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internal/mcp: simplify content

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Now that the protocol package is merged into the mcp package, clean up
the higher level 'Content' union types, in favor of types constructors.

Change-Id: I37bedb0ff0a296eef799ba65c37ca7f94ee1dbbe
Reviewed-on: https://go-review.googlesource.com/c/tools/+/672415
Reviewed-by: Jonathan Amsterdam <jba@google.com>
TryBot-Bypass: Jonathan Amsterdam <jba@google.com>
This commit is contained in:
Rob Findley 2025-05-13 21:51:26 +00:00 • committed by Jonathan Amsterdam
commit dac5be2c50
1 changed files with 107 additions and 207 deletions
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174
mcp/content.go
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@ -11,37 +11,25 @@ import (
// The []byte fields below are marked omitzero, not omitempty:
// we want to marshal an empty byte slice.
// TODO(jba): figure out how to fix this for 1.23.
// WireContent is the wire format for content.
// Content is the wire format for content.
// It represents the protocol types TextContent, ImageContent, AudioContent
// and EmbeddedResource.
// The Type field distinguishes them. In the protocol, each type has a constant
// value for the field.
// At most one of Text, Data, and Resource is non-zero.
type WireContent struct {
Type string `json:"type"`
Text string `json:"text,omitempty"`
MIMEType string `json:"mimeType,omitempty"`
Data []byte `json:"data,omitzero"`
Resource *WireResource `json:"resource,omitempty"`
Annotations *Annotations `json:"annotations,omitempty"`
type Content struct {
Type string `json:"type"`
Text string `json:"text,omitempty"`
MIMEType string `json:"mimeType,omitempty"`
Data []byte `json:"data,omitzero"`
Resource *ResourceContents `json:"resource,omitempty"`
Annotations *Annotations `json:"annotations,omitempty"`
}
// A WireResource is either a TextResourceContents or a BlobResourceContents.
// See https://github.com/modelcontextprotocol/modelcontextprotocol/blob/main/schema/2025-03-26/schema.ts#L524-L551
// for the inheritance structure.
// If Blob is nil, this is a TextResourceContents; otherwise it's a BlobResourceContents.
//
// The URI field describes the resource location.
type WireResource struct {
URI string `json:"uri,"`
MIMEType string `json:"mimeType,omitempty"`
Text string `json:"text"`
Blob []byte `json:"blob,omitzero"`
}
func (c *WireContent) UnmarshalJSON(data []byte) error {
type wireContent WireContent // for naive unmarshaling
func (c *Content) UnmarshalJSON(data []byte) error {
type wireContent Content // for naive unmarshaling
var c2 wireContent
if err := json.Unmarshal(data, &c2); err != nil {
return err
@ -51,77 +39,44 @@ func (c *WireContent) UnmarshalJSON(data []byte) error {
default:
return fmt.Errorf("unrecognized content type %s", c.Type)
}
*c = WireContent(c2)
*c = Content(c2)
return nil
}
// Content is the union of supported content types: [TextContent],
// [ImageContent], [AudioContent], and [ResourceContent].
func NewTextContent(text string) Content {
return Content{Type: "text", Text: text}
}
func NewImageContent(data []byte, mimeType string) Content {
return Content{Type: "image", Data: data, MIMEType: mimeType}
}
func NewAudioContent(data []byte, mimeType string) Content {
return Content{Type: "audio", Data: data, MIMEType: mimeType}
}
func NewResourceContent(resource ResourceContents) Content {
return Content{Type: "resource", Resource: &resource}
}
// A ResourceContents is either a TextResourceContents or a BlobResourceContents.
// See https://github.com/modelcontextprotocol/modelcontextprotocol/blob/main/schema/2025-03-26/schema.ts#L524-L551
// for the inheritance structure.
// If Blob is nil, this is a TextResourceContents; otherwise it's a BlobResourceContents.
//
// ToWire converts content to its jsonrpc2 wire format.
type Content interface {
// TODO: unexport this, and move the tests that use it to this package.
ToWire() WireContent
// The URI field describes the resource location.
type ResourceContents struct {
URI string `json:"uri,"`
MIMEType string `json:"mimeType,omitempty"`
Text string `json:"text,omitempty"`
Blob []byte `json:"blob,omitzero"`
}
// TextContent is a textual content.
type TextContent struct {
Text string
}
func (c TextContent) ToWire() WireContent {
return WireContent{Type: "text", Text: c.Text}
}
// ImageContent contains base64-encoded image data.
type ImageContent struct {
Data []byte // base64-encoded
MIMEType string
}
func (c ImageContent) ToWire() WireContent {
return WireContent{Type: "image", MIMEType: c.MIMEType, Data: c.Data}
}
// AudioContent contains base64-encoded audio data.
type AudioContent struct {
Data []byte
MIMEType string
}
func (c AudioContent) ToWire() WireContent {
return WireContent{Type: "audio", MIMEType: c.MIMEType, Data: c.Data}
}
// ResourceContent contains embedded resources.
type ResourceContent struct {
Resource EmbeddedResource
}
func (r ResourceContent) ToWire() WireContent {
res := r.Resource.toWire()
return WireContent{Type: "resource", Resource: &res}
}
type EmbeddedResource interface {
toWire() WireResource
}
// The {Text,Blob}ResourceContents types match the protocol definitions,
// but we represent both as a single type on the wire.
// A TextResourceContents is the contents of a text resource.
type TextResourceContents struct {
URI string
MIMEType string
Text string
}
func (r TextResourceContents) toWire() WireResource {
return WireResource{
URI: r.URI,
MIMEType: r.MIMEType,
Text: r.Text,
func NewTextResourceContents(uri, mimeType, text string) ResourceContents {
return ResourceContents{
URI: uri,
MIMEType: mimeType,
Text: text,
// Blob is nil, indicating this is a TextResourceContents.
}
}
@ -133,43 +88,10 @@ type BlobResourceContents struct {
Blob []byte
}
func (r BlobResourceContents) toWire() WireResource {
return WireResource{
URI: r.URI,
MIMEType: r.MIMEType,
Blob: r.Blob,
}
}
// ContentFromWireContent converts content from the jsonrpc2 wire format to a
// typed Content value.
func ContentFromWireContent(c WireContent) Content {
switch c.Type {
case "text":
return TextContent{Text: c.Text}
case "image":
return ImageContent{Data: c.Data, MIMEType: c.MIMEType}
case "audio":
return AudioContent{Data: c.Data, MIMEType: c.MIMEType}
case "resource":
r := ResourceContent{}
if c.Resource != nil {
if c.Resource.Blob != nil {
r.Resource = BlobResourceContents{
URI: c.Resource.URI,
MIMEType: c.Resource.MIMEType,
Blob: c.Resource.Blob,
}
} else {
r.Resource = TextResourceContents{
URI: c.Resource.URI,
MIMEType: c.Resource.MIMEType,
Text: c.Resource.Text,
}
}
}
return r
default:
panic(fmt.Sprintf("unrecognized wire content type %q", c.Type))
func NewBlobResourceContents(uri, mimeType string, blob []byte) ResourceContents {
return ResourceContents{
URI: uri,
MIMEType: mimeType,
Blob: blob,
}
}