Retrofit MCP host onto libmcp

1 files changed, 88 insertions, 0 deletions

diff --git a/crates/fidget-spinner-cli/src/mcp/output.rs b/crates/fidget-spinner-cli/src/mcp/output.rs
new file mode 100644
index 0000000..58f7eb4
--- /dev/null
+++ b/crates/fidget-spinner-cli/src/mcp/output.rs
@@ -0,0 +1,88 @@
+use libmcp::{JsonPorcelainConfig, RenderMode, render_json_porcelain};
+use serde::Serialize;
+use serde_json::{Map, Value, json};
+
+use crate::mcp::fault::{FaultKind, FaultRecord, FaultStage};
+
+pub(crate) fn split_render_mode(
+    arguments: Value,
+    operation: &str,
+    stage: FaultStage,
+) -> Result<(RenderMode, Value), FaultRecord> {
+    let Value::Object(mut object) = arguments else {
+        return Ok((RenderMode::Porcelain, arguments));
+    };
+    let render = object
+        .remove("render")
+        .map(|value| {
+            serde_json::from_value::<RenderMode>(value).map_err(|error| {
+                FaultRecord::new(
+                    FaultKind::InvalidInput,
+                    stage,
+                    operation,
+                    format!("invalid render mode: {error}"),
+                )
+            })
+        })
+        .transpose()?
+        .unwrap_or(RenderMode::Porcelain);
+    Ok((render, Value::Object(object)))
+}
+
+pub(crate) fn tool_success(
+    value: &impl Serialize,
+    render: RenderMode,
+    stage: FaultStage,
+    operation: &str,
+) -> Result<Value, FaultRecord> {
+    let structured = serde_json::to_value(value).map_err(|error| {
+        FaultRecord::new(FaultKind::Internal, stage, operation, error.to_string())
+    })?;
+    tool_success_from_value(structured, render, stage, operation)
+}
+
+pub(crate) fn tool_success_from_value(
+    structured: Value,
+    render: RenderMode,
+    stage: FaultStage,
+    operation: &str,
+) -> Result<Value, FaultRecord> {
+    let text = match render {
+        RenderMode::Porcelain => render_json_porcelain(&structured, JsonPorcelainConfig::default()),
+        RenderMode::Json => crate::to_pretty_json(&structured).map_err(|error| {
+            FaultRecord::new(FaultKind::Internal, stage, operation, error.to_string())
+        })?,
+    };
+    Ok(json!({
+        "content": [{
+            "type": "text",
+            "text": text,
+        }],
+        "structuredContent": structured,
+        "isError": false,
+    }))
+}
+
+pub(crate) fn with_render_property(schema: Value) -> Value {
+    let Value::Object(mut object) = schema else {
+        return schema;
+    };
+
+    let properties = object
+        .entry("properties".to_owned())
+        .or_insert_with(|| Value::Object(Map::new()));
+    if let Value::Object(properties) = properties {
+        let _ = properties.insert(
+            "render".to_owned(),
+            json!({
+                "type": "string",
+                "enum": ["porcelain", "json"],
+                "description": "Output mode. Defaults to porcelain for model-friendly summaries."
+            }),
+        );
+    }
+    let _ = object
+        .entry("additionalProperties".to_owned())
+        .or_insert(Value::Bool(false));
+    Value::Object(object)
+}