recv_parse_log_rec violates its contract re. incomplete recs for MLOG_CHECKPOINT

Copy of

[13 Aug 16:21] Laurynas Biveinis
Description:
recv_parse_log_rec is documented as follows:

** Tries to parse a single log record.
...
@param[in] ptr pointer to a buffer
@param[in] end_ptr end of the buffer
...
@return length of the record, or 0 if the record was not complete */

The record is complete if its length <= end_ptr - ptr, in which case length is returned, otherwise the record is incomplete and zero is returned. This is true for all the record types except for MLOG_CHECKPOINT, for which SIZE_OF_MLOG_CHECKPOINT is returned regardless of end_ptr - ptr. Then the caller handles the incomplete record case itself. This could be a problem for patches that reuse recv_parse_log_rec for something else.

A uniform incomplete record handling regardless of the record type would be cleaner.

This state of things could be a result of MLOG_CHECKPOINT being one-byte record originally, and handled as other one byte records in this function.

How to repeat:
Code analysis.

Suggested fix:
@@ -2338,7 +2349,8 @@ recv_parse_log_rec(
                return(1);
        case MLOG_CHECKPOINT:
                *type = static_cast<mlog_id_t>(*ptr);
- return(SIZE_OF_MLOG_CHECKPOINT);
+ return ((end_ptr - ptr < SIZE_OF_MLOG_CHECKPOINT)
+ ? 0 : SIZE_OF_MLOG_CHECKPOINT);
        case MLOG_MULTI_REC_END | MLOG_SINGLE_REC_FLAG:
        case MLOG_DUMMY_RECORD | MLOG_SINGLE_REC_FLAG:
        case MLOG_CHECKPOINT | MLOG_SINGLE_REC_FLAG:
@@ -2563,9 +2575,6 @@ loop:
                        /* Do nothing */
                        break;
                case MLOG_CHECKPOINT:
- if (end_ptr < ptr + SIZE_OF_MLOG_CHECKPOINT) {
- return(false);
- }
 #if SIZE_OF_MLOG_CHECKPOINT != 1 + 8
 # error SIZE_OF_MLOG_CHECKPOINT != 1 + 8
 #endif