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layout default
title Chapter 2: Client Transport and Capability Negotiation
nav_order 2
parent MCP Swift SDK Tutorial

Chapter 2: Client Transport and Capability Negotiation

Welcome to Chapter 2: Client Transport and Capability Negotiation. In this part of MCP Swift SDK Tutorial: Building MCP Clients and Servers in Swift, you will build an intuitive mental model first, then move into concrete implementation details and practical production tradeoffs.

Transport and capability negotiation choices drive most client-side behavior variance.

Learning Goals

  • choose between stdio and HTTP client transport paths
  • interpret initialization results and capability availability
  • handle capability mismatch behavior intentionally
  • keep transport configuration explicit in app architecture

Transport Decision Guide

Transport Best Fit
StdioTransport local subprocess workflows
HTTPClientTransport remote MCP endpoints with optional streaming

Source References

Summary

You now have a client setup model that keeps capability assumptions and transport behavior aligned.

Next: Chapter 3: Tools, Resources, Prompts, and Request Patterns

Source Code Walkthrough

Sources/MCP/Client/Client.swift

The Capabilities interface in Sources/MCP/Client/Client.swift handles a key part of this chapter's functionality:

    /// The client capabilities
    public struct Capabilities: Hashable, Codable, Sendable {
        /// The roots capabilities
        public struct Roots: Hashable, Codable, Sendable {
            /// Whether the list of roots has changed
            public var listChanged: Bool?

            public init(listChanged: Bool? = nil) {
                self.listChanged = listChanged
            }
        }

        /// The sampling capabilities
        public struct Sampling: Hashable, Sendable {
            /// Tools sub-capability for sampling
            public struct Tools: Hashable, Codable, Sendable {
                public init() {}
            }

            /// Context sub-capability for sampling
            public struct Context: Hashable, Codable, Sendable {
                public init() {}
            }

            /// Whether tools are supported in sampling
            public var tools: Tools?
            /// Whether context is supported in sampling
            public var context: Context?

            public init(tools: Tools? = nil, context: Context? = nil) {
                self.tools = tools

This interface is important because it defines how MCP Swift SDK Tutorial: Building MCP Clients and Servers in Swift implements the patterns covered in this chapter.

Sources/MCP/Client/Client.swift

The Roots interface in Sources/MCP/Client/Client.swift handles a key part of this chapter's functionality:

    public struct Capabilities: Hashable, Codable, Sendable {
        /// The roots capabilities
        public struct Roots: Hashable, Codable, Sendable {
            /// Whether the list of roots has changed
            public var listChanged: Bool?

            public init(listChanged: Bool? = nil) {
                self.listChanged = listChanged
            }
        }

        /// The sampling capabilities
        public struct Sampling: Hashable, Sendable {
            /// Tools sub-capability for sampling
            public struct Tools: Hashable, Codable, Sendable {
                public init() {}
            }

            /// Context sub-capability for sampling
            public struct Context: Hashable, Codable, Sendable {
                public init() {}
            }

            /// Whether tools are supported in sampling
            public var tools: Tools?
            /// Whether context is supported in sampling
            public var context: Context?

            public init(tools: Tools? = nil, context: Context? = nil) {
                self.tools = tools
                self.context = context
            }

This interface is important because it defines how MCP Swift SDK Tutorial: Building MCP Clients and Servers in Swift implements the patterns covered in this chapter.

Sources/MCP/Client/Client.swift

The Sampling interface in Sources/MCP/Client/Client.swift handles a key part of this chapter's functionality:

        /// The sampling capabilities
        public struct Sampling: Hashable, Sendable {
            /// Tools sub-capability for sampling
            public struct Tools: Hashable, Codable, Sendable {
                public init() {}
            }

            /// Context sub-capability for sampling
            public struct Context: Hashable, Codable, Sendable {
                public init() {}
            }

            /// Whether tools are supported in sampling
            public var tools: Tools?
            /// Whether context is supported in sampling
            public var context: Context?

            public init(tools: Tools? = nil, context: Context? = nil) {
                self.tools = tools
                self.context = context
            }
        }

        /// The elicitation capabilities
        public struct Elicitation: Hashable, Sendable {
            /// Form-based elicitation sub-capability
            public struct Form: Hashable, Codable, Sendable {
                public init() {}
            }

            /// URL-based elicitation sub-capability

This interface is important because it defines how MCP Swift SDK Tutorial: Building MCP Clients and Servers in Swift implements the patterns covered in this chapter.

Sources/MCP/Client/Client.swift

The Tools interface in Sources/MCP/Client/Client.swift handles a key part of this chapter's functionality:

        /// The sampling capabilities
        public struct Sampling: Hashable, Sendable {
            /// Tools sub-capability for sampling
            public struct Tools: Hashable, Codable, Sendable {
                public init() {}
            }

            /// Context sub-capability for sampling
            public struct Context: Hashable, Codable, Sendable {
                public init() {}
            }

            /// Whether tools are supported in sampling
            public var tools: Tools?
            /// Whether context is supported in sampling
            public var context: Context?

            public init(tools: Tools? = nil, context: Context? = nil) {
                self.tools = tools
                self.context = context
            }
        }

        /// The elicitation capabilities
        public struct Elicitation: Hashable, Sendable {
            /// Form-based elicitation sub-capability
            public struct Form: Hashable, Codable, Sendable {
                public init() {}
            }

            /// URL-based elicitation sub-capability
            public struct URL: Hashable, Codable, Sendable {

This interface is important because it defines how MCP Swift SDK Tutorial: Building MCP Clients and Servers in Swift implements the patterns covered in this chapter.

How These Components Connect

flowchart TD
    A[Capabilities]
    B[Roots]
    C[Sampling]
    D[Tools]
    E[Context]
    A --> B
    B --> C
    C --> D
    D --> E
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