Fix potential memory issues

[grantzhou]

Summary of Fixes:

1. Buffer Overflow Prevention (src/backend/converter/format_converter.c):

   • Function: derive_decimal_string_from_byte
   • Issue: The function used a fixed-size stack buffer char digits[128] to store the decimal representation of a byte array. For arbitrarily large precision numbers (supported by Debezium/Java BigDecimal), this could overflow if the input byte array exceeded approximately 53 bytes.
   • Fix: Changed digits to be dynamically allocated (palloc) based on the input length (len * 3 + 1), ensuring it can hold any converted value. Added pfree(digits) before returning.

2. Memory Leak Fix (src/backend/converter/format_converter.c):

   • Function: handle_base64_to_numeric_with_scale
   • Issue: The function called derive_decimal_string_from_byte which returns an allocated string (value), but never freed it after using it to format the buffer. This would cause a memory leak for every numeric value processed.
   • Fix: Added pfree(value) immediately after it is used.

3. Crash Prevention & Memory Leak Fix (src/backend/synchdb/synchdb.c):

   • Function: dbz_engine_get_offset
   • Issue 1 (Crash): The code called *(env)->CallObjectMethod(...) to get a Java string. It checked for JNI exceptions, but did not check if the returned result was NULL (which can happen without an exception). Passing NULL to (*env)->GetStringUTFChars would
     cause a JVM crash.
   • Issue 2 (Leak): The local reference jdstdb (created via NewStringUTF) was not being deleted in either the exception handling block or the success path, leading to a JNI local reference leak.
   • Fix: Added an explicit check if (result == NULL) to handle null returns safely. Added (*env)->DeleteLocalRef(env, jdstdb) to all exit paths (exception, null-return, and success).

Additional Notes:

• The codebase relies heavily on JNI. Ensure that the JVM is properly configured and that DBZ_ENGINE_JAR_FILE is accessible.
• The OLR client uses a large buffer (64MB default). Monitor memory usage if running many OLR connectors.
• Error handling in synchdb.c often sets a shared memory error message. Ensure monitoring tools check this state.