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mcp: move to 2025-06-18 schema (#8)

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* mcp: move to 2025-06-18 schema

Add types and fields for the latest MCP schema.

The main challenge here was dealing with the presence of _meta fields
on many types, like Tool, Prompt and Resource.

- Distinguish between the _meta field of a request's params, which
  includes a progress token, from the _meta field on other types,
  which is simply a map.

- Redefine GetMeta to return a pointer to the map. We wanted to avoid
  that, but I don't see a clean way to do so. An alternative would be
  to have GetMeta return a map, and SetMeta to set it.

- Provide GetProgressToken for requests only (not notifications or other
  types).

- Still to do: deal with the meta and annotation fields of ContentBlock,
  which are currently duplicated for Resource and ResourceContents.

* Meta and progress token redesign
This commit is contained in:
Jonathan Amsterdam 2025-06-25 09:48:33 -04:00 • committed by GitHub
commit 3da831b0c9
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1 changed files with 372 additions and 249 deletions
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82
mcp/content.go
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@ -10,58 +10,67 @@ import (
"fmt"
)
// Content is the wire format for content.
// It represents the protocol types TextContent, ImageContent, AudioContent
// and EmbeddedResource.
// Use [NewTextContent], [NewImageContent], [NewAudioContent] or [NewResourceContent]
// to create one.
// A ContentBlock is one of a TextContent, ImageContent, AudioContent
// ResourceLink, or EmbeddedResource.
// Use [NewTextContent], [NewImageContent], [NewAudioContent], [NewResourceLink]
// or [NewResourceContents] to create one.
//
// The Type field must be one of "text", "image", "audio" or "resource". The
// constructors above populate this field appropriately.
// Although at most one of Text, Data, and Resource should be non-zero, consumers of Content
// use the Type field to determine which value to use; values in the other fields are ignored.
type Content struct {
Type string `json:"type"`
Text string `json:"text,omitempty"`
MIMEType string `json:"mimeType,omitempty"`
Data []byte `json:"data,omitempty"`
Resource *ResourceContents `json:"resource,omitempty"`
Annotations *Annotations `json:"annotations,omitempty"`
// The Type field must be one of "text", "image", "audio", "resource_link" or "resource".
// The constructors above populate this field appropriately.
// Although at most one of Text, Data, ResourceLink and Resource should be non-zero,
// consumers of ContentBlock use the Type field to determine which value to use;
// values in the other fields are ignored.
// TODO(jba,rfindley): rethink this type. Each kind (text, image, etc.) should have its own
// meta and annotations, otherwise they're duplicated for Resource and ResourceContents.
type ContentBlock struct {
Meta map[string]any `json:"_meta,omitempty"`
Type string `json:"type"`
Text string `json:"text,omitempty"`
MIMEType string `json:"mimeType,omitempty"`
Data []byte `json:"data,omitempty"`
ResourceLink *Resource `json:"resource_link,omitempty"`
Resource *ResourceContents `json:"resource,omitempty"`
Annotations *Annotations `json:"annotations,omitempty"`
}
func (c *Content) UnmarshalJSON(data []byte) error {
type wireContent Content // for naive unmarshaling
func (c *ContentBlock) UnmarshalJSON(data []byte) error {
type wireContent ContentBlock // for naive unmarshaling
var c2 wireContent
if err := json.Unmarshal(data, &c2); err != nil {
return err
}
switch c2.Type {
case "text", "image", "audio", "resource":
case "text", "image", "audio", "resource", "resource_link":
default:
return fmt.Errorf("unrecognized content type %s", c.Type)
}
*c = Content(c2)
*c = ContentBlock(c2)
return nil
}
// NewTextContent creates a [Content] with text.
func NewTextContent(text string) *Content {
return &Content{Type: "text", Text: text}
// NewTextContent creates a [ContentBlock] with text.
func NewTextContent(text string) *ContentBlock {
return &ContentBlock{Type: "text", Text: text}
}
// NewImageContent creates a [Content] with image data.
func NewImageContent(data []byte, mimeType string) *Content {
return &Content{Type: "image", Data: data, MIMEType: mimeType}
// NewImageContent creates a [ContentBlock] with image data.
func NewImageContent(data []byte, mimeType string) *ContentBlock {
return &ContentBlock{Type: "image", Data: data, MIMEType: mimeType}
}
// NewAudioContent creates a [Content] with audio data.
func NewAudioContent(data []byte, mimeType string) *Content {
return &Content{Type: "audio", Data: data, MIMEType: mimeType}
// NewAudioContent creates a [ContentBlock] with audio data.
func NewAudioContent(data []byte, mimeType string) *ContentBlock {
return &ContentBlock{Type: "audio", Data: data, MIMEType: mimeType}
}
// NewResourceContent creates a [Content] with an embedded resource.
func NewResourceContent(resource *ResourceContents) *Content {
return &Content{Type: "resource", Resource: resource}
// NewResourceLink creates a [ContentBlock] with a [Resource].
func NewResourceLink(r *Resource) *ContentBlock {
return &ContentBlock{Type: "resource_link", ResourceLink: r}
}
// NewResourceContents creates a [ContentBlock] with an embedded resource (a [ResourceContents]).
func NewResourceContents(rc *ResourceContents) *ContentBlock {
return &ContentBlock{Type: "resource", Resource: rc}
}
// ResourceContents represents the union of the spec's {Text,Blob}ResourceContents types.
@ -71,10 +80,11 @@ func NewResourceContent(resource *ResourceContents) *Content {
// A ResourceContents is either a TextResourceContents or a BlobResourceContents.
// Use [NewTextResourceContents] or [NextBlobResourceContents] to create one.
type ResourceContents struct {
URI string `json:"uri"` // resource location; must not be empty
MIMEType string `json:"mimeType,omitempty"`
Text string `json:"text"`
Blob []byte `json:"blob,omitempty"` // if nil, then text; else blob
Meta map[string]any `json:"_meta,omitempty"`
URI string `json:"uri"` // resource location; must not be empty
MIMEType string `json:"mimeType,omitempty"`
Text string `json:"text"`
Blob []byte `json:"blob,omitempty"` // if nil, then text; else blob
}
func (r ResourceContents) MarshalJSON() ([]byte, error) {