MQTT / MQTTPacket

Basic C library for MQTT packet serialization and deserialization

Dependents:   MQTT MQTT MQTT MQTT ... more

Fork of MQTTPacket by MQTT

This library is part of the EclipseTM Paho project; specifically the embedded client.

A basic MQTT library in C for packet serialization and deserialization

MQTTPacket.c@17:c5bd28cc139a, 2014-08-01 (annotated)

Committer:
icraggs
Date:
Fri Aug 01 17:25:52 2014 +0000
Revision:
17:c5bd28cc139a
Parent:
14:c2052aee81de
Child:
18:bf36e077e7b8
Initializations to remove compiler warnings

Who changed what in which revision?

UserRevisionLine numberNew contents of line
icraggs 0:7734401cc1b4 1 /*******************************************************************************
icraggs 0:7734401cc1b4 2 * Copyright (c) 2014 IBM Corp.
icraggs 0:7734401cc1b4 3 *
icraggs 0:7734401cc1b4 4 * All rights reserved. This program and the accompanying materials
icraggs 0:7734401cc1b4 5 * are made available under the terms of the Eclipse Public License v1.0
icraggs 0:7734401cc1b4 6 * and Eclipse Distribution License v1.0 which accompany this distribution.
icraggs 0:7734401cc1b4 7 *
icraggs 0:7734401cc1b4 8 * The Eclipse Public License is available at
icraggs 0:7734401cc1b4 9 * http://www.eclipse.org/legal/epl-v10.html
icraggs 0:7734401cc1b4 10 * and the Eclipse Distribution License is available at
icraggs 0:7734401cc1b4 11 * http://www.eclipse.org/org/documents/edl-v10.php.
icraggs 0:7734401cc1b4 12 *
icraggs 0:7734401cc1b4 13 * Contributors:
icraggs 0:7734401cc1b4 14 * Ian Craggs - initial API and implementation and/or initial documentation
icraggs 0:7734401cc1b4 15 *******************************************************************************/
icraggs 0:7734401cc1b4 16
icraggs 0:7734401cc1b4 17 #include "StackTrace.h"
icraggs 0:7734401cc1b4 18 #include "MQTTPacket.h"
icraggs 0:7734401cc1b4 19
icraggs 0:7734401cc1b4 20 #include <string.h>
icraggs 0:7734401cc1b4 21
icraggs 0:7734401cc1b4 22 /**
icraggs 0:7734401cc1b4 23 * Encodes the message length according to the MQTT algorithm
icraggs 0:7734401cc1b4 24 * @param buf the buffer into which the encoded data is written
icraggs 0:7734401cc1b4 25 * @param length the length to be encoded
icraggs 0:7734401cc1b4 26 * @return the number of bytes written to buffer
icraggs 0:7734401cc1b4 27 */
Ian Craggs 14:c2052aee81de 28 int MQTTPacket_encode(unsigned char* buf, int length)
icraggs 0:7734401cc1b4 29 {
icraggs 0:7734401cc1b4 30 int rc = 0;
icraggs 0:7734401cc1b4 31
icraggs 0:7734401cc1b4 32 FUNC_ENTRY;
icraggs 0:7734401cc1b4 33 do
icraggs 0:7734401cc1b4 34 {
icraggs 0:7734401cc1b4 35 char d = length % 128;
icraggs 0:7734401cc1b4 36 length /= 128;
icraggs 0:7734401cc1b4 37 /* if there are more digits to encode, set the top bit of this digit */
icraggs 0:7734401cc1b4 38 if (length > 0)
icraggs 0:7734401cc1b4 39 d |= 0x80;
icraggs 0:7734401cc1b4 40 buf[rc++] = d;
icraggs 0:7734401cc1b4 41 } while (length > 0);
icraggs 0:7734401cc1b4 42 FUNC_EXIT_RC(rc);
icraggs 0:7734401cc1b4 43 return rc;
icraggs 0:7734401cc1b4 44 }
icraggs 0:7734401cc1b4 45
icraggs 0:7734401cc1b4 46
icraggs 0:7734401cc1b4 47 /**
icraggs 0:7734401cc1b4 48 * Decodes the message length according to the MQTT algorithm
icraggs 0:7734401cc1b4 49 * @param getcharfn pointer to function to read the next character from the data source
icraggs 0:7734401cc1b4 50 * @param value the decoded length returned
icraggs 0:7734401cc1b4 51 * @return the number of bytes read from the socket
icraggs 0:7734401cc1b4 52 */
Ian Craggs 14:c2052aee81de 53 int MQTTPacket_decode(int (*getcharfn)(unsigned char*, int), int* value)
icraggs 0:7734401cc1b4 54 {
Ian Craggs 14:c2052aee81de 55 unsigned char c;
icraggs 0:7734401cc1b4 56 int multiplier = 1;
icraggs 0:7734401cc1b4 57 int len = 0;
icraggs 0:7734401cc1b4 58 #define MAX_NO_OF_REMAINING_LENGTH_BYTES 4
icraggs 0:7734401cc1b4 59
icraggs 0:7734401cc1b4 60 FUNC_ENTRY;
icraggs 0:7734401cc1b4 61 *value = 0;
icraggs 0:7734401cc1b4 62 do
icraggs 0:7734401cc1b4 63 {
icraggs 0:7734401cc1b4 64 int rc = MQTTPACKET_READ_ERROR;
icraggs 0:7734401cc1b4 65
icraggs 0:7734401cc1b4 66 if (++len > MAX_NO_OF_REMAINING_LENGTH_BYTES)
icraggs 0:7734401cc1b4 67 {
icraggs 0:7734401cc1b4 68 rc = MQTTPACKET_READ_ERROR; /* bad data */
icraggs 0:7734401cc1b4 69 goto exit;
icraggs 0:7734401cc1b4 70 }
icraggs 0:7734401cc1b4 71 rc = (*getcharfn)(&c, 1);
icraggs 0:7734401cc1b4 72 if (rc != 1)
icraggs 0:7734401cc1b4 73 goto exit;
icraggs 0:7734401cc1b4 74 *value += (c & 127) * multiplier;
icraggs 0:7734401cc1b4 75 multiplier *= 128;
icraggs 0:7734401cc1b4 76 } while ((c & 128) != 0);
icraggs 0:7734401cc1b4 77 exit:
icraggs 0:7734401cc1b4 78 FUNC_EXIT_RC(len);
icraggs 0:7734401cc1b4 79 return len;
icraggs 0:7734401cc1b4 80 }
icraggs 0:7734401cc1b4 81
icraggs 0:7734401cc1b4 82
icraggs 0:7734401cc1b4 83 int MQTTPacket_len(int rem_len)
icraggs 0:7734401cc1b4 84 {
icraggs 0:7734401cc1b4 85 rem_len += 1; /* header byte */
icraggs 0:7734401cc1b4 86
icraggs 0:7734401cc1b4 87 /* now remaining_length field */
icraggs 0:7734401cc1b4 88 if (rem_len < 128)
icraggs 0:7734401cc1b4 89 rem_len += 1;
icraggs 0:7734401cc1b4 90 else if (rem_len < 16384)
icraggs 0:7734401cc1b4 91 rem_len += 2;
icraggs 0:7734401cc1b4 92 else if (rem_len < 2097151)
icraggs 0:7734401cc1b4 93 rem_len += 3;
icraggs 0:7734401cc1b4 94 else
icraggs 0:7734401cc1b4 95 rem_len += 4;
icraggs 0:7734401cc1b4 96 return rem_len;
icraggs 0:7734401cc1b4 97 }
icraggs 0:7734401cc1b4 98
icraggs 0:7734401cc1b4 99
Ian Craggs 14:c2052aee81de 100 static unsigned char* bufptr;
icraggs 0:7734401cc1b4 101
Ian Craggs 14:c2052aee81de 102 int bufchar(unsigned char* c, int count)
icraggs 0:7734401cc1b4 103 {
icraggs 0:7734401cc1b4 104 int i;
icraggs 0:7734401cc1b4 105
icraggs 0:7734401cc1b4 106 for (i = 0; i < count; ++i)
icraggs 0:7734401cc1b4 107 *c = *bufptr++;
icraggs 0:7734401cc1b4 108 return count;
icraggs 0:7734401cc1b4 109 }
icraggs 0:7734401cc1b4 110
icraggs 0:7734401cc1b4 111
Ian Craggs 14:c2052aee81de 112 int MQTTPacket_decodeBuf(unsigned char* buf, int* value)
icraggs 0:7734401cc1b4 113 {
icraggs 0:7734401cc1b4 114 bufptr = buf;
icraggs 0:7734401cc1b4 115 return MQTTPacket_decode(bufchar, value);
icraggs 0:7734401cc1b4 116 }
icraggs 0:7734401cc1b4 117
icraggs 0:7734401cc1b4 118
icraggs 0:7734401cc1b4 119 /**
icraggs 0:7734401cc1b4 120 * Calculates an integer from two bytes read from the input buffer
icraggs 0:7734401cc1b4 121 * @param pptr pointer to the input buffer - incremented by the number of bytes used & returned
icraggs 0:7734401cc1b4 122 * @return the integer value calculated
icraggs 0:7734401cc1b4 123 */
Ian Craggs 14:c2052aee81de 124 int readInt(unsigned char** pptr)
icraggs 0:7734401cc1b4 125 {
Ian Craggs 14:c2052aee81de 126 unsigned char* ptr = *pptr;
Ian Craggs 14:c2052aee81de 127 int len = 256*(*ptr) + (*(ptr+1));
icraggs 0:7734401cc1b4 128 *pptr += 2;
icraggs 0:7734401cc1b4 129 return len;
icraggs 0:7734401cc1b4 130 }
icraggs 0:7734401cc1b4 131
icraggs 0:7734401cc1b4 132
icraggs 0:7734401cc1b4 133 /**
icraggs 0:7734401cc1b4 134 * Reads one character from the input buffer.
icraggs 0:7734401cc1b4 135 * @param pptr pointer to the input buffer - incremented by the number of bytes used & returned
icraggs 0:7734401cc1b4 136 * @return the character read
icraggs 0:7734401cc1b4 137 */
Ian Craggs 14:c2052aee81de 138 char readChar(unsigned char** pptr)
icraggs 0:7734401cc1b4 139 {
icraggs 0:7734401cc1b4 140 char c = **pptr;
icraggs 0:7734401cc1b4 141 (*pptr)++;
icraggs 0:7734401cc1b4 142 return c;
icraggs 0:7734401cc1b4 143 }
icraggs 0:7734401cc1b4 144
icraggs 0:7734401cc1b4 145
icraggs 0:7734401cc1b4 146 /**
icraggs 0:7734401cc1b4 147 * Writes one character to an output buffer.
icraggs 0:7734401cc1b4 148 * @param pptr pointer to the output buffer - incremented by the number of bytes used & returned
icraggs 0:7734401cc1b4 149 * @param c the character to write
icraggs 0:7734401cc1b4 150 */
Ian Craggs 14:c2052aee81de 151 void writeChar(unsigned char** pptr, char c)
icraggs 0:7734401cc1b4 152 {
icraggs 0:7734401cc1b4 153 **pptr = c;
icraggs 0:7734401cc1b4 154 (*pptr)++;
icraggs 0:7734401cc1b4 155 }
icraggs 0:7734401cc1b4 156
icraggs 0:7734401cc1b4 157
icraggs 0:7734401cc1b4 158 /**
icraggs 0:7734401cc1b4 159 * Writes an integer as 2 bytes to an output buffer.
icraggs 0:7734401cc1b4 160 * @param pptr pointer to the output buffer - incremented by the number of bytes used & returned
icraggs 0:7734401cc1b4 161 * @param anInt the integer to write
icraggs 0:7734401cc1b4 162 */
Ian Craggs 14:c2052aee81de 163 void writeInt(unsigned char** pptr, int anInt)
icraggs 0:7734401cc1b4 164 {
Ian Craggs 14:c2052aee81de 165 **pptr = (unsigned char)(anInt / 256);
icraggs 0:7734401cc1b4 166 (*pptr)++;
Ian Craggs 14:c2052aee81de 167 **pptr = (unsigned char)(anInt % 256);
icraggs 0:7734401cc1b4 168 (*pptr)++;
icraggs 0:7734401cc1b4 169 }
icraggs 0:7734401cc1b4 170
icraggs 0:7734401cc1b4 171
icraggs 0:7734401cc1b4 172 /**
icraggs 0:7734401cc1b4 173 * Writes a "UTF" string to an output buffer. Converts C string to length-delimited.
icraggs 0:7734401cc1b4 174 * @param pptr pointer to the output buffer - incremented by the number of bytes used & returned
icraggs 0:7734401cc1b4 175 * @param string the C string to write
icraggs 0:7734401cc1b4 176 */
Ian Craggs 14:c2052aee81de 177 void writeCString(unsigned char** pptr, const char* string)
icraggs 0:7734401cc1b4 178 {
icraggs 0:7734401cc1b4 179 int len = strlen(string);
icraggs 0:7734401cc1b4 180 writeInt(pptr, len);
icraggs 0:7734401cc1b4 181 memcpy(*pptr, string, len);
icraggs 0:7734401cc1b4 182 *pptr += len;
icraggs 0:7734401cc1b4 183 }
icraggs 0:7734401cc1b4 184
icraggs 0:7734401cc1b4 185
icraggs 0:7734401cc1b4 186 int getLenStringLen(char* ptr)
icraggs 0:7734401cc1b4 187 {
icraggs 0:7734401cc1b4 188 int len = 256*((unsigned char)(*ptr)) + (unsigned char)(*(ptr+1));
icraggs 0:7734401cc1b4 189 return len;
icraggs 0:7734401cc1b4 190 }
icraggs 0:7734401cc1b4 191
icraggs 0:7734401cc1b4 192
Ian Craggs 14:c2052aee81de 193 void writeMQTTString(unsigned char** pptr, MQTTString mqttstring)
icraggs 0:7734401cc1b4 194 {
icraggs 0:7734401cc1b4 195 if (mqttstring.lenstring.len > 0)
icraggs 0:7734401cc1b4 196 {
icraggs 0:7734401cc1b4 197 writeInt(pptr, mqttstring.lenstring.len);
icraggs 0:7734401cc1b4 198 memcpy(*pptr, mqttstring.lenstring.data, mqttstring.lenstring.len);
icraggs 0:7734401cc1b4 199 *pptr += mqttstring.lenstring.len;
icraggs 0:7734401cc1b4 200 }
icraggs 0:7734401cc1b4 201 else if (mqttstring.cstring)
icraggs 0:7734401cc1b4 202 writeCString(pptr, mqttstring.cstring);
icraggs 3:4a4f8699f935 203 else
icraggs 3:4a4f8699f935 204 writeInt(pptr, 0);
icraggs 0:7734401cc1b4 205 }
icraggs 0:7734401cc1b4 206
icraggs 0:7734401cc1b4 207
icraggs 0:7734401cc1b4 208 /**
icraggs 0:7734401cc1b4 209 * @param mqttstring the MQTTString structure into which the data is to be read
icraggs 0:7734401cc1b4 210 * @param pptr pointer to the output buffer - incremented by the number of bytes used & returned
icraggs 0:7734401cc1b4 211 * @param enddata pointer to the end of the data: do not read beyond
icraggs 0:7734401cc1b4 212 * @return 1 if successful, 0 if not
icraggs 0:7734401cc1b4 213 */
Ian Craggs 14:c2052aee81de 214 int readMQTTLenString(MQTTString* mqttstring, unsigned char** pptr, unsigned char* enddata)
icraggs 0:7734401cc1b4 215 {
icraggs 0:7734401cc1b4 216 int rc = 0;
icraggs 0:7734401cc1b4 217
icraggs 0:7734401cc1b4 218 FUNC_ENTRY;
icraggs 0:7734401cc1b4 219 /* the first two bytes are the length of the string */
icraggs 0:7734401cc1b4 220 if (enddata - (*pptr) > 1) /* enough length to read the integer? */
icraggs 0:7734401cc1b4 221 {
icraggs 0:7734401cc1b4 222 mqttstring->lenstring.len = readInt(pptr); /* increments pptr to point past length */
icraggs 0:7734401cc1b4 223 if (&(*pptr)[mqttstring->lenstring.len] <= enddata)
icraggs 0:7734401cc1b4 224 {
Ian Craggs 14:c2052aee81de 225 mqttstring->lenstring.data = (char*)*pptr;
icraggs 0:7734401cc1b4 226 *pptr += mqttstring->lenstring.len;
icraggs 0:7734401cc1b4 227 rc = 1;
icraggs 0:7734401cc1b4 228 }
icraggs 0:7734401cc1b4 229 }
Ian Craggs 6:68a06bea5429 230 mqttstring->cstring = NULL;
icraggs 0:7734401cc1b4 231 FUNC_EXIT_RC(rc);
icraggs 0:7734401cc1b4 232 return rc;
icraggs 0:7734401cc1b4 233 }
icraggs 0:7734401cc1b4 234
icraggs 0:7734401cc1b4 235
icraggs 0:7734401cc1b4 236 /**
icraggs 0:7734401cc1b4 237 * Return the length of the MQTTstring - C string if there is one, otherwise the length delimited string
icraggs 0:7734401cc1b4 238 * @param mqttstring the string to return the length of
icraggs 0:7734401cc1b4 239 * @return the length of the string
icraggs 0:7734401cc1b4 240 */
icraggs 0:7734401cc1b4 241 int MQTTstrlen(MQTTString mqttstring)
icraggs 0:7734401cc1b4 242 {
icraggs 0:7734401cc1b4 243 int rc = 0;
icraggs 0:7734401cc1b4 244
icraggs 0:7734401cc1b4 245 if (mqttstring.cstring)
icraggs 0:7734401cc1b4 246 rc = strlen(mqttstring.cstring);
icraggs 0:7734401cc1b4 247 else
icraggs 0:7734401cc1b4 248 rc = mqttstring.lenstring.len;
icraggs 0:7734401cc1b4 249 return rc;
icraggs 0:7734401cc1b4 250 }
icraggs 0:7734401cc1b4 251
icraggs 0:7734401cc1b4 252
Ian Craggs 8:b97b9873af52 253 /**
Ian Craggs 8:b97b9873af52 254 * Compares an MQTTString to a C string
Ian Craggs 8:b97b9873af52 255 * @param a the MQTTString to compare
Ian Craggs 8:b97b9873af52 256 * @param bptr the C string to compare
Ian Craggs 8:b97b9873af52 257 * @return boolean - equal or not
Ian Craggs 8:b97b9873af52 258 */
icraggs 5:eea71419676a 259 int MQTTPacket_equals(MQTTString* a, char* bptr)
icraggs 5:eea71419676a 260 {
icraggs 5:eea71419676a 261 int alen = 0,
icraggs 5:eea71419676a 262 blen = 0;
icraggs 5:eea71419676a 263 char *aptr;
icraggs 5:eea71419676a 264
icraggs 5:eea71419676a 265 if (a->cstring)
icraggs 5:eea71419676a 266 {
icraggs 5:eea71419676a 267 aptr = a->cstring;
icraggs 5:eea71419676a 268 alen = strlen(a->cstring);
icraggs 5:eea71419676a 269 }
icraggs 5:eea71419676a 270 else
icraggs 5:eea71419676a 271 {
icraggs 5:eea71419676a 272 aptr = a->lenstring.data;
icraggs 5:eea71419676a 273 alen = a->lenstring.len;
icraggs 5:eea71419676a 274 }
icraggs 5:eea71419676a 275 blen = strlen(bptr);
icraggs 5:eea71419676a 276
icraggs 5:eea71419676a 277 return (alen == blen) && (strncmp(aptr, bptr, alen) == 0);
icraggs 5:eea71419676a 278 }
icraggs 5:eea71419676a 279
icraggs 5:eea71419676a 280
icraggs 0:7734401cc1b4 281 /**
icraggs 0:7734401cc1b4 282 * Helper function to read packet data from some source into a buffer
icraggs 0:7734401cc1b4 283 * @param buf the buffer into which the packet will be serialized
icraggs 0:7734401cc1b4 284 * @param buflen the length in bytes of the supplied buffer
icraggs 0:7734401cc1b4 285 * @param getfn pointer to a function which will read any number of bytes from the needed source
icraggs 0:7734401cc1b4 286 * @return integer MQTT packet type, or -1 on error
icraggs 0:7734401cc1b4 287 */
Ian Craggs 14:c2052aee81de 288 int MQTTPacket_read(unsigned char* buf, int buflen, int (*getfn)(unsigned char*, int))
icraggs 0:7734401cc1b4 289 {
icraggs 0:7734401cc1b4 290 int rc = -1;
icraggs 17:c5bd28cc139a 291 MQTTHeader header = {0};
icraggs 0:7734401cc1b4 292 int len = 0;
icraggs 0:7734401cc1b4 293 int rem_len = 0;
icraggs 0:7734401cc1b4 294
icraggs 0:7734401cc1b4 295 /* 1. read the header byte. This has the packet type in it */
icraggs 0:7734401cc1b4 296 if ((*getfn)(buf, 1) != 1)
icraggs 0:7734401cc1b4 297 goto exit;
icraggs 0:7734401cc1b4 298
icraggs 0:7734401cc1b4 299 len = 1;
icraggs 0:7734401cc1b4 300 /* 2. read the remaining length. This is variable in itself */
icraggs 0:7734401cc1b4 301 MQTTPacket_decode(getfn, &rem_len);
icraggs 0:7734401cc1b4 302 len += MQTTPacket_encode(buf + 1, rem_len); /* put the original remaining length back into the buffer */
icraggs 0:7734401cc1b4 303
icraggs 0:7734401cc1b4 304 /* 3. read the rest of the buffer using a callback to supply the rest of the data */
icraggs 0:7734401cc1b4 305 if ((*getfn)(buf + len, rem_len) != rem_len)
icraggs 0:7734401cc1b4 306 goto exit;
icraggs 0:7734401cc1b4 307
icraggs 0:7734401cc1b4 308 header.byte = buf[0];
icraggs 0:7734401cc1b4 309 rc = header.bits.type;
icraggs 0:7734401cc1b4 310 exit:
icraggs 0:7734401cc1b4 311 return rc;
icraggs 0:7734401cc1b4 312 }
icraggs 0:7734401cc1b4 313