How to fix implementation of `pkcs8::der::Decode` is not general enough error in Rust

Question

I am trying to use the pkcs8 crate to load a private key but getting compilation error that I am not sure how to fix.

My code is basically like this

fn load_private_key_from_pem(private_key_path: &str) -> PrivateKeyInfo<'static> {
    let byte_slice: &[u8] = &fs::read(private_key_path).expect("Loading pem file failed");
    PrivateKeyInfo::from_pem(byte_slice).expect("Decoding private key pem file failed")
}

But this fails with the compilation error

error: implementation of `pkcs8::der::Decode` is not general enough
   --> src/tests/load_pem.rs:147:5
    |
147 |     PrivateKeyInfo::from_pem(byte_slice).expect("Decoding private key pem file failed")
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ implementation of `pkcs8::der::Decode` is not general enough
    |
    = note: `PrivateKeyInfo<'_>` must implement `pkcs8::der::Decode<'0>`, for any lifetime `'0`...
    = note: ...but it actually implements `pkcs8::der::Decode<'1>`, for some specific lifetime `'1`

What is the explanation behind this error? And how would go about fixing it?

I don't know this crate, but you can't use `from_pem()` with `PrivateKeyInfo`. You have to find another way. Maybe try looking at how it is implemented. — Chayim Friedman, Jul 25 '23 at 10:09
But do you know why it cannot be used? I mean the crate does provide `from_pem()` on `PrivateKeyInfo` — Finlay Weber, Jul 25 '23 at 10:18
It does not. rustdoc is at fault for making it seems like it does, but it does not. — Chayim Friedman, Jul 25 '23 at 10:18
If `use pkcs8::der::DecodePem;` is in scope, then the `from_pem()` is usable on `PrivateKeyInfo` though. Because if that is not the case, I think I will be getting a different compilation error? — Finlay Weber, Jul 25 '23 at 10:21
No, it is not usable on it. Because of lifetimes errors and not of trait errors, so that's why you're getting this error and not another. But it is not usable on it, ever. — Chayim Friedman, Jul 25 '23 at 10:22
Okay. That's a bit confusing, but thanks for pointing this out — Finlay Weber, Jul 25 '23 at 10:22
Reading the implementation of `from_pem()`, you can do the same. — Chayim Friedman, Jul 25 '23 at 10:23

How to fix implementation of `pkcs8::der::Decode` is not general enough error in Rust

0 Answers0