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

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

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"
+        ))),
+    }
+}