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Preserve large-integer precision when decoding tool arguments #528

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f806932
Preserve large-integer precision when decoding tool arguments
PratikDhanave Jul 17, 2026
081b78e
Reject trailing data after the JSON value in applySchema
PratikDhanave Jul 18, 2026
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13 changes: 12 additions & 1 deletion agent/format/jsonformat/encoding.go
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Original file line number Diff line number Diff line change
Expand Up @@ -3,8 +3,10 @@
package jsonformat

import (
"bytes"
"encoding/json"
"fmt"
"io"

Comment on lines 5 to 10

@PratikDhanave PratikDhanave Jul 18, 2026

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Done — added the io import and a strict trailing-data check (dec.Token() must return io.EOF). Note: validate() can't also use UseNumber — json.Number is a string type the jsonschema validator rejects as a non-integer, which broke every test; left as a comment in the PR.

"github.com/google/jsonschema-go/jsonschema"
)
Expand Down Expand Up @@ -69,9 +71,18 @@ func (f *Format) Normalize(v any) error {
func applySchema(data json.RawMessage, resolved *jsonschema.Resolved) (json.RawMessage, error) {
var v any
if len(data) > 0 {
if err := json.Unmarshal(data, &v); err != nil {
// Decode with UseNumber so integers beyond 2^53 are not silently
// truncated by being decoded into float64 and re-marshalled.
dec := json.NewDecoder(bytes.NewReader(data))
dec.UseNumber()
if err := dec.Decode(&v); err != nil {
Comment on lines +74 to +78

@PratikDhanave PratikDhanave Jul 22, 2026

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The UseNumber decode preserves large-integer precision in the result value the tool receives. validate() re-decodes separately only for schema checking (pre-existing behavior) — json.Number is a string kind the jsonschema validator rejects as non-integer, so it can't be used there. The precision fix applies where it matters (the decoded result) without altering validation.

return nil, fmt.Errorf("unmarshaling arguments: %w", err)
}
// Unlike json.Unmarshal, json.Decoder tolerates trailing data after the
// first value; reject it so validation is not looser than before.
if _, err := dec.Token(); err != io.EOF {
return nil, fmt.Errorf("unmarshaling arguments: unexpected trailing data after JSON value")
}
}
if err := resolved.ApplyDefaults(&v); err != nil {
return nil, fmt.Errorf("applying schema defaults: %w", err)
Expand Down
27 changes: 27 additions & 0 deletions agent/format/jsonformat/encoding_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -133,3 +133,30 @@ func TestNormalizeEmptyStruct(t *testing.T) {
t.Fatalf("Normalize: %v", err)
}
}

// Integer arguments beyond 2^53 must survive Unmarshal: decoding through an
// interface{} as float64 would silently truncate them.
func TestFormat_Unmarshal_PreservesLargeIntegerPrecision(t *testing.T) {
type output struct {
N int64 `json:"n"`
}
format := requireFormat(t, jsonformat.MustFor[output]())
var out output
if err := format.Unmarshal([]byte(`{"n":9007199254740993}`), &out); err != nil {
t.Fatalf("Unmarshal: %v", err)
}
if out.N != 9007199254740993 {
t.Errorf("N = %d, want 9007199254740993 (large-integer precision lost)", out.N)
}
}

func TestFormat_Unmarshal_RejectsTrailingData(t *testing.T) {
type output struct {
N int `json:"n"`
}
format := requireFormat(t, jsonformat.MustFor[output]())
var out output
if err := format.Unmarshal([]byte(`{"n":1} {"n":2}`), &out); err == nil {
t.Fatal("expected an error for trailing data after the JSON value, got nil")
}
}
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