Support multi-line headers in COPY FROM command.

The COPY FROM command now accepts a non-negative integer for the HEADER option,
allowing multiple header lines to be skipped. This is useful when the input
contains multi-line headers that should be ignored during data import.

Author: Shinya Kato <shinya11.kato@gmail.com>
Co-authored-by: Fujii Masao <masao.fujii@gmail.com>
Reviewed-by: Yugo Nagata <nagata@sraoss.co.jp>
Discussion: https://postgr.es/m/CAOzEurRPxfzbxqeOPF_AGnAUOYf=Wk0we+1LQomPNUNtyZGBZw@mail.gmail.com

src/test/regress/expected/copy.out

@@ -81,6 +81,29 @@ copy copytest4 to stdout (header);
 c1	colname with tab: \t
 1	a
 2	b
+-- test multi-line header line feature
+create temp table copytest5 (c1 int);
+copy copytest5 from stdin (format csv, header 2);
+copy copytest5 to stdout (header);
+c1
+1
+2
+truncate copytest5;
+copy copytest5 from stdin (format csv, header 4);
+select count(*) from copytest5;
+ count 
+-------
+     0
+(1 row)
+
+truncate copytest5;
+copy copytest5 from stdin (format csv, header 5);
+select count(*) from copytest5;
+ count 
+-------
+     0
+(1 row)
+
 -- test copy from with a partitioned table
 create table parted_copytest (
 	a int,
@@ -224,7 +247,7 @@ alter table header_copytest add column c text;
 copy header_copytest to stdout with (header match);
 ERROR:  cannot use "match" with HEADER in COPY TO
 copy header_copytest from stdin with (header wrong_choice);
-ERROR:  header requires a Boolean value or "match"
+ERROR:  header requires a Boolean value, a non-negative integer, or the string "match"
 -- works
 copy header_copytest from stdin with (header match);
 copy header_copytest (c, a, b) from stdin with (header match);

src/test/regress/expected/copy2.out

@@ -132,6 +132,12 @@ COPY x from stdin with (reject_limit 1);
 ERROR:  COPY REJECT_LIMIT requires ON_ERROR to be set to IGNORE
 COPY x from stdin with (on_error ignore, reject_limit 0);
 ERROR:  REJECT_LIMIT (0) must be greater than zero
+COPY x from stdin with (header -1);
+ERROR:  a negative integer value cannot be specified for header
+COPY x from stdin with (header 2.5);
+ERROR:  header requires a Boolean value, a non-negative integer, or the string "match"
+COPY x to stdout with (header 2);
+ERROR:  cannot use multi-line header in COPY TO
 -- too many columns in column list: should fail
 COPY x (a, b, c, d, e, d, c) from stdin;
 ERROR:  column "d" specified more than once

src/test/regress/sql/copy.sql

@@ -94,6 +94,36 @@ this is just a line full of junk that would error out if parsed
 
 copy copytest4 to stdout (header);
 
+-- test multi-line header line feature
+
+create temp table copytest5 (c1 int);
+
+copy copytest5 from stdin (format csv, header 2);
+this is a first header line.
+this is a second header line.
+1
+2
+\.
+copy copytest5 to stdout (header);
+
+truncate copytest5;
+copy copytest5 from stdin (format csv, header 4);
+this is a first header line.
+this is a second header line.
+1
+2
+\.
+select count(*) from copytest5;
+
+truncate copytest5;
+copy copytest5 from stdin (format csv, header 5);
+this is a first header line.
+this is a second header line.
+1
+2
+\.
+select count(*) from copytest5;
+
 -- test copy from with a partitioned table
 create table parted_copytest (
 	a int,

src/test/regress/sql/copy2.sql

@@ -90,6 +90,9 @@ COPY x to stdout (format BINARY, on_error unsupported);
 COPY x from stdin (log_verbosity unsupported);
 COPY x from stdin with (reject_limit 1);
 COPY x from stdin with (on_error ignore, reject_limit 0);
+COPY x from stdin with (header -1);
+COPY x from stdin with (header 2.5);
+COPY x to stdout with (header 2);
 
 -- too many columns in column list: should fail
 COPY x (a, b, c, d, e, d, c) from stdin;