libstore: use runProgram2 for ssh connections

we do not need explict redirection management now, and dieWithParent
doesn't need an override either. we'd much prefer to kill ssh if the
process in charge exits; even ssh multiplexers are not fazed by this

Change-Id: I81e28b7605df73c887878ea4716228c7ad0f5c6f

lix/libstore/ssh.cc

@@ -6,6 +6,7 @@
 #include "lix/libutil/file-descriptor.hh"
 #include "lix/libutil/finally.hh"
 #include "lix/libutil/logging.hh"
+#include "lix/libutil/processes.hh"
 #include "lix/libutil/strings.hh"
 #include "lix/libstore/temporary-dir.hh"
 #include <sys/socket.h>
@@ -54,8 +55,6 @@ std::unique_ptr<SSH::Connection> SSH::startCommand(const std::string & command)
 {
     auto [parent, child] = SocketPair::stream();
     auto conn = std::make_unique<Connection>();
-    ProcessOptions options;
-    options.dieWithParent = false;
 
     std::optional<Finally<std::function<void()>>> resumeLoggerDefer;
     if (!fakeSSH) {
@@ -63,41 +62,29 @@ std::unique_ptr<SSH::Connection> SSH::startCommand(const std::string & command)
         resumeLoggerDefer.emplace([&]() { logger->resume(); });
     }
 
-    Strings args;
+    RunOptions options;
 
     // We specifically spawn bash here, to (hopefully) get
     // reasonably POSIX-y semantics for the things we're about
     // to do next.
     if (fakeSSH) {
-        args = {"bash", "-c", command};
+        options.program = "bash";
+        options.args = {"-c", command};
     } else {
-        args = {"ssh", host.c_str(), "-x", "-T"};
-        addCommonSSHOpts(args);
-        args.push_back(command);
+        options.program = "ssh";
+        options.args = {host.c_str(), "-x", "-T"};
+        addCommonSSHOpts(options.args);
+        options.args.push_back(command);
     }
 
-    printMsg(lvlChatty, "running ssh: %s", concatMapStringsSep(" ", args, shellEscape));
+    options.redirections.push_back({.dup = STDIN_FILENO, .from = child.get()});
+    options.redirections.push_back({.dup = STDOUT_FILENO, .from = child.get()});
+    if (logFD != -1) {
+        options.redirections.push_back({.dup = STDERR_FILENO, .from = logFD});
+    }
 
-    conn->sshPid = startProcess([&]() {
-        restoreProcessContext();
-
-        parent.close();
-
-        if (dup2(child.get(), STDIN_FILENO) == -1) {
-            throw SysError("duping over stdin");
-        }
-        if (dup2(child.get(), STDOUT_FILENO) == -1) {
-            throw SysError("duping over stdout");
-        }
-        if (logFD != -1 && dup2(logFD, STDERR_FILENO) == -1) {
-            throw SysError("duping over stderr");
-        }
-
-        sys::execvp(*args.begin(), args);
-
-        // could not exec ssh/bash
-        throw SysError("unable to execute '%s'", args.front());
-    }, options);
+    auto [pid, _stdout] = runProgram2(options).release();
+    conn->sshPid = std::move(pid);
 
     child.close();