Could not find openssl in backend - server

Question

Error I get:
error[E0433]: failed to resolve: could not find `openssl` in `backend`
--> ...\src\...\swagger-0.12.1\src\connector.rs:41:34
|
41 | native_tls::backend::openssl::TlsConnectorBuilderExt::from_openssl(ssl);
| ^^^^^^^ could not find `openssl` in `backend`
error[E0433]: failed to resolve: could not find `openssl` in `backend`
--> ...\swagger-0.12.1\src\connector.rs:85:34
|
85 | native_tls::backend::openssl::TlsConnectorBuilderExt::from_openssl(ssl);
| ^^^^^^^ could not find `openssl` in `backend`
Compiling hyper v0.2.1
error: expected identifier, found `"rustc-serialize"`
--> ...\hyper-0.2.1\src\lib.rs:129:14
|
129 | extern crate "rustc-serialize" as serialize;
| ^^^^^^^^^^^^^^^^^ expected identifier
Generated a server stub user swagger. Ran into issues where cargo couldn't find openssl, giving an error like 'custom build something openssl-sys 0.9.24'. This was a known issue and I overcame it by downloading vcpkg, and using vcpkg to download openssl. Then using environment variables to point to the download folder so cargo could use openssl. But now the error seems to be that openssl doesn't exist in backend?
It also seems to specific to windows, any ideas?
Tried changing the version of native-tls to the most up to date version but it doesn't seem to have an affect at all. It looks like swagger's dependencies need updating but I literally just generated this stub...

Answer 1

You've landed on a flaw from the Rust documentation tools; it picks up what is in a package, but doesn't show the limits.
The backend module definition is defined as:
#[cfg(any(target_os = "macos", target_os = "ios"))]
pub mod security_framework;
#[cfg(target_os = "windows")]
pub mod schannel;
#[cfg(not(any(target_os = "macos", target_os = "windows", target_os = "ios")))]
pub mod openssl;
In other words, the situation is the following:
If you are on linux (i.e. not macOS, not windows, not iOS), then openssl is available
If you are on windows, then schannel is available
If you are on MacOS or iOS security_framework is available
You should, however, not be trying to target a specific backend, as this defeats the purpose of the library. Instead of importing native_tls::backend::openssl::TlsConnectorBuilderExt, import native_tls::TlsConnectorBuilder and let it decide what backend you need.
This may be easier said than done, however, since by the looks of your error this is caused by a third-party library, which indicates that it was only tested on Linux.