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diff --git a/third_party/rust/icu_provider/src/buf.rs b/third_party/rust/icu_provider/src/buf.rs
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+// This file is part of ICU4X. For terms of use, please see the file
+// called LICENSE at the top level of the ICU4X source tree
+// (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ).
+
+//! Traits for data providers that produce opaque buffers.
+
+use crate::prelude::*;
+
+/// [`DataMarker`] for raw buffers. Returned by [`BufferProvider`].
+///
+/// The data is expected to be deserialized before it can be used; see
+/// [`DataPayload::into_deserialized`].
+#[allow(clippy::exhaustive_structs)] // marker type
+#[derive(Debug)]
+pub struct BufferMarker;
+
+impl DataMarker for BufferMarker {
+    type Yokeable = &'static [u8];
+}
+
+/// A data provider that returns opaque bytes.
+///
+/// Generally, these bytes are expected to be deserializable with Serde. To get an object
+/// implementing [`DataProvider`] via Serde, use [`as_deserializing()`].
+///
+/// Passing a  `BufferProvider` to a `*_with_buffer_provider` constructor requires enabling
+/// the deserialization Cargo feature for the expected format(s):
+/// - `deserialize_json`
+/// - `deserialize_postcard_1`
+/// - `deserialize_bincode_1`
+///
+/// Along with [`DataProvider`], this is one of the two foundational traits in this crate.
+///
+/// [`BufferProvider`] can be made into a trait object. It is used over FFI.
+///
+/// # Examples
+///
+/// ```
+/// # #[cfg(feature = "deserialize_json")] {
+/// use icu_locid::locale;
+/// use icu_provider::hello_world::*;
+/// use icu_provider::prelude::*;
+/// use std::borrow::Cow;
+///
+/// let buffer_provider = HelloWorldProvider.into_json_provider();
+///
+/// let req = DataRequest {
+///     locale: &locale!("de").into(),
+///     metadata: Default::default(),
+/// };
+///
+/// // Deserializing manually
+/// assert_eq!(
+///     serde_json::from_slice::<HelloWorldV1>(
+///         buffer_provider
+///             .load_buffer(HelloWorldV1Marker::KEY, req)
+///             .expect("load should succeed")
+///             .take_payload()
+///             .unwrap()
+///             .get()
+///     )
+///     .expect("should deserialize"),
+///     HelloWorldV1 {
+///         message: Cow::Borrowed("Hallo Welt"),
+///     },
+/// );
+///
+/// // Deserialize automatically
+/// let deserializing_provider: &dyn DataProvider<HelloWorldV1Marker> =
+///     &buffer_provider.as_deserializing();
+///
+/// assert_eq!(
+///     deserializing_provider
+///         .load(req)
+///         .expect("load should succeed")
+///         .take_payload()
+///         .unwrap()
+///         .get(),
+///     &HelloWorldV1 {
+///         message: Cow::Borrowed("Hallo Welt"),
+///     },
+/// );
+/// # }
+/// ```
+///
+/// [`as_deserializing()`]: AsDeserializingBufferProvider::as_deserializing
+pub trait BufferProvider {
+    /// Loads a [`DataPayload`]`<`[`BufferMarker`]`>` according to the key and request.
+    fn load_buffer(
+        &self,
+        key: DataKey,
+        req: DataRequest,
+    ) -> Result<DataResponse<BufferMarker>, DataError>;
+}
+
+impl<'a, T: BufferProvider + ?Sized> BufferProvider for &'a T {
+    fn load_buffer(
+        &self,
+        key: DataKey,
+        req: DataRequest,
+    ) -> Result<DataResponse<BufferMarker>, DataError> {
+        (**self).load_buffer(key, req)
+    }
+}
+
+impl<T: BufferProvider + ?Sized> BufferProvider for alloc::boxed::Box<T> {
+    fn load_buffer(
+        &self,
+        key: DataKey,
+        req: DataRequest,
+    ) -> Result<DataResponse<BufferMarker>, DataError> {
+        (**self).load_buffer(key, req)
+    }
+}
+
+impl<T: BufferProvider + ?Sized> BufferProvider for alloc::rc::Rc<T> {
+    fn load_buffer(
+        &self,
+        key: DataKey,
+        req: DataRequest,
+    ) -> Result<DataResponse<BufferMarker>, DataError> {
+        (**self).load_buffer(key, req)
+    }
+}
+
+#[cfg(target_has_atomic = "ptr")]
+impl<T: BufferProvider + ?Sized> BufferProvider for alloc::sync::Arc<T> {
+    fn load_buffer(
+        &self,
+        key: DataKey,
+        req: DataRequest,
+    ) -> Result<DataResponse<BufferMarker>, DataError> {
+        (**self).load_buffer(key, req)
+    }
+}
+
+/// An enum expressing all Serde formats known to ICU4X.
+#[derive(Debug, PartialEq, Eq, Hash, Copy, Clone)]
+#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
+#[non_exhaustive]
+pub enum BufferFormat {
+    /// Serialize using JavaScript Object Notation (JSON).
+    Json,
+    /// Serialize using Bincode version 1.
+    Bincode1,
+    /// Serialize using Postcard version 1.
+    Postcard1,
+}
+
+impl BufferFormat {
+    /// Returns an error if the buffer format is not enabled.
+    pub fn check_available(&self) -> Result<(), DataError> {
+        match self {
+            #[cfg(feature = "deserialize_json")]
+            BufferFormat::Json => Ok(()),
+
+            #[cfg(feature = "deserialize_bincode_1")]
+            BufferFormat::Bincode1 => Ok(()),
+
+            #[cfg(feature = "deserialize_postcard_1")]
+            BufferFormat::Postcard1 => Ok(()),
+
+            // Allowed for cases in which all features are enabled
+            #[allow(unreachable_patterns)]
+            _ => Err(DataErrorKind::UnavailableBufferFormat(*self).into_error()),
+        }
+    }
+}