encoder, reencoder: Distinguish between syntax errors and I/O errors

4 files changed, 46 insertions, 3 deletions

diff --git a/ReleaseNotes.md b/ReleaseNotes.md
index 9974f0e..e00bf10 100644
--- a/ReleaseNotes.md
+++ b/ReleaseNotes.md
@@ -8,6 +8,13 @@
      a user of lowmemjson's native APIs does not need to import
      `encoding/json` or compat/json in order to use them.
 
+   - Encoder, ReEncoder: If there was an error writing to the output
+     stream, it may have returned a `*ReEncodeSyntaxError` even though
+     it's not a syntax issue, or may have returned the underlying
+     error without wrapping it.  If there is an error writing to the
+     output, Encoder and ReEncoder now return `*EncodeWriteError` and
+     `*ReEncodeWriteError` respectively.
+
 # v0.3.5 (2023-02-10)
 
   Theme: Compatibility bugfixes
diff --git a/encode.go b/encode.go
index b6541cd..d39c862 100644
--- a/encode.go
+++ b/encode.go
@@ -83,6 +83,12 @@ func (enc *Encoder) Encode(obj any) (err error) {
 		enc.w.par.Reset()
 	}
 	if err := encode(enc.w, reflect.ValueOf(obj), enc.w.BackslashEscape, false, 0, map[any]struct{}{}); err != nil {
+		if rwe, ok := err.(*ReEncodeWriteError); ok {
+			err = &EncodeWriteError{
+				Err:    rwe.Err,
+				Offset: rwe.Offset,
+			}
+		}
 		return err
 	}
 	if enc.isRoot {
diff --git a/errors.go b/errors.go
index 0a47db4..516018c 100644
--- a/errors.go
+++ b/errors.go
@@ -121,6 +121,18 @@ func (e *DecodeError) Unwrap() error { return e.Err }
 
 // encode errors ///////////////////////////////////////////////////////////////////////////////////
 
+// A EncodeWriteError is returned from Encode if there is an error
+// writing to the output stream.
+type EncodeWriteError struct {
+	Err    error
+	Offset int64
+}
+
+func (e *EncodeWriteError) Error() string {
+	return fmt.Sprintf("json: I/O error at output byte %v: %v", e.Offset, e.Err)
+}
+func (e *EncodeWriteError) Unwrap() error { return e.Err }
+
 // An EncodeTypeError is returned by Encode when attempting to encode
 // an unsupported type.
 //
@@ -155,6 +167,18 @@ func (e *EncodeMethodError) Unwrap() error { return e.Err }
 
 // reencode errors /////////////////////////////////////////////////////////////////////////////////
 
+// A ReEncodeWriteError is returned from ReEncoder's methods if there
+// is an error writing to the output stream.
+type ReEncodeWriteError struct {
+	Err    error
+	Offset int64
+}
+
+func (e *ReEncodeWriteError) Error() string {
+	return fmt.Sprintf("json: I/O error at output byte %v: %v", e.Offset, e.Err)
+}
+func (e *ReEncodeWriteError) Unwrap() error { return e.Err }
+
 // A ReEncodeSyntaxError is returned from ReEncoder's methods if there
 // is a syntax error in the input.
 type ReEncodeSyntaxError struct {
diff --git a/reencode.go b/reencode.go
index e48c58c..d19dc1a 100644
--- a/reencode.go
+++ b/reencode.go
@@ -232,7 +232,7 @@ func (enc *ReEncoder) Close() error {
 	}
 	if len(enc.barriers) == 0 {
 		if err := enc.handleRune(0, jsonparse.RuneTypeError, enc.stackSize()); err != nil {
-			enc.err = &ReEncodeSyntaxError{
+			enc.err = &ReEncodeWriteError{
 				Err:    err,
 				Offset: enc.inputPos,
 			}
@@ -274,8 +274,14 @@ rehandle:
 		}
 		return enc.written, enc.err
 	}
-	enc.err = enc.handleRune(c, t, enc.stackSize())
-	if enc.err == nil && t == jsonparse.RuneTypeEOF {
+	if err := enc.handleRune(c, t, enc.stackSize()); err != nil {
+		enc.err = &ReEncodeWriteError{
+			Err:    err,
+			Offset: enc.inputPos,
+		}
+		return enc.written, enc.err
+	}
+	if t == jsonparse.RuneTypeEOF {
 		if enc.AllowMultipleValues && len(enc.barriers) == 0 {
 			enc.par.Reset()
 			goto rehandle