Diff: MQTTPacket.c

Revision:

0:7734401cc1b4

Child:

3:4a4f8699f935

--- /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;
+}
+
+