unrealircd/src/modules/websocket.c

/*
 * websocket - WebSocket support (RFC6455)
 * (C)Copyright 2016 Bram Matthys and the UnrealIRCd team
 * License: GPLv2
 * This module was sponsored by Aberrant Software Inc.
 */
   
#include "unrealircd.h"
#include <limits.h>

#define WEBSOCKET_VERSION "1.0.0"

ModuleHeader MOD_HEADER(websocket)
  = {
	"websocket",
	WEBSOCKET_VERSION,
	"WebSocket support (RFC6455)",
	"3.2-b8-1",
	NULL 
    };

#if CHAR_MIN < 0
 #error "In UnrealIRCd char should always be unsigned. Check your compiler"
#endif

struct _websocketuser {
	char get; /**< GET initiated */
	char handshake_completed; /**< Handshake completed, use data frames */
	char *handshake_key; /**< Handshake key (used during handshake) */
	char *lefttoparse; /**< Leftover buffer to parse */
	int lefttoparselen; /**< Length of lefttoparse buffer */
};
typedef struct _websocketuser WebSocketUser;

#define WSU(cptr)	((WebSocketUser *)moddata_client(cptr, websocket_md).ptr)

#define WEBSOCKET_MAGIC_KEY "258EAFA5-E914-47DA-95CA-C5AB0DC85B11" /* see RFC6455 */

#define WSOP_CONTINUATION 0x00
#define WSOP_TEXT         0x01
#define WSOP_BINARY       0x02
#define WSOP_CLOSE        0x08
#define WSOP_PING         0x09
#define WSOP_PONG         0x0a

/* Forward declarations */
int websocket_packet_out(aClient *from, aClient *to, char **msg, int *length);
int websocket_packet_in(aClient *sptr, char *readbuf, int *length);
void websocket_mdata_free(ModData *m);
int websocket_handle_packet(aClient *sptr, char *readbuf, int length);
int websocket_handle_handshake(aClient *sptr, char *readbuf, int *length);
int websocket_complete_handshake(aClient *sptr);
int websocket_handle_packet_ping(aClient *sptr, char *buf, int len);
int websocket_handle_packet_pong(aClient *sptr, char *buf, int len);
int websocket_create_frame(int opcode, char **buf, int *len);
int websocket_send_frame(aClient *sptr, int opcode, char *buf, int len);

/* Global variables */
ModDataInfo *websocket_md;

MOD_INIT(websocket)
{
	ModDataInfo mreq;

	MARK_AS_OFFICIAL_MODULE(modinfo);
	
	HookAdd(modinfo->handle, HOOKTYPE_PACKET, 0, websocket_packet_out);
	HookAdd(modinfo->handle, HOOKTYPE_RAWPACKET_IN, 0, websocket_packet_in);
	
	memset(&mreq, 0, sizeof(mreq));
	mreq.name = "websocket";
	mreq.serialize = NULL;
	mreq.unserialize = NULL;
	mreq.free = websocket_mdata_free;
	mreq.sync = 0;
	mreq.type = MODDATATYPE_CLIENT;
	websocket_md = ModDataAdd(modinfo->handle, mreq);

	return MOD_SUCCESS;
}

MOD_LOAD(websocket)
{
	if (SHOWCONNECTINFO)
	{
		config_warn("I'm disabling set::options::show-connect-info for you "
		            "as this setting is incompatible with the websocket module.");
		SHOWCONNECTINFO = 0;
	}
	
	return MOD_SUCCESS;
}

MOD_UNLOAD(websocket)
{
	return MOD_SUCCESS;
}

/** UnrealIRCd internals: free WebSocketUser object. */
void websocket_mdata_free(ModData *m)
{
	WebSocketUser *wsu = (WebSocketUser *)m->ptr;
	if (wsu)
	{
		safefree(wsu->handshake_key);
		safefree(wsu->lefttoparse);
		MyFree(m->ptr);
	}
}

/** Outgoing packet hook.
 * This transforms the output to be Websocket-compliant, if necessary.
 */
int websocket_packet_out(aClient *from, aClient *to, char **msg, int *length)
{
	if (MyConnect(to) && WSU(to) && WSU(to)->handshake_completed)
	{
		websocket_create_frame(WSOP_BINARY, msg, length);
		return 0;
	}
	return 0;
}

int websocket_handle_websocket(aClient *sptr, char *readbuf2, int length2)
{
	int n;
	char *ptr;
	int length;
	int length1 = WSU(sptr)->lefttoparselen;
	char readbuf[4096];
	
	length = length1 + length2;
	if (length > sizeof(readbuf)-1)
	{
		dead_link(sptr, "Illegal buffer stacking/Excess flood");
		return 0;
	}
	
	if (length1 > 0)
		memcpy(readbuf, WSU(sptr)->lefttoparse, length1);
	memcpy(readbuf+length1, readbuf2, length2);

	safefree(WSU(sptr)->lefttoparse);
	WSU(sptr)->lefttoparselen = 0;
	
	ptr = readbuf;
	do {
		n = websocket_handle_packet(sptr, ptr, length);
		if (n < 0)
			return -1; /* killed -- STOP processing */
		if (n == 0)
		{
			/* Short read. Stop processing for now, but save data for next time */
			safefree(WSU(sptr)->lefttoparse);
			WSU(sptr)->lefttoparse = MyMallocEx(length);
			WSU(sptr)->lefttoparselen = length;
			memcpy(WSU(sptr)->lefttoparse, ptr, length);
			return 0;
		}
		length -= n;
		ptr += n;
		if (length < 0)
			abort(); /* less than 0 is impossible */
	} while(length > 0);

	return 0;
}

/** Incoming packet hook.
 * This processes Websocket frames, if this is a websocket connection.
 * NOTE The different return values:
 * -1 means: don't touch this client anymore, it has or might have been killed!
 * 0 means: don't process this data, but you can read another packet if you want
 * >0 means: process this data (regular IRC data, non-websocket stuff)
 */
int websocket_packet_in(aClient *sptr, char *readbuf, int *length)
{
	if ((sptr->local->receiveM == 0) && !WSU(sptr) && (*length > 8) && !strncmp(readbuf, "GET ", 4))
	{
		/* Allocate a new WebSocketUser struct for this session */
		moddata_client(sptr, websocket_md).ptr = MyMallocEx(sizeof(WebSocketUser));
		WSU(sptr)->get = 1;
	}

	if (!WSU(sptr))
		return 1; /* "normal" IRC client */
	
	if (WSU(sptr)->handshake_completed)
		return websocket_handle_websocket(sptr, readbuf, *length);
	/* else.. */
	return websocket_handle_handshake(sptr, readbuf, length);
}

/** Helper function to parse the HTTP header consisting of multiple 'Key: value' pairs */
int websocket_handshake_helper(char *buffer, int len, char **key, char **value, char **lastloc, int *end_of_request)
{
	static char buf[4096], *nextptr;
	char *p;
	char *k = NULL, *v = NULL;
	int foundlf = 0;
	
	if (buffer)
	{
		/* Initialize */
		if (len > sizeof(buf) - 1)
			len = sizeof(buf) - 1;

		memcpy(buf, buffer, len);
		buf[len] = '\0';
		nextptr = buf;
	}
	
	*end_of_request = 0;
	
	p = nextptr;
	
	if (!p)
	{
		*key = *value = NULL;
		return 0; /* done processing data */
	}
	
	if (!strncmp(p, "\n", 1) || !strncmp(p, "\r\n", 2))
	{
		*key = *value = NULL;
		*end_of_request = 1;
		return 0;
	}

	/* Note: p *could* point to the NUL byte ('\0') */
	
	/* Special handling for GET line itself. */
	if (!strncmp(p, "GET ", 4))
	{
		k = "GET";
		p += 4;
		v = p; /* SET VALUE */
		nextptr = NULL; /* set to "we are done" in case next for loop fails */
		for (; *p; p++)
		{
			if (*p == ' ')
			{
				*p = '\0'; /* terminate before "HTTP/1.X" part */
			}
			else if (*p == '\r')
			{
				*p = '\0'; /* eat silently, but don't consider EOL */
			}
			else if (*p == '\n')
			{
				*p = '\0';
				nextptr = p+1; /* safe, there is data or at least a \0 there */
				break;
			}
		}
		*key = k;
		*value = v;
		return 1;
	}

	/* Header parsing starts here.
	 * Example line "Host: www.unrealircd.org"
	 */
	k = p; /* SET KEY */
	
	/* First check if the line contains a terminating \n. If not, don't process it
	 * as it may have been a cut header.
	 */
	for (; *p; p++)
	{
		if (*p == '\n')
		{
			foundlf = 1;
			break;
		}
	}
	
	if (!foundlf)
	{
		*key = *value = NULL;
		*lastloc = k;
		return 0;
	}
	
	p = k;
	
	for (; *p; p++)
	{
		if ((*p == '\n') || (*p == '\r'))
		{
			/* Reached EOL but 'value' not found */
			*p = '\0';
			break;
		}
		if (*p == ':')
		{
			*p++ = '\0';
			if (*p++ != ' ')
				break; /* missing mandatory space after ':' */
			
			v = p; /* SET VALUE */
			nextptr = NULL; /* set to "we are done" in case next for loop fails */
			for (; *p; p++)
			{
				if (*p == '\r')
				{
					*p = '\0'; /* eat silently, but don't consider EOL */
				}
				else if (*p == '\n')
				{
					*p = '\0';
					nextptr = p+1; /* safe, there is data or at least a \0 there */
					break;
				}
			}
			/* A key-value pair was succesfully parsed, return it */
			*key = k;
			*value = v;
			return 1;
		}
	}
	
	/* Fatal parse error */
	*key = *value = NULL;
	return 0;
}

/** Handle client GET WebSocket handshake.
 * Yes, I'm going to assume that the header fits in one packet and one packet only.
 */
int websocket_handle_handshake(aClient *sptr, char *readbuf, int *length)
{
	char *key, *value;
	int r, end_of_request;
	char netbuf[2048];
	char *lastloc = NULL;
	int n, maxcopy, nprefix=0;

	/** Frame re-assembling starts here **/
	*netbuf = '\0';
	if (WSU(sptr)->lefttoparse)
	{
		strlcpy(netbuf, WSU(sptr)->lefttoparse, sizeof(netbuf));
		nprefix = strlen(netbuf);
	}
	maxcopy = sizeof(netbuf) - nprefix - 1;
	/* (Need to some manual checking here as strlen() can't be safely used
	 *  on readbuf. Same is true for strlncat since it uses strlen().)
	 */
	n = *length;
	if (n > maxcopy)
		n = maxcopy;
	if (n <= 0)
	{
		dead_link(sptr, "Oversized line");
		return -1;
	}
	memcpy(netbuf+nprefix, readbuf, n); /* SAFE: see checking above */
	netbuf[n+nprefix] = '\0';
	safefree(WSU(sptr)->lefttoparse);

	/** Now step through the lines.. **/
	for (r = websocket_handshake_helper(netbuf, strlen(netbuf), &key, &value, &lastloc, &end_of_request);
	     r;
	     r = websocket_handshake_helper(NULL, 0, &key, &value, &lastloc, &end_of_request))
	{
		if (!stricmp(key, "Sec-WebSocket-Key"))
		{
			if (strchr(value, ':'))
			{
				/* This would cause unserialization issues. Should be base64 anyway */
				dead_link(sptr, "Invalid characters in Sec-WebSocket-Key");
				return -1;
			}
			safestrdup(WSU(sptr)->handshake_key, value);
		}
	}
	
	if (end_of_request)
	{
		if (!WSU(sptr)->handshake_key)
		{
			dead_link(sptr, "Invalid WebSocket request");
			return -1;
		}
		websocket_complete_handshake(sptr);
		return 0;
	}

	if (lastloc)
	{
		/* Last line was cut somewhere, save it for next round. */
		safefree(WSU(sptr)->lefttoparse);
		WSU(sptr)->lefttoparse = strdup(lastloc);
	}
	return 0; /* don't let UnrealIRCd process this */
}

/** Complete the handshake by sending the appropriate HTTP 101 response etc. */
int websocket_complete_handshake(aClient *sptr)
{
	char buf[512], hashbuf[64];
	SHA_CTX hash;
	char sha1out[20]; /* 160 bits */
	
	WSU(sptr)->handshake_completed = 1;

	snprintf(buf, sizeof(buf), "%s%s", WSU(sptr)->handshake_key, WEBSOCKET_MAGIC_KEY);
	SHA1_Init(&hash);
	SHA1_Update(&hash, buf, strlen(buf));
	SHA1_Final(sha1out, &hash);
	
	b64_encode(sha1out, sizeof(sha1out), hashbuf, sizeof(hashbuf));
	
	snprintf(buf, sizeof(buf),
	         "HTTP/1.1 101 Switching Protocols\r\n"
	         "Upgrade: websocket\r\n"
	         "Connection: Upgrade\r\n"
	         "Sec-WebSocket-Accept: %s\r\n"
	         "\r\n",
	         hashbuf);
	
	/* Caution: we bypass sendQ flood checking by doing it this way.
	 * Risk is minimal, though, as we only permit limited text only
	 * once per session.
	 */
	dbuf_put(&sptr->local->sendQ, buf, strlen(buf));
	send_queued(sptr);
	
	return 0;
}

/* Add LF (if needed) to a buffer. Max 4K. */
void add_lf_if_needed(char **buf, int *len)
{
	static char newbuf[4096];
	char *b = *buf;
	int l = *len;

	if (l <= 0)
		return; /* too short */

	if (b[l - 1] == '\n')
		return; /* already contains \n */

	if (l >= sizeof(newbuf)-2)
		l = sizeof(newbuf)-2; /* cut-off if necessary */

	memcpy(newbuf, b, l);
	newbuf[l] = '\n';
	newbuf[l + 1] = '\0'; /* not necessary, but I like zero termination */
	l++;
	*buf = newbuf; /* new buffer */
	*len = l; /* new length */
}

/** WebSocket packet handler.
 * For more information on the format, check out page 28 of RFC6455.
 * @returns The number of bytes processed (the size of the frame)
 *          OR 0 to indicate a possible short read (want more data)
 *          OR -1 in case of an error.
 */
int websocket_handle_packet(aClient *sptr, char *readbuf, int length)
{
	char fin; /**< Final fragment */
	char opcode; /**< Opcode */
	char masked; /**< Masked */
	int len; /**< Length of the packet */
	char maskkey[4]; /**< Key used for masking */
	char *p, *payload;
	int total_packet_size;
	
	if (length < 4)
	{
		/* WebSocket packet too short */
		return 0;
	}
	
	fin    = readbuf[0] & 0x80;
	opcode = readbuf[0] & 0x7F;
	masked = readbuf[1] & 0x80;
	len    = readbuf[1] & 0x7F;
	p = &readbuf[2]; /* point to next element */
	
	/* actually 'fin' is unused.. we don't care. */
	
	if (!masked)
	{
		dead_link(sptr, "WebSocket packet not masked");
		return -1; /* Having the masked bit set is required (RFC6455 p29) */
	}
	
	if (len == 127)
	{
		dead_link(sptr, "WebSocket packet with insane size");
		return -1; /* Packets requiring 64bit lengths are not supported. Would be insane. */
	}

	total_packet_size = len + 2 + 4; /* 2 for header, 4 for mask key, rest for payload */

	/* Early (minimal) length check */
	if (length < total_packet_size)
	{
		/* WebSocket frame too short */
		return 0;
	}

	/* Len=126 is special. It indicates the data length is actually "126 or more" */
	if (len == 126)
	{
		/* Extended payload length (16 bit). For packets of >=126 bytes */
		len = (readbuf[2] << 8) + readbuf[3];
		if (len < 126)
		{
			dead_link(sptr, "WebSocket protocol violation (extended payload length too short)");
			return -1; /* This is a violation (not a short read), see page 29 */
		}
		p += 2; /* advance pointer 2 bytes */
		
		/* Need to check the length again, now it has changed: */
		if (length < len + 4 + 4)
		{
			/* WebSocket frame too short */
			return 0;
		}
		/* And update the packet size */
		total_packet_size = len + 4 + 4; /* 4 for header, 4 for mask key, rest for payload */
	}
	
	memcpy(maskkey, p, 4);
	p+= 4;
	payload = (len > 0) ? p : NULL;

	if (len > 0)
	{
		/* Unmask this thing (page 33, section 5.3) */
		int n;
		char v;
		for (n = 0; n < len; n++)
		{
			v = *p;
			*p++ = v ^ maskkey[n % 4];
		}
	}
	
	switch(opcode)
	{
		case WSOP_CONTINUATION:
		case WSOP_TEXT:
		case WSOP_BINARY:
			add_lf_if_needed(&payload, &len);
			if (!process_packet(sptr, payload, len, 1)) /* let UnrealIRCd process this data */
				return -1; /* fatal error occured (such as flood kill) */
			return total_packet_size;
		
		case WSOP_CLOSE:
			dead_link(sptr, "Connection closed"); /* TODO: Improve I guess */
			return -1;
		
		case WSOP_PING:
			if (websocket_handle_packet_ping(sptr, payload, len) < 0)
				return -1;
			return total_packet_size;
		
		case WSOP_PONG:
			if (websocket_handle_packet_pong(sptr, payload, len) < 0)
				return -1;
			return total_packet_size;
		
		default:
			dead_link(sptr, "WebSocket: Unknown opcode");
			return -1;
	}

	return -1; /* NOTREACHED */
}

int websocket_handle_packet_ping(aClient *sptr, char *buf, int len)
{
	if (len > 500)
	{
		dead_link(sptr, "WebSocket: oversized PING request");
		return -1;
	}
	websocket_send_frame(sptr, WSOP_PONG, buf, len);
	sptr->local->since++; /* lag penalty of 1 second */
	return 0;
}

int websocket_handle_packet_pong(aClient *sptr, char *buf, int len)
{
	/* We don't care */
	return 0;
}

/** Create a frame. Used for OUTGOING data. */
int websocket_create_frame(int opcode, char **buf, int *len)
{
	static char sendbuf[8192];
	
	sendbuf[0] = opcode | 0x80; /* opcode & final */
	
	if (*len > sizeof(sendbuf) - 8)
		abort(); /* should never happen (safety) */

	/* strip LF */
	if (*len > 0)
	{
		if (*(*buf + *len - 1) == '\n')
			*len = *len - 1;
	}
	/* strip CR */
	if (*len > 0)
	{
		if (*(*buf + *len - 1) == '\r')
			*len = *len - 1;
	}

	if (*len < 126)
	{
		/* Short payload */
		sendbuf[1] = (char)*len;
		memcpy(&sendbuf[2], *buf, *len);
		*buf = sendbuf;
		*len += 2;
	} else {
		/* Long payload */
		sendbuf[1] = 126;
		sendbuf[2] = (char)((*len >> 8) & 0xFF);
		sendbuf[3] = (char)(*len & 0xFF);
		memcpy(&sendbuf[4], *buf, *len);
		*buf = sendbuf;
		*len += 4;
	}
	return 0;
}

/** Create and send a frame */
int websocket_send_frame(aClient *sptr, int opcode, char *buf, int len)
{
	char *b = buf;
	int l = len;
	
	if (websocket_create_frame(opcode, &b, &l) < 0)
		return -1;
	
	if (DBufLength(&sptr->local->sendQ) > get_sendq(sptr))
	{
		dead_link(sptr, "Max SendQ exceeded");
		return -1;
	}
	
	dbuf_put(&sptr->local->sendQ, b, l);
	send_queued(sptr);
	return 0;
}