Enum McpError 

pub enum McpError {
    Connection {
        code: i32,
        message: String,
        source: Option<Box<dyn Error + Send + Sync>>,
    },
    Transport {
        code: i32,
        message: String,
        source: Option<Box<dyn Error + Send + Sync>>,
    },
    Protocol {
        code: i32,
        message: String,
    },
    Timeout {
        code: i32,
        message: String,
        duration: Duration,
    },
    Cancelled {
        code: i32,
        message: String,
        reason: Option<String>,
    },
    Server {
        code: i32,
        message: String,
        data: Option<Value>,
    },
    Validation {
        code: i32,
        message: String,
        errors: Vec<String>,
    },
    Config {
        code: i32,
        message: String,
        source: Option<Box<dyn Error + Send + Sync>>,
    },
    Io {
        code: i32,
        message: String,
        source: Error,
    },
    Serialization {
        code: i32,
        message: String,
        source: Error,
    },
    Lifecycle {
        code: i32,
        message: String,
        server_name: Option<String>,
    },
    Tool {
        code: i32,
        message: String,
        tool_name: Option<String>,
    },
    PermissionDenied {
        code: i32,
        message: String,
        tool_name: Option<String>,
    },
}

MCP Error type with structured code and message.

All MCP operation failures return this error type, which contains:

• A numeric error code (following JSON-RPC 2.0 conventions)
• A human-readable error message
• Optional additional data

This satisfies Requirement 8.1: “WHEN an MCP operation fails THEN the System SHALL return a structured error with code and message”

Variants

Connection

Connection-related errors (establishing, maintaining connections)

Fields

code: i32

Error code

message: String

Human-readable error message

source: Option<Box<dyn Error + Send + Sync>>

Optional source error

Transport

Transport layer errors (stdio, HTTP, WebSocket communication)

Fields

code: i32

Error code

message: String

Human-readable error message

source: Option<Box<dyn Error + Send + Sync>>

Optional source error

Protocol

Protocol errors (handshake, version negotiation, message format)

Fields

code: i32

Error code

message: String

Human-readable error message

Timeout

Request timeout

Fields

code: i32

Error code

message: String

Human-readable error message

duration: Duration

Duration before timeout occurred

Cancelled

Operation was cancelled

Fields

code: i32

Error code

message: String

Human-readable error message

reason: Option<String>

Optional reason for cancellation

Server

Server returned an error

Fields

code: i32

Error code from server

message: String

Error message from server

data: Option<Value>

Optional additional data from server

Validation

Validation errors (config, arguments, schema)

Fields

code: i32

Error code

message: String

Human-readable error message

errors: Vec<String>

Validation error details

Config

Configuration errors (loading, saving, parsing)

Fields

code: i32

Error code

message: String

Human-readable error message

source: Option<Box<dyn Error + Send + Sync>>

Optional source error

Io

IO errors

Fields

code: i32

Error code

message: String

Human-readable error message

source: Error

Source IO error

Serialization

Serialization/deserialization errors

Fields

code: i32

Error code

message: String

Human-readable error message

source: Error

Source error

Lifecycle

Lifecycle management errors

Fields

code: i32

Error code

message: String

Human-readable error message

server_name: Option<String>

Server name if applicable

Tool

Tool execution errors

Fields

code: i32

Error code

message: String

Human-readable error message

tool_name: Option<String>

Tool name

PermissionDenied

Permission denied errors

Fields

code: i32

Error code

message: String

Human-readable error message

tool_name: Option<String>

Tool name if applicable

Implementations

impl McpError

pub fn code(&self) -> i32

Returns the error code

pub fn message(&self) -> &str

Returns the error message

pub fn connection(message: impl Into<String>) -> Self

Create a connection error

pub fn connection_with_source( message: impl Into<String>, source: impl Error + Send + Sync + 'static, ) -> Self

Create a connection error with source

pub fn transport(message: impl Into<String>) -> Self

Create a transport error

pub fn transport_with_source( message: impl Into<String>, source: impl Error + Send + Sync + 'static, ) -> Self

Create a transport error with source

pub fn protocol(message: impl Into<String>) -> Self

Create a protocol error

pub fn timeout(message: impl Into<String>, duration: Duration) -> Self

Create a timeout error

pub fn cancelled(message: impl Into<String>, reason: Option<String>) -> Self

Create a cancelled error

pub fn server( code: i32, message: impl Into<String>, data: Option<Value>, ) -> Self

Create a server error

pub fn validation(message: impl Into<String>, errors: Vec<String>) -> Self

Create a validation error

pub fn config(message: impl Into<String>) -> Self

Create a config error

pub fn config_with_source( message: impl Into<String>, source: impl Error + Send + Sync + 'static, ) -> Self

Create a config error with source

pub fn lifecycle( message: impl Into<String>, server_name: Option<String>, ) -> Self

Create a lifecycle error

pub fn tool(message: impl Into<String>, tool_name: Option<String>) -> Self

Create a tool error

pub fn permission_denied(message: impl Into<String>) -> Self

Create a permission denied error

pub fn permission_denied_for_tool( message: impl Into<String>, tool_name: impl Into<String>, ) -> Self

Create a permission denied error with tool name

Trait Implementations

impl Debug for McpError

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

Formats the value using the given formatter.

impl Display for McpError

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

Formats the value using the given formatter.

impl Error for McpError

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<&McpError> for StructuredError

fn from(err: &McpError) -> Self

Converts to this type from the input type.

impl From<Error> for McpError

fn from(err: Error) -> Self

Converts to this type from the input type.

impl From<Error> for McpError

fn from(err: Error) -> Self

Converts to this type from the input type.

impl From<ErrorData> for McpError

Convert from rmcp::ErrorData to McpError

fn from(err: ErrorData) -> Self

Converts to this type from the input type.

impl From<McpError> for StructuredError

fn from(err: McpError) -> Self

Converts to this type from the input type.