feat(model): add json schema generation support for all model types (#176)

* feat(model): add json schema generation support for all model types

This commit adds JSON Schema support for all model types by implementing
`schemars::JsonSchema` trait. The feature is gated behind the new
`schemars` feature flag. This enables automatic schema generation for
API documentation and validation purposes. Added tests to verify schema
generation for client and server JSON-RPC messages.

* fix(model): add manual json schema implementation for `NumberOrString`

This commit adds a manual implementation of `JsonSchema` trait for the
`NumberOrString` enum to properly represent its union type nature in
JSON Schema. The schema now correctly specifies that the type can be
either a number or a string using the `oneOf` validation keyword.

* fix(model): skip extensions field in json schema generation

The `Extensions` type was incorrectly included in JSON schema
generation, which could lead to confusing API documentation. This commit
adds `#[schemars(skip)]` attribute to all `extensions` fields in request
and notification structs, and removes the manual `JsonSchema`
implementation for the `Extensions` type since it's an internal
implementation detail that shouldn't be exposed in the schema.

crates/rmcp/src/model/annotated.rs

@@ -10,6 +10,7 @@ use super::{
 
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize, Default)]
 #[serde(rename_all = "camelCase")]
+#[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
 pub struct Annotations {
     #[serde(skip_serializing_if = "Option::is_none")]
     pub audience: Option<Vec<Role>>,
@@ -36,6 +37,7 @@ impl Annotations {
 }
 
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
+#[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
 pub struct Annotated<T: AnnotateAble> {
     #[serde(flatten)]
     pub raw: T,

crates/rmcp/src/model/capabilities.rs

@@ -8,6 +8,7 @@ pub type ExperimentalCapabilities = BTreeMap<String, JsonObject>;
 
 #[derive(Debug, Serialize, Deserialize, Clone, PartialEq, Default)]
 #[serde(rename_all = "camelCase")]
+#[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
 pub struct PromptsCapability {
     #[serde(skip_serializing_if = "Option::is_none")]
     pub list_changed: Option<bool>,
@@ -15,6 +16,7 @@ pub struct PromptsCapability {
 
 #[derive(Debug, Serialize, Deserialize, Clone, PartialEq, Default)]
 #[serde(rename_all = "camelCase")]
+#[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
 pub struct ResourcesCapability {
     #[serde(skip_serializing_if = "Option::is_none")]
     pub subscribe: Option<bool>,
@@ -24,6 +26,7 @@ pub struct ResourcesCapability {
 
 #[derive(Debug, Serialize, Deserialize, Clone, PartialEq, Default)]
 #[serde(rename_all = "camelCase")]
+#[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
 pub struct ToolsCapability {
     #[serde(skip_serializing_if = "Option::is_none")]
     pub list_changed: Option<bool>,
@@ -31,6 +34,7 @@ pub struct ToolsCapability {
 
 #[derive(Debug, Serialize, Deserialize, Clone, PartialEq, Default)]
 #[serde(rename_all = "camelCase")]
+#[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
 pub struct RootsCapabilities {
     pub list_changed: Option<bool>,
 }
@@ -46,6 +50,7 @@ pub struct RootsCapabilities {
 ///     .build();
 /// ```
 #[derive(Debug, Serialize, Deserialize, Clone, PartialEq, Default)]
+#[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
 pub struct ClientCapabilities {
     #[serde(skip_serializing_if = "Option::is_none")]
     pub experimental: Option<ExperimentalCapabilities>,
@@ -70,6 +75,7 @@ pub struct ClientCapabilities {
 /// ```
 #[derive(Debug, Serialize, Deserialize, Clone, PartialEq, Default)]
 #[serde(rename_all = "camelCase")]
+#[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
 pub struct ServerCapabilities {
     #[serde(skip_serializing_if = "Option::is_none")]
     pub experimental: Option<ExperimentalCapabilities>,

crates/rmcp/src/model/content.rs

@@ -8,12 +8,14 @@ use super::{AnnotateAble, Annotated, resource::ResourceContents};
 
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
 #[serde(rename_all = "camelCase")]
+#[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
 pub struct RawTextContent {
     pub text: String,
 }
 pub type TextContent = Annotated<RawTextContent>;
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
 #[serde(rename_all = "camelCase")]
+#[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
 pub struct RawImageContent {
     /// The base64-encoded image
     pub data: String,
@@ -23,6 +25,7 @@ pub struct RawImageContent {
 pub type ImageContent = Annotated<RawImageContent>;
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
 #[serde(rename_all = "camelCase")]
+#[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
 pub struct RawEmbeddedResource {
     pub resource: ResourceContents,
 }
@@ -39,6 +42,7 @@ impl EmbeddedResource {
 
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
 #[serde(rename_all = "camelCase")]
+#[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
 pub struct RawAudioContent {
     pub data: String,
     pub mime_type: String,
@@ -48,6 +52,7 @@ pub type AudioContent = Annotated<RawAudioContent>;
 
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
 #[serde(tag = "type", rename_all = "camelCase")]
+#[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
 pub enum RawContent {
     Text(RawTextContent),
     Image(RawImageContent),

crates/rmcp/src/model/prompt.rs

@@ -10,6 +10,7 @@ use super::{
 /// A prompt that can be used to generate text from a model
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
 #[serde(rename_all = "camelCase")]
+#[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
 pub struct Prompt {
     /// The name of the prompt
     pub name: String,
@@ -42,6 +43,7 @@ impl Prompt {
 
 /// Represents a prompt argument that can be passed to customize the prompt
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
+#[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
 pub struct PromptArgument {
     /// The name of the argument
     pub name: String,
@@ -56,6 +58,7 @@ pub struct PromptArgument {
 /// Represents the role of a message sender in a prompt conversation
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
 #[serde(rename_all = "camelCase")]
+#[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
 pub enum PromptMessageRole {
     User,
     Assistant,
@@ -64,6 +67,7 @@ pub enum PromptMessageRole {
 /// Content types that can be included in prompt messages
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
 #[serde(tag = "type", rename_all = "camelCase")]
+#[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
 pub enum PromptMessageContent {
     /// Plain text content
     Text { text: String },
@@ -84,6 +88,7 @@ impl PromptMessageContent {
 
 /// A message in a prompt conversation
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
+#[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
 pub struct PromptMessage {
     /// The role of the message sender
     pub role: PromptMessageRole,

crates/rmcp/src/model/resource.rs

@@ -5,6 +5,7 @@ use super::Annotated;
 /// Represents a resource in the extension with metadata
 #[derive(Debug, Serialize, Deserialize, Clone, PartialEq)]
 #[serde(rename_all = "camelCase")]
+#[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
 pub struct RawResource {
     /// URI representing the resource location (e.g., "file:///path/to/file" or "str:///content")
     pub uri: String,
@@ -28,6 +29,7 @@ pub type Resource = Annotated<RawResource>;
 
 #[derive(Debug, Serialize, Deserialize, Clone, PartialEq)]
 #[serde(rename_all = "camelCase")]
+#[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
 pub struct RawResourceTemplate {
     pub uri_template: String,
     pub name: String,
@@ -41,6 +43,7 @@ pub type ResourceTemplate = Annotated<RawResourceTemplate>;
 
 #[derive(Debug, Serialize, Deserialize, Clone, PartialEq)]
 #[serde(rename_all = "camelCase", untagged)]
+#[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
 pub enum ResourceContents {
     TextResourceContents {
         uri: String,

crates/rmcp/src/model/tool.rs

@@ -10,6 +10,7 @@ use super::JsonObject;
 /// A tool that can be used by a model.
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
 #[serde(rename_all = "camelCase")]
+#[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
 pub struct Tool {
     /// The name of the tool
     pub name: Cow<'static, str>,
@@ -33,6 +34,7 @@ pub struct Tool {
 /// received from untrusted servers.
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize, Default)]
 #[serde(rename_all = "camelCase")]
+#[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
 pub struct ToolAnnotations {
     /// A human-readable title for the tool.
     pub title: Option<String>,