chore(mcp): Add helpers to parse parameters (#2821)

Signed-off-by: Colin Walters <walters@verbum.org>

crates/goose-mcp/src/computercontroller/mod.rs

@@ -12,7 +12,9 @@ use tokio::{process::Command, sync::mpsc};
 use std::os::unix::fs::PermissionsExt;
 
 use mcp_core::{
-    handler::{PromptError, ResourceError, ToolError},
+    handler::{
+        require_str_parameter, require_u64_parameter, PromptError, ResourceError, ToolError,
+    },
     protocol::ServerCapabilities,
 };
 use mcp_server::router::CapabilitiesBuilder;
@@ -595,11 +597,7 @@ impl ComputerControllerRouter {
     }
 
     async fn web_scrape(&self, params: Value) -> Result<Vec<Content>, ToolError> {
-        let url = params
-            .get("url")
-            .and_then(|v| v.as_str())
-            .ok_or_else(|| ToolError::InvalidParameters("Missing 'url' parameter".into()))?;
-
+        let url = require_str_parameter(&params, "url")?;
         let save_as = params
             .get("save_as")
             .and_then(|v| v.as_str())
@@ -916,20 +914,9 @@ impl ComputerControllerRouter {
                 ))])
             }
             "update_cell" => {
-                let row = params.get("row").and_then(|v| v.as_u64()).ok_or_else(|| {
-                    ToolError::InvalidParameters("Missing 'row' parameter".into())
-                })?;
-
-                let col = params.get("col").and_then(|v| v.as_u64()).ok_or_else(|| {
-                    ToolError::InvalidParameters("Missing 'col' parameter".into())
-                })?;
-
-                let value = params
-                    .get("value")
-                    .and_then(|v| v.as_str())
-                    .ok_or_else(|| {
-                        ToolError::InvalidParameters("Missing 'value' parameter".into())
-                    })?;
+                let row = require_u64_parameter(&params, "row")?;
+                let col = require_u64_parameter(&params, "col")?;
+                let value = require_str_parameter(&params, "value")?;
 
                 let worksheet_name = params
                     .get("worksheet")

crates/goose-mcp/src/developer/mod.rs

@@ -24,7 +24,7 @@ use url::Url;
 
 use include_dir::{include_dir, Dir};
 use mcp_core::{
-    handler::{PromptError, ResourceError, ToolError},
+    handler::{require_str_parameter, PromptError, ResourceError, ToolError},
     protocol::ServerCapabilities,
 };
 
@@ -919,12 +919,7 @@ impl DeveloperRouter {
                 self.text_editor_view(&path, view_range).await
             }
             "write" => {
-                let file_text = params
-                    .get("file_text")
-                    .and_then(|v| v.as_str())
-                    .ok_or_else(|| {
-                        ToolError::InvalidParameters("Missing 'file_text' parameter".into())
-                    })?;
+                let file_text = require_str_parameter(&params, "file_text")?;
 
                 self.text_editor_write(&path, file_text).await
             }

crates/goose/src/agents/extension_manager.rs

@@ -3,6 +3,7 @@ use axum::http::{HeaderMap, HeaderName};
 use chrono::{DateTime, TimeZone, Utc};
 use futures::stream::{FuturesUnordered, StreamExt};
 use futures::{future, FutureExt};
+use mcp_core::handler::require_str_parameter;
 use mcp_core::{ToolCall, ToolError};
 use rmcp::service::ClientInitializeError;
 use rmcp::transport::streamable_http_client::StreamableHttpClientTransportConfig;
@@ -551,11 +552,7 @@ impl ExtensionManager {
 
     // Function that gets executed for read_resource tool
     pub async fn read_resource(&self, params: Value) -> Result<Vec<Content>, ToolError> {
-        let uri = params
-            .get("uri")
-            .and_then(|v| v.as_str())
-            .ok_or_else(|| ToolError::InvalidParameters("Missing 'uri' parameter".to_string()))?;
-
+        let uri = require_str_parameter(&params, "uri")?;
         let extension_name = params.get("extension_name").and_then(|v| v.as_str());
 
         // If extension name is provided, we can just look it up

crates/mcp-core/src/handler.rs

@@ -1,6 +1,6 @@
 use serde::{Deserialize, Serialize};
 #[allow(unused_imports)] // this is used in schema below
-use serde_json::json;
+use serde_json::{json, Value};
 use thiserror::Error;
 
 #[non_exhaustive]
@@ -35,3 +35,32 @@ pub enum PromptError {
     #[error("Prompt not found: {0}")]
     NotFound(String),
 }
+
+/// Helper function to require a string, returning a ToolError
+pub fn require_str_parameter<'a>(
+    v: &'a serde_json::Value,
+    name: &str,
+) -> Result<&'a str, ToolError> {
+    let v = v
+        .get(name)
+        .ok_or_else(|| ToolError::InvalidParameters(format!("The parameter {name} is required")))?;
+    match v.as_str() {
+        Some(r) => Ok(r),
+        None => Err(ToolError::InvalidParameters(format!(
+            "The parameter {name} must be a string"
+        ))),
+    }
+}
+
+/// Helper function to require a u64, returning a ToolError
+pub fn require_u64_parameter(v: &serde_json::Value, name: &str) -> Result<u64, ToolError> {
+    let v = v
+        .get(name)
+        .ok_or_else(|| ToolError::InvalidParameters(format!("The parameter {name} is required")))?;
+    match v.as_u64() {
+        Some(r) => Ok(r),
+        None => Err(ToolError::InvalidParameters(format!(
+            "The parameter {name} must be a number"
+        ))),
+    }
+}