feat: add async wrapper for resolver

Added behind the async feature, and adds the futures-channel dep to
to the deps enabled by async.

This PR is an upstreaming of nginx-acme::net::resolver, see: https://github.com/nginx/nginx-acme/blob/main/src/net/resolver.rs

Co-authored-by: Evgeny Shirykalov <e.shirykalov@f5.com>

Author: pchickey

Cargo.lock

@@ -42,6 +42,7 @@ async-task = { version = "4.7.1", optional = true }
 lock_api = "0.4.13"
 nginx-sys = { path = "nginx-sys", version = "0.5.0-beta"}
 pin-project-lite = { version = "0.2.16", optional = true }
+futures-channel = { version = "0.3.31", optional = true }
 
 [features]
 default = ["std"]
@@ -50,6 +51,7 @@ async = [
     "alloc",
     "dep:async-task",
     "dep:pin-project-lite",
+    "dep:futures-channel",
 ]
 # Provides APIs that require allocations via the `alloc` crate.
 alloc = ["allocator-api2/alloc"]

Cargo.toml

@@ -2,5 +2,7 @@
 pub use self::sleep::{sleep, Sleep};
 pub use self::spawn::{spawn, Task};
 
+pub mod resolver;
+
 mod sleep;
 mod spawn;

src/async_/mod.rs

@@ -0,0 +1,237 @@
+// Copyright (c) F5, Inc.
+//
+// This source code is licensed under the Apache License, Version 2.0 license found in the
+// LICENSE file in the root directory of this source tree.
+
+//! Wrapper for the nginx resolver.
+//!
+//! See <https://nginx.org/en/docs/http/ngx_http_core_module.html#resolver>.
+
+use core::ffi::c_void;
+use core::ptr::NonNull;
+use std::boxed::Box;
+use std::fmt;
+use std::string::{String, ToString};
+
+use crate::{
+    collections::Vec,
+    core::Pool,
+    ffi::{
+        ngx_addr_t, ngx_msec_t, ngx_resolve_name, ngx_resolve_start, ngx_resolver_ctx_t,
+        ngx_resolver_t, ngx_str_t,
+    },
+};
+use futures_channel::oneshot::{channel, Sender};
+use nginx_sys::{
+    NGX_RESOLVE_FORMERR, NGX_RESOLVE_NOTIMP, NGX_RESOLVE_NXDOMAIN, NGX_RESOLVE_REFUSED,
+    NGX_RESOLVE_SERVFAIL, NGX_RESOLVE_TIMEDOUT,
+};
+
+/// Error type for all uses of `Resolver`.
+#[derive(Debug)]
+pub enum Error {
+    /// No resolver configured
+    NoResolver,
+    /// Resolver error, with context of name being resolved
+    Resolver(ResolverError, String),
+    /// Allocation failed
+    AllocationFailed,
+    /// Unexpected error
+    Unexpected(String),
+}
+
+impl fmt::Display for Error {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            Error::NoResolver => write!(f, "No resolver configured"),
+            Error::Resolver(err, context) => write!(f, "{err}: resolving `{context}`"),
+            Error::AllocationFailed => write!(f, "Allocation failed"),
+            Error::Unexpected(err) => write!(f, "Unexpected error: {err}"),
+        }
+    }
+}
+impl std::error::Error for Error {}
+
+/// These cases directly reflect the NGX_RESOLVE_ error codes,
+/// plus a timeout, and a case for an unknown error where a known
+/// NGX_RESOLVE_ should be.
+#[derive(Debug)]
+pub enum ResolverError {
+    /// Format error (NGX_RESOLVE_FORMERR)
+    Format,
+    /// Server failure (NGX_RESOLVE_SERVFAIL)
+    ServFail,
+    /// Host not found (NGX_RESOLVE_NXDOMAIN)
+    NXDomain,
+    /// Unimplemented (NGX_RESOLVE_NOTIMP)
+    Unimplemented,
+    /// Operatio refused (NGX_RESOLVE_REFUSED)
+    Refused,
+    /// Timed out (NGX_RESOLVE_TIMEDOUT)
+    TimedOut,
+    /// Unknown NGX_RESOLVE error
+    Unknown(isize),
+}
+impl fmt::Display for ResolverError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            ResolverError::Format => write!(f, "Format error"),
+            ResolverError::ServFail => write!(f, "Server Failure"),
+            ResolverError::NXDomain => write!(f, "Host not found"),
+            ResolverError::Unimplemented => write!(f, "Unimplemented"),
+            ResolverError::Refused => write!(f, "Refused"),
+            ResolverError::TimedOut => write!(f, "Timed out"),
+            ResolverError::Unknown(code) => write!(f, "Unknown NGX_RESOLVE error {code}"),
+        }
+    }
+}
+impl std::error::Error for ResolverError {}
+
+/// Convert from the NGX_RESOLVE_ error codes. Fails if code was success.
+impl TryFrom<isize> for ResolverError {
+    type Error = ();
+    fn try_from(code: isize) -> Result<ResolverError, Self::Error> {
+        match code as u32 {
+            0 => Err(()),
+            NGX_RESOLVE_FORMERR => Ok(ResolverError::Format),
+            NGX_RESOLVE_SERVFAIL => Ok(ResolverError::ServFail),
+            NGX_RESOLVE_NXDOMAIN => Ok(ResolverError::NXDomain),
+            NGX_RESOLVE_NOTIMP => Ok(ResolverError::Unimplemented),
+            NGX_RESOLVE_REFUSED => Ok(ResolverError::Refused),
+            NGX_RESOLVE_TIMEDOUT => Ok(ResolverError::TimedOut),
+            _ => Ok(ResolverError::Unknown(code)),
+        }
+    }
+}
+
+type Res = Result<Vec<ngx_addr_t>, Error>;
+
+struct ResCtx<'a> {
+    ctx: Option<*mut ngx_resolver_ctx_t>,
+    sender: Option<Sender<Res>>,
+    pool: &'a Pool,
+}
+
+impl Drop for ResCtx<'_> {
+    fn drop(&mut self) {
+        if let Some(ctx) = self.ctx.take() {
+            unsafe {
+                nginx_sys::ngx_resolve_name_done(ctx);
+            }
+        }
+    }
+}
+
+fn copy_resolved_addr(
+    addr: *mut nginx_sys::ngx_resolver_addr_t,
+    pool: &Pool,
+) -> Result<ngx_addr_t, Error> {
+    let addr = NonNull::new(addr).ok_or(Error::Unexpected(
+        "null ngx_resolver_addr_t in ngx_resolver_ctx_t.addrs".to_string(),
+    ))?;
+    let addr = unsafe { addr.as_ref() };
+
+    let sockaddr = pool.alloc(addr.socklen as usize) as *mut nginx_sys::sockaddr;
+    if sockaddr.is_null() {
+        Err(Error::AllocationFailed)?;
+    }
+    unsafe {
+        addr.sockaddr
+            .cast::<u8>()
+            .copy_to_nonoverlapping(sockaddr.cast(), addr.socklen as usize)
+    };
+
+    let name =
+        unsafe { ngx_str_t::from_bytes(pool.as_ref() as *const _ as *mut _, addr.name.as_bytes()) }
+            .ok_or(Error::AllocationFailed)?;
+
+    Ok(ngx_addr_t {
+        sockaddr,
+        socklen: addr.socklen,
+        name,
+    })
+}
+
+/// A wrapper for an ngx_resolver_t which provides an async Rust API
+pub struct Resolver {
+    resolver: NonNull<ngx_resolver_t>,
+    timeout: ngx_msec_t,
+}
+
+impl Resolver {
+    /// Create a new `Resolver` from existing pointer to `ngx_resolver_t` and
+    /// timeout.
+    pub fn from_resolver(resolver: NonNull<ngx_resolver_t>, timeout: ngx_msec_t) -> Self {
+        Self { resolver, timeout }
+    }
+
+    /// Resolve a name into a set of addresses.
+    ///
+    /// The set of addresses may not be deterministic, because the
+    /// implementation of the resolver may race multiple DNS requests.
+    pub async fn resolve(&self, name: &ngx_str_t, pool: &Pool) -> Res {
+        unsafe {
+            let ctx: *mut ngx_resolver_ctx_t =
+                ngx_resolve_start(self.resolver.as_ptr(), core::ptr::null_mut());
+            if ctx.is_null() {
+                Err(Error::AllocationFailed)?
+            }
+            if ctx as isize == -1 {
+                Err(Error::NoResolver)?
+            }
+
+            let (sender, receiver) = channel::<Res>();
+            let rctx = Box::new(ResCtx {
+                ctx: Some(ctx),
+                sender: Some(sender),
+                pool,
+            });
+
+            (*ctx).name = *name;
+            (*ctx).timeout = self.timeout;
+            (*ctx).set_cancelable(1);
+            (*ctx).handler = Some(Self::resolve_handler);
+            (*ctx).data = Box::into_raw(rctx) as *mut c_void;
+
+            let ret = ngx_resolve_name(ctx);
+            if ret != 0 {
+                Err(Error::Resolver(
+                    ResolverError::try_from(ret).expect("nonzero, checked above"),
+                    name.to_string(),
+                ))?;
+            }
+
+            receiver
+                .await
+                .map_err(|_| Error::Resolver(ResolverError::TimedOut, name.to_string()))?
+        }
+    }
+
+    unsafe extern "C" fn resolve_handler(ctx: *mut ngx_resolver_ctx_t) {
+        let mut rctx = *Box::from_raw((*ctx).data as *mut ResCtx);
+        rctx.ctx.take();
+        if let Some(sender) = rctx.sender.take() {
+            let _ = sender.send(Self::resolve_result(ctx, rctx.pool));
+        }
+        nginx_sys::ngx_resolve_name_done(ctx);
+    }
+
+    fn resolve_result(ctx: *mut ngx_resolver_ctx_t, pool: &Pool) -> Res {
+        let ctx = unsafe { ctx.as_ref().unwrap() };
+        let s = ctx.state;
+        if s != 0 {
+            Err(Error::Resolver(
+                ResolverError::try_from(s).expect("nonzero, checked above"),
+                ctx.name.to_string(),
+            ))?;
+        }
+        if ctx.addrs.is_null() {
+            Err(Error::AllocationFailed)?;
+        }
+        let mut out = Vec::new();
+        for i in 0..ctx.naddrs {
+            out.push(copy_resolved_addr(unsafe { ctx.addrs.add(i) }, pool)?);
+        }
+        Ok(out)
+    }
+}