protocol

mcp_resource_protocol

Protocol for Logtalk objects that provide resources to be exposed via an MCP (Model Context Protocol) server. Implementing objects must define the set of resources available and handle resource read requests. Applications may also expose parameterized resources using URI templates. Resources expose data and content from the application that MCP clients can access. Used by both the 2025-06-18 and 2026-07-28 adapters.

Availability:
logtalk_load(mcp_server(loader))
Author: Paulo Moura
Version: 1:0:0
Date: 2026-09-02
Compilation flags:
static
Dependencies:
(none)
Remarks:

  • Capabilities: Objects providing resources must declare resources in their capabilities/1 predicate (from the mcp_tool_protocol protocol). The server will then advertise the resources capability and handle resources/list, resources/templates/list, and resources/read requests.

  • Resource descriptors: Each resource is described by a resource(URI, Name, Description, MimeType) or resource(URI, Name, Title, Description, MimeType) term where URI is the resource identifier (an atom), Name is a human-readable name (an atom), Title is an optional human-friendly display name (an atom), Description is a human-readable description (an atom), and MimeType is the MIME type of the resource content (an atom, e.g. 'text/plain').

  • Resource template descriptors: Parameterized resources are optionally described by resource_template(URITemplate, Name, Description, MimeType) or resource_template(URITemplate, Name, Title, Description, MimeType) terms. URITemplate is an RFC 6570 URI template atom. Template listing is validated as a whole: an invalid template raises a domain_error(uri_template, URITemplate) error and no partial list is advertised. The server advertises valid templates without expanding them; applications validate, authorize, and read concrete expanded URIs using resource_read/3.

  • Resource contents: The resource_read/3 predicate must return a result term. The result must be contents(ContentList) where each item is text_content(URI, MimeType, Text) for text resources or blob_content(URI, MimeType, Base64Data) for binary resources encoded as base64.

  • Multi-round (2026-07-28): For the 2026-07-28 adapter, applications that need additional input during a resource read implement resource_read_round/4 from the mcp_multiround_protocol. Existing resource_read/3 remains valid and is wrapped as a complete result when the round hook is absent.

  • Caching (2026-07-28): Complete resources/read results may include cache fields (ttlMs, cacheScope) derived from mcp_cache_protocol or server options. Cache fields are never attached to input_required results.

Inherited public predicates:
(none)

Public predicates

resources/1

Returns a list of resource descriptors available from this object. Each descriptor is a compound term resource(URI, Name, Description, MimeType) or resource(URI, Name, Title, Description, MimeType) where URI is the resource identifier (an atom, typically a URI like logtalk://my-app/data), Name is a human-readable name (an atom), Title is an optional human-friendly display name (an atom), Description is a human-readable description (an atom), and MimeType is the MIME type (an atom, e.g. 'text/plain', 'application/json').

Compilation flags:
static
Template:
resources(Resources)
Mode and number of proofs:
resources(-list(compound)) - one

resource_templates/1

Optional. Returns a list of parameterized resource descriptors. Each descriptor is a resource_template(URITemplate, Name, Description, MimeType) or resource_template(URITemplate, Name, Title, Description, MimeType) term. URITemplate is an RFC 6570 URI template atom. Concrete expanded URIs are handled by resource_read/3.

Compilation flags:
static
Template:
resource_templates(ResourceTemplates)
Mode and number of proofs:
resource_templates(-list(compound)) - zero_or_one

resource_read/3

Handles a resource read request. URI is the resource identifier (as declared in resources/1), Arguments is a list of ArgumentName-Value pairs (currently unused but reserved for future use), and Result is unified with the resource result. The result must be contents(ContentList) where each content item is either text_content(URI, MimeType, Text) for text resources or blob_content(URI, MimeType, Base64Data) for binary resources encoded as base64. Text and Base64Data must be atoms.

Compilation flags:
static
Template:
resource_read(URI,Arguments,Result)
Mode and number of proofs:
resource_read(+atom,+list(pair),--compound) - one

Protected predicates

(none)

Private predicates

(none)

Operators

(none)