Add HEADER support to COPY text format

The COPY CSV format supports the HEADER option to output a header
line.  This patch adds the same option to the default text format.  On
input, the HEADER option causes the first line to be skipped, same as
with CSV.

Author: Rémi Lapeyre <remi.lapeyre@lenstra.fr>
Discussion: https://www.postgresql.org/message-id/flat/CAF1-J-0PtCWMeLtswwGV2M70U26n4g33gpe1rcKQqe6wVQDrFA@mail.gmail.com

contrib/file_fdw/expected/file_fdw.out

@@ -50,14 +50,12 @@ CREATE USER MAPPING FOR regress_no_priv_user SERVER file_server;
 -- validator tests
 CREATE FOREIGN TABLE tbl () SERVER file_server OPTIONS (format 'xml');  -- ERROR
 ERROR:  COPY format "xml" not recognized
-CREATE FOREIGN TABLE tbl () SERVER file_server OPTIONS (format 'text', header 'true');      -- ERROR
-ERROR:  COPY HEADER available only in CSV mode
 CREATE FOREIGN TABLE tbl () SERVER file_server OPTIONS (format 'text', quote ':');          -- ERROR
 ERROR:  COPY quote available only in CSV mode
 CREATE FOREIGN TABLE tbl () SERVER file_server OPTIONS (format 'text', escape ':');         -- ERROR
 ERROR:  COPY escape available only in CSV mode
 CREATE FOREIGN TABLE tbl () SERVER file_server OPTIONS (format 'binary', header 'true');    -- ERROR
-ERROR:  COPY HEADER available only in CSV mode
+ERROR:  cannot specify HEADER in BINARY mode
 CREATE FOREIGN TABLE tbl () SERVER file_server OPTIONS (format 'binary', quote ':');        -- ERROR
 ERROR:  COPY quote available only in CSV mode
 CREATE FOREIGN TABLE tbl () SERVER file_server OPTIONS (format 'binary', escape ':');       -- ERROR

contrib/file_fdw/sql/file_fdw.sql

@@ -56,7 +56,6 @@ CREATE USER MAPPING FOR regress_no_priv_user SERVER file_server;
 
 -- validator tests
 CREATE FOREIGN TABLE tbl () SERVER file_server OPTIONS (format 'xml');  -- ERROR
-CREATE FOREIGN TABLE tbl () SERVER file_server OPTIONS (format 'text', header 'true');      -- ERROR
 CREATE FOREIGN TABLE tbl () SERVER file_server OPTIONS (format 'text', quote ':');          -- ERROR
 CREATE FOREIGN TABLE tbl () SERVER file_server OPTIONS (format 'text', escape ':');         -- ERROR
 CREATE FOREIGN TABLE tbl () SERVER file_server OPTIONS (format 'binary', header 'true');    -- ERROR

doc/src/sgml/ref/copy.sgml

@@ -277,7 +277,7 @@ COPY { <replaceable class="parameter">table_name</replaceable> [ ( <replaceable
       Specifies that the file contains a header line with the names of each
       column in the file.  On output, the first line contains the column
       names from the table, and on input, the first line is ignored.
-      This option is allowed only when using <literal>CSV</literal> format.
+      This option is not allowed when using <literal>binary</literal> format.
      </para>
     </listitem>
    </varlistentry>

src/backend/commands/copy.c

@@ -555,10 +555,10 @@ ProcessCopyOptions(ParseState *pstate,
 				 errmsg("COPY delimiter cannot be \"%s\"", opts_out->delim)));
 
 	/* Check header */
-	if (!opts_out->csv_mode && opts_out->header_line)
+	if (opts_out->binary && opts_out->header_line)
 		ereport(ERROR,
 				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-				 errmsg("COPY HEADER available only in CSV mode")));
+				 errmsg("cannot specify HEADER in BINARY mode")));
 
 	/* Check quote */
 	if (!opts_out->csv_mode && opts_out->quote != NULL)

src/backend/commands/copyto.c

@@ -863,8 +863,11 @@ DoCopyTo(CopyToState cstate)
 
 				colname = NameStr(TupleDescAttr(tupDesc, attnum - 1)->attname);
 
-				CopyAttributeOutCSV(cstate, colname, false,
+				if (cstate->opts.csv_mode)
+					CopyAttributeOutCSV(cstate, colname, false,
 									list_length(cstate->attnumlist) == 1);
+				else
+					CopyAttributeOutText(cstate, colname);
 			}
 
 			CopySendEndOfRow(cstate);

src/include/commands/copy.h

@@ -32,7 +32,7 @@ typedef struct CopyFormatOptions
 	bool		binary;			/* binary format? */
 	bool		freeze;			/* freeze rows on loading? */
 	bool		csv_mode;		/* Comma Separated Value format? */
-	bool		header_line;	/* CSV header line? */
+	bool		header_line;	/* header line? */
 	char	   *null_print;		/* NULL marker string (server encoding!) */
 	int			null_print_len; /* length of same */
 	char	   *null_print_client;	/* same converted to file encoding */

src/test/regress/expected/copy.out

@@ -120,6 +120,14 @@ copy copytest3 to stdout csv header;
 c1,"col with , comma","col with "" quote"
 1,a,1
 2,b,2
+create temp table copytest4 (
+	c1 int,
+	"colname with tab: 	" text);
+copy copytest4 from stdin (header);
+copy copytest4 to stdout (header);
+c1	colname with tab: \t
+1	a
+2	b
 -- test copy from with a partitioned table
 create table parted_copytest (
 	a int,

src/test/regress/sql/copy.sql

@@ -160,6 +160,18 @@ this is just a line full of junk that would error out if parsed
 
 copy copytest3 to stdout csv header;
 
+create temp table copytest4 (
+	c1 int,
+	"colname with tab: 	" text);
+
+copy copytest4 from stdin (header);
+this is just a line full of junk that would error out if parsed
+1	a
+2	b
+\.
+
+copy copytest4 to stdout (header);
+
 -- test copy from with a partitioned table
 create table parted_copytest (
 	a int,