Ashley Mills
This is CoAP library with a focus on simplicity. It offers minimal CoAP PDU construction and decoding to and from byte buffers.
Dependents: cantcoap_cellular_test yeswecancoap
Teaser
CoAP implementation that focuses on simplicity by offering a minimal set of functions and straightforward interface.
CoapPDU *pdu = new CoapPDU(); pdu->setType(CoapPDU::COAP_CONFIRMABLE); pdu->setCode(CoapPDU::COAP_GET); pdu->setToken((uint8_t*)"\3\2\1\0",4); pdu->setMessageID(0x0005); pdu->setURI((char*)"test",4); // send packet ret = send(sockfd,pdu->getPDUPointer(),pdu->getPDULength(),0);
...
// receive packet
ret = recvfrom(sockfd,&buffer,BUF_LEN,0,(sockaddr*)&recvAddr,&recvAddrLen);
CoapPDU *recvPDU = new CoapPDU((uint8_t*)buffer,ret);
if(recvPDU->validate()) {
recvPDU->getURI(uriBuffer,URI_BUF_LEN,&recvURILen);
...
}
Long description
This is a CoAP implementation with a focus on simplicity. The library only provides PDU construction and de-construction.
The user is expected to deal with retransmissions, timeouts, and message ID matching themselves. This isn’t as arduous as it sounds and makes a lot more sense on a constrained device.
Imagine for example a simple microcontroller sensor that only reports readings once every 15 minutes, and only sends a few packets each time. Do you really need a complicated framework to deal with acknowledgements and re-transmissions?
Since CoAP recommends you only send one packet at at time, this means you only need to keep track of one on-going transaction at a time. Yeah... I think you’re capable of this.
Furthermore, the timers and interrupt processes between different embedded processor architectures, vary quite a bit. So it often makes sense to write the packet sending processes yourself.
Finally, you might be sending the packets over odd transport bearers such as a SMS (woah dude, that's just totally wild) or a simple radio bearer. In which case, it’s easiest to deal with buffers. If I built retransmission handlers, they’d all be UDP/IP specific and would bloat the code for no reason.
Resources
Github page for the cantcoap library is here:
https://github.com/staropram/cantcoap
Doxygen for the library is here:
http://staropram.github.io/cantcoap/index.html
Examples
Construction
There are a couple of different ways to construct a PDU depending on whether you want the library to allocate memory for you, or whether you have an external buffer you want to use. You can also re-purpose existing objects.
Using a managed object
The simplest usage scenario hands control of memory allocation to the library:
CoapPDU *pdu = new CoapPDU(); ... pdu->setType(CoapPDU::COAP_CONFIRMABLE); pdu->setCode(CoapPDU::COAP_GET); pdu->addOption(11,5,(uint8_t*)"hello"); pdu->addOption(11,5,(uint8_t*)"there"); pdu->addOption(11,6,(uint8_t*)"server");
In this case you just call the default constructor. That's it. The library handles memory from there-on out. For example, when adding each of those options, the library will realloc the pdu to accomodate space for them. It will also shrink the PDU if something changes (like the token length) so that it always uses the minimum amount of memory.
When you free the PDU, all data including the buffer is deleted. The PDU can also be reused as shown below.
Using an external buffer for memory
There are two obvious reasons why you would do this:
1. The buffer contains a CoAP PDU and you want to access the data in the PDU. 2. Buffers cost space and allocating memory consumes processor resources. On embedded targets it is often simpler to reuse buffers where possible.
The first instance is a special case and requires some extra work. Just using an external buffer is as simple as follows:
uint8_t *buffer[100]; CoapPDU *pdu = new CoapPDU((uint8_t*)buffer,100,0); ... pdu->setType(CoapPDU::COAP_CONFIRMABLE); pdu->setCode(CoapPDU::COAP_GET); pdu->addOption(11,5,(uint8_t*)"hello"); pdu->addOption(11,5,(uint8_t*)"there"); pdu->addOption(11,6,(uint8_t*)"server");
The PDU is constructed as normal except that the memory of your buffer is used instead of allocated memory.
A call such as this:
pdu->addOption(11,5,(uint8_t*)"hello");
Will fail if there is no space left in the buffer.
When you delete the object, the buffer is not freed. Hey, it's your buffer mannn!
Reusing an existing object
Regardless of whether you constructed a PDU using either of the above methods, you can always reuse it:
pdu->reset(); ... pdu->setType(CoapPDU::COAP_CONFIRMABLE); pdu->setCode(CoapPDU::COAP_GET); pdu->addOption(11,5,(uint8_t*)"hello"); pdu->addOption(11,5,(uint8_t*)"there"); pdu->addOption(11,6,(uint8_t*)"server");
The only difference is that if the PDU was initially constructed using managed-memory, then it will continue to have managed-memory. Whereas if the PDU was constructed with an external buffer, then you are limited in space by the size of the buffer you used.
Receving CoAP packets over a network or something
In this case you have a CoAP PDU in a buffer you just gobbled from a socket and want to read it:
uint8_t *buffer[100];
int ret = recvfrom(sockfd,&buffer,BUF_LEN,0,(sockaddr*)&recvAddr,&recvAddrLen);
CoapPDU *recvPDU = new CoapPDU((uint8_t*)buffer,ret,100);
if(recvPDU->validate()) {
recvPDU->printHuman();
// do your work
}
You must call CoapPDU::validate() and get a positive response before accessing any of the data members. This sets up some internal pionters and so on, so if you fail to do it, undefined behaviour will result.
Note that the constructor is just a shorthand for the external-buffer-constructor explained above, and you can use the long form if you want. For example. you might want to use the long form if you have a buffer bigger than the PDU and you expect to reuse it.
You can reuse this object by resetting it as above.
If you reuse such an object, you need to set the PDU length manually because there is no way to deduce the PDU length using validate():
// earlier
#define BUFLEN 500
char buffer[BUFLEN];
CoapPDU *recvPDU = new CoapPDU((uint8_t*)buffer,BUFLEN,BUFLEN);
...
while(1) {
// receive packet
ret = sockfd,&buffer,BUFLEN,0);
if(ret==-1) {
INFO("Error receiving data");
// handle error
}
// validate packet
// you should also check that ret doesn't exceed buffer length
recvPDU->setPDULength(ret);
if(recvPDU->validate()!=1) {
INFO("Malformed CoAP packet");
// handle error
}
}
cantcoap.h
- Committer:
- ashleymills
- Date:
- 2014-01-30
- Revision:
- 1:5eec2844ad47
- Parent:
- 0:3d62a105fd34
File content as of revision 1:5eec2844ad47:
/**
Copyright (c) 2013, Ashley Mills.
All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:
1. Redistributions of source code must retain the above copyright notice, this
list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright notice,
this list of conditions and the following disclaimer in the documentation
and/or other materials provided with the distribution.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#pragma once
#include <stdint.h>
#define COAP_HDR_SIZE 4
#define COAP_OPTION_HDR_BYTE 1
// CoAP PDU format
// 0 1 2 3
// 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// |Ver| T | TKL | Code | Message ID |
// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// | Token (if any, TKL bytes) ...
// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// | Options (if any) ...
// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// |1 1 1 1 1 1 1 1| Payload (if any) ...
// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
class CoapPDU {
public:
/// CoAP message types. Note, values only work as enum.
enum Type {
COAP_CONFIRMABLE=0x00,
COAP_NON_CONFIRMABLE=0x10,
COAP_ACKNOWLEDGEMENT=0x20,
COAP_RESET=0x30
};
// CoAP response codes.
enum Code {
COAP_EMPTY=0x00,
COAP_GET,
COAP_POST,
COAP_PUT,
COAP_DELETE,
COAP_CREATED=0x41,
COAP_DELETED,
COAP_VALID,
COAP_CHANGED,
COAP_CONTENT,
COAP_BAD_REQUEST=0x80,
COAP_UNAUTHORIZED,
COAP_BAD_OPTION,
COAP_FORBIDDEN,
COAP_NOT_FOUND,
COAP_METHOD_NOT_ALLOWED,
COAP_NOT_ACCEPTABLE,
COAP_PRECONDITION_FAILED=0x8C,
COAP_REQUEST_ENTITY_TOO_LARGE=0x8D,
COAP_UNSUPPORTED_CONTENT_FORMAT=0x8F,
COAP_INTERNAL_SERVER_ERROR=0xA0,
COAP_NOT_IMPLEMENTED,
COAP_BAD_GATEWAY,
COAP_SERVICE_UNAVAILABLE,
COAP_GATEWAY_TIMEOUT,
COAP_PROXYING_NOT_SUPPORTED,
COAP_UNDEFINED_CODE=0xFF
};
/// CoAP option numbers.
enum Option {
COAP_OPTION_IF_MATCH=1,
COAP_OPTION_URI_HOST=3,
COAP_OPTION_ETAG,
COAP_OPTION_IF_NONE_MATCH,
COAP_OPTION_OBSERVE,
COAP_OPTION_URI_PORT,
COAP_OPTION_LOCATION_PATH,
COAP_OPTION_URI_PATH=11,
COAP_OPTION_CONTENT_FORMAT,
COAP_OPTION_MAX_AGE=14,
COAP_OPTION_URI_QUERY,
COAP_OPTION_ACCEPT=17,
COAP_OPTION_LOCATION_QUERY=20,
COAP_OPTION_BLOCK2=23,
COAP_OPTION_BLOCK1=27,
COAP_OPTION_SIZE2,
COAP_OPTION_PROXY_URI=35,
COAP_OPTION_PROXY_SCHEME=39,
COAP_OPTION_SIZE1=60
};
/// CoAP content-formats.
enum ContentFormat {
COAP_CONTENT_FORMAT_TEXT_PLAIN = 0,
COAP_CONTENT_FORMAT_APP_LINK = 40,
COAP_CONTENT_FORMAT_APP_XML,
COAP_CONTENT_FORMAT_APP_OCTET,
COAP_CONTENT_FORMAT_APP_EXI = 47,
COAP_CONTENT_FORMAT_APP_JSON = 50
};
/// Sequence of these is returned by CoapPDU::getOptions()
struct CoapOption {
uint16_t optionDelta;
uint16_t optionNumber;
uint16_t optionValueLength;
int totalLength;
uint8_t *optionPointer;
uint8_t *optionValuePointer;
};
// construction and destruction
CoapPDU();
CoapPDU(uint8_t *pdu, int pduLength);
CoapPDU(uint8_t *buffer, int bufferLength, int pduLength);
~CoapPDU();
int reset();
int validate();
// version
int setVersion(uint8_t version);
uint8_t getVersion();
// message type
void setType(CoapPDU::Type type);
CoapPDU::Type getType();
// tokens
int setTokenLength(uint8_t tokenLength);
int getTokenLength();
uint8_t* getTokenPointer();
int setToken(uint8_t *token, uint8_t tokenLength);
// message code
void setCode(CoapPDU::Code code);
CoapPDU::Code getCode();
CoapPDU::Code httpStatusToCode(int httpStatus);
// message ID
int setMessageID(uint16_t messageID);
uint16_t getMessageID();
// options
int addOption(uint16_t optionNumber, uint16_t optionLength, uint8_t *optionValue);
// gets a list of all options
CoapOption* getOptions();
int getNumOptions();
// shorthand helpers
int setURI(char *uri);
int setURI(char *uri, int urilen);
int getURI(char *dst, int dstlen, int *outLen);
int addURIQuery(char *query);
// content format helper
int setContentFormat(CoapPDU::ContentFormat format);
// payload
uint8_t* mallocPayload(int bytes);
int setPayload(uint8_t *value, int len);
uint8_t* getPayloadPointer();
int getPayloadLength();
uint8_t* getPayloadCopy();
// pdu
int getPDULength();
uint8_t* getPDUPointer();
void setPDULength(int len);
// debugging
static void printBinary(uint8_t b);
void print();
void printBin();
void printHex();
void printOptionHuman(uint8_t *option);
void printHuman();
void printPDUAsCArray();
private:
// variables
uint8_t *_pdu;
int _pduLength;
int _constructedFromBuffer;
int _bufferLength;
uint8_t *_payloadPointer;
int _payloadLength;
int _numOptions;
uint16_t _maxAddedOptionNumber;
// functions
void shiftPDUUp(int shiftOffset, int shiftAmount);
void shiftPDUDown(int startLocation, int shiftOffset, int shiftAmount);
uint8_t codeToValue(CoapPDU::Code c);
// option stuff
int findInsertionPosition(uint16_t optionNumber, uint16_t *prevOptionNumber);
int computeExtraBytes(uint16_t n);
int insertOption(int insertionPosition, uint16_t optionDelta, uint16_t optionValueLength, uint8_t *optionValue);
uint16_t getOptionDelta(uint8_t *option);
void setOptionDelta(int optionPosition, uint16_t optionDelta);
uint16_t getOptionValueLength(uint8_t *option);
};
/*
#define COAP_CODE_EMPTY 0x00
// method codes 0.01-0.31
#define COAP_CODE_GET 0x01
#define COAP_CODE_POST 0x02
#define COAP_CODE_PUT 0x03
#define COAP_CODE_DELETE 0x04
// Response codes 2.00 - 5.31
// 2.00 - 2.05
#define COAP_CODE_CREATED 0x41
#define COAP_CODE_DELETED 0x42
#define COAP_CODE_VALID 0x43
#define COAP_CODE_CHANGED 0x44
#define COAP_CODE_CONTENT 0x45
// 4.00 - 4.15
#define COAP_CODE_BAD_REQUEST 0x80
#define COAP_CODE_UNAUTHORIZED 0x81
#define COAP_CODE_BAD_OPTION 0x82
#define COAP_CODE_FORBIDDEN 0x83
#define COAP_CODE_NOT_FOUND 0x84
#define COAP_CODE_METHOD_NOT_ALLOWED 0x85
#define COAP_CODE_NOT_ACCEPTABLE 0x86
#define COAP_CODE_PRECONDITION_FAILED 0x8C
#define COAP_CODE_REQUEST_ENTITY_TOO_LARGE 0x8D
#define COAP_CODE_UNSUPPORTED_CONTENT_FORMAT 0x8F
// 5.00 - 5.05
#define COAP_CODE_INTERNAL_SERVER_ERROR 0xA0
#define COAP_CODE_NOT_IMPLEMENTED 0xA1
#define COAP_CODE_BAD_GATEWAY 0xA2
#define COAP_CODE_SERVICE_UNAVAILABLE 0xA3
#define COAP_CODE_GATEWAY_TIMEOUT 0xA4
#define COAP_CODE_PROXYING_NOT_SUPPORTED 0xA5
*/
