util.hh File Reference

#include <algorithm>
#include <cerrno>
#include <cstddef>
#include <cstdint>
#include <iterator>
#include <ostream>
#include <random>
#include <string>
#include <system_error>
#include <vector>

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Classes
class	InternetChecksum
	The internet checksum algorithm. More...
class	tagged_error
	std::system_error plus the name of what was being attempted More...
class	unix_error
	a tagged_error for syscalls More...

Functions
std::mt19937	get_random_generator ()
	Seed a fast random generator. More...
void	hexdump (const char *data, const size_t len, const size_t indent=0)
	Hexdump the contents of a packet (or any other sequence of bytes) More...
void	hexdump (const uint8_t *data, const size_t len, const size_t indent=0)
	Hexdump the contents of a packet (or any other sequence of bytes) More...
int	SystemCall (const char *attempt, const int return_value, const int errno_mask=0)
	Error-checking wrapper for most syscalls. More...
int	SystemCall (const std::string &attempt, const int return_value, const int errno_mask=0)
	Version of SystemCall that takes a C++ std::string. More...
uint64_t	timestamp_ms ()
	Get the time in milliseconds since the program began. More...

Function Documentation

get_random_generator()

std::mt19937 get_random_generator

(

)

Seed a fast random generator.

A properly seeded mt19937 generator takes a lot of entropy!

This code borrows from the following:

• https://kristerw.blogspot.com/2017/05/seeding-stdmt19937-random-number-engine.html
• http://www.pcg-random.org/posts/cpps-random_device.html

Definition at line 64 of file util.cc.

hexdump() [1/2]

void hexdump	(	const char *	data,
		const size_t	len,
		const size_t	indent = 0
	)

Hexdump the contents of a packet (or any other sequence of bytes)

hexdump() [2/2]

void hexdump	(	const uint8_t *	data,
		const size_t	len,
		const size_t	indent = 0
	)

Hexdump the contents of a packet (or any other sequence of bytes)

SystemCall() [1/2]

int SystemCall	(	const char *	attempt,
		const int	return_value,
		const int	errno_mask
	)

Error-checking wrapper for most syscalls.

Parameters

[in]	attempt	is the name of the syscall to try (for error reporting)
[in]	return_value	is the return value of the syscall
[in]	errno_mask	is any errno value that is acceptable, e.g., EAGAIN when reading a non-blocking fd

This function works for any syscall that returns less than 0 on error and sets errno:

For example, to wrap a call to open(2), you might say:

const int foo_fd = SystemCall("open", ::open("/tmp/foo", O_RDWR));

If you don't have permission to open the file, SystemCall will throw a std::runtime_error. If you don't want to throw in that case, you can pass EACCESS in errno_mask:

// open a file, or print an error if permission was denied
const int foo_fd = SystemCall("open", ::open("/tmp/foo", O_RDWR), EACCESS);
if (foo_fd < 0) {
    std::cerr << "Access to /tmp/foo was denied." << std::endl;
}

Definition at line 42 of file util.cc.

SystemCall() [2/2]

int SystemCall	(	const string &	attempt,
		const int	return_value,
		const int	errno_mask
	)

Version of SystemCall that takes a C++ std::string.

Parameters

[in]	attempt	is the name of the syscall to try (for error reporting)
[in]	return_value	is the return value of the syscall
[in]	errno_mask	is any errno value that is acceptable, e.g., EAGAIN when reading a non-blocking fd

see the other SystemCall() documentation for more details

Definition at line 54 of file util.cc.

timestamp_ms()

uint64_t timestamp_ms

(

)

Get the time in milliseconds since the program began.

Returns

the number of milliseconds since the program started

Definition at line 14 of file util.cc.