encoding/json: report true from v2 Decoder.More when an error is pending

Historically, Decoder.More reports true when the next read will
return an error. Adjust the v2 Decoder to follow this behavior.

Fixes #76467

Change-Id: I03bfa391e4e89ada8ca869db43c1d0bb63cc0413
Reviewed-on: https://go-review.googlesource.com/c/go/+/728300
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Auto-Submit: Damien Neil <dneil@google.com>
Reviewed-by: Joseph Tsai <joetsai@digital-static.net>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

diff --git a/src/encoding/json/stream_test.go b/src/encoding/json/stream_test.go
index 0e937cfaa13c783387a8468a5a0ecc6ccff62f98..ba3bc4002b1ceb25c8cc148cf2d1d519fff2adb0 100644 (file)
--- a/src/encoding/json/stream_test.go
+++ b/src/encoding/json/stream_test.go
@@ -459,6 +459,9 @@ func TestDecodeInStream(t *testing.T) {
                {CaseName: Name(""), json: ` \a`, expTokens: []any{
                        &SyntaxError{"invalid character '\\\\' looking for beginning of value", 1},
                }},
+               {CaseName: Name(""), json: `,`, expTokens: []any{
+                       &SyntaxError{"invalid character ',' looking for beginning of value", 0},
+               }},
        }
        for _, tt := range tests {
                t.Run(tt.Name, func(t *testing.T) {
@@ -467,6 +470,15 @@ func TestDecodeInStream(t *testing.T) {
                                var got any
                                var err error
 
+                               wantMore := true
+                               switch want {
+                               case Delim(']'), Delim('}'):
+                                       wantMore = false
+                               }
+                               if got := dec.More(); got != wantMore {
+                                       t.Fatalf("%s:\n\tinput: %s\n\tdec.More() = %v, want %v (next token: %T(%v))", tt.Where, tt.json, got, wantMore, want, want)
+                               }
+
                                if dt, ok := want.(decodeThis); ok {
                                        want = dt.v
                                        err = dec.Decode(&got)

diff --git a/src/encoding/json/v2_stream.go b/src/encoding/json/v2_stream.go
index dcee553ee13336e20548d2324fd40c22e3357636..ca0822cb7336cba4d5ddd87b6c58d1475ac4cae4 100644 (file)
--- a/src/encoding/json/v2_stream.go
+++ b/src/encoding/json/v2_stream.go
@@ -197,6 +197,9 @@ func (d Delim) String() string {
 // to mark the start and end of arrays and objects.
 // Commas and colons are elided.
 func (dec *Decoder) Token() (Token, error) {
+       if dec.err != nil {
+               return nil, dec.err
+       }
        tok, err := dec.dec.ReadToken()
        if err != nil {
                // Historically, v1 would report just [io.EOF] if
@@ -238,7 +241,20 @@ func (dec *Decoder) Token() (Token, error) {
 func (dec *Decoder) More() bool {
        dec.hadPeeked = true
        k := dec.dec.PeekKind()
-       return k > 0 && k != ']' && k != '}'
+       if k == 0 {
+               if dec.err == nil {
+                       // PeekKind doesn't distinguish between EOF and error,
+                       // so read the next token to see which we get.
+                       _, err := dec.dec.ReadToken()
+                       if err == nil {
+                               // This is only possible if jsontext violates its documentation.
+                               err = errors.New("json: successful read after failed peek")
+                       }
+                       dec.err = transformSyntacticError(err)
+               }
+               return dec.err != io.EOF
+       }
+       return k != ']' && k != '}'
 }
 
 // InputOffset returns the input stream byte offset of the current decoder position.

diff --git a/src/encoding/json/v2_stream_test.go b/src/encoding/json/v2_stream_test.go
index 0885631fb5937fb663b6886a18b74c38a83ee83f..d7f9f110848add592652adb40f43eab909f3b640 100644 (file)
--- a/src/encoding/json/v2_stream_test.go
+++ b/src/encoding/json/v2_stream_test.go
@@ -439,6 +439,9 @@ func TestDecodeInStream(t *testing.T) {
                {CaseName: Name(""), json: ` \a`, expTokens: []any{
                        &SyntaxError{"invalid character '\\\\' looking for beginning of value", len64(` `)},
                }},
+               {CaseName: Name(""), json: `,`, expTokens: []any{
+                       &SyntaxError{"invalid character ',' looking for beginning of value", 0},
+               }},
        }
        for _, tt := range tests {
                t.Run(tt.Name, func(t *testing.T) {
@@ -447,6 +450,15 @@ func TestDecodeInStream(t *testing.T) {
                                var got any
                                var err error
 
+                               wantMore := true
+                               switch want {
+                               case Delim(']'), Delim('}'):
+                                       wantMore = false
+                               }
+                               if got := dec.More(); got != wantMore {
+                                       t.Fatalf("%s:\n\tinput: %s\n\tdec.More() = %v, want %v (next token: %T(%v)) rem:%q", tt.Where, tt.json, got, wantMore, want, want, tt.json[dec.InputOffset():])
+                               }
+
                                if dt, ok := want.(decodeThis); ok {
                                        want = dt.v
                                        err = dec.Decode(&got)