84 lines
1.9 KiB
Go
84 lines
1.9 KiB
Go
// Copyright 2025 The Go MCP SDK Authors. All rights reserved.
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// Use of this source code is governed by the license
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// that can be found in the LICENSE file.
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// Package json provides internal JSON utilities.
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package json
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import (
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"bytes"
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"fmt"
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"io"
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"github.com/segmentio/encoding/json"
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)
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// defaultMaxDepth is the maximum JSON nesting depth accepted by [Unmarshal].
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// Realistic MCP payloads nest only a handful of levels, so 1000 is far more
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// than any legitimate message requires while keeping worst-case parse cost
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// bounded.
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const defaultMaxDepth = 1000
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// errMaxDepthExceeded is returned by [Unmarshal] when the input nests deeper than [defaultMaxDepth].
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var errMaxDepthExceeded = fmt.Errorf("json: exceeded maximum nesting depth of %d", defaultMaxDepth)
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type Decoder struct {
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dec *json.Decoder
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}
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func NewDecoder(r io.Reader) *Decoder {
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dec := json.NewDecoder(r)
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dec.DontMatchCaseInsensitiveStructFields()
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return &Decoder{dec: dec}
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}
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func (d *Decoder) Decode(v any) error {
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return d.dec.Decode(v)
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}
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func Unmarshal(data []byte, v any) error {
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if err := checkMaxDepth(data, defaultMaxDepth); err != nil {
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return err
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}
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return NewDecoder(bytes.NewReader(data)).Decode(v)
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}
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// checkMaxDepth scans data once and reports [errMaxDepthExceeded] if the
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// nesting of JSON objects and arrays exceeds maxDepth. It is a lightweight pass which
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// tracks '{' and '[' against '}' and ']' while skipping over the contents of strings.
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func checkMaxDepth(data []byte, maxDepth int) error {
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var (
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depth int
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inString bool
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escaped bool
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)
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for _, b := range data {
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if inString {
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switch {
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case escaped:
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escaped = false
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case b == '\\':
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escaped = true
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case b == '"':
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inString = false
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}
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continue
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}
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switch b {
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case '"':
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inString = true
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case '{', '[':
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depth++
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if depth > maxDepth {
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return errMaxDepthExceeded
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}
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case '}', ']':
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if depth > 0 {
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depth--
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}
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}
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}
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return nil
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}
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