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#include "file-system.hh"
#include "processes.hh"
#include "unix-domain-socket.hh"
#include "strings.hh"
#include <sys/socket.h>
#include <sys/un.h>
#include <unistd.h>
namespace nix {
AutoCloseFD createUnixDomainSocket()
{
AutoCloseFD fdSocket{socket(PF_UNIX, SOCK_STREAM
#ifdef SOCK_CLOEXEC
| SOCK_CLOEXEC
#endif
, 0)};
if (!fdSocket)
throw SysError("cannot create Unix domain socket");
closeOnExec(fdSocket.get());
return fdSocket;
}
AutoCloseFD createUnixDomainSocket(const Path & path, mode_t mode)
{
auto fdSocket = nix::createUnixDomainSocket();
bind(fdSocket.get(), path);
chmodPath(path.c_str(), mode);
if (listen(fdSocket.get(), 100) == -1)
throw SysError("cannot listen on socket '%1%'", path);
return fdSocket;
}
/**
* Workaround for the max length of Unix socket names being between 102
* (darwin) and 108 (Linux), which is extremely short. This limitation is
* caused by historical restrictions on sizeof(struct sockaddr):
* https://unix.stackexchange.com/a/367012.
*
* Our solution here is to start a process inheriting the socket, chdir into
* the directory of the socket, then connect with just the filename. This is
* rather silly but it works around working directory being process-wide state,
* and is as clearly sound as possible.
*/
static void bindConnectProcHelper(
std::string_view operationName, auto && operation,
int 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)) {
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);
}
} 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(int fd, const std::string & path)
{
unlink(path.c_str());
bindConnectProcHelper("bind", ::bind, fd, path);
}
void connect(int fd, const std::string & path)
{
bindConnectProcHelper("connect", ::connect, fd, path);
}
}
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