iroh-dns 1.0.0

DNS-based endpoint discovery for iroh
Documentation 
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//! Android system DNS reader.
//!
//! Forwards to [`hickory_resolver::system_conf::read_system_conf`], which
//! reads `LinkProperties.getDnsServers()` through [`ndk_context`]. iroh on
//! Android therefore requires [`ndk_context`] to be initialized before any
//! [`DnsResolver`] is constructed, either by ndk-glue or android-activity
//! (both do this before `main`) or by an explicit
//! [`install_android_jni_context`] call.
//!
//! Without an initialized [`ndk_context`], the JNI lookup panics. Debug
//! builds wrap the call in `std::panic::catch_unwind` so unit tests on
//! Android (where no JVM is in scope) fall back to the resolver's
//! default servers instead of aborting the test binary. Release builds
//! let the panic propagate; uninitialized [`ndk_context`] in production
//! is a programming error and should surface loudly.
//!
//! [`DnsResolver`]: crate::dns::DnsResolver
//! [`ndk_context`]: https://docs.rs/ndk-context

use std::ffi::c_void;

use hickory_resolver::{
    config::{ResolverConfig, ResolverOpts},
    net::NetError,
};

/// Reads the active network's DNS configuration via JNI.
pub(crate) fn read_system_conf() -> Result<(ResolverConfig, ResolverOpts), NetError> {
    #[cfg(debug_assertions)]
    {
        use std::panic::{AssertUnwindSafe, catch_unwind};
        match catch_unwind(AssertUnwindSafe(
            hickory_resolver::system_conf::read_system_conf,
        )) {
            Ok(Ok(conf)) => Ok(conf),
            Ok(Err(err)) => Err(NetError::from(err)),
            Err(_) => Err(NetError::Msg(
                "ndk_context not initialized; call install_android_jni_context".to_string(),
            )),
        }
    }
    #[cfg(not(debug_assertions))]
    Ok(hickory_resolver::system_conf::read_system_conf()?)
}

/// Publishes a `JavaVM` and `Application` `Context` to [`ndk_context`] so
/// iroh's system DNS reader can use JNI.
///
/// The default [`DnsResolver`] reads DNS configuration through JNI and panics
/// if [`ndk_context`] has not been initialized. Apps that already initialize
/// the context (directly, or via ndk-glue or android-activity) do not need
/// this. Apps that don't use either glue crate must call this once at
/// process startup, before any `DnsResolver` or `Endpoint` is constructed.
///
/// Pass the `JavaVM` from `JNI_OnLoad` (or `JNIEnv::GetJavaVM`) and a JNI
/// global reference to the singleton `Application` from
/// `ActivityThread.currentApplication()`. Both pointers must remain valid
/// until the process exits.
///
/// # Safety
///
/// See [`ndk_context::initialize_android_context`].
///
/// [`DnsResolver`]: crate::dns::DnsResolver
/// [`ndk_context`]: https://docs.rs/ndk-context
pub unsafe fn install_android_jni_context(java_vm: *mut c_void, application_context: *mut c_void) {
    unsafe {
        ndk_context::initialize_android_context(java_vm, application_context);
    }
}