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Merged
merged 4 commits into from
Sep 22, 2025
Merged

mcp: update to jsonschema that does not validate structs #511

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bd8c842
mcp: update to jsonschema that does not validate structs
jba Sep 22, 2025
a205a5a
fix toolschemas
jba Sep 22, 2025
9744f55
fix toolschemas
jba Sep 22, 2025
7f76d2e
fix TypeSchemas
jba Sep 22, 2025
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2 changes: 1 addition & 1 deletion examples/server/auth-middleware/go.mod
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Original file line number Diff line number Diff line change
Expand Up @@ -8,7 +8,7 @@ require (
)

require (
github.com/google/jsonschema-go v0.2.3 // indirect
github.com/google/jsonschema-go v0.2.4-0.20250922144851-e08864c65371 // indirect
github.com/yosida95/uritemplate/v3 v3.0.2 // indirect
)

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4 changes: 2 additions & 2 deletions examples/server/auth-middleware/go.sum
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Original file line number Diff line number Diff line change
Expand Up @@ -2,8 +2,8 @@ github.com/golang-jwt/jwt/v5 v5.2.2 h1:Rl4B7itRWVtYIHFrSNd7vhTiz9UpLdi6gZhZ3wEeD
github.com/golang-jwt/jwt/v5 v5.2.2/go.mod h1:pqrtFR0X4osieyHYxtmOUWsAWrfe1Q5UVIyoH402zdk=
github.com/google/go-cmp v0.7.0 h1:wk8382ETsv4JYUZwIsn6YpYiWiBsYLSJiTsyBybVuN8=
github.com/google/go-cmp v0.7.0/go.mod h1:pXiqmnSA92OHEEa9HXL2W4E7lf9JzCmGVUdgjX3N/iU=
github.com/google/jsonschema-go v0.2.3 h1:dkP3B96OtZKKFvdrUSaDkL+YDx8Uw9uC4Y+eukpCnmM=
github.com/google/jsonschema-go v0.2.3/go.mod h1:r5quNTdLOYEz95Ru18zA0ydNbBuYoo9tgaYcxEYhJVE=
github.com/google/jsonschema-go v0.2.4-0.20250922144851-e08864c65371 h1:e1VCqWtKpTYBOBhPcgGV5whTlMFpTbH5Ghm56wpxBsk=
github.com/google/jsonschema-go v0.2.4-0.20250922144851-e08864c65371/go.mod h1:r5quNTdLOYEz95Ru18zA0ydNbBuYoo9tgaYcxEYhJVE=
github.com/yosida95/uritemplate/v3 v3.0.2 h1:Ed3Oyj9yrmi9087+NczuL5BwkIc4wvTb5zIM+UJPGz4=
github.com/yosida95/uritemplate/v3 v3.0.2/go.mod h1:ILOh0sOhIJR3+L/8afwt/kE++YT040gmv5BQTMR2HP4=
golang.org/x/tools v0.34.0 h1:qIpSLOxeCYGg9TrcJokLBG4KFA6d795g0xkBkiESGlo=
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2 changes: 1 addition & 1 deletion examples/server/rate-limiting/go.mod
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Original file line number Diff line number Diff line change
Expand Up @@ -8,7 +8,7 @@ require (
)

require (
github.com/google/jsonschema-go v0.2.3 // indirect
github.com/google/jsonschema-go v0.2.4-0.20250922144851-e08864c65371 // indirect
github.com/yosida95/uritemplate/v3 v3.0.2 // indirect
)

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4 changes: 2 additions & 2 deletions examples/server/rate-limiting/go.sum
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Original file line number Diff line number Diff line change
@@ -1,7 +1,7 @@
github.com/google/go-cmp v0.7.0 h1:wk8382ETsv4JYUZwIsn6YpYiWiBsYLSJiTsyBybVuN8=
github.com/google/go-cmp v0.7.0/go.mod h1:pXiqmnSA92OHEEa9HXL2W4E7lf9JzCmGVUdgjX3N/iU=
github.com/google/jsonschema-go v0.2.3 h1:dkP3B96OtZKKFvdrUSaDkL+YDx8Uw9uC4Y+eukpCnmM=
github.com/google/jsonschema-go v0.2.3/go.mod h1:r5quNTdLOYEz95Ru18zA0ydNbBuYoo9tgaYcxEYhJVE=
github.com/google/jsonschema-go v0.2.4-0.20250922144851-e08864c65371 h1:e1VCqWtKpTYBOBhPcgGV5whTlMFpTbH5Ghm56wpxBsk=
github.com/google/jsonschema-go v0.2.4-0.20250922144851-e08864c65371/go.mod h1:r5quNTdLOYEz95Ru18zA0ydNbBuYoo9tgaYcxEYhJVE=
github.com/yosida95/uritemplate/v3 v3.0.2 h1:Ed3Oyj9yrmi9087+NczuL5BwkIc4wvTb5zIM+UJPGz4=
github.com/yosida95/uritemplate/v3 v3.0.2/go.mod h1:ILOh0sOhIJR3+L/8afwt/kE++YT040gmv5BQTMR2HP4=
golang.org/x/time v0.12.0 h1:ScB/8o8olJvc+CQPWrK3fPZNfh7qgwCrY0zJmoEQLSE=
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73 changes: 47 additions & 26 deletions examples/server/toolschemas/main.go
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Original file line number Diff line number Diff line change
Expand Up @@ -58,11 +58,11 @@
if err := json.Unmarshal(req.Params.Arguments, &input); err != nil {
return errf("failed to unmarshal arguments: %v", err), nil
}
if err := t.inputSchema.Validate(input); err != nil {
if err := validateStruct(input, t.inputSchema); err != nil {
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This isn't right: once we re-marshal, we're no longer validating the original JSON.

For example, suppose the input contains "foo": 0, and the struct has omitempty for the Foo field, and "foo" is required. Then the original input is valid, but the re-marshalled input is not.

This is why we should expose helpers for this...

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Good point!

return errf("invalid input: %v", err), nil
}
output := Output{Greeting: "Hi " + input.Name}
if err := t.outputSchema.Validate(output); err != nil {
if err := validateStruct(output, t.outputSchema); err != nil {
return errf("tool produced invalid output: %v", err), nil
}
outputJSON, err := json.Marshal(output)
Expand All @@ -75,6 +75,50 @@
}, nil
}

// validateStruct validates x against schema by first changing the struct to
// a map[string]any, then validating that.
func validateStruct(x any, res *jsonschema.Resolved) error {
data, err := json.Marshal(x)
if err != nil {
return err
}
var m map[string]any
if err := json.Unmarshal(data, &m); err != nil {
return err
}
return res.Validate(m)
}

var (
inputSchema = &jsonschema.Schema{
Type: "object",
Properties: map[string]*jsonschema.Schema{
"name": {Type: "string", MaxLength: jsonschema.Ptr(10)},
},
}
outputSchema = &jsonschema.Schema{
Type: "object",
Properties: map[string]*jsonschema.Schema{
"greeting": {Type: "string"},
},
}
)

func newManualGreeter() (*manualGreeter, error) {
resIn, err := inputSchema.Resolve(nil)
if err != nil {
return nil, err
}
resOut, err := outputSchema.Resolve(nil)
if err != nil {
return nil, err
}
return &manualGreeter{
inputSchema: resIn,
outputSchema: resOut,
}, nil
}

func main() {
server := mcp.NewServer(&mcp.Implementation{Name: "greeter"}, nil)

Expand All @@ -90,30 +134,7 @@
//
// We don't need to do all this work: below, we use jsonschema.For to start
// from the default schema.
var (
manual manualGreeter
err error
)
inputSchema := &jsonschema.Schema{
Type: "object",
Properties: map[string]*jsonschema.Schema{
"name": {Type: "string", MaxLength: jsonschema.Ptr(10)},
},
}
manual.inputSchema, err = inputSchema.Resolve(nil)
if err != nil {
log.Fatal(err)
}
outputSchema := &jsonschema.Schema{
Type: "object",
Properties: map[string]*jsonschema.Schema{
"greeting": {Type: "string"},
},
}
manual.outputSchema, err = outputSchema.Resolve(nil)
if err != nil {
log.Fatal(err)
}
manual, err := newManualGreeter()

Check failure on line 137 in examples/server/toolschemas/main.go

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this value of err is never used (SA4006)
server.AddTool(&mcp.Tool{
Name: "manual greeting",
InputSchema: inputSchema,
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31 changes: 31 additions & 0 deletions examples/server/toolschemas/main_test.go
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Original file line number Diff line number Diff line change
@@ -0,0 +1,31 @@
// Copyright 2025 The Go MCP SDK Authors. All rights reserved.
// Use of this source code is governed by an MIT-style
// license that can be found in the LICENSE file.

package main

import (
"context"
"encoding/json"
"testing"

"github.com/modelcontextprotocol/go-sdk/mcp"
)

func TestGreet(t *testing.T) {
manual, err := newManualGreeter()
if err != nil {
t.Fatal(err)
}
res, err := manual.greet(context.Background(), &mcp.CallToolRequest{
Params: &mcp.CallToolParamsRaw{
Arguments: json.RawMessage(`{"name": "Bob"}`),
},
})
if err != nil {
t.Fatal(err)
}
if res.IsError {
t.Fatalf("tool error: %q", res.Content[0].(*mcp.TextContent).Text)
}
}
2 changes: 1 addition & 1 deletion go.mod
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Original file line number Diff line number Diff line change
Expand Up @@ -5,7 +5,7 @@ go 1.23.0
require (
github.com/golang-jwt/jwt/v5 v5.2.2
github.com/google/go-cmp v0.7.0
github.com/google/jsonschema-go v0.2.3
github.com/google/jsonschema-go v0.2.4-0.20250922144851-e08864c65371
github.com/yosida95/uritemplate/v3 v3.0.2
golang.org/x/tools v0.34.0
)
2 changes: 2 additions & 0 deletions go.sum
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Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,8 @@ github.com/google/go-cmp v0.7.0 h1:wk8382ETsv4JYUZwIsn6YpYiWiBsYLSJiTsyBybVuN8=
github.com/google/go-cmp v0.7.0/go.mod h1:pXiqmnSA92OHEEa9HXL2W4E7lf9JzCmGVUdgjX3N/iU=
github.com/google/jsonschema-go v0.2.3 h1:dkP3B96OtZKKFvdrUSaDkL+YDx8Uw9uC4Y+eukpCnmM=
github.com/google/jsonschema-go v0.2.3/go.mod h1:r5quNTdLOYEz95Ru18zA0ydNbBuYoo9tgaYcxEYhJVE=
github.com/google/jsonschema-go v0.2.4-0.20250922144851-e08864c65371 h1:e1VCqWtKpTYBOBhPcgGV5whTlMFpTbH5Ghm56wpxBsk=
github.com/google/jsonschema-go v0.2.4-0.20250922144851-e08864c65371/go.mod h1:r5quNTdLOYEz95Ru18zA0ydNbBuYoo9tgaYcxEYhJVE=
github.com/yosida95/uritemplate/v3 v3.0.2 h1:Ed3Oyj9yrmi9087+NczuL5BwkIc4wvTb5zIM+UJPGz4=
github.com/yosida95/uritemplate/v3 v3.0.2/go.mod h1:ILOh0sOhIJR3+L/8afwt/kE++YT040gmv5BQTMR2HP4=
golang.org/x/tools v0.34.0 h1:qIpSLOxeCYGg9TrcJokLBG4KFA6d795g0xkBkiESGlo=
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