CppCMS/private/email.h

//////////////////////////////////////////////////////////////////////
// C++Mail wrapper
// Written by Jonathan A. Foster <jon@jfpossibiliteis.com>
// Started April 1st, 2021
//
// The idea is simple: A C++ class that can be used to send an email.
// This will work by using popen() to open "mail" and allow writing
// the email to it in standard stream fashion. This is being developed
// for use with C++CMS to allow emailing error reports when there is a
// crash (500 page).
//
// *WARN*: Requires C++11 to work. Something in the type compatibility
// testing is misisng in previous releases.
//
// NOTE: I'm making this an "include" library since I don't want to
// get into the CMake learning curve at this time. Its problematic
// enough just getting this wedged in.
//
// NOTE: I found the basic popen() C++ wrapper on-line somewhere. I
// don't remember where or who wrote it. It has been changed slightly.
//
// WARN: errors are essentially ignored. In other words the return of
// pclose() isn't tested. Nor is the original popen() verified.
//
// TODO: error handling :-D
//////////////////////////////////////////////////////////////////////
#ifndef JFP_EMAIL_WRAPPER_H
#define JFP_EMAIL_WRAPPER_H
#include <stdio.h>
#include <streambuf>
#include <ostream>
#include <memory>
namespace JFP {



//////////////////////////////////////////////////////////////////////
// A function to escape strings for building shell commands
//////////////////////////////////////////////////////////////////////

// transform a copy so we don't cause an unexpected alteration, hence
// the "const".
std::string esc(const std::string s) {
  std::string r = s;
  for(
    auto it=r.find("'");
    it!=std::string::npos;
    it=r.find("'", it+4)
  ) r.replace(it, 1, "'\\''");
  return '\''+r+'\'';
}



//////////////////////////////////////////////////////////////////////
// A "streambuf" descendant to write to a popen(..., "w") FILE
//////////////////////////////////////////////////////////////////////

struct FILEbuf: public std::streambuf {
  enum { bufsize = 4*1024 };
  char   buffer[bufsize];
  FILE*  fp;
  int    (*close)(FILE*);

  int overflow(int c) {
    if(c!=std::char_traits<char>::eof()) {
      *this->pptr() = std::char_traits<char>::to_char_type(c);
      this->pbump(1);
    }
    return this->sync()
      ? std::char_traits<char>::eof()
      : std::char_traits<char>::not_eof(c);
  }

  int sync() {
    std::streamsize size(this->pptr()-this->pbase());
    std::streamsize done(this->fp ? fwrite(this->pbase(), 1, size, this->fp) : 0);
    this->setp(this->pbase(), this->epptr());
    return size == done ? 0 : -1;
  }

  FILEbuf(FILE* _fp, int(*_close)(FILE*) = fclose): fp(_fp), close(_close) {
    this->setp(this->buffer, this->buffer+(this->fp ? bufsize-1 : 0));
  }

  ~FILEbuf() { this->sync(); this->fp && this->close(this->fp); }
};



//////////////////////////////////////////////////////////////////////
// Now attach it to an ostream object, which will also perform the
// popen() call.
//////////////////////////////////////////////////////////////////////

struct popeno: public std::ostream, private virtual FILEbuf {
  popeno(std::string const& cmd):
    FILEbuf(popen(cmd.c_str(), "w"), pclose),
    std::ios(static_cast<std::streambuf*>(this)),
    std::ostream(static_cast<std::streambuf*>(this))
  { }

  popeno(popeno &&old):
    FILEbuf(fp, close),
    std::ios(static_cast<std::streambuf*>(this)),
    std::ostream(static_cast<std::streambuf*>(this))
  {
    old.sync(); // flush buffer so we don't need to copy it.
  }
};



//////////////////////////////////////////////////////////////////////
// And now for a simplistic mailer
//
// This wrapper is basically needed to do the string /math/ for the
// popeno constructor since the command string has to be passed to
// inherited constructors prior to our constructor code being run.
//
// TODO: refactor to provide a cleaner and email only interface.
//////////////////////////////////////////////////////////////////////

popeno eMail(const std::string &to, const std::string &subject) {
  popeno r("mail -s "+esc(subject)+" "+esc(to));
  return r;
}



//////////////////////////////////////////////////////////////////////
// EXAMPLE
//////////////////////////////////////////////////////////////////////
/*
int main(int argc, char **argv) {
  eMail("jon@jfpi.net", "Test from C++")
      << "Greetings earthling\n"
      << "\n"
      << "- ChipMaster\n";
}*/



} // JFP
#endif