libutil: move unix chdir+bind/connect to libexec

Change-Id: Ie07ece701454153d3d5c6c34e5613c0d1d5fae03

lix/libexec/common.hh

@@ -1,15 +1,19 @@
 #pragma once
 ///@file common setup/utility header for libexec helpers
 
+#include <cctype>
 #include <cerrno>
+#include <cinttypes>
 #include <cstdio>
 #include <cstdlib>
 #include <cstring>
 #include <fcntl.h>
 #include <format> // IWYU pragma: keep
+#include <limits>
 #include <span>
 #include <string> // IWYU pragma: keep
 #include <string_view>
+#include <type_traits>
 #include <unistd.h>
 
 /// file descriptor of the error reporting pipe. anything written to this pipe
@@ -37,6 +41,34 @@ inline void die(std::string_view msg)
     exit(252);
 }
 
+/// converts an argument to an integer or dies with a message.
+template<typename T, size_t N>
+    requires std::is_integral_v<T>
+T argToInt(const char (&argName)[N], const char * str)
+{
+    // this should really just wrap std::from_chars, but macos doesn't have it.
+    for (const auto c : std::string_view(str)) {
+        if (c != '-' && !std::isdigit(c)) {
+            die(std::format("invalid {} argument", argName));
+        }
+    }
+
+    char * end = nullptr;
+    const auto tmp = [&] {
+        if constexpr (std::is_signed_v<T>) {
+            return std::strtoimax(str, &end, 10); // NOLINT(lix-unsafe-c-calls): str is a C string
+        } else {
+            return std::strtoumax(str, &end, 10); // NOLINT(lix-unsafe-c-calls): str is a C string
+        }
+    }();
+
+    if (!end || *end || tmp < std::numeric_limits<T>::min() || tmp > std::numeric_limits<T>::max()) {
+        die(std::format("invalid {} argument", argName));
+    }
+
+    return tmp;
+}
+
 /// check syscall result and immediately terminate with a message on failure.
 #define DIE_UNLESS_SYS(name, expr)                             \
     ([&] {                                                     \

lix/libexec/meson.build

@@ -11,3 +11,10 @@ run_pager = executable(
   install : true,
   install_dir : libexecdir / 'lix',
 )
+
+unix_bind_connect = executable(
+  'unix-bind-connect',
+  files('unix-bind-connect.cc'),
+  install : true,
+  install_dir : libexecdir / 'lix',
+)

lix/libexec/unix-bind-connect.cc

@@ -0,0 +1,34 @@
+#include "common.hh"
+#include <sys/socket.h>
+#include <sys/un.h>
+
+LIBEXEC_HELPER(4)
+
+int helperMain(const char *, std::span<char *> args) noexcept
+{
+    int socket = argToInt<int>("socket", args[0]);
+    std::string_view method = args[1];
+    const auto dir = args[2];
+    const auto name = args[3];
+
+    DIE_UNLESS_SYS("chdir", chdir(dir));
+
+    struct sockaddr_un addr;
+    addr.sun_family = AF_UNIX;
+
+    if (auto nameLen = strlen(name); nameLen + 1 >= sizeof(addr.sun_path)) {
+        die(std::format("socket path {}/{} is too long", dir, name));
+    } else {
+        memcpy(addr.sun_path, name, nameLen + 1);
+    }
+
+    if (method == "bind") {
+        DIE_UNLESS_SYS("bind", bind(socket, reinterpret_cast<struct sockaddr *>(&addr), sizeof(addr)));
+    } else if (method == "connect") {
+        DIE_UNLESS_SYS("connect", connect(socket, reinterpret_cast<struct sockaddr *>(&addr), sizeof(addr)));
+    } else {
+        die(std::format("invalid method %s", method));
+    }
+
+    return 0;
+}

lix/libutil/unix-domain-socket.cc

@@ -4,6 +4,7 @@
 #include "lix/libutil/unix-domain-socket.hh"
 #include "lix/libutil/strings.hh"
 
+#include <string>
 #include <sys/socket.h>
 #include <sys/un.h>
 #include <unistd.h>
@@ -64,36 +65,12 @@ static void bindConnectProcHelper(
     auto * psaddr = reinterpret_cast<struct sockaddr *>(&addr);
 
     if (path.size() + 1 >= sizeof(addr.sun_path)) {
-        Pipe pipe;
-        pipe.create();
-        Pid pid{startProcess([&] {
-            try {
-                pipe.readSide.close();
-                Path dir = dirOf(path);
-                if (sys::chdir(dir) == -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);
-        }
+        runHelper(
+            "unix-bind-connect",
+            {.args =
+                 {std::to_string(fd), std::string(operationName), dirOf(path), std::string(baseNameOf(path))},
+             .redirections = {{.dup = fd, .from = fd}}}
+        ).waitAndCheck();
     } else {
         memcpy(addr.sun_path, path.c_str(), path.size() + 1);
         if (operation(fd, psaddr, sizeof(addr)) == -1)