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The Go program is connecting to the wrong abstract socket (or, equivalently, the C program is binding to the wrong abstract socket).

Your bind() is made against an abstract namespace UNIX socket address of length sizeof(struct sockaddr_un). If I am reading the Go implementation correctly, however, your connect() is performed against a socket address of length nine: two bytes for sa_family, and seven bytes, in this case, for len(name).

Those are different sockets.

In the abstract namespace, NULLs aren't special, so "\0uds-js" is one valid socket address, and "\0uds-js\0\0\0\0\0\0\0\0..." is a different valid address.

strace both processes looking at the C program's bind() and the Go program's connect(). I expect you will see that they call those functions with different socklen_t arguments.