Crate hclient_core 

Plugin contract for hclient: the traits a backend, a runtime or a resolver implements, and the vocabulary types they exchange.

The Send rule

The seam traits declare no Send/Sync bounds. Transport, Timer and the middleware traits leave Send-ness to auto-traits through impl Future, because a bound declared where the type is abstract is forced on every backend — including ones that cannot meet it, such as a single-threaded embedded runtime whose connect future holds a RefCell.

Bounds do appear in three places, and each is a value a caller hands over rather than a demand on an implementor:

• Error’s source is Send + Sync, or a client could not build an error from a backend’s at all.
• RequestBody’s rewind factory and streaming arm.
• unversioned::erased’s two aliases, which a facade writes at its own use site to put a transport behind an Arc. It is not a seam: a blanket impl covers every Transport, so no backend implements or is taxed by it, and one that cannot meet the bound is refused at a constructor rather than at a trait.

Every such site carries a send-bound-exception marker naming the amendment that admits it, and scripts/no-send-or-sync-in-the-core-surface.sh fails closed on one that does not. grep is therefore the authority on which sites exist; this list says what kind they are.

Modules

unversioned

Semver quarantine

Structs

AllowEarlyData

The caller’s per-request statement that this request may go into TLS 1.3 early data (0-RTT).

Capabilities

What the transport can do in this process, right now.

Error

Clone is deliberate: reqwest’s opaque, unclonable error is a source of constant complaints (reqwest#1053).

RequireVersion

The caller’s per-request statement that this request needs a particular HTTP version, and must fail rather than go out over another one.

TimeoutSupport

Timeouts

The timeout triple — wasi:http’s shape, the richest of the ambient models.

UnsupportedCapability

A setting the chosen transport cannot honor.

VersionNotAvailable

A RequireVersion demand the connection in hand does not satisfy.

Enums

CancelSupport

Whether dropping the future returned by Transport::execute stops the exchange — see that method’s doc comment for the contract itself, of which this enum is the one honest way out.

DecompressionSupport

Whether the transport hands back a response body it has already decoded, or the bytes exactly as the server put them on the wire.

EarlyDataSupport

Whether a transport can put a request into TLS 1.3 early data (0-RTT).

ErrorKind

The error’s category. Exists so the consumer doesn’t have to classify errors by substring-matching on Display.

Phase

RedirectSupport

Who follows a redirect chain: nobody, Client, or the backend.

RequestBody

A request body with an explicit replay contract.

RetryKind

Whether this body can be replayed — known before sending.

ReuseSupport

Whether a request may travel over a connection an earlier request already used, or whether every request opens a socket of its own.

TlsSupport

Functions

bare_host

The host a URI names, with an IPv6 literal’s brackets removed.

check_version

The one comparison, shared by every transport that honours a demand.

Type Aliases

RewindFactory

Send + Sync bounds — a documented exception to the crate invariant “declare Send/Sync nowhere” (spec amendment-C2, sibling of C1 on crate::Error). Without them RequestBody would be !Send, so http::Request<RequestBody> would be !Send, so the future Transport::execute returns would be !Send for every backend — tokio::spawn(client.get(u).send()) would never build. Sync is only needed here, for Arc: Arc<T>: Send requires T: Send + Sync, whereas Box<T>: Send (see RequestBody::Streaming) requires only T: Send.