notes.md

Beej's Guide to Netowrking

// sa_data contains a destination address and port number for the socket.
// This is rather unwieldy since you don’t want to tediously pack the address
// in the sa_data by hand.
struct sockaddr {
    unsigned short    sa_family;    // address family, AF_xxx
    char              sa_data[14];  // 14 bytes of protocol address
};

// To deal with struct sockaddr, programmers created a parallel
// structure: struct sockaddr_in (“in” for “Internet”) to be used with IPv4.
struct sockaddr_in {
    short int          sin_family;  // Address family, AF_INET
    unsigned short int sin_port;    // Port number
    struct in_addr     sin_addr;    // Internet address
    unsigned char      sin_zero[8]; // Same size as struct sockaddr
};

struct in_addr {
    uint32_t s_addr; // that's a 32-bit int (4 bytes)
};

struct sockaddr_in sa; // IPv4

// See, inet_pton() returns -1 on error, or 0 if the address is messed up.
inet_pton(AF_INET, "10.12.110.57", &(sa.sin_addr)); // IPv4

char ip4[INET_ADDRSTRLEN];  // space to hold the IPv4 string

// “ntop” means “network to presentation”—you can call it
// “network to printable” if that’s easier to remember
inet_ntop(AF_INET, &(sa.sin_addr), ip4, INET_ADDRSTRLEN);
printf("The IPv4 address is: %s\n", ip4);

Reusable

int on = 1;
setsockopt(sock, SOL_SOCKET,  SO_REUSEADDR, (char *)&on, sizeof(on));

Timeout

I think I like timeout better than nonblocking or select. select has to be done everytime you read a socket and nonblocking raises signals that need to be caught.

struct timeval tv;
long sec = 0;
long msec = 0;

int timeout = 5000; // msec

if (timeout >= 1000) {
    sec = (long)timeout/1000;
    timeout %= 1000;
}

tv.tv_sec = sec;
tv.tv_usec = msec * 1000;

err = ::setsockopt(sock, SOL_SOCKET, SO_RCVTIMEO, &tv, sizeof(tv));

Nonblocking

int on = 1;
int err = 0;

// this appears unnecessary ... it will enable nonblocking, but you still
// need select to set timeout
err = ioctl(sock, FIONBIO, (char *)&on);

// set timeout for 100 ms
timeout.tv_sec  = 0;
timeout.tv_usec = 100 * 1000; // this is usec (1000usec = 1msec)

fd_set readfds;         // read file descriptor
FD_ZERO(&readfds);      // clear
FD_SET(sock, &readfds); // puts sock into fd_set

// if err is 0, then nothing happened
err = select(sock + 1, &working_set, NULL, NULL, &timeout);

// unnecessary, but you can check to see if data there ... err above already
// tells you that.
if (FD_ISSET(sock, &readfds) == 0) { /* no data */ }

On success, select() and pselect() return the number of file descriptors contained in the three returned descriptor sets (that is, the total number of bits that are set in readfds, writefds, exceptfds). The return value may be zero if the timeout expired before any file descriptors became ready.

On error, -1 is returned, and errno is set to indicate the error; the file descriptor sets are unmodified, and timeout becomes undefined.

ref

CMake

Setup your source like:

main.cpp
CMakeTexts.txt

To pull this library from github and use it in a program, set your CMakeTexts.txt up like:

cmake_minimum_required(VERSION 3.10.0)
project(ps VERSION 0.0.1 LANGUAGES CXX)

set(CMAKE_CXX_STANDARD 20)
set(CMAKE_CXX_STANDARD_REQUIRED ON)
set(CMAKE_CXX_EXTENSIONS OFF)

cmake_host_system_information(RESULT HOST QUERY HOSTNAME)
cmake_host_system_information(RESULT OSN QUERY OS_NAME)
cmake_host_system_information(RESULT OS_VERSION QUERY OS_RELEASE)
cmake_host_system_information(RESULT PROC QUERY PROCESSOR_DESCRIPTION)

message(STATUS "-------------------------------------")
message(STATUS "  Project: ${PROJECT_NAME}")
message(STATUS "  C++ ${CMAKE_CXX_STANDARD}")
message(STATUS "-------------------------------------")
message(STATUS " ${HOST}")
message(STATUS " ${OSN}: ${OS_VERSION}")
message(STATUS " ${PROC}")
message(STATUS "-------------------------------------")


# Library =====================================================================

include(ExternalProject)
ExternalProject_Add(marko-proj
  GIT_REPOSITORY    https://github.com/gecko-robotics/marko.cpp.git
  GIT_TAG           main
  SOURCE_DIR        "${CMAKE_CURRENT_BINARY_DIR}/marko/src"
  BINARY_DIR        "${CMAKE_CURRENT_BINARY_DIR}/marko"
  # CONFIGURE_COMMAND ""
  BUILD_COMMAND     "make"
  INSTALL_COMMAND   ""
  # TEST_COMMAND      ""
)

SET(MARKO_INCLUDE_DIR ${CMAKE_CURRENT_BINARY_DIR}/marko/src/include)
SET(MARKO_LIB_DIR ${CMAKE_CURRENT_BINARY_DIR}/marko)

# Binary ======================================================================
add_executable(${PROJECT_NAME} ps.cpp)
add_dependencies(${PROJECT_NAME} marko-proj)
target_include_directories(${PROJECT_NAME} PRIVATE ${MARKO_INCLUDE_DIR})
target_link_libraries(${PROJECT_NAME} PRIVATE marko)
target_link_directories(${PROJECT_NAME} PRIVATE ${MARKO_LIB_DIR})

Now do:

mkdir build
cd build
cmake ..
make