next && e->child->next->type & string)
				msg = e->child->next->value;
			L(d->log, "%s sent %s%s%s", remote, errtype, msg ? ": " : "", msg ? msg : "");
			break;
		default: // NOTE01 sending an error is unfortunately bad in this case, since clever hackers can force two servers speaking entirely different UDP based protcols into sending error messages to each other, telling one another that they don't understand each other's messages.
			int len = b2json_length(b);
			char json[len+1];
			b2json(json, b);
			json[len] = '\0';
			L(dht->log, "%s sent an unknown type: %s");
			// send_error(d, b, &addr, addrlen, 203, "unknown type");
			break;
	}
	struct bdecoding * trans_id = bpath(b, "t");
	free_bencoding(b);
}

/**
 * does periodic work for the library, called every 13 minutes
 *
 * namely, it sends UDP packets:
 * 	- announcing all torrents with announce
 * 	- searching deeper DHT storage nodes for torrents with keep and announce
 * 	- get_peers on torrents with keep
 *
 * this can be a lot of packets, so please keep number of torrents with keep and announce low
 */

/**
 * does work; syncs with the network, handles incoming queries.
 *
 * call this:
 * 	- whenever socket can be read from (via poll/epoll/select/...)
 * 	- every 13 minutes, even if it was called for incoming packets in this time period
 * 		+ stale buckets are refreshed
 *		+ peers are refetched for joined torrents and announcements are sent
 *		+ calling it more often is discouraged, since every periodic call sends out UDP packets for PEX and DHT searches/announces of torrents
 *
 * @param d	[in]	dht library handle
 */

void work (struct dht * d) {
	char packet[65536];
	struct sockaddr_in6 addr;
	socklen_t addrlen = sizeof addr;
	int ret = recvfrom(d->socket, packet, 65536, MSG_DONTWAIT | MSG_TRUNC, &addr, &addrlen);
	if (addrlen != sizeof add)
		L(d->log, "addrlen changed, not parsing packet");
	else if (ret > 65536)
		L(d->log, "recvfrom()d larger packet than 65536, not parsing packet");
	else if (ret < 0) {
		if (ret != EAGAIN)
			L(d->log, "recvfrom(): %s", strerror(errno));
		else
			periodic(d);
	} else
		handle(d, packet, ret, addr);
}