From d005bade7f3339cc68bee12ce13d863d51d54dc4 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Tue, 16 Jan 2024 15:23:46 +0100
Subject: [PATCH] connect(): Propagate errno from the child process

This is necessary on macOS since addTempRoot() relies on errno.
---
 src/libutil/unix-domain-socket.cc | 39 +++++++++++++++++++++----------
 1 file changed, 27 insertions(+), 12 deletions(-)

diff --git a/src/libutil/unix-domain-socket.cc b/src/libutil/unix-domain-socket.cc
index 8949461d2..05bbb5ba3 100644
--- a/src/libutil/unix-domain-socket.cc
+++ b/src/libutil/unix-domain-socket.cc
@@ -1,6 +1,7 @@
 #include "file-system.hh"
 #include "processes.hh"
 #include "unix-domain-socket.hh"
+#include "util.hh"
 
 #include <sys/socket.h>
 #include <sys/un.h>
@@ -75,21 +76,35 @@ void connect(int fd, const std::string & path)
     addr.sun_family = AF_UNIX;
 
     if (path.size() + 1 >= sizeof(addr.sun_path)) {
+        Pipe pipe;
+        pipe.create();
         Pid pid = startProcess([&]() {
-            Path dir = dirOf(path);
-            if (chdir(dir.c_str()) == -1)
-                throw SysError("chdir to '%s' failed", dir);
-            std::string base(baseNameOf(path));
-            if (base.size() + 1 >= sizeof(addr.sun_path))
-                throw Error("socket path '%s' is too long", base);
-            memcpy(addr.sun_path, base.c_str(), base.size() + 1);
-            if (connect(fd, (struct sockaddr *) &addr, sizeof(addr)) == -1)
-                throw SysError("cannot connect to socket at '%s'", path);
-            _exit(0);
+            try {
+                pipe.readSide.close();
+                Path dir = dirOf(path);
+                if (chdir(dir.c_str()) == -1)
+                    throw SysError("chdir to '%s' failed", dir);
+                std::string base(baseNameOf(path));
+                if (base.size() + 1 >= sizeof(addr.sun_path))
+                    throw Error("socket path '%s' is too long", base);
+                memcpy(addr.sun_path, base.c_str(), base.size() + 1);
+                if (connect(fd, (struct sockaddr *) &addr, sizeof(addr)) == -1)
+                    throw SysError("cannot connect to socket at '%s'", path);
+                writeFull(pipe.writeSide.get(), "0\n");
+            } catch (SysError & e) {
+                writeFull(pipe.writeSide.get(), fmt("%d\n", e.errNo));
+            } catch (...) {
+                writeFull(pipe.writeSide.get(), "-1\n");
+            }
         });
-        int status = pid.wait();
-        if (status != 0)
+        pipe.writeSide.close();
+        auto errNo = string2Int<int>(chomp(drainFD(pipe.readSide.get())));
+        if (!errNo || *errNo == -1)
             throw Error("cannot connect to socket at '%s'", path);
+        else if (*errNo > 0) {
+            errno = *errNo;
+            throw SysError("cannot connect to socket at '%s'", path);
+        }
     } else {
         memcpy(addr.sun_path, path.c_str(), path.size() + 1);
         if (connect(fd, (struct sockaddr *) &addr, sizeof(addr)) == -1)