syscall: why doesn't Accept4 read from accept4's *len result parameter?

[bradfitz]

Question from Rob:

The accept4 system call has a in+out socklen_t *addrlen parameter.

In syscall_linux.go, we use it as an in parameter, but never read the result:

func Accept4(fd int, flags int) (nfd int, sa Sockaddr, err error) {
        var rsa RawSockaddrAny
        var len _Socklen = SizeofSockaddrAny
        nfd, err = accept4(fd, &rsa, &len, flags)
        if err != nil {
                return
        }
        sa, err = anyToSockaddr(&rsa)
        if err != nil {
                Close(nfd)
                nfd = 0
        }
        return
}


Likewise in Darwin (https://golang.org/cl/68880043/).

Should we?

Or is func anyToSockaddr safe as-is?  Why?

[bradfitz]

Comment 1:

Oh, because types_$GOOS.go defines a union struct:
union sockaddr_all {                                                                    
                                       
        struct sockaddr s1;     // this one gets used for fields                                                                
        struct sockaddr_in s2;  // these pad it out                                                                             
        struct sockaddr_in6 s3;                                                                                                 
        struct sockaddr_un s4;                                                                                                  
        struct sockaddr_dl s5;                                                                                                  
};                                                                                      
                                       
                                                                                                                                
struct sockaddr_any {                                                                   
                                       
        struct sockaddr addr;                                                                                                   
        char pad[sizeof(union sockaddr_all) - sizeof(struct sockaddr)];                                                         
};                                                                                      
                                       
And the SizeofSockaddrAny is SizeofSockaddrAny = C.sizeof_struct_sockaddr_any, the
maximum size of any address we can accept.

[bradfitz]

Comment 2:

This issue was closed by revision 0399b97.

Status changed to Fixed.

[remyoudompheng]

Comment 3:

For issue #7354 I propose to read it.

[bradfitz]

Comment 4:

That's even better.