Move /src to /subprojects

This will facilitate breaking up Nix into multiple packages for each
component with Meson.

subprojects/libutil/unix-domain-socket.cc

@@ -0,0 +1,117 @@
+#include "file-system.hh"
+#include "unix-domain-socket.hh"
+#include "util.hh"
+
+#ifdef _WIN32
+# include <winsock2.h>
+# include <afunix.h>
+#else
+# include <sys/socket.h>
+# include <sys/un.h>
+# include "processes.hh"
+#endif
+#include <unistd.h>
+
+namespace nix {
+
+AutoCloseFD createUnixDomainSocket()
+{
+    AutoCloseFD fdSocket = toDescriptor(socket(PF_UNIX, SOCK_STREAM
+        #ifdef SOCK_CLOEXEC
+        | SOCK_CLOEXEC
+        #endif
+        , 0));
+    if (!fdSocket)
+        throw SysError("cannot create Unix domain socket");
+#ifndef _WIN32
+    unix::closeOnExec(fdSocket.get());
+#endif
+    return fdSocket;
+}
+
+
+AutoCloseFD createUnixDomainSocket(const Path & path, mode_t mode)
+{
+    auto fdSocket = nix::createUnixDomainSocket();
+
+    bind(fdSocket.get(), path);
+
+    if (chmod(path.c_str(), mode) == -1)
+        throw SysError("changing permissions on '%1%'", path);
+
+    if (listen(toSocket(fdSocket.get()), 100) == -1)
+        throw SysError("cannot listen on socket '%1%'", path);
+
+    return fdSocket;
+}
+
+static void bindConnectProcHelper(
+    std::string_view operationName, auto && operation,
+    Socket fd, const std::string & path)
+{
+    struct sockaddr_un addr;
+    addr.sun_family = AF_UNIX;
+
+    // Casting between types like these legacy C library interfaces
+    // require is forbidden in C++. To maintain backwards
+    // compatibility, the implementation of the bind/connect functions
+    // contains some hints to the compiler that allow for this
+    // special case.
+    auto * psaddr = reinterpret_cast<struct sockaddr *>(&addr);
+
+    if (path.size() + 1 >= sizeof(addr.sun_path)) {
+#ifdef _WIN32
+        throw Error("cannot %s to socket at '%s': path is too long", operationName, path);
+#else
+        Pipe pipe;
+        pipe.create();
+        Pid pid = startProcess([&] {
+            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 (operation(fd, psaddr, sizeof(addr)) == -1)
+                    throw SysError("cannot %s to socket at '%s'", operationName, 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");
+            }
+        });
+        pipe.writeSide.close();
+        auto errNo = string2Int<int>(chomp(drainFD(pipe.readSide.get())));
+        if (!errNo || *errNo == -1)
+            throw Error("cannot %s to socket at '%s'", operationName, path);
+        else if (*errNo > 0) {
+            errno = *errNo;
+            throw SysError("cannot %s to socket at '%s'", operationName, path);
+        }
+#endif
+    } else {
+        memcpy(addr.sun_path, path.c_str(), path.size() + 1);
+        if (operation(fd, psaddr, sizeof(addr)) == -1)
+            throw SysError("cannot %s to socket at '%s'", operationName, path);
+    }
+}
+
+
+void bind(Socket fd, const std::string & path)
+{
+    unlink(path.c_str());
+
+    bindConnectProcHelper("bind", ::bind, fd, path);
+}
+
+
+void connect(Socket fd, const std::string & path)
+{
+    bindConnectProcHelper("connect", ::connect, fd, path);
+}
+
+}