1 files changed, 169 insertions, 0 deletions
diff --git a/third_party/rust/neqo-crypto/src/ext.rs b/third_party/rust/neqo-crypto/src/ext.rs
new file mode 100644
index 0000000000..310e87a1b7
--- /dev/null
+++ b/third_party/rust/neqo-crypto/src/ext.rs
@@ -0,0 +1,169 @@
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use std::{
+    cell::RefCell,
+    convert::TryFrom,
+    os::raw::{c_uint, c_void},
+    pin::Pin,
+    rc::Rc,
+};
+
+use crate::{
+    agentio::as_c_void,
+    constants::{Extension, HandshakeMessage, TLS_HS_CLIENT_HELLO, TLS_HS_ENCRYPTED_EXTENSIONS},
+    err::Res,
+    ssl::{
+        PRBool, PRFileDesc, SECFailure, SECStatus, SECSuccess, SSLAlertDescription,
+        SSLExtensionHandler, SSLExtensionWriter, SSLHandshakeType,
+    },
+};
+
+experimental_api!(SSL_InstallExtensionHooks(
+    fd: *mut PRFileDesc,
+    extension: u16,
+    writer: SSLExtensionWriter,
+    writer_arg: *mut c_void,
+    handler: SSLExtensionHandler,
+    handler_arg: *mut c_void,
+));
+
+pub enum ExtensionWriterResult {
+    Write(usize),
+    Skip,
+}
+
+pub enum ExtensionHandlerResult {
+    Ok,
+    Alert(crate::constants::Alert),
+}
+
+pub trait ExtensionHandler {
+    fn write(&mut self, msg: HandshakeMessage, _d: &mut [u8]) -> ExtensionWriterResult {
+        match msg {
+            TLS_HS_CLIENT_HELLO | TLS_HS_ENCRYPTED_EXTENSIONS => ExtensionWriterResult::Write(0),
+            _ => ExtensionWriterResult::Skip,
+        }
+    }
+
+    fn handle(&mut self, msg: HandshakeMessage, _d: &[u8]) -> ExtensionHandlerResult {
+        match msg {
+            TLS_HS_CLIENT_HELLO | TLS_HS_ENCRYPTED_EXTENSIONS => ExtensionHandlerResult::Ok,
+            _ => ExtensionHandlerResult::Alert(110), // unsupported_extension
+        }
+    }
+}
+
+type BoxedExtensionHandler = Box<Rc<RefCell<dyn ExtensionHandler>>>;
+
+pub struct ExtensionTracker {
+    extension: Extension,
+    handler: Pin<Box<BoxedExtensionHandler>>,
+}
+
+impl ExtensionTracker {
+    // Technically the as_mut() call here is the only unsafe bit,
+    // but don't call this function lightly.
+    unsafe fn wrap_handler_call<F, T>(arg: *mut c_void, f: F) -> T
+    where
+        F: FnOnce(&mut dyn ExtensionHandler) -> T,
+    {
+        let rc = arg.cast::<BoxedExtensionHandler>().as_mut().unwrap();
+        f(&mut *rc.borrow_mut())
+    }
+
+    #[allow(clippy::cast_possible_truncation, clippy::cast_sign_loss)]
+    unsafe extern "C" fn extension_writer(
+        _fd: *mut PRFileDesc,
+        message: SSLHandshakeType::Type,
+        data: *mut u8,
+        len: *mut c_uint,
+        max_len: c_uint,
+        arg: *mut c_void,
+    ) -> PRBool {
+        let d = std::slice::from_raw_parts_mut(data, max_len as usize);
+        Self::wrap_handler_call(arg, |handler| {
+            // Cast is safe here because the message type is always part of the enum
+            match handler.write(message as HandshakeMessage, d) {
+                ExtensionWriterResult::Write(sz) => {
+                    *len = c_uint::try_from(sz).expect("integer overflow from extension writer");
+                    1
+                }
+                ExtensionWriterResult::Skip => 0,
+            }
+        })
+    }
+
+    unsafe extern "C" fn extension_handler(
+        _fd: *mut PRFileDesc,
+        message: SSLHandshakeType::Type,
+        data: *const u8,
+        len: c_uint,
+        alert: *mut SSLAlertDescription,
+        arg: *mut c_void,
+    ) -> SECStatus {
+        let d = std::slice::from_raw_parts(data, len as usize);
+        #[allow(clippy::cast_possible_truncation, clippy::cast_sign_loss)]
+        Self::wrap_handler_call(arg, |handler| {
+            // Cast is safe here because the message type is always part of the enum
+            match handler.handle(message as HandshakeMessage, d) {
+                ExtensionHandlerResult::Ok => SECSuccess,
+                ExtensionHandlerResult::Alert(a) => {
+                    *alert = a;
+                    SECFailure
+                }
+            }
+        })
+    }
+
+    /// Use the provided handler to manage an extension.  This is quite unsafe.
+    ///
+    /// # Safety
+    ///
+    /// The holder of this `ExtensionTracker` needs to ensure that it lives at
+    /// least as long as the file descriptor, as NSS provides no way to remove
+    /// an extension handler once it is configured.
+    ///
+    /// # Errors
+    ///
+    /// If the underlying NSS API fails to register a handler.
+    pub unsafe fn new(
+        fd: *mut PRFileDesc,
+        extension: Extension,
+        handler: Rc<RefCell<dyn ExtensionHandler>>,
+    ) -> Res<Self> {
+        // The ergonomics here aren't great for users of this API, but it's
+        // horrific here. The pinned outer box gives us a stable pointer to the inner
+        // box.  This is the pointer that is passed to NSS.
+        //
+        // The inner box points to the reference-counted object.  This inner box is
+        // what we end up with a reference to in callbacks.  That extra wrapper around
+        // the Rc avoid any touching of reference counts in callbacks, which would
+        // inevitably lead to leaks as we don't control how many times the callback
+        // is invoked.
+        //
+        // This way, only this "outer" code deals with the reference count.
+        let mut tracker = Self {
+            extension,
+            handler: Box::pin(Box::new(handler)),
+        };
+        SSL_InstallExtensionHooks(
+            fd,
+            extension,
+            Some(Self::extension_writer),
+            as_c_void(&mut tracker.handler),
+            Some(Self::extension_handler),
+            as_c_void(&mut tracker.handler),
+        )?;
+        Ok(tracker)
+    }
+}
+
+impl std::fmt::Debug for ExtensionTracker {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+        write!(f, "ExtensionTracker: {:?}", self.extension)
+    }
+}