[mrpt-comms]

Detailed Description

Communication utilities: serial ports, networking (TCP, DNS,...), pub/sub nodelets.

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Library mrpt-comms

[New in MRPT 2.0.0]

This C++ library is part of MRPT and can be installed in Debian-based systems with:

    sudo apt install libmrpt-comms-dev

Find below some examples of use.

Nodelets-like Pub/Sub mechanism

MRPT provides a Publisher/Subscriber (Pub/Sub) pattern implementation for intra-process (multiple threads) zero-copy super fast communication.

Thread creation and handling is the responsibility of the user.

The main concepts are:

• A topic: the name of a shared variable. If you are familiar with ROS, you already know what a topic is. Topics are identified by unique strings, e.g. odometry, scan.
• Directory: The central hub that holds all references to existing topics. Usually only one should exist per process, but there is no actual limitation.
• Subscriber: An object that binds to a given topic and allows a user-given function to be called whenever new data is published to the topic.
• Publish: The operation of publishing a new data piece to a named topic. It's important to note that the call is blocking: all subscribers are executed from the thread invoking publish(). Users are encouraged to design subscribers such that their execution time are minimized, delegating heavy computation to other worker threads.

All these concepts are illustrated in the example below. Note that different subscribers are created: with a lambda, with a regular function, a std::bind(), etc.

See: comms_nodelets_example/NodeletsTest_impl.cpp

#include <mrpt/comms/nodelets.h>
#include <mrpt/poses/CPose3D.h>
#include <cstdio>  // printf()
#include <thread>
#include <chrono>
#include <iostream>

// Test payload:
const mrpt::poses::CPose3D p_tx(1.0, 2.0, 3.0, 0.2, 0.4, 0.6);

// Create the topic directory. Only once per process, and must be shared
// by all nodelets/threads.
auto dir = mrpt::comms::TopicDirectory::create();

void thread_publisher()
{
    using namespace mrpt::comms;
    using namespace std;

    try
    {
#ifdef NODELETS_TEST_VERBOSE
        printf("[publisher] Started\n");
#endif

        for (int i = 0; i < 5; i++)
        {
            std::this_thread::sleep_for(100ms);
            dir->getTopic("/robot/odom")->publish(p_tx);
        }

#ifdef NODELETS_TEST_VERBOSE
        printf("[publisher] Finish\n");
#endif
    }
    catch (std::exception& e)
    {
        cerr << e.what() << endl;
    }
    catch (...)
    {
        printf("[thread_publisher] Runtime error!\n");
    }
}

void onNewMsg(const mrpt::poses::CPose3D& p)
{
#ifdef NODELETS_TEST_VERBOSE
    std::cout << "sub2: rx CPose3D" << p.asString() << std::endl;
#endif
}

void onNewMsg2(int idx, const mrpt::poses::CPose3D& p)
{
#ifdef NODELETS_TEST_VERBOSE
    std::cout << "onNewMsg2: idx=" << idx << " rx CPose3D" << p.asString()
              << std::endl;
#endif
}

void thread_subscriber()
{
    using namespace mrpt::comms;
    using namespace std;

    try
    {
#ifdef NODELETS_TEST_VERBOSE
        printf("[subscriber] Connecting\n");
#endif

#ifdef NODELETS_TEST_VERBOSE
        printf("[subscriber] Connected. Waiting for a message...\n");
#endif

        // Create a subscriber with a lambda:
        Subscriber::Ptr sub1 =
            dir->getTopic("/robot/odom")
                ->createSubscriber<mrpt::poses::CPose3D>(
                    [](const mrpt::poses::CPose3D& p_rx) -> void {
#ifdef NODELETS_TEST_VERBOSE
                        std::cout << "sub1: rx CPose3D" << p_rx.asString()
                                  << std::endl;
#endif
                        nodelets_test_passed_ok = (p_rx == p_tx);
                    });

        // Create a subscriber with a regular function via std::function:
        auto sub2 = dir->getTopic("/robot/odom")
                        ->createSubscriber<mrpt::poses::CPose3D>(
                            std::function<void(const mrpt::poses::CPose3D&)>(
                                &onNewMsg));

        // Create a subscriber with a regular function:
        auto sub3 = dir->getTopic("/robot/odom")
                        ->createSubscriber<mrpt::poses::CPose3D>(&onNewMsg);

        // Create a subscriber with std::bind:
        using namespace std::placeholders;
        auto sub4 = dir->getTopic("/robot/odom")
                        ->createSubscriber<mrpt::poses::CPose3D>(std::bind(
                            onNewMsg2, 123 /*fixed 1st argument*/,
                            _1 /* 2nd arg is the subscribed data */));

        // wait for messages to arrive.
        // The nodelet is up and live until "sub" gets out of scope.
        std::this_thread::sleep_for(1000ms);

#ifdef NODELETS_TEST_VERBOSE
        printf("[subscriber] Finish\n");
#endif
    }
    catch (std::exception& e)
    {
        cerr << e.what() << endl;
    }
    catch (...)
    {
        cerr << "[thread_subscriber] Runtime error!" << endl;
    }
}

void NodeletsTest()
{
    using namespace std::chrono_literals;

    std::thread(thread_publisher).detach();
    std::thread(thread_subscriber).detach();
    std::this_thread::sleep_for(1000ms);
}

HTTP request methods

mrpt::comms::net::http_get() is an easy way to GET an HTTP resource from any C++ program. You can also use mrpt::comms::net::http_request() to access APIs requiring the POST method.

See: comms_http_client/test.cpp

#include <mrpt/comms/net_utils.h>
#include <iostream>

using namespace mrpt;
using namespace mrpt::comms;
using namespace mrpt::comms::net;
using namespace std;

string url = "http://www.google.es/";

void Test_HTTP_get()
{
    string content;
    string errmsg;
    mrpt::system::TParameters<string> out_headers;

    cout << "Retrieving " << url << "..." << endl;

    ERRORCODE_HTTP ret = http_get(
        url, content, errmsg, 80, "", "", nullptr, nullptr, &out_headers);

    if (ret != net::erOk)
    {
        cout << " Error: " << errmsg << endl;
        return;
    }

    string typ = out_headers.has("Content-Type") ? out_headers["Content-Type"]
                                                 : string("???");

    cout << "Ok: " << content.size() << " bytes of type: " << typ << endl;
    // cout << content << endl;
}

Classes
class	mrpt::comms::CClientTCPSocket
	A TCP socket that can be connected to a TCP server, implementing MRPT's CStream interface for passing objects as well as generic read/write methods. More...
struct	mrpt::comms::TFTDIDevice
	A list of FTDI devices and their descriptors. More...
class	mrpt::comms::CInterfaceFTDI
	A definition of a CStream actually representing a USB connection to a FTDI chip. More...
class	mrpt::comms::CSerialPort
	A communications serial port built as an implementation of a utils::CStream. More...
class	mrpt::comms::CServerTCPSocket
	A TCP socket that can be wait for client connections to enter. More...
class	mrpt::comms::Subscriber
	Nodelet-like Pub/Sub communications (in #include <mrpt/comms/nodelets.h>) More...

Namespaces
	mrpt::comms::net
	A set of useful routines for networking.

Enumerations
enum	mrpt::comms::net::ERRORCODE_HTTP {   mrpt::comms::net::erOk = 0, mrpt::comms::net::erBadURL, mrpt::comms::net::erCouldntConnect, mrpt::comms::net::erNotFound,   mrpt::comms::net::erOtherHTTPError }
	Possible returns from a HTTP request. More...

Functions
ERRORCODE_HTTP	mrpt::comms::net::http_get (const string &url, std::vector< uint8_t > &out_content, string &out_errormsg, int port=80, const string &auth_user=string(), const string &auth_pass=string(), int *out_http_responsecode=nullptr, mrpt::system::TParameters< string > *extra_headers=nullptr, mrpt::system::TParameters< string > *out_headers=nullptr, int timeout_ms=1000)
	Perform an HTTP GET operation (version for retrieving the data as a std::vector<uint8_t>) More...
ERRORCODE_HTTP	mrpt::comms::net::http_get (const string &url, string &out_content, string &out_errormsg, int port=80, const string &auth_user=string(), const string &auth_pass=string(), int *out_http_responsecode=nullptr, mrpt::system::TParameters< string > *extra_headers=nullptr, mrpt::system::TParameters< string > *out_headers=nullptr, int timeout_ms=1000)
	Perform an HTTP GET operation (version for retrieving the data as text) More...
ERRORCODE_HTTP	mrpt::comms::net::http_request (const string &http_method, const string &http_send_content, const string &url, std::vector< uint8_t > &out_content, string &out_errormsg, int port=80, const string &auth_user=string(), const string &auth_pass=string(), int *out_http_responsecode=nullptr, mrpt::system::TParameters< string > *extra_headers=nullptr, mrpt::system::TParameters< string > *out_headers=nullptr, int timeout_ms=1000)
	Generic function for HTTP GET & POST methods. More...
bool	mrpt::comms::net::DNS_resolve_async (const std::string &server_name, std::string &out_ip, const unsigned int timeout_ms=3000)
	Resolve a server address by its name, returning its IP address as a string - This method has a timeout for the maximum time to wait for the DNS server. More...
std::string	mrpt::comms::net::getLastSocketErrorStr ()
	Returns a description of the last Sockets error. More...
bool	mrpt::comms::net::Ping (const std::string &address, const int max_attempts, std::string *output_str=NULL)
	Ping an IP address. More...

Enumeration Type Documentation

ERRORCODE_HTTP

enum mrpt::comms::net::ERRORCODE_HTTP

Possible returns from a HTTP request.

Enumerator
erOk
erBadURL
erCouldntConnect
erNotFound
erOtherHTTPError

Definition at line 31 of file net_utils.h.

Function Documentation

DNS_resolve_async()

bool mrpt::comms::net::DNS_resolve_async	(	const std::string &	server_name,
		std::string &	out_ip,
		const unsigned int	timeout_ms = 3000
	)

Resolve a server address by its name, returning its IP address as a string - This method has a timeout for the maximum time to wait for the DNS server.

For example: server_name="www.google.com" -> out_ip="209.85.227.99"

Returns

true on success, false on timeout or other error.

Definition at line 404 of file net_utils.cpp.

References mrpt::system::os::memcpy(), and status.

Referenced by mrpt::comms::CClientTCPSocket::connect().

getLastSocketErrorStr()

std::string mrpt::comms::net::getLastSocketErrorStr

(

)

Returns a description of the last Sockets error.

Definition at line 480 of file net_utils.cpp.

References mrpt::format().

Referenced by mrpt::comms::CServerTCPSocket::getLastErrorStr(), mrpt::comms::CClientTCPSocket::getLastErrorStr(), mrpt::hwdrivers::CVelodyneScanner::initialize(), and mrpt::hwdrivers::CVelodyneScanner::internal_receive_UDP_packet().

http_get() [1/2]

ERRORCODE_HTTP mrpt::comms::net::http_get	(	const string &	url,
		std::vector< uint8_t > &	out_content,
		string &	out_errormsg,
		int	port = 80,
		const string &	auth_user = string(),
		const string &	auth_pass = string(),
		int *	out_http_responsecode = nullptr,
		mrpt::system::TParameters< string > *	extra_headers = nullptr,
		mrpt::system::TParameters< string > *	out_headers = nullptr,
		int	timeout_ms = 1000
	)

Perform an HTTP GET operation (version for retrieving the data as a std::vector<uint8_t>)

Parameters

url	Must be a simple string of the form "http://<servername>/<relative-address>".
port	The server port, if different from 80.
extra_headers	If provided, the given extra HTTP headers will be sent.
out_errormsg	On exit will contain a description of the error or "Ok".
out_content	The buffer with the retrieved data.
out_http_responsecode	If provided, will hold the HTTP code, eg: 200, 404...
out_headers	If provided, a copy of all the headers returned by the server will be saved here.
auth_user	Send a basic HTTP authorization request with the given user & password.
auth_pass	Send a basic HTTP authorization request with the given user & password.

Returns

The error or success code.

See also

http_request()

Examples:

comms_http_client/test.cpp.

Definition at line 386 of file net_utils.cpp.

References mrpt::comms::net::http_request(), and url.

Referenced by mrpt::hwdrivers::CRovio::captureImageAsync(), mrpt::hwdrivers::CRovio::general_command(), mrpt::comms::net::http_get(), mrpt::hwdrivers::CRovio::initialize(), mrpt::hwdrivers::CRovio::path_management(), mrpt::hwdrivers::CRovio::pathRename(), mrpt::hwdrivers::CNTRIPClient::retrieveListOfMountpoints(), and mrpt::hwdrivers::CRovio::send_cmd_action().

http_get() [2/2]

ERRORCODE_HTTP mrpt::comms::net::http_get	(	const string &	url,
		string &	out_content,
		string &	out_errormsg,
		int	port = 80,
		const string &	auth_user = string(),
		const string &	auth_pass = string(),
		int *	out_http_responsecode = nullptr,
		mrpt::system::TParameters< string > *	extra_headers = nullptr,
		mrpt::system::TParameters< string > *	out_headers = nullptr,
		int	timeout_ms = 1000
	)

Perform an HTTP GET operation (version for retrieving the data as text)

Parameters

url	Must be a simple string of the form "http://<servername>/<relative-address>".
port	The server port, if different from 80.
extra_headers	If provided, the given extra HTTP headers will be sent.
out_errormsg	On exit will contain a description of the error or "Ok".
out_content	The buffer with the retrieved data.
out_http_responsecode	If provided, will hold the HTTP code, eg: 200, 404...
out_headers	If provided, a copy of all the headers returned by the server will be saved here.
auth_user	Send a basic HTTP authorization request with the given user & password.
auth_pass	Send a basic HTTP authorization request with the given user & password.

Returns

The error or success code.

See also

http_request()

Definition at line 51 of file net_utils.cpp.

References mrpt::comms::net::http_get(), mrpt::system::os::memcpy(), and url.

http_request()

ERRORCODE_HTTP mrpt::comms::net::http_request	(	const string &	http_method,
		const string &	http_send_content,
		const string &	url,
		std::vector< uint8_t > &	out_content,
		string &	out_errormsg,
		int	port = 80,
		const string &	auth_user = string(),
		const string &	auth_pass = string(),
		int *	out_http_responsecode = nullptr,
		mrpt::system::TParameters< string > *	extra_headers = nullptr,
		mrpt::system::TParameters< string > *	out_headers = nullptr,
		int	timeout_ms = 1000
	)

Generic function for HTTP GET & POST methods.

See also

http_get

Definition at line 69 of file net_utils.cpp.

References mrpt::comms::CClientTCPSocket::connect(), mrpt::system::encodeBase64(), mrpt::comms::net::erBadURL, mrpt::comms::net::erCouldntConnect, mrpt::comms::net::erOk, mrpt::comms::net::erOtherHTTPError, mrpt::format(), mrpt::system::TParameters< T >::has(), mrpt::comms::CClientTCPSocket::isConnected(), mrpt::system::os::memcpy(), mrpt::comms::CClientTCPSocket::readAsync(), mrpt::comms::CClientTCPSocket::sendString(), mrpt::system::CTicTac::Tac(), mrpt::system::CTicTac::Tic(), mrpt::system::tokenize(), url, and val.

Referenced by mrpt::comms::net::http_get(), and mrpt::hwdrivers::CVelodyneScanner::internal_send_http_post().

Ping()

bool mrpt::comms::net::Ping	(	const std::string &	address,
		const int	max_attempts,
		std::string *	output_str = NULL
	)

Ping an IP address.

Parameters

[in]	address	Address to ping.
[in]	max_attempts	Number of attempts to try and ping.
[out]	output	String containing output information

Returns

True if responsive, false otherwise.

Note

{ I am redirecting stderr to stdout, so that the overall process is simplified. Otherwise see: https://jineshkj.wordpress.com/2006/12/22/how-to-capture-stdin-stdout-and-stderr-of-child-program/ }

Definition at line 498 of file net_utils.cpp.

References mrpt::system::executeCommand(), and mrpt::to_string().