MDEV-12720 recovery fails with "Generic error" for ROW_FORMAT=compressed

This bug was introduced in the fix of MDEV-12123, which invoked
page_zip_write_header() in the wrong way.

page_zip_write_header(): Assert that the length is not zero, to
be compatible with page_zip_parse_write_header().

btr_root_raise_and_insert(): Update the uncompressed page and then
invoke page_zip_write_header() with the correct length.

mysql-test/suite/innodb_zip/r/recover.result

+#
+# MDEV-12720 recovery fails with "Generic error"
+# for ROW_FORMAT=compressed
+#
+CREATE TABLE a(i INT PRIMARY KEY AUTO_INCREMENT, s VARCHAR(255)) ENGINE=InnoDB
+ROW_FORMAT=COMPRESSED KEY_BLOCK_SIZE=1;
+BEGIN;
+insert into a(i) select null;
+insert into a select null, uuid() from a a, a b, a c;
+insert into a select null, uuid() from a a, a b, a c;
+insert into a select null, uuid() from a a, a b, a c;
+SET GLOBAL innodb_flush_log_at_trx_commit=1;
+COMMIT;
+SELECT COUNT(*) from a;
+COUNT(*)
+1010
+DROP TABLE a;

mysql-test/suite/innodb_zip/t/recover.test

+--source include/have_innodb.inc
+--source include/have_innodb_max_16k.inc
+--source include/not_embedded.inc
+
+--echo #
+--echo # MDEV-12720 recovery fails with "Generic error"
+--echo # for ROW_FORMAT=compressed
+--echo #
+CREATE TABLE a(i INT PRIMARY KEY AUTO_INCREMENT, s VARCHAR(255)) ENGINE=InnoDB
+ROW_FORMAT=COMPRESSED KEY_BLOCK_SIZE=1;
+
+BEGIN;
+insert into a(i) select null;
+insert into a select null, uuid() from a a, a b, a c;
+insert into a select null, uuid() from a a, a b, a c;
+insert into a select null, uuid() from a a, a b, a c;
+SET GLOBAL innodb_flush_log_at_trx_commit=1;
+COMMIT;
+
+--let $shutdown_timeout=0
+--source include/restart_mysqld.inc
+
+SELECT COUNT(*) from a;
+DROP TABLE a;

storage/innobase/btr/btr0btr.cc

@@ -1991,10 +1991,9 @@ btr_root_raise_and_insert(
 		longer is a leaf page. (Older versions of InnoDB did
 		set PAGE_MAX_TRX_ID on all secondary index pages.) */
 		if (root_page_zip) {
-			page_zip_write_header(
-				root_page_zip,
-				PAGE_HEADER + PAGE_MAX_TRX_ID
-				+ root, 0, mtr);
+			byte* p = PAGE_HEADER + PAGE_MAX_TRX_ID + root;
+			memset(p, 0, 8);
+			page_zip_write_header(root_page_zip, p, 8, mtr);
 		} else {
 			mlog_write_ull(PAGE_HEADER + PAGE_MAX_TRX_ID
 				       + root, 0, mtr);
@@ -2004,10 +2003,9 @@ btr_root_raise_and_insert(
 		root page; on other clustered index pages, we want to reserve
 		the field PAGE_MAX_TRX_ID for future use. */
 		if (new_page_zip) {
-			page_zip_write_header(
-				new_page_zip,
-				PAGE_HEADER + PAGE_MAX_TRX_ID
-				+ new_page, 0, mtr);
+			byte* p = PAGE_HEADER + PAGE_MAX_TRX_ID + new_page;
+			memset(p, 0, 8);
+			page_zip_write_header(new_page_zip, p, 8, mtr);
 		} else {
 			mlog_write_ull(PAGE_HEADER + PAGE_MAX_TRX_ID
 				       + new_page, 0, mtr);

storage/innobase/page/page0zip.cc

@@ -4634,6 +4634,7 @@ page_zip_write_header_log(
 #if PAGE_DATA > 255
 # error "PAGE_DATA > 255"
 #endif
+	ut_ad(length > 0);
 	ut_ad(length < 256);
 
 	/* If no logging is requested, we may return now */