Enum RequestMetaError 

pub enum RequestMetaError {
    Absent,
    Malformed,
    MissingVersion,
    MalformedVersion,
    MissingCapabilities,
    MalformedLogLevel,
    MalformedCapabilities,
}

Why a _meta block could not be read.

Split by cause because the three faults have three different answers, and one error type would force every caller to re-derive which it had:

• Absent is a pre-2026-07-28 request, or one from a client that negotiated an older revision. It is not a fault at all.
• MissingVersion and MissingCapabilities are SEP-2575’s own -32602 Invalid params cases, and the suite checks them separately.
• MalformedVersion is the same fault with a different cause: the key was there and its value was not a revision. The spec answers that with UnsupportedProtocolVersionError — an unsupported version, not a malformed request — so it cannot collapse into the missing case.

Variants

Absent

No _meta at all, which is the shape of every pre-2026-07-28 request.

Malformed

_meta is present and is not a JSON object.

MissingVersion

_meta names no io.modelcontextprotocol/protocolVersion.

MalformedVersion

The named version is not one this crate knows.

MissingCapabilities

_meta names no io.modelcontextprotocol/clientCapabilities.

MalformedLogLevel

io.modelcontextprotocol/logLevel is present and is not a level the specification names.

MalformedCapabilities

The capabilities value is present and is not a JSON object.

Trait Implementations

impl Clone for RequestMetaError

fn clone(&self) -> Self

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for RequestMetaError

impl Debug for RequestMetaError

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

Formats the value using the given formatter.

impl Display for RequestMetaError

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

Formats the value using the given formatter.

impl Eq for RequestMetaError

impl Error for RequestMetaError

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 PartialEq for RequestMetaError

fn eq(&self, other: &Self) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl StructuralPartialEq for RequestMetaError