c-cote

Zero-configuration microservices library in C. Built in support for a variable number of master processes, service advertising and channel messaging.

This repository is not a fork of cote ! It has the same behavior but it is a complete library written in C in order to be portable and used in various applications. The goal of this library is to be fully compatible with cote Node.js version and permit discovery, monitoring and communications between applications written in C and Javascript.

Features

• zero-dependency: microservices fully written in C
• zero-configuration: no IP address, no ports, no routing to configure
• decentralized: no fixed parts, no "manager" nodes, no single point of failure
• auto-discovery: services discover each other without a central bookkeeper
• fault-tolerant: don't lose any requests when a service is down (a buffer is used and requests are dropped anyway if impossible to send)
• scalable: horizontally scale to any number of machines
• performant: process thousands of messages per second
• humanized API: extremely simple to get started with a reasonable API!

Building

Build libcote.so with the following commands:

mkdir build
cd build
cmake ..
make

Installing

Install libcote.so with the following commands:

make install

Protocol

Cote uses the extremely simple AMP protocol to send messages on the wire.

The libcote.so library depends of libdiscover.so from c-discover, libaxon.so from c-axon and libamp.so from c-amp.

Compatibility

This library is compatible with cote release 1.0.0.

Examples

Build examples with the following commands:

mkdir build
cd build
cmake -DENABLE_COTE_EXAMPLES=ON .
make

Pub / Sub

Pub instances distribute messages to all connected Sub clients using a broadcast mechanism. Messages are sent each time to all available sockets. Pub instances have no queing mechanism.

Sub instances receives messages from Pub servers.

Sub instances may optionally subscribe to one or more "topics" (the first multipart value), using string patterns or regular expressions.

Req / Rep

Req instances distribute messages to connected Rep servers using a Round-Robin mechanism. Messages are sent each time to the next available socket. Req instances have also a queing mechanism to handle loss of connections and send them upton the next connection. A timeout is specified to wait the reply.

Rep instances receives messages from Req clients and reply (or not).

Monitor

Provide a simple application to show the nodes currently discovered.

Performances

Performances have not been evaluated yet.

What's it good for?

This goal of this library is to provide a C implementation of the original cote Node.js version. This allow a communication between processes written using different languages.

API

cote_t *cote_create(char *type, char *name)

Create a new cote instance of type type which is "pub", "sub", "req", "rep" or "mon". The name of the instance is nameand is visible in the Monitor example application.

int cote_set_option(cote_t *cote, char *option, void *value)

Set cote instance option to the wanted value which is passed by address. The following table shows the available options and their default value. Options must be set before starting the instance.

Option	Type	Default
helloInterval	int	2000ms
checkInterval	int	4000ms
nodeTimeout	int	5000ms
masterTimeout	int	6000ms
address	char *	"0.0.0.0"
port	uint16_t	12345
broadcast	char *	"255.255.255.255"
multicast	char *	NULL
multicastTTL	unsigned char	1
unicast	char *	NULL
key	char *	NULL
mastersRequired	int	1
weight	double	Computed on startup
client	bool	false
reuseAddr	bool	true
ignoreProcess	bool	false
ignoreInstance	bool	false
advertisement	cJSON *	NULL
hostname	char *	Retrieved on startup
namespace	char *	NULL
useHostNames	bool	false
advertisement	cJSON *	NULL
broadcasts	cJSON *	NULL
subscribesTo	cJSON *	NULL
requests	cJSON *	NULL
respondsTo	cJSON *	NULL

❗ No key available today. Encryption of data is not available. First because I have not found any simple and satisfying library to do it, and then because the Cipher initialization used in discover Node.js version is currently deprecated.

int cote_start(cote_t *cote)

Start the cote instance.

int cote_advertise(cote_t *cote, cJSON *advertisement)

Set advertisement object. Can be used after starting the instance to update the advertisement content.

int cote_on(cote_t *cote, char *topic, void *fct, void *user)

Register a callback fct on the event topic. An optionnal user argument is available. The following table shows the available topics and their callback prototype.

Topic	Callback	Description
added	void *(*fct)(struct cote_s *, discover_node_t *, void *)	Called when a node is discovered
removed	void *(*fct)(struct cote_s *, discover_node_t *, void *)	Called when a node has disappeared
message	amp_msg_t *(*fct)(struct cote_s *, amp_msg_t *, void *)	Called when a message is received
error	void *(*fct)(struct cote_s *, char *, void *)	Called when an error occured

int cote_subscribe(cote_t *cote, char *topic, void *fct, void *user)

Subscribe a callback fct on the topic. An optionnal user argument is available. Can be called to update a subscription.

int cote_unsubscribe(cote_t *cote, char *topic)

Unsubscribe to the topic.

int cote_send(cote_t *cote, char *topic, int count, ...)

Send data. The count value indicate the amount of fields. ... expects the fields with type and value for each of them. Requester should terminate the list of argument by an amp_msg_t ** to receive the response from the Replier and a timeout int value.

amp_msg_t *cote_reply(cote_t *cote, int count, ...)

Format a new reply (Replier instances only). The count value indicate the amount of fields. ... expects the fields with type and value for each of them.

void cote_release(cote_t *cote)

Release internal memory and stop cote instance. All sockets are closed. Must be called to free ressources.

License

MIT