MQTTPacket
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Diff: MQTTPacket.c
- Revision:
- 0:7734401cc1b4
- Child:
- 3:4a4f8699f935
diff -r 000000000000 -r 7734401cc1b4 MQTTPacket.c --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/MQTTPacket.c Tue Feb 04 22:31:32 2014 +0000 @@ -0,0 +1,283 @@ +/******************************************************************************* + * Copyright (c) 2014 IBM Corp. + * + * All rights reserved. This program and the accompanying materials + * are made available under the terms of the Eclipse Public License v1.0 + * and Eclipse Distribution License v1.0 which accompany this distribution. + * + * The Eclipse Public License is available at + * http://www.eclipse.org/legal/epl-v10.html + * and the Eclipse Distribution License is available at + * http://www.eclipse.org/org/documents/edl-v10.php. + * + * Contributors: + * Ian Craggs - initial API and implementation and/or initial documentation + *******************************************************************************/ + +#include "StackTrace.h" +#include "MQTTPacket.h" + +#include <string.h> + +/** + * Encodes the message length according to the MQTT algorithm + * @param buf the buffer into which the encoded data is written + * @param length the length to be encoded + * @return the number of bytes written to buffer + */ +int MQTTPacket_encode(char* buf, int length) +{ + int rc = 0; + + FUNC_ENTRY; + do + { + char d = length % 128; + length /= 128; + /* if there are more digits to encode, set the top bit of this digit */ + if (length > 0) + d |= 0x80; + buf[rc++] = d; + } while (length > 0); + FUNC_EXIT_RC(rc); + return rc; +} + + +/** + * Decodes the message length according to the MQTT algorithm + * @param getcharfn pointer to function to read the next character from the data source + * @param value the decoded length returned + * @return the number of bytes read from the socket + */ +int MQTTPacket_decode(int (*getcharfn)(char*, int), int* value) +{ + char c; + int multiplier = 1; + int len = 0; +#define MAX_NO_OF_REMAINING_LENGTH_BYTES 4 + + FUNC_ENTRY; + *value = 0; + do + { + int rc = MQTTPACKET_READ_ERROR; + + if (++len > MAX_NO_OF_REMAINING_LENGTH_BYTES) + { + rc = MQTTPACKET_READ_ERROR; /* bad data */ + goto exit; + } + rc = (*getcharfn)(&c, 1); + if (rc != 1) + goto exit; + *value += (c & 127) * multiplier; + multiplier *= 128; + } while ((c & 128) != 0); +exit: + FUNC_EXIT_RC(len); + return len; +} + + +int MQTTPacket_len(int rem_len) +{ + rem_len += 1; /* header byte */ + + /* now remaining_length field */ + if (rem_len < 128) + rem_len += 1; + else if (rem_len < 16384) + rem_len += 2; + else if (rem_len < 2097151) + rem_len += 3; + else + rem_len += 4; + return rem_len; +} + + +static char* bufptr; + +int bufchar(char* c, int count) +{ + int i; + + for (i = 0; i < count; ++i) + *c = *bufptr++; + return count; +} + + +int MQTTPacket_decodeBuf(char* buf, int* value) +{ + bufptr = buf; + return MQTTPacket_decode(bufchar, value); +} + + +/** + * Calculates an integer from two bytes read from the input buffer + * @param pptr pointer to the input buffer - incremented by the number of bytes used & returned + * @return the integer value calculated + */ +int readInt(char** pptr) +{ + char* ptr = *pptr; + int len = 256*((unsigned char)(*ptr)) + (unsigned char)(*(ptr+1)); + *pptr += 2; + return len; +} + + +/** + * Reads one character from the input buffer. + * @param pptr pointer to the input buffer - incremented by the number of bytes used & returned + * @return the character read + */ +char readChar(char** pptr) +{ + char c = **pptr; + (*pptr)++; + return c; +} + + +/** + * Writes one character to an output buffer. + * @param pptr pointer to the output buffer - incremented by the number of bytes used & returned + * @param c the character to write + */ +void writeChar(char** pptr, char c) +{ + **pptr = c; + (*pptr)++; +} + + +/** + * Writes an integer as 2 bytes to an output buffer. + * @param pptr pointer to the output buffer - incremented by the number of bytes used & returned + * @param anInt the integer to write + */ +void writeInt(char** pptr, int anInt) +{ + **pptr = (char)(anInt / 256); + (*pptr)++; + **pptr = (char)(anInt % 256); + (*pptr)++; +} + + +/** + * Writes a "UTF" string to an output buffer. Converts C string to length-delimited. + * @param pptr pointer to the output buffer - incremented by the number of bytes used & returned + * @param string the C string to write + */ +void writeCString(char** pptr, char* string) +{ + int len = strlen(string); + writeInt(pptr, len); + memcpy(*pptr, string, len); + *pptr += len; +} + + +int getLenStringLen(char* ptr) +{ + int len = 256*((unsigned char)(*ptr)) + (unsigned char)(*(ptr+1)); + return len; +} + + +void writeMQTTString(char** pptr, MQTTString mqttstring) +{ + if (mqttstring.lenstring.len > 0) + { + writeInt(pptr, mqttstring.lenstring.len); + memcpy(*pptr, mqttstring.lenstring.data, mqttstring.lenstring.len); + *pptr += mqttstring.lenstring.len; + } + else if (mqttstring.cstring) + writeCString(pptr, mqttstring.cstring); +} + + +/** + * @param mqttstring the MQTTString structure into which the data is to be read + * @param pptr pointer to the output buffer - incremented by the number of bytes used & returned + * @param enddata pointer to the end of the data: do not read beyond + * @return 1 if successful, 0 if not + */ +int readMQTTLenString(MQTTString* mqttstring, char** pptr, char* enddata) +{ + int rc = 0; + + FUNC_ENTRY; + /* the first two bytes are the length of the string */ + if (enddata - (*pptr) > 1) /* enough length to read the integer? */ + { + mqttstring->lenstring.len = readInt(pptr); /* increments pptr to point past length */ + if (&(*pptr)[mqttstring->lenstring.len] <= enddata) + { + mqttstring->lenstring.data = *pptr; + *pptr += mqttstring->lenstring.len; + rc = 1; + } + } + FUNC_EXIT_RC(rc); + return rc; +} + + +/** + * Return the length of the MQTTstring - C string if there is one, otherwise the length delimited string + * @param mqttstring the string to return the length of + * @return the length of the string + */ +int MQTTstrlen(MQTTString mqttstring) +{ + int rc = 0; + + if (mqttstring.cstring) + rc = strlen(mqttstring.cstring); + else + rc = mqttstring.lenstring.len; + return rc; +} + + +/** + * Helper function to read packet data from some source into a buffer + * @param buf the buffer into which the packet will be serialized + * @param buflen the length in bytes of the supplied buffer + * @param getfn pointer to a function which will read any number of bytes from the needed source + * @return integer MQTT packet type, or -1 on error + */ +int MQTTPacket_read(char* buf, int buflen, int (*getfn)(char*, int)) +{ + int rc = -1; + MQTTHeader header; + int len = 0; + int rem_len = 0; + + /* 1. read the header byte. This has the packet type in it */ + if ((*getfn)(buf, 1) != 1) + goto exit; + + len = 1; + /* 2. read the remaining length. This is variable in itself */ + MQTTPacket_decode(getfn, &rem_len); + len += MQTTPacket_encode(buf + 1, rem_len); /* put the original remaining length back into the buffer */ + + /* 3. read the rest of the buffer using a callback to supply the rest of the data */ + if ((*getfn)(buf + len, rem_len) != rem_len) + goto exit; + + header.byte = buf[0]; + rc = header.bits.type; +exit: + return rc; +} + +