path: root/third_party/nix/src/libstore/ssh.cc

#include "libstore/ssh.hh"

#include <utility>

#include <absl/strings/match.h>
#include <absl/strings/str_split.h>

namespace nix {

SSHMaster::SSHMaster(const std::string& host, std::string keyFile,
                     bool useMaster, bool compress, int logFD)
    : host(host),
      fakeSSH(host == "localhost"),
      keyFile(std::move(keyFile)),
      useMaster(useMaster && !fakeSSH),
      compress(compress),
      logFD(logFD) {
  if (host.empty() || absl::StartsWith(host, "-")) {
    throw Error("invalid SSH host name '%s'", host);
  }
}

void SSHMaster::addCommonSSHOpts(Strings& args) {
  for (auto& i :
       absl::StrSplit(getEnv("NIX_SSHOPTS"), absl::ByAnyChar(" \t\n\r"),
                      absl::SkipEmpty())) {
    args.push_back(std::string(i));
  }
  if (!keyFile.empty()) {
    args.insert(args.end(), {"-i", keyFile});
  }
  if (compress) {
    args.push_back("-C");
  }
}

std::unique_ptr<SSHMaster::Connection> SSHMaster::startCommand(
    const std::string& command) {
  Path socketPath = startMaster();

  Pipe in;
  Pipe out;
  in.create();
  out.create();

  auto conn = std::make_unique<Connection>();
  ProcessOptions options;
  options.dieWithParent = false;

  conn->sshPid = startProcess(
      [&]() {
        restoreSignals();

        close(in.writeSide.get());
        close(out.readSide.get());

        if (dup2(in.readSide.get(), STDIN_FILENO) == -1) {
          throw SysError("duping over stdin");
        }
        if (dup2(out.writeSide.get(), STDOUT_FILENO) == -1) {
          throw SysError("duping over stdout");
        }
        if (logFD != -1 && dup2(logFD, STDERR_FILENO) == -1) {
          throw SysError("duping over stderr");
        }

        Strings args;

        if (fakeSSH) {
          args = {"bash", "-c"};
        } else {
          args = {"ssh", host, "-x", "-a"};
          addCommonSSHOpts(args);
          if (!socketPath.empty()) {
            args.insert(args.end(), {"-S", socketPath});
          }
          // TODO(tazjin): Abseil verbosity flag
          /*if (verbosity >= lvlChatty) {
              args.push_back("-v");
              }*/
        }

        args.push_back(command);
        execvp(args.begin()->c_str(), stringsToCharPtrs(args).data());

        // could not exec ssh/bash
        throw SysError("unable to execute '%s'", args.front());
      },
      options);

  in.readSide = -1;
  out.writeSide = -1;

  conn->out = std::move(out.readSide);
  conn->in = std::move(in.writeSide);

  return conn;
}

Path SSHMaster::startMaster() {
  if (!useMaster) {
    return "";
  }

  auto state(state_.lock());

  if (state->sshMaster != -1) {
    return state->socketPath;
  }

  state->tmpDir =
      std::make_unique<AutoDelete>(createTempDir("", "nix", true, true, 0700));

  state->socketPath = Path(*state->tmpDir) + "/ssh.sock";

  Pipe out;
  out.create();

  ProcessOptions options;
  options.dieWithParent = false;

  state->sshMaster = startProcess(
      [&]() {
        restoreSignals();

        close(out.readSide.get());

        if (dup2(out.writeSide.get(), STDOUT_FILENO) == -1) {
          throw SysError("duping over stdout");
        }

        Strings args = {"ssh", host,
                        "-M",  "-N",
                        "-S",  state->socketPath,
                        "-o",  "LocalCommand=echo started",
                        "-o",  "PermitLocalCommand=yes"};
        // if (verbosity >= lvlChatty) { args.push_back("-v"); }
        addCommonSSHOpts(args);
        execvp(args.begin()->c_str(), stringsToCharPtrs(args).data());

        throw SysError("unable to execute '%s'", args.front());
      },
      options);

  out.writeSide = -1;

  std::string reply;
  try {
    reply = readLine(out.readSide.get());
  } catch (EndOfFile& e) {
  }

  if (reply != "started") {
    throw Error("failed to start SSH master connection to '%s'", host);
  }

  return state->socketPath;
}

}  // namespace nix