Bug#22540: Incorrect value in column End_log_pos of SHOW BINLOG EVENTS using InnoDB

previous correction didn't. make sure "tail" is fixed up
when filling cache several times; rework formulae.

mysql-test/t/binlog.test

@@ -4,7 +4,6 @@
 -- source include/have_log_bin.inc
 -- source include/not_embedded.inc
 -- source include/have_innodb.inc
--- source include/have_log_bin.inc
 
 --disable_warnings
 drop table if exists t1, t2;
@@ -137,4 +136,34 @@ show binlog events from 0;
 
 set session autocommit = @ac;
 
+# now show that nothing breaks if we need to read from the cache more
+# than once, resulting in split event-headers
+
+set @bcs = @@binlog_cache_size;
+set @ac = @@autocommit;
+
+set global binlog_cache_size=4096;
+set autocommit= 0;
+reset master;
+
+create table t1 (a int) engine=innodb;
+
+let $1=400;
+disable_query_log;
+begin;
+while ($1)
+{
+ eval insert into t1 values( $1 );
+ dec $1;
+}
+commit;
+enable_query_log;
+
+show binlog events from 0;
+
+drop table t1;
+
+set global binlog_cache_size=@bcs;
+set session autocommit = @ac;
+
 --echo End of 5.0 tests

sql/log.cc

@@ -1918,30 +1918,24 @@ bool MYSQL_LOG::write(THD *thd, IO_CACHE *cache, Log_event *commit_event)
         memcpy((char *)cache->read_pos, &header[carry], LOG_EVENT_HEADER_LEN - carry);
 
         /* next event header at ... */
-        hdr_offs = LOG_EVENT_HEADER_LEN - carry +
-          uint4korr(&header[EVENT_LEN_OFFSET]);
+        hdr_offs = uint4korr(&header[EVENT_LEN_OFFSET]) - carry;
 
         carry= 0;
       }
 
       /* if there is anything to write, process it. */
 
-      if(likely(length > 0))
+      if (likely(length > 0))
       {
         /*
-          next header beyond current read-buffer? we'll get it later
-          (though not necessarily in the very next iteration).
+          process all event-headers in this (partial) cache.
+          if next header is beyond current read-buffer,
+          we'll get it later (though not necessarily in the
+          very next iteration, just "eventually").
         */
 
-        if (hdr_offs >= length)
-          hdr_offs -= length;
-        else
+        while (hdr_offs < length)
         {
-
-          /* process all event-headers in this (partial) cache. */
-
-          do {
-
           /*
             partial header only? save what we can get, process once
             we get the rest.
@@ -1968,8 +1962,17 @@ bool MYSQL_LOG::write(THD *thd, IO_CACHE *cache, Log_event *commit_event)
             hdr_offs += uint4korr(log_pos);
 
           }
-          } while (hdr_offs < length);
         }
+
+        /*
+          Adjust hdr_offs. Note that this doesn't mean it will necessarily
+          be valid in the next iteration; if the current event is very long,
+          it may take a couple of read-iterations (and subsequent fixings
+          of hdr_offs) for it to become valid again.
+          if we had a split header, hdr_offs was already fixed above.
+        */
+        if (carry == 0)
+          hdr_offs -= length;
       }
 
       /* Write data to the binary log file */