Implement SEP-1577: Sampling With Tools (#628)

* feat: implement SEP-1577 sampling with tools support

* feat: add TryFrom<Content> for backward-compatible migration

crates/rmcp/src/model/capabilities.rs

@@ -194,6 +194,19 @@ pub struct ElicitationCapability {
     pub schema_validation: Option<bool>,
 }
 
+/// Sampling capability with optional sub-capabilities (SEP-1577).
+#[derive(Debug, Serialize, Deserialize, Clone, PartialEq, Default)]
+#[serde(rename_all = "camelCase")]
+#[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
+pub struct SamplingCapability {
+    /// Support for `tools` and `toolChoice` parameters
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub tools: Option<JsonObject>,
+    /// Support for `includeContext` (soft-deprecated)
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub context: Option<JsonObject>,
+}
+
 ///
 /// # Builder
 /// ```rust
@@ -217,8 +230,9 @@ pub struct ClientCapabilities {
     pub extensions: Option<ExtensionCapabilities>,
     #[serde(skip_serializing_if = "Option::is_none")]
     pub roots: Option<RootsCapabilities>,
+    /// Capability for LLM sampling requests (SEP-1577)
     #[serde(skip_serializing_if = "Option::is_none")]
-    pub sampling: Option<JsonObject>,
+    pub sampling: Option<SamplingCapability>,
     /// Capability to handle elicitation requests from servers for interactive user input
     #[serde(skip_serializing_if = "Option::is_none")]
     pub elicitation: Option<ElicitationCapability>,
@@ -449,7 +463,7 @@ builder! {
         experimental: ExperimentalCapabilities,
         extensions: ExtensionCapabilities,
         roots: RootsCapabilities,
-        sampling: JsonObject,
+        sampling: SamplingCapability,
         elicitation: ElicitationCapability,
         tasks: TasksCapability,
     }
@@ -466,6 +480,26 @@ impl<const E: bool, const EXT: bool, const S: bool, const EL: bool, const TASKS:
     }
 }
 
+impl<const E: bool, const EXT: bool, const R: bool, const EL: bool, const TASKS: bool>
+    ClientCapabilitiesBuilder<ClientCapabilitiesBuilderState<E, EXT, R, true, EL, TASKS>>
+{
+    /// Enable tool calling in sampling requests
+    pub fn enable_sampling_tools(mut self) -> Self {
+        if let Some(c) = self.sampling.as_mut() {
+            c.tools = Some(JsonObject::default());
+        }
+        self
+    }
+
+    /// Enable context inclusion in sampling (soft-deprecated)
+    pub fn enable_sampling_context(mut self) -> Self {
+        if let Some(c) = self.sampling.as_mut() {
+            c.context = Some(JsonObject::default());
+        }
+        self
+    }
+}
+
 #[cfg(feature = "elicitation")]
 impl<const E: bool, const EXT: bool, const R: bool, const S: bool, const TASKS: bool>
     ClientCapabilitiesBuilder<ClientCapabilitiesBuilderState<E, EXT, R, S, true, TASKS>>

crates/rmcp/src/model/content.rs

@@ -59,6 +59,137 @@ pub struct RawAudioContent {
 
 pub type AudioContent = Annotated<RawAudioContent>;
 
+/// Tool call request from assistant (SEP-1577).
+#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+#[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
+pub struct ToolUseContent {
+    /// Unique identifier for this tool call
+    pub id: String,
+    /// Name of the tool to call
+    pub name: String,
+    /// Input arguments for the tool
+    pub input: super::JsonObject,
+    /// Optional metadata (preserved for caching)
+    #[serde(rename = "_meta", skip_serializing_if = "Option::is_none")]
+    pub meta: Option<super::Meta>,
+}
+
+/// Tool execution result in user message (SEP-1577).
+#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+#[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
+pub struct ToolResultContent {
+    /// Optional metadata
+    #[serde(rename = "_meta", skip_serializing_if = "Option::is_none")]
+    pub meta: Option<super::Meta>,
+    /// ID of the corresponding tool use
+    pub tool_use_id: String,
+    /// Content blocks returned by the tool
+    #[serde(default, skip_serializing_if = "Vec::is_empty")]
+    pub content: Vec<Content>,
+    /// Optional structured result
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub structured_content: Option<super::JsonObject>,
+    /// Whether tool execution failed
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub is_error: Option<bool>,
+}
+
+impl ToolUseContent {
+    pub fn new(id: impl Into<String>, name: impl Into<String>, input: super::JsonObject) -> Self {
+        Self {
+            id: id.into(),
+            name: name.into(),
+            input,
+            meta: None,
+        }
+    }
+}
+
+impl ToolResultContent {
+    pub fn new(tool_use_id: impl Into<String>, content: Vec<Content>) -> Self {
+        Self {
+            meta: None,
+            tool_use_id: tool_use_id.into(),
+            content,
+            structured_content: None,
+            is_error: None,
+        }
+    }
+
+    pub fn error(tool_use_id: impl Into<String>, content: Vec<Content>) -> Self {
+        Self {
+            meta: None,
+            tool_use_id: tool_use_id.into(),
+            content,
+            structured_content: None,
+            is_error: Some(true),
+        }
+    }
+}
+
+/// Assistant message content types (SEP-1577).
+#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
+#[serde(tag = "type", rename_all = "snake_case")]
+#[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
+pub enum AssistantMessageContent {
+    Text(RawTextContent),
+    Image(RawImageContent),
+    Audio(RawAudioContent),
+    ToolUse(ToolUseContent),
+}
+
+/// User message content types (SEP-1577).
+#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
+#[serde(tag = "type", rename_all = "snake_case")]
+#[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
+pub enum UserMessageContent {
+    Text(RawTextContent),
+    Image(RawImageContent),
+    Audio(RawAudioContent),
+    ToolResult(ToolResultContent),
+}
+
+impl AssistantMessageContent {
+    /// Create a text content
+    pub fn text(text: impl Into<String>) -> Self {
+        Self::Text(RawTextContent {
+            text: text.into(),
+            meta: None,
+        })
+    }
+
+    /// Create a tool use content
+    pub fn tool_use(
+        id: impl Into<String>,
+        name: impl Into<String>,
+        input: super::JsonObject,
+    ) -> Self {
+        Self::ToolUse(ToolUseContent::new(id, name, input))
+    }
+}
+
+impl UserMessageContent {
+    /// Create a text content
+    pub fn text(text: impl Into<String>) -> Self {
+        Self::Text(RawTextContent {
+            text: text.into(),
+            meta: None,
+        })
+    }
+
+    /// Create a tool result content
+    pub fn tool_result(tool_use_id: impl Into<String>, content: Vec<Content>) -> Self {
+        Self::ToolResult(ToolResultContent::new(tool_use_id, content))
+    }
+
+    /// Create an error tool result content
+    pub fn tool_result_error(tool_use_id: impl Into<String>, content: Vec<Content>) -> Self {
+        Self::ToolResult(ToolResultContent::error(tool_use_id, content))
+    }
+}
+
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
 #[serde(tag = "type", rename_all = "snake_case")]
 #[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]