feat: add resource_link support to tools and prompts (#381)

* feat: add resource_link support to tools and prompts

* chore: remove unused serde_json import from test_resource_link_integration.rs

* chore: remove unused serde_json import from test_resource_link.rs

Author: aharvard

crates/rmcp/src/model/content.rs

@@ -51,13 +51,14 @@ pub struct RawAudioContent {
 pub type AudioContent = Annotated<RawAudioContent>;
 
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
-#[serde(tag = "type", rename_all = "camelCase")]
+#[serde(tag = "type", rename_all = "snake_case")]
 #[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
 pub enum RawContent {
     Text(RawTextContent),
     Image(RawImageContent),
     Resource(RawEmbeddedResource),
     Audio(AudioContent),
+    ResourceLink(super::resource::RawResource),
 }
 
 pub type Content = Annotated<RawContent>;
@@ -123,6 +124,19 @@ impl RawContent {
             _ => None,
         }
     }
+
+    /// Get the resource link if this is a ResourceLink variant
+    pub fn as_resource_link(&self) -> Option<&super::resource::RawResource> {
+        match self {
+            RawContent::ResourceLink(link) => Some(link),
+            _ => None,
+        }
+    }
+
+    /// Create a resource link content
+    pub fn resource_link(resource: super::resource::RawResource) -> Self {
+        RawContent::ResourceLink(resource)
+    }
 }
 
 impl Content {
@@ -145,6 +159,11 @@ impl Content {
     pub fn json<S: Serialize>(json: S) -> Result<Self, crate::ErrorData> {
         RawContent::json(json).map(|c| c.no_annotation())
     }
+
+    /// Create a resource link content
+    pub fn resource_link(resource: super::resource::RawResource) -> Self {
+        RawContent::resource_link(resource).no_annotation()
+    }
 }
 
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
@@ -207,4 +226,47 @@ mod tests {
         assert!(json.contains("mimeType"));
         assert!(!json.contains("mime_type"));
     }
+
+    #[test]
+    fn test_resource_link_serialization() {
+        use super::super::resource::RawResource;
+
+        let resource_link = RawContent::ResourceLink(RawResource {
+            uri: "file:///test.txt".to_string(),
+            name: "test.txt".to_string(),
+            description: Some("A test file".to_string()),
+            mime_type: Some("text/plain".to_string()),
+            size: Some(100),
+        });
+
+        let json = serde_json::to_string(&resource_link).unwrap();
+        println!("ResourceLink JSON: {}", json);
+
+        // Verify it contains the correct type tag
+        assert!(json.contains("\"type\":\"resource_link\""));
+        assert!(json.contains("\"uri\":\"file:///test.txt\""));
+        assert!(json.contains("\"name\":\"test.txt\""));
+    }
+
+    #[test]
+    fn test_resource_link_deserialization() {
+        let json = r#"{
+            "type": "resource_link",
+            "uri": "file:///example.txt",
+            "name": "example.txt",
+            "description": "Example file",
+            "mimeType": "text/plain"
+        }"#;
+
+        let content: RawContent = serde_json::from_str(json).unwrap();
+
+        if let RawContent::ResourceLink(resource) = content {
+            assert_eq!(resource.uri, "file:///example.txt");
+            assert_eq!(resource.name, "example.txt");
+            assert_eq!(resource.description, Some("Example file".to_string()));
+            assert_eq!(resource.mime_type, Some("text/plain".to_string()));
+        } else {
+            panic!("Expected ResourceLink variant");
+        }
+    }
 }

crates/rmcp/src/model/prompt.rs

@@ -66,7 +66,7 @@ pub enum PromptMessageRole {
 
 /// Content types that can be included in prompt messages
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
-#[serde(tag = "type", rename_all = "camelCase")]
+#[serde(tag = "type", rename_all = "snake_case")]
 #[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
 pub enum PromptMessageContent {
     /// Plain text content
@@ -78,12 +78,22 @@ pub enum PromptMessageContent {
     },
     /// Embedded server-side resource
     Resource { resource: EmbeddedResource },
+    /// A link to a resource that can be fetched separately
+    ResourceLink {
+        #[serde(flatten)]
+        link: super::resource::Resource,
+    },
 }
 
 impl PromptMessageContent {
     pub fn text(text: impl Into<String>) -> Self {
         Self::Text { text: text.into() }
     }
+
+    /// Create a resource link content
+    pub fn resource_link(resource: super::resource::Resource) -> Self {
+        Self::ResourceLink { link: resource }
+    }
 }
 
 /// A message in a prompt conversation
@@ -151,6 +161,14 @@ impl PromptMessage {
             },
         }
     }
+
+    /// Create a new resource link message
+    pub fn new_resource_link(role: PromptMessageRole, resource: super::resource::Resource) -> Self {
+        Self {
+            role,
+            content: PromptMessageContent::ResourceLink { link: resource },
+        }
+    }
 }
 
 #[cfg(test)]
@@ -173,4 +191,43 @@ mod tests {
         assert!(json.contains("mimeType"));
         assert!(!json.contains("mime_type"));
     }
+
+    #[test]
+    fn test_prompt_message_resource_link_serialization() {
+        use super::super::resource::RawResource;
+
+        let resource = RawResource::new("file:///test.txt", "test.txt");
+        let message =
+            PromptMessage::new_resource_link(PromptMessageRole::User, resource.no_annotation());
+
+        let json = serde_json::to_string(&message).unwrap();
+        println!("PromptMessage with ResourceLink JSON: {}", json);
+
+        // Verify it contains the correct type tag
+        assert!(json.contains("\"type\":\"resource_link\""));
+        assert!(json.contains("\"uri\":\"file:///test.txt\""));
+        assert!(json.contains("\"name\":\"test.txt\""));
+    }
+
+    #[test]
+    fn test_prompt_message_content_resource_link_deserialization() {
+        let json = r#"{
+            "type": "resource_link",
+            "uri": "file:///example.txt",
+            "name": "example.txt",
+            "description": "Example file",
+            "mimeType": "text/plain"
+        }"#;
+
+        let content: PromptMessageContent = serde_json::from_str(json).unwrap();
+
+        if let PromptMessageContent::ResourceLink { link } = content {
+            assert_eq!(link.uri, "file:///example.txt");
+            assert_eq!(link.name, "example.txt");
+            assert_eq!(link.description, Some("Example file".to_string()));
+            assert_eq!(link.mime_type, Some("text/plain".to_string()));
+        } else {
+            panic!("Expected ResourceLink variant");
+        }
+    }
 }

crates/rmcp/tests/test_message_schema/client_json_rpc_message_schema.json

@@ -133,6 +133,23 @@
           "required": [
             "type"
           ]
+        },
+        {
+          "type": "object",
+          "properties": {
+            "type": {
+              "type": "string",
+              "const": "resource_link"
+            }
+          },
+          "allOf": [
+            {
+              "$ref": "#/definitions/RawResource"
+            }
+          ],
+          "required": [
+            "type"
+          ]
         }
       ]
     },
@@ -899,6 +916,47 @@
         "mimeType"
       ]
     },
+    "RawResource": {
+      "description": "Represents a resource in the extension with metadata",
+      "type": "object",
+      "properties": {
+        "description": {
+          "description": "Optional description of the resource",
+          "type": [
+            "string",
+            "null"
+          ]
+        },
+        "mimeType": {
+          "description": "MIME type of the resource content (\"text\" or \"blob\")",
+          "type": [
+            "string",
+            "null"
+          ]
+        },
+        "name": {
+          "description": "Name of the resource",
+          "type": "string"
+        },
+        "size": {
+          "description": "The size of the raw resource content, in bytes (i.e., before base64 encoding or any tokenization), if known.\n\nThis can be used by Hosts to display file sizes and estimate context window us",
+          "type": [
+            "integer",
+            "null"
+          ],
+          "format": "uint32",
+          "minimum": 0
+        },
+        "uri": {
+          "description": "URI representing the resource location (e.g., \"file:///path/to/file\" or \"str:///content\")",
+          "type": "string"
+        }
+      },
+      "required": [
+        "uri",
+        "name"
+      ]
+    },
     "RawTextContent": {
       "type": "object",
       "properties": {