MQTTPacket.c

00001 /*******************************************************************************
00002  * Copyright (c) 2014 IBM Corp.
00003  *
00004  * All rights reserved. This program and the accompanying materials
00005  * are made available under the terms of the Eclipse Public License v1.0
00006  * and Eclipse Distribution License v1.0 which accompany this distribution.
00007  *
00008  * The Eclipse Public License is available at
00009  *    http://www.eclipse.org/legal/epl-v10.html
00010  * and the Eclipse Distribution License is available at
00011  *   http://www.eclipse.org/org/documents/edl-v10.php.
00012  *
00013  * Contributors:
00014  *    Ian Craggs - initial API and implementation and/or initial documentation
00015  *    Sergio R. Caprile - non-blocking packet read functions for stream transport
00016  *******************************************************************************/
00017 
00018 #include "StackTrace.h"
00019 #include "MQTTPacket.h"
00020 
00021 #include <string.h>
00022 
00023 /**
00024  * Encodes the message length according to the MQTT algorithm
00025  * @param buf the buffer into which the encoded data is written
00026  * @param length the length to be encoded
00027  * @return the number of bytes written to buffer
00028  */
00029 int MQTTPacket_encode(unsigned char* buf, int length)
00030 {
00031     int rc = 0;
00032 
00033     FUNC_ENTRY;
00034     do
00035     {
00036         char d = length % 128;
00037         length /= 128;
00038         /* if there are more digits to encode, set the top bit of this digit */
00039         if (length > 0)
00040             d |= 0x80;
00041         buf[rc++] = d;
00042     } while (length > 0);
00043     FUNC_EXIT_RC(rc);
00044     return rc;
00045 }
00046 
00047 
00048 /**
00049  * Decodes the message length according to the MQTT algorithm
00050  * @param getcharfn pointer to function to read the next character from the data source
00051  * @param value the decoded length returned
00052  * @return the number of bytes read from the socket
00053  */
00054 int MQTTPacket_decode(int (*getcharfn)(unsigned char*, int), int* value)
00055 {
00056     unsigned char c;
00057     int multiplier = 1;
00058     int len = 0;
00059 #define MAX_NO_OF_REMAINING_LENGTH_BYTES 4
00060 
00061     FUNC_ENTRY;
00062     *value = 0;
00063     do
00064     {
00065         int rc = MQTTPACKET_READ_ERROR;
00066 
00067         if (++len > MAX_NO_OF_REMAINING_LENGTH_BYTES)
00068         {
00069             rc = MQTTPACKET_READ_ERROR; /* bad data */
00070             goto exit;
00071         }
00072         rc = (*getcharfn)(&c, 1);
00073         if (rc != 1)
00074             goto exit;
00075         *value += (c & 127) * multiplier;
00076         multiplier *= 128;
00077     } while ((c & 128) != 0);
00078 exit:
00079     FUNC_EXIT_RC(len);
00080     return len;
00081 }
00082 
00083 
00084 int MQTTPacket_len(int rem_len)
00085 {
00086     rem_len += 1; /* header byte */
00087 
00088     /* now remaining_length field */
00089     if (rem_len < 128)
00090         rem_len += 1;
00091     else if (rem_len < 16384)
00092         rem_len += 2;
00093     else if (rem_len < 2097151)
00094         rem_len += 3;
00095     else
00096         rem_len += 4;
00097     return rem_len;
00098 }
00099 
00100 
00101 static unsigned char* bufptr;
00102 
00103 int bufchar(unsigned char* c, int count)
00104 {
00105     int i;
00106 
00107     for (i = 0; i < count; ++i)
00108         *c = *bufptr++;
00109     return count;
00110 }
00111 
00112 
00113 int MQTTPacket_decodeBuf(unsigned char* buf, int* value)
00114 {
00115     bufptr = buf;
00116     return MQTTPacket_decode(bufchar, value);
00117 }
00118 
00119 /**
00120  * Calculates an integer from two bytes read from the input buffer
00121  * @param pptr pointer to the input buffer - incremented by the number of bytes used & returned
00122  * @return the integer value calculated
00123  */
00124 int readInt(unsigned char** pptr)
00125 {
00126     unsigned char* ptr = *pptr;
00127     int len = 256*(*ptr) + (*(ptr+1));
00128     *pptr += 2;
00129     return len;
00130 }
00131 
00132 
00133 /**
00134  * Reads one character from the input buffer.
00135  * @param pptr pointer to the input buffer - incremented by the number of bytes used & returned
00136  * @return the character read
00137  */
00138 char readChar(unsigned char** pptr)
00139 {
00140     char c = **pptr;
00141     (*pptr)++;
00142     return c;
00143 }
00144 
00145 
00146 /**
00147  * Writes one character to an output buffer.
00148  * @param pptr pointer to the output buffer - incremented by the number of bytes used & returned
00149  * @param c the character to write
00150  */
00151 void writeChar(unsigned char** pptr, char c)
00152 {
00153     **pptr = c;
00154     (*pptr)++;
00155 }
00156 
00157 
00158 /**
00159  * Writes an integer as 2 bytes to an output buffer.
00160  * @param pptr pointer to the output buffer - incremented by the number of bytes used & returned
00161  * @param anInt the integer to write
00162  */
00163 void writeInt(unsigned char** pptr, int anInt)
00164 {
00165     **pptr = (unsigned char)(anInt / 256);
00166     (*pptr)++;
00167     **pptr = (unsigned char)(anInt % 256);
00168     (*pptr)++;
00169 }
00170 
00171 
00172 /**
00173  * Writes a "UTF" string to an output buffer.  Converts C string to length-delimited.
00174  * @param pptr pointer to the output buffer - incremented by the number of bytes used & returned
00175  * @param string the C string to write
00176  */
00177 void writeCString(unsigned char** pptr, const char* string)
00178 {
00179     int len = strlen(string);
00180     writeInt(pptr, len);
00181     memcpy(*pptr, string, len);
00182     *pptr += len;
00183 }
00184 
00185 
00186 int getLenStringLen(char* ptr)
00187 {
00188     int len = 256*((unsigned char)(*ptr)) + (unsigned char)(*(ptr+1));
00189     return len;
00190 }
00191 
00192 void writeMQTTString(unsigned char** pptr, MQTTString mqttstring)
00193 {
00194     if (mqttstring.lenstring.len > 0)
00195     {
00196         writeInt(pptr, mqttstring.lenstring.len);
00197         memcpy(*pptr, mqttstring.lenstring.data, mqttstring.lenstring.len);
00198         *pptr += mqttstring.lenstring.len;
00199     }
00200     else if (mqttstring.cstring)
00201         writeCString(pptr, mqttstring.cstring);
00202     else
00203         writeInt(pptr, 0);
00204 }
00205 
00206 
00207 /**
00208  * @param mqttstring the MQTTString structure into which the data is to be read
00209  * @param pptr pointer to the output buffer - incremented by the number of bytes used & returned
00210  * @param enddata pointer to the end of the data: do not read beyond
00211  * @return 1 if successful, 0 if not
00212  */
00213 int readMQTTLenString(MQTTString* mqttstring, unsigned char** pptr, unsigned char* enddata)
00214 {
00215     int rc = 0;
00216 
00217     FUNC_ENTRY;
00218     /* the first two bytes are the length of the string */
00219     if (enddata - (*pptr) > 1) /* enough length to read the integer? */
00220     {
00221         mqttstring->lenstring.len = readInt(pptr); /* increments pptr to point past length */
00222         if (&(*pptr)[mqttstring->lenstring.len] <= enddata)
00223         {
00224             mqttstring->lenstring.data = (char*)*pptr;
00225             *pptr += mqttstring->lenstring.len;
00226             rc = 1;
00227         }
00228     }
00229     mqttstring->cstring = NULL;
00230     FUNC_EXIT_RC(rc);
00231     return rc;
00232 }
00233 
00234 
00235 /**
00236  * Return the length of the MQTTstring - C string if there is one, otherwise the length delimited string
00237  * @param mqttstring the string to return the length of
00238  * @return the length of the string
00239  */
00240 int MQTTstrlen(MQTTString mqttstring)
00241 {
00242     int rc = 0;
00243 
00244     if (mqttstring.cstring)
00245         rc = strlen(mqttstring.cstring);
00246     else
00247         rc = mqttstring.lenstring.len;
00248     return rc;
00249 }
00250 
00251 
00252 /**
00253  * Compares an MQTTString to a C string
00254  * @param a the MQTTString to compare
00255  * @param bptr the C string to compare
00256  * @return boolean - equal or not
00257  */
00258 int MQTTPacket_equals(MQTTString* a, char* bptr)
00259 {
00260     int alen = 0,
00261         blen = 0;
00262     char *aptr;
00263     
00264     if (a->cstring)
00265     {
00266         aptr = a->cstring;
00267         alen = strlen(a->cstring);
00268     }
00269     else
00270     {
00271         aptr = a->lenstring.data;
00272         alen = a->lenstring.len;
00273     }
00274     blen = strlen(bptr);
00275     
00276     return (alen == blen) && (strncmp(aptr, bptr, alen) == 0);
00277 }
00278 
00279 
00280 /**
00281  * Helper function to read packet data from some source into a buffer
00282  * @param buf the buffer into which the packet will be serialized
00283  * @param buflen the length in bytes of the supplied buffer
00284  * @param getfn pointer to a function which will read any number of bytes from the needed source
00285  * @return integer MQTT packet type, or -1 on error
00286  * @note  the whole message must fit into the caller's buffer
00287  */
00288 int MQTTPacket_read(unsigned char* buf, int buflen, int (*getfn)(unsigned char*, int))
00289 {
00290     int rc = -1;
00291     MQTTHeader header = {0};
00292     int len = 0;
00293     int rem_len = 0;
00294 
00295     /* 1. read the header byte.  This has the packet type in it */
00296     if ((*getfn)(buf, 1) != 1)
00297         goto exit;
00298 
00299     len = 1;
00300     /* 2. read the remaining length.  This is variable in itself */
00301     MQTTPacket_decode(getfn, &rem_len);
00302     len += MQTTPacket_encode(buf + 1, rem_len); /* put the original remaining length back into the buffer */
00303 
00304     /* 3. read the rest of the buffer using a callback to supply the rest of the data */
00305     if((rem_len + len) > buflen)
00306         goto exit;
00307     if (rem_len && ((*getfn)(buf + len, rem_len) != rem_len))
00308         goto exit;
00309 
00310     header.byte = buf[0];
00311     rc = header.bits.type;
00312 exit:
00313     return rc;
00314 }
00315 
00316 /**
00317  * Decodes the message length according to the MQTT algorithm, non-blocking
00318  * @param trp pointer to a transport structure holding what is needed to solve getting data from it
00319  * @param value the decoded length returned
00320  * @return integer the number of bytes read from the socket, 0 for call again, or -1 on error
00321  */
00322 static int MQTTPacket_decodenb(MQTTTransport *trp)
00323 {
00324     unsigned char c;
00325     int rc = MQTTPACKET_READ_ERROR;
00326 
00327     FUNC_ENTRY;
00328     if(trp->len == 0){      /* initialize on first call */
00329         trp->multiplier = 1;
00330         trp->rem_len = 0;
00331     }
00332     do {
00333         int frc;
00334         if (trp->len >= MAX_NO_OF_REMAINING_LENGTH_BYTES)
00335             goto exit;
00336         if ((frc=(*trp->getfn)(trp->sck, &c, 1)) == -1)
00337             goto exit;
00338         if (frc == 0){
00339             rc = 0;
00340             goto exit;
00341         }
00342         ++(trp->len);
00343         trp->rem_len += (c & 127) * trp->multiplier;
00344         trp->multiplier *= 128;
00345     } while ((c & 128) != 0);
00346     rc = trp->len;
00347 exit:
00348     FUNC_EXIT_RC(rc);
00349     return rc;
00350 }
00351 
00352 /**
00353  * Helper function to read packet data from some source into a buffer, non-blocking
00354  * @param buf the buffer into which the packet will be serialized
00355  * @param buflen the length in bytes of the supplied buffer
00356  * @param trp pointer to a transport structure holding what is needed to solve getting data from it
00357  * @return integer MQTT packet type, 0 for call again, or -1 on error
00358  * @note  the whole message must fit into the caller's buffer
00359  */
00360 int MQTTPacket_readnb(unsigned char* buf, int buflen, MQTTTransport *trp)
00361 {
00362     int rc = -1, frc;
00363     MQTTHeader header = {0};
00364 
00365     switch(trp->state){
00366     default:
00367         trp->state = 0;
00368         /*FALLTHROUGH*/
00369     case 0:
00370         /* read the header byte.  This has the packet type in it */
00371         if ((frc=(*trp->getfn)(trp->sck, buf, 1)) == -1)
00372             goto exit;
00373         if (frc == 0)
00374             return 0;
00375         trp->len = 0;
00376         ++trp->state;
00377         /*FALLTHROUGH*/
00378         /* read the remaining length.  This is variable in itself */
00379     case 1:
00380         if((frc=MQTTPacket_decodenb(trp)) == MQTTPACKET_READ_ERROR)
00381             goto exit;
00382         if(frc == 0)
00383             return 0;
00384         trp->len = 1 + MQTTPacket_encode(buf + 1, trp->rem_len); /* put the original remaining length back into the buffer */
00385         if((trp->rem_len + trp->len) > buflen)
00386             goto exit;
00387         ++trp->state;
00388         /*FALLTHROUGH*/
00389     case 2:
00390         if(trp->rem_len){
00391             /* read the rest of the buffer using a callback to supply the rest of the data */
00392             if ((frc=(*trp->getfn)(trp->sck, buf + trp->len, trp->rem_len)) == -1)
00393                 goto exit;
00394             if (frc == 0)
00395                 return 0;
00396             trp->rem_len -= frc;
00397             trp->len += frc;
00398             if(trp->rem_len)
00399                 return 0;
00400         }
00401         header.byte = buf[0];
00402         rc = header.bits.type;
00403         break;
00404     }
00405 
00406 exit:
00407     trp->state = 0;
00408     return rc;
00409 }
00410