Module protocol 

Dual-era MCP protocol implementation.

This module contains the core protocol types and message handling for the Model Context Protocol revisions 2026-07-28 and 2025-11-25, including JSON-RPC serialization, validation, stateless request envelopes, safe revision selection, and typed protocol objects.

Protocol Structure

The MCP protocol is built on JSON-RPC 2.0 with extensions for:

• Bidirectional Communication: Both client and server can send requests
• Capability Negotiation: Dynamic feature discovery
• Content Types: Rich content including text, images, and resources
• Batch Operations: Efficient bulk request processing

Core Types

JSON-RPC Messages

use prism_mcp_rs::protocol::{
    JsonRpcRequest, JsonRpcResponse, JsonRpcError, JsonRpcMessage
};
use serde_json::json;

// Create a request
let request = JsonRpcRequest::new(
    json!("1"),
    "tools/list".to_string(),
    None::<()>,
).unwrap();

// Create a success response
let response = JsonRpcResponse::success_unchecked(
    json!("1"),
    json!({"tools": []}),
);

// Create an error response
let error = JsonRpcError::method_not_found(json!("1"));

Error Handling

use prism_mcp_rs::protocol::{JsonRpcError, error_codes};
use serde_json::json;

// Standard JSON-RPC errors
let parse_err = JsonRpcError::parse_error(json!(null));
let method_err = JsonRpcError::method_not_found(json!("1"));
let invalid_params = JsonRpcError::invalid_params(json!("1"));

// MCP-specific errors
let tool_err = JsonRpcError::tool_not_found(json!("1"), "unknown-tool");
let resource_err = JsonRpcError::resource_not_found(json!("1"), "missing.txt");

// Custom errors with error codes
let custom_err = JsonRpcError::new(
    json!("1"),
    error_codes::INTERNAL_ERROR,
    "Internal server error".to_string()
);

Protocol Flow

• 2026-07-28: the client sends server/discover, then includes its revision, identity, and capabilities in every request _meta object.
• 2025-11-25: the client performs initialize, retains negotiated connection state, and sends the initialized notification.

ProtocolMode::Auto prefers 2026 and permits a 2025 fallback only when server/discover is explicitly rejected as an unknown method.

Features

• Type Safety: Strongly typed protocol messages
• Validation: Request and response validation
• Extensibility: Support for custom methods and capabilities
• Batch Processing: Efficient bulk operations
• Metadata: Rich metadata for all protocol objects

Re-exports

pub use error_helpers::IntoJsonRpcMessage;

pub use metadata::MetadataBuilder;

pub use metadata::ProtocolCapabilities;

pub use roots_types::ListRootsRequest;

pub use roots_types::RootsListChangedNotification;

pub use types::error_codes;

pub use types::AnnotationAudience;

pub use types::Annotations;

pub use types::AudioContent;

pub use types::BaseMetadata;

pub use types::CallToolResult;

pub use types::ClientCapabilities;

pub use types::ClientInfo;

pub use types::CompletionsCapability;

pub use types::Content;

pub use types::ContentBlock;

pub use types::CreateMessageResult;

pub use types::Cursor;

pub use types::DangerLevel;

pub use types::ElicitationAction;

pub use types::ElicitationCapability;

pub use types::ElicitationSchema;

pub use types::EmbeddedResource;

pub use types::ErrorObject;

pub use types::GetPromptResult;

pub use types::Icon;

pub use types::IconTheme;

pub use types::ImageContent;

pub use types::Implementation;

pub use types::JsonRpcBatchRequest;

pub use types::JsonRpcBatchResponse;

pub use types::JsonRpcError;

pub use types::JsonRpcId;

pub use types::JsonRpcMessage;

pub use types::JsonRpcNotification;

pub use types::JsonRpcRequest;

pub use types::JsonRpcRequestOrNotification;

pub use types::JsonRpcResponse;

pub use types::JsonRpcResponseOrError;

pub use types::LoggingCapability;

pub use types::LoggingLevel;

pub use types::ModelHint;

pub use types::ModelPreferences;

pub use types::Notification;

pub use types::NotificationParams;

pub use types::PaginatedRequest;

pub use types::PaginatedResult;

pub use types::PrimitiveSchemaDefinition;

pub use types::ProgressToken;

pub use types::Prompt;

pub use types::PromptArgument;

pub use types::PromptInfo;

pub use types::PromptMessage;

pub use types::PromptResult;

pub use types::PromptsCapability;

pub use types::Request;

pub use types::RequestId;

pub use types::RequestMeta;

pub use types::RequestParams;

pub use types::Resource;

pub use types::ResourceContents;

pub use types::ResourceInfo;

pub use types::ResourceLink;

pub use types::ResourceTemplate;

pub use types::ResourcesCapability;

pub use types::Role;

pub use types::RootsCapability;

pub use types::SamplingCapability;

pub use types::SamplingContent;

pub use types::SamplingMessage;

pub use types::SamplingToolChoice;

pub use types::ServerCapabilities;

pub use types::ServerInfo;

pub use types::StopReason;

pub use types::TextContent;

pub use types::Tool;

pub use types::ToolAnnotations;

pub use types::ToolInfo;

pub use types::ToolInputSchema;

pub use types::ToolOutputSchema;

pub use types::ToolResult;

pub use types::ToolsCapability;

pub use types::JSONRPC_VERSION;

pub use types::LATEST_PROTOCOL_VERSION;

pub use types::PROTOCOL_VERSION;

pub use version::decode_http_header_value;

pub use version::decorate_modern_request;

pub use version::decorate_modern_result;

pub use version::encode_http_header_value;

pub use version::is_cacheable_method;

pub use version::is_legacy_only_method;

pub use version::is_method_not_found;

pub use version::json_rpc_error_details;

pub use version::modern_request_context;

pub use version::request_protocol_version;

pub use version::request_routing_name;

pub use version::tool_call_headers;

pub use version::tool_header_mappings;

pub use version::validate_http_headers;

pub use version::validate_tool_call_headers;

pub use version::CacheScope;

pub use version::ConnectResult;

pub use version::DiscoverParams;

pub use version::DiscoverResult as ModernDiscoverResult;

pub use version::InputRequiredResult;

pub use version::ModernRequestContext;

pub use version::NegotiatedProtocol;

pub use version::OperationResult;

pub use version::ProtocolEra;

pub use version::ProtocolMode;

pub use version::RequestMetaObject;

pub use version::ResultType;

pub use version::ToolHeaderMapping;

pub use version::CLIENT_CAPABILITIES_META_KEY;

pub use version::CLIENT_INFO_META_KEY;

pub use version::HEADER_MISMATCH;

pub use version::LEGACY_PROTOCOL_VERSION;

pub use version::MCP_METHOD_HEADER;

pub use version::MCP_NAME_HEADER;

pub use version::MCP_PROTOCOL_VERSION_HEADER;

pub use version::MISSING_REQUIRED_CLIENT_CAPABILITY;

pub use version::MODERN_PROTOCOL_VERSION;

pub use version::PROTOCOL_VERSION_META_KEY;

pub use version::SERVER_INFO_META_KEY;

pub use version::SUPPORTED_PROTOCOL_VERSIONS;

pub use version::UNSUPPORTED_PROTOCOL_VERSION;

pub use methods::CANCELLED;

pub use methods::COMPLETION_COMPLETE;

pub use methods::ELICITATION_COMPLETE;

pub use methods::INITIALIZE;

pub use methods::INITIALIZED;

pub use methods::LOGGING_MESSAGE;

pub use methods::LOGGING_SET_LEVEL;

pub use methods::PING;

pub use methods::PROGRESS;

pub use methods::PROMPTS_GET;

pub use methods::PROMPTS_LIST;

pub use methods::PROMPTS_LIST_CHANGED;

pub use methods::RESOURCES_LIST;

pub use methods::RESOURCES_LIST_CHANGED;

pub use methods::RESOURCES_READ;

pub use methods::RESOURCES_SUBSCRIBE;

pub use methods::RESOURCES_TEMPLATES_LIST;

pub use methods::RESOURCES_UNSUBSCRIBE;

pub use methods::RESOURCES_UPDATED;

pub use methods::ROOTS_LIST;

pub use methods::ROOTS_LIST_CHANGED;

pub use methods::RPC_DISCOVER;

pub use methods::SAMPLING_CREATE_MESSAGE;

pub use methods::SERVER_DISCOVER;

pub use methods::SUBSCRIPTIONS_ACKNOWLEDGED;

pub use methods::SUBSCRIPTIONS_LISTEN;

pub use methods::TASKS_CANCEL;

pub use methods::TASKS_GET;

pub use methods::TASKS_SEND;

pub use methods::TASKS_STATUS;

pub use methods::TASKS_STATUS_UPDATE;

pub use methods::TASKS_UPDATE;

pub use methods::TOOLS_CALL;

pub use methods::TOOLS_LIST;

pub use methods::TOOLS_LIST_CHANGED;

pub use batch::*;

pub use discovery::*;

pub use messages::*;

pub use missing_types::*;

pub use schema_introspection::*;

pub use subscriptions::*;

pub use tasks::*;

pub use validation::*;

Modules

batch

JSON-RPC Batch Request/Response Support (2025-11-25)

discovery

RPC Discovery Module for MCP Protocol

error_helpers

JSON-RPC error response helper functions

messages

MCP Protocol Messages

metadata

methods

MCP Protocol Method Constants

missing_types

Missing Types Module for Test Compatibility

roots_types

Roots Types for MCP Protocol (2025-11-25)

schema_introspection

improved Schema Introspection for MCP Protocol (2025-11-25)

subscriptions

MCP 2026-07-28 notification subscription types.

tasks

io.modelcontextprotocol/tasks extension types (SEP-2663).

types

Shared MCP protocol types for the 2025-11-25 and 2026-07-28 revisions.

validation

MCP protocol validation utilities (2025-03-26)

version

Protocol revision negotiation and MCP 2026-07-28 wire envelopes.

Constants

MCP_PROTOCOL_VERSION