---
title: Rust SDK 0.4.0
summary: null
url: https://www.fastly.com/documentation/reference/changes/2020/06/rust-sdk-0.4.0
---

## Added

- Added `get_header_value` method to `fastly::request::RequestHandle`.

- Added specific error types for some API calls:

- `fastly::error::SendError` is returned by APIs that send backend requests. Note that the common case for a failed request remains an `Ok` result with a 5xx status code response.

- `fastly::error::BufferSizeError` is returned by handle API calls that can fail due to an insufficient buffer size.

- Added `RequestExt::send_async_streaming()` and `RequestHandle::send_async_streaming()`, which allow programs to continue writing bytes to upstream request bodies after the headers have been sent.

- Added `Backend::name()` to get the string representation of a backend.

- Added `ResponseExt::backend()` to retrieve the `Backend` a response came from.

- Added `ResponseExt::backend_request()` and `ResponseExt::take_backend_request()` to retrieve the `Request` that this response was returned from, minus the body which is consumed when the request is sent. The `take` variant takes ownership of the `Request` so that it can be subsequently reused for another backend request.

- Added `PendingRequest::sent_req()` to retrieve the `Request` that was sent, minus the body which is consumed when the request is sent.

## Changed

- Removed `Result` return types from various functions and methods. Internal errors will now cause a panic. This primarily impacts the `Body`, `BodyHandle`, `RequestHandle`, and `ResponseHandle` types. This helps remove noise from `?` operators in cases where user programs cannot realistically recover from the error.

- `get_header_value` methods for `RequestHandle` and `ResponseHandle` will now return `Ok(None)` if the header does not exist, rather than an empty header.

- `Response::send_downstream()` and `ResponseHandle::send_downstream()` now begin sending the responses immediately, rather than when the program exits.

- Renamed `Backend::new()` to `Backend::from_name()`, and deprecated the old name.

## Deprecated

- Deprecated `Backend::new()` in favor of `Backend::from_name()`.

## Removed

- Removed `fastly::abi` submodule from the public interface.

- Removed `impl From for PendingRequest`, as `PendingRequests` now must be build with the backend `Request` they were sent with.