internal/mcp/internal/util: add Wrapf

Add Wrapf, a function that helps with error wrapping.

Change-Id: I102695f75e4d217e09f828f4723cbfcbbe83f887
Reviewed-on: https://go-review.googlesource.com/c/tools/+/679177
Reviewed-by: Robert Findley <rfindley@google.com>
Reviewed-by: Sam Thanawalla <samthanawalla@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

internal/util/util.go

@@ -6,6 +6,7 @@ package util
 
 import (
 	"cmp"
+	"fmt"
 	"iter"
 	"reflect"
 	"slices"
@@ -73,3 +74,10 @@ func FieldJSONInfo(f reflect.StructField) JSONInfo {
 	}
 	return info
 }
+
+// Wrapf wraps *errp with the given formatted message if *errp is not nil.
+func Wrapf(errp *error, format string, args ...any) {
+	if *errp != nil {
+		*errp = fmt.Errorf("%s: %w", fmt.Sprintf(format, args...), *errp)
+	}
+}

jsonschema/json_pointer.go

@@ -26,6 +26,8 @@ import (
 	"reflect"
 	"strconv"
 	"strings"
+
+	"github.com/modelcontextprotocol/go-sdk/internal/util"
 )
 
 var (
@@ -69,7 +71,7 @@ func parseJSONPointer(ptr string) (segments []string, err error) {
 // This implementation suffices for JSON Schema: pointers are applied only to Schemas,
 // and refer only to Schemas.
 func dereferenceJSONPointer(s *Schema, sptr string) (_ *Schema, err error) {
-	defer wrapf(&err, "JSON Pointer %q", sptr)
+	defer util.Wrapf(&err, "JSON Pointer %q", sptr)
 
 	segments, err := parseJSONPointer(sptr)
 	if err != nil {

jsonschema/util.go

@@ -282,10 +282,3 @@ func assert(cond bool, msg string) {
 		panic("assertion failed: " + msg)
 	}
 }
-
-// wrapf wraps *errp with the given formatted message if *errp is not nil.
-func wrapf(errp *error, format string, args ...any) {
-	if *errp != nil {
-		*errp = fmt.Errorf("%s: %w", fmt.Sprintf(format, args...), *errp)
-	}
-}

jsonschema/validate.go

@@ -73,7 +73,7 @@ type state struct {
 
 // validate validates the reflected value of the instance.
 func (st *state) validate(instance reflect.Value, schema *Schema, callerAnns *annotations) (err error) {
-	defer wrapf(&err, "validating %s", schema)
+	defer util.Wrapf(&err, "validating %s", schema)
 
 	// Maintain a stack for dynamic schema resolution.
 	st.stack = append(st.stack, schema) // push
@@ -607,7 +607,7 @@ func (rs *Resolved) ApplyDefaults(instancep any) error {
 // Leave this as a potentially recursive helper function, because we'll surely want
 // to apply defaults on sub-schemas someday.
 func (st *state) applyDefaults(instancep reflect.Value, schema *Schema) (err error) {
-	defer wrapf(&err, "applyDefaults: schema %s, instance %v", schema, instancep)
+	defer util.Wrapf(&err, "applyDefaults: schema %s, instance %v", schema, instancep)
 
 	instance := instancep.Elem()
 	if instance.Kind() == reflect.Map || instance.Kind() == reflect.Struct {

mcp/resource.go

@@ -16,6 +16,7 @@ import (
 	"strings"
 
 	"github.com/modelcontextprotocol/go-sdk/internal/jsonrpc2"
+	"github.com/modelcontextprotocol/go-sdk/internal/util"
 )
 
 // A ServerResource associates a Resource with its handler.
@@ -122,11 +123,7 @@ func fileRoots(rawRoots []*Root) ([]string, error) {
 
 // fileRoot returns the absolute path for Root.
 func fileRoot(root *Root) (_ string, err error) {
-	defer func() {
-		if err != nil {
-			err = fmt.Errorf("root %q: %w", root.URI, err)
-		}
-	}()
+	defer util.Wrapf(&err, "root %q", root.URI)
 
 	// Convert to absolute file path.
 	rurl, err := url.Parse(root.URI)

mcp/server.go

@@ -18,6 +18,7 @@ import (
 	"sync"
 
 	"github.com/modelcontextprotocol/go-sdk/internal/jsonrpc2"
+	"github.com/modelcontextprotocol/go-sdk/internal/util"
 )
 
 const DefaultPageSize = 1000
@@ -296,11 +297,7 @@ func fileResourceHandler(dir string) ResourceHandler {
 		panic(err)
 	}
 	return func(ctx context.Context, ss *ServerSession, params *ReadResourceParams) (_ *ReadResourceResult, err error) {
-		defer func() {
-			if err != nil {
-				err = fmt.Errorf("reading resource %s: %w", params.URI, err)
-			}
-		}()
+		defer util.Wrapf(&err, "reading resource %s", params.URI)
 
 		// TODO: use a memoizing API here.
 		rootRes, err := ss.ListRoots(ctx, nil)