BARANTMail/SMTPServer.cpp

#include "SMTPServer.h"
#include "Log.h"
#include "SendMail.h"
#include "SpamAssassinFilter.h"
#include "File.h"
#include <thread>

namespace mail {

   SMTPServer::SMTPServer(core::EPoll &ePoll, std::string hostName, MailFileSystem &mailFileSystem,
                          core::IPAddress ipAddress, core::TLSInfo *tlsInfo, bool watchQueue,
                          DKIMSigner *dkimSigner)
	: core::TCPServer(ePoll, ipAddress, tlsInfo, " ", 1, "SMTP Server"), core::INotify(ePoll), ePoll(ePoll), hostName(hostName), mailFileSystem(mailFileSystem), dkimSigner(dkimSigner) {
	   commands.add(_smtp_auth, "AUTH");
	   commands.add(_smtp_data, "DATA");
	   commands.add(_smtp_ehlo, "EHLO");
	   commands.add(_smtp_expn, "EXPN");
	   commands.add(_smtp_helo, "HELO");
	   commands.add(_smtp_help, "HELP");
	   commands.add(_smtp_mail, "MAIL");
	   commands.add(_smtp_noop, "NOOP");
	   commands.add(_smtp_quit, "QUIT");
	   commands.add(_smtp_rcpt, "RCPT");
	   commands.add(_smtp_rset, "RSET");
	   commands.add(_smtp_vrfy, "VRFY");
	   if (watchQueue) {
	      processExisting();
	      wd = addWatch(mailFileSystem.getQueuePath());
	   }
	}

   SMTPSession * SMTPServer::getSocketAccept(core::EPoll &ePoll) {
      return new SMTPSession(ePoll, *this);
   }

   void SMTPServer::sessionErrorHandler(std::string errorString, std::stringstream &out) {
      out << "252 " << errorString << CRLF;
   }
   
   void SMTPServer::deliverToMailbox(coreutils::ZString &mailbox, coreutils::ZString &messageId,
                                      SpamAssassinFilter::Result &scan) {
      // The destination folder has to be picked AFTER the scan runs,
      // not before - this used to always build an "/Inbox/" path
      // regardless of what spamd found, so a correctly-flagged spam
      // message (isSpam true, logged as "(flagged as spam)" right
      // below) still landed straight in Inbox every time; the Spam
      // folder existed and was reachable, it just never received
      // anything. scan.isSpam is only meaningful when scan.ok is
      // true (spamd fails open - see SpamAssassinFilter.h's own doc
      // comment - an unreachable scanner must not silently reroute
      // every message to Spam).
      coreutils::MString path;
      path << mailFileSystem.getMailBoxPath(mailbox)
           << ((scan.ok && scan.isSpam) ? "/Spam/" : "/Inbox/") << messageId;

      coreutils::File mailFile(path, O_CREAT | O_WRONLY, 0660);
      mailFile.write(scan.scanned);

      coreutils::Log(coreutils::LOG_INFO) << "Message " << messageId << " delivered to recipient " << mailbox
         << (scan.ok && scan.isSpam ? " (flagged as spam)" : "") << ".";
   }

   void SMTPServer::inCreate(coreutils::ZString &name) {
      coreutils::Log(coreutils::LOG_DEBUG_2) << "inCreate; [" << name << "]";
      name.split("|");
      // Three parts now: messageid|recipient|sender - see
      // __SMTP_DATA::queueMail()'s own doc comment for why the sender
      // had to be added alongside the recipient.
      if(name.getList().size() > 2) {
         bool exists = mailFileSystem.ifMailBoxExists(name[1]);
         // An alias is a plain file (not a directory) at the same
         // level a mailbox would be - see MailFileSystem's own doc
         // comment on createAlias()/ifAliasExists(). Only checked when
         // it isn't a real mailbox, so a mailbox and an alias can never
         // both match the same address.
         bool isAlias = !exists && mailFileSystem.ifAliasExists(name[1]);
         coreutils::MString from;
         from << mailFileSystem.getQueuePath() << "/" << name;
         if(exists || isAlias) {
	    // Scanned on the way into the recipient's own Inbox, not the
	    // outbound relay path below - spamd's added X-Spam-* headers
	    // are for whatever reads this recipient's mailbox, and a
	    // message this server relays onward gets scored by ITS
	    // destination's own filtering, same as any other MTA. Reading
	    // the whole file in (rather than the plain link() this branch
	    // used to do) is unavoidable now that spamd may have rewritten
	    // the content the recipient actually needs to receive.
	    coreutils::File queuedFile(from, O_RDONLY);
	    queuedFile.read();
	    SpamAssassinFilter::Result scan = SpamAssassinFilter::scan(queuedFile.asString());

	    if (isAlias) {
	       // One shared scan result delivered to every target - an
	       // alias should carry one spam verdict for the message, not
	       // a separately re-scanned copy per target.
	       std::vector<coreutils::MString> targets = mailFileSystem.getAliasMailboxes(name[1]);
	       for (auto &target : targets)
	          deliverToMailbox(target, name[0], scan);
	    } else {
	       deliverToMailbox(name[1], name[0], scan);
	    }

	    int rc = unlink(from.c_str());
         } else {
            // Not a local mailbox - relay it out over SMTP. SendMail's
            // own send() is a plain blocking call (see its doc comment
            // for why) - queued delivery wants fire-and-forget, so this
            // owns the heap-allocated SendMail itself and runs it on its
            // own detached thread rather than blocking this EPoll
            // worker thread for however long the remote host takes.
            coreutils::MString sender(name[2]);
            coreutils::MString recipient(name[1]);
            coreutils::File queuedFile(from, O_RDONLY);
            queuedFile.read();
            coreutils::MString mailData(queuedFile.asString());
            SendMail *outbound = new SendMail(hostName, mailFileSystem.getSendLogPath().str(),
                                               name[0].str(), sender, recipient, mailData, dkimSigner);
            // The queue file's content is already fully read into
            // mailData above, so it's safe to unlink it now rather
            // than after the detached thread finishes (which may be
            // arbitrarily later, or never, if the process restarts
            // first) - previously this was never unlinked at all,
            // meaning processExisting() re-relayed every message still
            // sitting here on every single restart, sending duplicate
            // copies (confirmed live: one message redelivered 35+
            // times across repeated crash-restarts).
            int rc = unlink(from.c_str());
            std::thread([outbound]() {
               try {
                  outbound->send();
               } catch (...) {
                  // An exception escaping a detached thread's entry
                  // function calls std::terminate() - crashing the
                  // entire process, not just this one relay attempt
                  // (this, combined with SIGPIPE previously not being
                  // ignored anywhere, is what turned an occasional
                  // failed delivery into repeated whole-server crashes
                  // - see main.cpp's new signal(SIGPIPE, SIG_IGN)).
                  coreutils::Log(coreutils::LOG_EXCEPT) << "Outbound relay threw an exception - message not delivered.";
               }
               delete outbound;
            }).detach();
         }
      }
   }
   
   void SMTPServer::processExisting() {
      for (const auto & entry : std::filesystem::directory_iterator(mailFileSystem.getQueuePath().str())) {
	 std::string temp(entry.path().filename().string());
	 coreutils::ZString temp2(temp);
	 inCreate(temp2);
      }
   }
   
}