Spec conformance: meta support and spec updates (#415)

* feat: add _meta to content blocks and embedded resources; update schemas

* feat: set default protocol version; add _meta to content blocks/resources; update schemas

* chore: format content.rs via rustfmt

* chore(protocol): keep LATEST at 2025-03-26 per review until full 2025-06-18 compliance

* feat(prompt): add constructors with optional meta for image and resource

- Keep text helper; meta is currently ignored for text until schema supports it.

* refactor(prompt): simplify constructors so meta is optional; remove duplicate non-meta variants

* fix: modify code comment about version

* refactor(prompt): rename meta parameters in new_resource function for clarity

crates/rmcp/src/model.rs

@@ -149,6 +149,7 @@ impl ProtocolVersion {
     pub const V_2025_06_18: Self = Self(Cow::Borrowed("2025-06-18"));
     pub const V_2025_03_26: Self = Self(Cow::Borrowed("2025-03-26"));
     pub const V_2024_11_05: Self = Self(Cow::Borrowed("2024-11-05"));
+    //  Keep LATEST at 2025-03-26 until full 2025-06-18 compliance and automated testing are in place.
     pub const LATEST: Self = Self::V_2025_03_26;
 }
 

crates/rmcp/src/model/annotated.rs

@@ -16,8 +16,8 @@ pub struct Annotations {
     pub audience: Option<Vec<Role>>,
     #[serde(skip_serializing_if = "Option::is_none")]
     pub priority: Option<f32>,
-    #[serde(skip_serializing_if = "Option::is_none")]
-    pub timestamp: Option<DateTime<Utc>>,
+    #[serde(skip_serializing_if = "Option::is_none", rename = "lastModified")]
+    pub last_modified: Option<DateTime<Utc>>,
 }
 
 impl Annotations {
@@ -30,7 +30,7 @@ impl Annotations {
         );
         Annotations {
             priority: Some(priority),
-            timestamp: Some(timestamp),
+            last_modified: Some(timestamp),
             audience: None,
         }
     }
@@ -72,7 +72,7 @@ impl<T: AnnotateAble> Annotated<T> {
         self.annotations.as_ref().and_then(|a| a.priority)
     }
     pub fn timestamp(&self) -> Option<DateTime<Utc>> {
-        self.annotations.as_ref().and_then(|a| a.timestamp)
+        self.annotations.as_ref().and_then(|a| a.last_modified)
     }
     pub fn with_audience(self, audience: Vec<Role>) -> Annotated<T>
     where
@@ -92,7 +92,7 @@ impl<T: AnnotateAble> Annotated<T> {
                 annotations: Some(Annotations {
                     audience: Some(audience),
                     priority: None,
-                    timestamp: None,
+                    last_modified: None,
                 }),
             }
         }
@@ -114,7 +114,7 @@ impl<T: AnnotateAble> Annotated<T> {
                 raw: self.raw,
                 annotations: Some(Annotations {
                     priority: Some(priority),
-                    timestamp: None,
+                    last_modified: None,
                     audience: None,
                 }),
             }
@@ -128,7 +128,7 @@ impl<T: AnnotateAble> Annotated<T> {
             Annotated {
                 raw: self.raw,
                 annotations: Some(Annotations {
-                    timestamp: Some(timestamp),
+                    last_modified: Some(timestamp),
                     ..annotations
                 }),
             }
@@ -136,7 +136,7 @@ impl<T: AnnotateAble> Annotated<T> {
             Annotated {
                 raw: self.raw,
                 annotations: Some(Annotations {
-                    timestamp: Some(timestamp),
+                    last_modified: Some(timestamp),
                     priority: None,
                     audience: None,
                 }),
@@ -211,7 +211,7 @@ pub trait AnnotateAble: sealed::Sealed {
         Self: Sized,
     {
         self.annotate(Annotations {
-            timestamp: Some(timestamp),
+            last_modified: Some(timestamp),
             ..Default::default()
         })
     }

crates/rmcp/src/model/content.rs

@@ -11,6 +11,9 @@ use super::{AnnotateAble, Annotated, resource::ResourceContents};
 #[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
 pub struct RawTextContent {
     pub text: String,
+    /// Optional protocol-level metadata for this content block
+    #[serde(rename = "_meta", skip_serializing_if = "Option::is_none")]
+    pub meta: Option<super::Meta>,
 }
 pub type TextContent = Annotated<RawTextContent>;
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
@@ -20,6 +23,9 @@ pub struct RawImageContent {
     /// The base64-encoded image
     pub data: String,
     pub mime_type: String,
+    /// Optional protocol-level metadata for this content block
+    #[serde(rename = "_meta", skip_serializing_if = "Option::is_none")]
+    pub meta: Option<super::Meta>,
 }
 
 pub type ImageContent = Annotated<RawImageContent>;
@@ -27,6 +33,7 @@ pub type ImageContent = Annotated<RawImageContent>;
 #[serde(rename_all = "camelCase")]
 #[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
 pub struct RawEmbeddedResource {
+    /// Optional protocol-level metadata for this content block
     #[serde(rename = "_meta", skip_serializing_if = "Option::is_none")]
     pub meta: Option<super::Meta>,
     pub resource: ResourceContents,
@@ -79,13 +86,17 @@ impl RawContent {
     }
 
     pub fn text<S: Into<String>>(text: S) -> Self {
-        RawContent::Text(RawTextContent { text: text.into() })
+        RawContent::Text(RawTextContent {
+            text: text.into(),
+            meta: None,
+        })
     }
 
     pub fn image<S: Into<String>, T: Into<String>>(data: S, mime_type: T) -> Self {
         RawContent::Image(RawImageContent {
             data: data.into(),
             mime_type: mime_type.into(),
+            meta: None,
         })
     }
 
@@ -209,6 +220,7 @@ mod tests {
         let image_content = RawImageContent {
             data: "base64data".to_string(),
             mime_type: "image/png".to_string(),
+            meta: None,
         };
 
         let json = serde_json::to_string(&image_content).unwrap();

crates/rmcp/src/model/prompt.rs

@@ -114,49 +114,59 @@ impl PromptMessage {
             content: PromptMessageContent::Text { text: text.into() },
         }
     }
+
+    /// Create a new image message. `meta` and `annotations` are optional.
     #[cfg(feature = "base64")]
     pub fn new_image(
         role: PromptMessageRole,
         data: &[u8],
         mime_type: &str,
+        meta: Option<crate::model::Meta>,
         annotations: Option<Annotations>,
     ) -> Self {
-        let mime_type = mime_type.into();
-
         let base64 = BASE64_STANDARD.encode(data);
-
         Self {
             role,
             content: PromptMessageContent::Image {
                 image: RawImageContent {
                     data: base64,
-                    mime_type,
+                    mime_type: mime_type.into(),
+                    meta,
                 }
                 .optional_annotate(annotations),
             },
         }
     }
 
-    /// Create a new resource message
+    /// Create a new resource message. `resource_meta`, `resource_content_meta`, and `annotations` are optional.
     pub fn new_resource(
         role: PromptMessageRole,
         uri: String,
-        mime_type: String,
+        mime_type: Option<String>,
         text: Option<String>,
+        resource_meta: Option<crate::model::Meta>,
+        resource_content_meta: Option<crate::model::Meta>,
         annotations: Option<Annotations>,
     ) -> Self {
-        let resource_contents = ResourceContents::TextResourceContents {
-            uri,
-            mime_type: Some(mime_type),
-            text: text.unwrap_or_default(),
-            meta: None,
+        let resource_contents = match text {
+            Some(t) => ResourceContents::TextResourceContents {
+                uri,
+                mime_type,
+                text: t,
+                meta: resource_content_meta,
+            },
+            None => ResourceContents::BlobResourceContents {
+                uri,
+                mime_type,
+                blob: String::new(),
+                meta: resource_content_meta,
+            },
         };
-
         Self {
             role,
             content: PromptMessageContent::Resource {
                 resource: RawEmbeddedResource {
-                    meta: None,
+                    meta: resource_meta,
                     resource: resource_contents,
                 }
                 .optional_annotate(annotations),
@@ -164,6 +174,16 @@ impl PromptMessage {
         }
     }
 
+    /// Note: PromptMessage text content does not carry protocol-level _meta per current schema.
+    /// This function exists for API symmetry but ignores the meta parameter.
+    pub fn new_text_with_meta<S: Into<String>>(
+        role: PromptMessageRole,
+        text: S,
+        _meta: Option<crate::model::Meta>,
+    ) -> Self {
+        Self::new_text(role, text)
+    }
+
     /// Create a new resource link message
     pub fn new_resource_link(role: PromptMessageRole, resource: super::resource::Resource) -> Self {
         Self {
@@ -184,6 +204,7 @@ mod tests {
         let image_content = RawImageContent {
             data: "base64data".to_string(),
             mime_type: "image/png".to_string(),
+            meta: None,
         };
 
         let json = serde_json::to_string(&image_content).unwrap();