Sodium.jl

module Sodium

export seal

using Base64: base64encode, base64decode

const SEALBYTES = Ref{Csize_t}()

struct SodiumError
    fun::Symbol
    code::Int
end

Base.showerror(io::IO, e::SodiumError) = print(io, "$(e.fun) returned error code $(e.code)")

macro check(ex::Expr)
    fun = ex.args[2].args[1]
    return quote
        code = $(esc(ex))
        code == 0 || throw(SodiumError($fun, code))
    end
end

function __init__()
    @check ccall((:sodium_init, :libsodium), Cint, ())
    SEALBYTES[] = ccall((:crypto_box_sealbytes, :libsodium), Csize_t, ())
end

seal(msg, pk::AbstractString) = base64encode(seal(msg, base64decode(pk)))
function seal(msg, pk)
    len = length(msg)
    dest = Vector{Cuchar}(undef, SEALBYTES[] + len)

    @check ccall(
        (:crypto_box_seal, :libsodium),
        Cint,
        (Ptr{Cuchar}, Ptr{Cuchar}, Culonglong, Ptr{Cuchar}),
        pointer(dest), pointer(msg), len, pointer(pk),
    )

    return dest
end

end