Error while copying a large file in pg_rewind

Hello all,

pg_rewind throws the following error when there is a file of large
size available in the Slave server's data directory.

unexpected result while sending file list: ERROR: value "2148000000"
is out of range for type integer
CONTEXT: COPY fetchchunks, line 2402, column begin: "2148000000"

How to reproduce
----------------------------
1. Set up replication between Server A(master) and Server B(slave)

2. Promote the slave server(Server B )

3. Stop the old master (Server A)

4. Create a large file in the newly promoted master's (Server B) data
directory using the below command

dd if=/dev/zero of=large.file bs=1024 count=4000000

[root(at)localhost data]# dd if=/dev/zero of=large.file bs=1024 count=4000000
4000000+0 records in
4000000+0 records out
4096000000 bytes (4.1 GB) copied, 8.32263 s, 492 MB/s

5. Execute pg_rewind command from old master(server A)

./pg_rewind -D /home/enterprisedb/master/ --debug --progress
--source-server="port=5661 user=enterprisedb dbname=edb"

IMHO, it seems to be a bug in pg_rewind.

As mentioned in pg_rewind documentation, there are few files which are
copied in whole.

"Copy all other files such as pg_xact and configuration files from the
source cluster to the target cluster (everything except the relation
files)." -- https://www.postgresql.org/docs/devel/static/app-pgrewind.html

Those files are copied in max CHUNKSIZE(default 1000000) bytes at a
time. In the process, pg_rewind creates a table with the following
schema and loads information about blocks that need to be copied.

CREATE TEMPORARY TABLE fetchchunks(path text, begin int4, len int4);

postgres=# select * from fetchchunks where begin != 0;
path | begin | len
-----------------------------------------+----------+---------
pg_wal/000000010000000000000002 | 1000000 | 1000000
pg_wal/000000010000000000000002 | 2000000 | 1000000
pg_wal/000000010000000000000002 | 3000000 | 1000000
pg_wal/000000010000000000000002 | 4000000 | 1000000
......
and so on.

The range for begin is between -2147483648 to +2147483647. For a 4GB
file, begin definitely goes beyond 2147483647 and it throws the
following error:
unexpected result while sending file list: ERROR: value "2148000000"
is out of range for type integer
CONTEXT: COPY fetchchunks, line 2659, column begin: "2148000000"

I guess we've to change the data type to bigint. Also, we need some
implementation of ntohl() for 8-byte data types. I've attached a
script to reproduce the error and a draft patch.

--
Thanks & Regards,
Kuntal Ghosh
EnterpriseDB: http://www.enterprisedb.com