Enum DownstreamError 

pub enum DownstreamError {
    Malformed,
    NoHandshake(ProtocolVersion),
    UnnegotiableVersion,
    Assemble(JsonObjectError),
}

Why a downstream handshake could not be settled.

Distinct from an upstream that cannot be reached: the upstream failed before negotiate was ever called, and this type is only ever about what the client in front of us said.

Variants

Malformed

The initialize request was not readable as an offer.

Collapsed to one variant for the same reason InitializeError is: the caller answers -32600 either way, and a proxy reporting which of six shapes failed would be telling the client about the proxy’s internals.

NoHandshake(ProtocolVersion)

The negotiation settled on a revision with no handshake.

SEP-2575 removed initialize from 2026-07-28, and negotiate_server echoes a revision it supports — so a client asking for exactly that one reaches here. It cannot on the path below, because such a client is walked back to the newest revision that has a handshake. It stays in the signature for the one case that walk-back cannot cover: a bridge restricted to revisions with no handshake at all, where there is nothing to walk back to.

UnnegotiableVersion

This build has no revisions to negotiate over at all.

Assemble(JsonObjectError)

The reply could not be assembled into an object.

Cannot happen for the body built below, which is a literal object of string members — but from_value is fallible and the honest signature is the one that says so. Inventing a second error for it would be a promise this function cannot keep.

Trait Implementations

impl Debug for DownstreamError

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Display for DownstreamError

fn fmt(&self, __formatter: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Error for DownstreamError

fn source(&self) -> Option<&(dyn Error + 'static)>

Returns the lower-level source of this error, if any.

fn description(&self) -> &str

👎Deprecated since 1.42.0:

use the Display impl or to_string()

fn cause(&self) -> Option<&dyn Error>

👎Deprecated since 1.33.0:

replaced by Error::source, which can support downcasting

fn provide<'a>(&'a self, request: &mut Request<'a>)

🔬This is a nightly-only experimental API. (error_generic_member_access)

Provides type-based access to context intended for error reports.

impl From<DownstreamError> for BridgeServeError

fn from(source: DownstreamError) -> Self

Converts to this type from the input type.

impl From<JsonObjectError> for DownstreamError

fn from(source: JsonObjectError) -> Self

Converts to this type from the input type.