Trait aws_smithy_http::response::ParseHttpResponse

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pub trait ParseHttpResponse {
    type Output;

    // Required methods
    fn parse_unloaded(&self, response: &mut Response) -> Option<Self::Output>;
    fn parse_loaded(&self, response: &Response<Bytes>) -> Self::Output;
}
Expand description

ParseHttpResponse is a generic trait for parsing structured data from HTTP responses.

It is designed to be nearly infinitely flexible, because Output is unconstrained, it can be used to support event streams, S3 streaming responses, regular request-response style operations, as well as any other HTTP-based protocol that we manage to come up with.

The split between parse_unloaded and parse_loaded enables keeping the parsing code pure and sync whenever possible and delegating the process of actually reading the HTTP response to the caller when the required behavior is simply “read to the end.”

It also enables this critical and core trait to avoid being async, and it makes code that uses the trait easier to test.

Required Associated Types§

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type Output

Output type of the HttpResponse.

For request/response style operations, this is typically something like: Result<ListTablesResponse, ListTablesError>

For streaming operations, this is something like: Result<EventStream<TranscribeStreamingEvent>, TranscribeStreamingError>

Required Methods§

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fn parse_unloaded(&self, response: &mut Response) -> Option<Self::Output>

Parse an HTTP request without reading the body. If the body must be provided to proceed, return None

This exists to serve APIs like S3::GetObject where the body is passed directly into the response and consumed by the client. However, even in the case of S3::GetObject, errors require reading the entire body.

This also facilitates EventStream and other streaming HTTP protocols by enabling the handler to take ownership of the HTTP response directly.

Currently parse_unloaded operates on a borrowed HTTP request to enable the caller to provide a raw HTTP response to the caller for inspection after the response is returned. For EventStream-like use cases, the caller can use mem::swap to replace the streaming body with an empty body as long as the body implements default.

We should consider if this is too limiting & if this should take an owned response instead.

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fn parse_loaded(&self, response: &Response<Bytes>) -> Self::Output

Parse an HTTP request from a fully loaded body. This is for standard request/response style APIs like AwsJson 1.0/1.1 and the error path of most streaming APIs

Using an explicit body type of Bytes here is a conscious decision—If you really need to precisely control how the data is loaded into memory (e.g. by using bytes::Buf), implement your handler in parse_unloaded.

Production code will never call parse_loaded without first calling parse_unloaded. However, in tests it may be easier to use parse_loaded directly. It is OK to panic in parse_loaded if parse_unloaded will never return None, however, it may make your code easier to test if an implementation is provided.

Implementors§