I am trying to include the libsodium into my Go project. For that, I've copied the repo inside my project
// #cgo CFLAGS: -I/mypath/libsodium/src/libsodium/include/sodium
// #include <stdlib.h>
// #include "crypto_sign_ed25519.h"
import "C"
When trying to build the project I get the following error:
/tmp/go-build/cgo-gcc-prolog:53: undefined reference to `crypto_sign_ed25519_pk_to_curve25519'
collect2: error: ld returned 1 exit status
The file can be found but the error is there. I've also tried to reference the '.c' file as well as to copy the crypto_sign_ed25519.h into the src folder but it does not work. My question is do I have to add LDFLAGS and therefore generate a .so file from the library or that is not needed and there is another possible way of doing it?
UPDATE: I've achieved to make it running by installing the library on my local ubuntu:
$ ./configure
$ make && make check
$ sudo make install
and adding // #cgo LDFLAGS: -L/usr/local/lib -lsodium But how can I do it without adding the local path?
You indeed need to link the library, the headers themselves are only the interface to the library and don't link the actual libsodium code to your binary.
Assuming libsodium ships a pkg-config file (it seems to be the case), you can use something like
// #cgo pkg-config: libsodium
// #include "crypto_sign_ed25519.h"
See https://golang.org/cmd/cgo/ for more information about pkg-config support.
To see what cflags/libs you'd be getting (so what cgo will use), run:
pkg-config --cflags --libs libsodium
After manually installing a library on Linux, you have to type ldconfig so that the linker becomes aware of it.
Also, in order to get libsodium prototypes, you should simply include <sodium.h> not <sodium/crypto_sign_ed25519.h> (not meant to be included directly), and call sodium_init() before any other function so that internal data structures are properly initialized.
See how this is done in existing bindings for Go: https://github.com/jamesruan/sodium/blob/master/core.go
You may want to use these bindings instead of reinventing your own. If they are missing some of the functions you need, their maintainers will probably be happy to accept your pull requests.
The two main Go bindings for libsodium that I am aware of are sodium and libsodium-go.