Implement IgnoreExtraFieldsFromTextual

codec.go

@@ -50,6 +50,12 @@ type CodecOption struct {
 	// Primarily used to handle edge cases where some Avro implementations allow string representations of null.
 	EnableStringNull bool
 
+	// IgnoreExtraFieldsFromTextual controls how unknown fields are handled during textual (JSON) decoding.
+	// When true, fields in the JSON input that are not defined in the Avro schema will be
+	// silently skipped. This enables forward-compatible schema evolution where consumers
+	// can process messages from producers using newer schemas with additional fields.
+	// When false (default), unknown fields cause a "cannot determine codec" error.
+	IgnoreExtraFieldsFromTextual bool
 	// EnableDecimalBinarySpecCompliantEncoding controls whether decimal values use
 	// Avro 1.10.2 spec-compliant encoding. When true:
 	// - Binary encoding uses two's-complement representation of the unscaled integer
@@ -91,6 +97,7 @@ type codecBuilder struct {
 func DefaultCodecOption() *CodecOption {
 	return &CodecOption{
 		EnableStringNull:                         true,
+		IgnoreExtraFieldsFromTextual:             false,
 		EnableDecimalBinarySpecCompliantEncoding: false,
 	}
 }

json_utils.go

@@ -0,0 +1,234 @@
+// Copyright [2019] LinkedIn Corp. Licensed under the Apache License, Version
+// 2.0 (the "License"); you may not use this file except in compliance with the
+// License.  You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+
+package goavro
+
+import (
+	"fmt"
+	"io"
+)
+
+// skipJSONValue advances the buffer past a single JSON value (object, array, string, number, bool, null).
+// This is used when IgnoreExtraFieldsFromTextual is enabled to skip over values of unknown fields.
+func skipJSONValue(buf []byte) ([]byte, error) {
+	if buf, _ = advanceToNonWhitespace(buf); len(buf) == 0 {
+		return nil, io.ErrShortBuffer
+	}
+
+	switch buf[0] {
+	case '{':
+		// Skip object: find matching closing brace
+		return skipJSONObject(buf)
+	case '[':
+		// Skip array: find matching closing bracket
+		return skipJSONArray(buf)
+	case '"':
+		// Skip string: find closing quote (handling escapes)
+		return skipJSONString(buf)
+	case 't':
+		// true
+		if len(buf) >= 4 && string(buf[:4]) == "true" {
+			return buf[4:], nil
+		}
+		return nil, fmt.Errorf("cannot skip JSON value: invalid literal starting with 't'")
+	case 'f':
+		// false
+		if len(buf) >= 5 && string(buf[:5]) == "false" {
+			return buf[5:], nil
+		}
+		return nil, fmt.Errorf("cannot skip JSON value: invalid literal starting with 'f'")
+	case 'n':
+		// null
+		if len(buf) >= 4 && string(buf[:4]) == "null" {
+			return buf[4:], nil
+		}
+		return nil, fmt.Errorf("cannot skip JSON value: invalid literal starting with 'n'")
+	default:
+		// Must be a number (or invalid)
+		if buf[0] == '-' || (buf[0] >= '0' && buf[0] <= '9') {
+			return skipJSONNumber(buf)
+		}
+		return nil, fmt.Errorf("cannot skip JSON value: unexpected character: %q", buf[0])
+	}
+}
+
+// skipJSONObject skips a JSON object starting with '{' and returns the buffer after the closing '}'.
+func skipJSONObject(buf []byte) ([]byte, error) {
+	if len(buf) == 0 || buf[0] != '{' {
+		return nil, fmt.Errorf("cannot skip JSON object: expected '{'")
+	}
+	buf = buf[1:] // consume '{'
+	var err error
+
+	if buf, _ = advanceToNonWhitespace(buf); len(buf) == 0 {
+		return nil, io.ErrShortBuffer
+	}
+
+	// Handle empty object
+	if buf[0] == '}' {
+		return buf[1:], nil
+	}
+
+	for len(buf) > 0 {
+		// Skip key (string)
+		if buf, err = skipJSONString(buf); err != nil {
+			return nil, err
+		}
+		// Skip colon
+		if buf, err = advanceAndConsume(buf, ':'); err != nil {
+			return nil, err
+		}
+		// Skip value
+		if buf, err = skipJSONValue(buf); err != nil {
+			return nil, err
+		}
+		// Check for comma or closing brace
+		if buf, _ = advanceToNonWhitespace(buf); len(buf) == 0 {
+			return nil, io.ErrShortBuffer
+		}
+		switch buf[0] {
+		case '}':
+			return buf[1:], nil
+		case ',':
+			buf = buf[1:]
+			if buf, _ = advanceToNonWhitespace(buf); len(buf) == 0 {
+				return nil, io.ErrShortBuffer
+			}
+		default:
+			return nil, fmt.Errorf("cannot skip JSON object: expected ',' or '}'; received: %q", buf[0])
+		}
+	}
+	return nil, io.ErrShortBuffer
+}
+
+// skipJSONArray skips a JSON array starting with '[' and returns the buffer after the closing ']'.
+func skipJSONArray(buf []byte) ([]byte, error) {
+	if len(buf) == 0 || buf[0] != '[' {
+		return nil, fmt.Errorf("cannot skip JSON array: expected '['")
+	}
+	buf = buf[1:] // consume '['
+	var err error
+
+	if buf, _ = advanceToNonWhitespace(buf); len(buf) == 0 {
+		return nil, io.ErrShortBuffer
+	}
+
+	// Handle empty array
+	if buf[0] == ']' {
+		return buf[1:], nil
+	}
+
+	for len(buf) > 0 {
+		// Skip value
+		if buf, err = skipJSONValue(buf); err != nil {
+			return nil, err
+		}
+		// Check for comma or closing bracket
+		if buf, _ = advanceToNonWhitespace(buf); len(buf) == 0 {
+			return nil, io.ErrShortBuffer
+		}
+		switch buf[0] {
+		case ']':
+			return buf[1:], nil
+		case ',':
+			buf = buf[1:]
+			if buf, _ = advanceToNonWhitespace(buf); len(buf) == 0 {
+				return nil, io.ErrShortBuffer
+			}
+		default:
+			return nil, fmt.Errorf("cannot skip JSON array: expected ',' or ']'; received: %q", buf[0])
+		}
+	}
+	return nil, io.ErrShortBuffer
+}
+
+// skipJSONString skips a JSON string starting with '"' and returns the buffer after the closing '"'.
+func skipJSONString(buf []byte) ([]byte, error) {
+	if buf, _ = advanceToNonWhitespace(buf); len(buf) == 0 {
+		return nil, io.ErrShortBuffer
+	}
+	if buf[0] != '"' {
+		return nil, fmt.Errorf("cannot skip JSON string: expected '\"'")
+	}
+	buf = buf[1:] // consume opening quote
+
+	for i := 0; i < len(buf); i++ {
+		switch buf[i] {
+		case '\\':
+			// Skip the next character (escaped)
+			i++
+		case '"':
+			// Found closing quote
+			return buf[i+1:], nil
+		}
+	}
+	return nil, io.ErrShortBuffer
+}
+
+// skipJSONNumber skips a JSON number and returns the buffer after the number.
+func skipJSONNumber(buf []byte) ([]byte, error) {
+	if len(buf) == 0 {
+		return nil, io.ErrShortBuffer
+	}
+
+	i := 0
+
+	// Optional minus sign
+	if buf[i] == '-' {
+		i++
+		if i >= len(buf) {
+			return nil, io.ErrShortBuffer
+		}
+	}
+
+	// Integer part
+	switch {
+	case buf[i] == '0':
+		i++
+	case buf[i] >= '1' && buf[i] <= '9':
+		for i < len(buf) && buf[i] >= '0' && buf[i] <= '9' {
+			i++
+		}
+	default:
+		return nil, fmt.Errorf("cannot skip JSON number: invalid character: %q", buf[i])
+	}
+
+	// Optional fractional part
+	if i < len(buf) && buf[i] == '.' {
+		i++
+		if i >= len(buf) || buf[i] < '0' || buf[i] > '9' {
+			return nil, fmt.Errorf("cannot skip JSON number: expected digit after decimal point")
+		}
+		for i < len(buf) && buf[i] >= '0' && buf[i] <= '9' {
+			i++
+		}
+	}
+
+	// Optional exponent part
+	if i < len(buf) && (buf[i] == 'e' || buf[i] == 'E') {
+		i++
+		if i >= len(buf) {
+			return nil, io.ErrShortBuffer
+		}
+		if buf[i] == '+' || buf[i] == '-' {
+			i++
+			if i >= len(buf) {
+				return nil, io.ErrShortBuffer
+			}
+		}
+		if buf[i] < '0' || buf[i] > '9' {
+			return nil, fmt.Errorf("cannot skip JSON number: expected digit in exponent")
+		}
+		for i < len(buf) && buf[i] >= '0' && buf[i] <= '9' {
+			i++
+		}
+	}
+
+	return buf[i:], nil
+}