Add header matching mode to COPY FROM

COPY FROM supports the HEADER option to silently discard the header
line from a CSV or text file.  It is possible to load by mistake a
file that matches the expected format, for example, if two text
columns have been swapped, resulting in garbage in the database.

This adds a new option value HEADER MATCH that checks the column names
in the header line against the actual column names and errors out if
they do not match.

Author: Rémi Lapeyre <remi.lapeyre@lenstra.fr>
Reviewed-by: Daniel Verite <daniel@manitou-mail.org>
Reviewed-by: Peter Eisentraut <peter.eisentraut@enterprisedb.com>
Discussion: https://www.postgresql.org/message-id/flat/CAF1-J-0PtCWMeLtswwGV2M70U26n4g33gpe1rcKQqe6wVQDrFA@mail.gmail.com

src/backend/commands/copy.c

@@ -313,6 +313,64 @@ DoCopy(ParseState *pstate, const CopyStmt *stmt,
 		table_close(rel, NoLock);
 }
 
+/*
+ * Extract a CopyHeaderChoice value from a DefElem.  This is like
+ * defGetBoolean() but also accepts the special value "match".
+ */
+static CopyHeaderChoice
+defGetCopyHeaderChoice(DefElem *def)
+{
+	/*
+	 * If no parameter given, assume "true" is meant.
+	 */
+	if (def->arg == NULL)
+		return COPY_HEADER_TRUE;
+
+	/*
+	 * Allow 0, 1, "true", "false", "on", "off", or "match".
+	 */
+	switch (nodeTag(def->arg))
+	{
+		case T_Integer:
+			switch (intVal(def->arg))
+			{
+				case 0:
+					return COPY_HEADER_FALSE;
+				case 1:
+					return COPY_HEADER_TRUE;
+				default:
+					/* otherwise, error out below */
+					break;
+			}
+			break;
+		default:
+			{
+				char	*sval = defGetString(def);
+
+				/*
+				 * The set of strings accepted here should match up with the
+				 * grammar's opt_boolean_or_string production.
+				 */
+				if (pg_strcasecmp(sval, "true") == 0)
+					return COPY_HEADER_TRUE;
+				if (pg_strcasecmp(sval, "false") == 0)
+					return COPY_HEADER_FALSE;
+				if (pg_strcasecmp(sval, "on") == 0)
+					return COPY_HEADER_TRUE;
+				if (pg_strcasecmp(sval, "off") == 0)
+					return COPY_HEADER_FALSE;
+				if (pg_strcasecmp(sval, "match") == 0)
+					return COPY_HEADER_MATCH;
+			}
+			break;
+	}
+	ereport(ERROR,
+				(errcode(ERRCODE_SYNTAX_ERROR),
+				 errmsg("%s requires a Boolean value or \"match\"",
+					def->defname)));
+	return COPY_HEADER_FALSE;	/* keep compiler quiet */
+}
+
 /*
  * Process the statement option list for COPY.
  *
@@ -394,7 +452,7 @@ ProcessCopyOptions(ParseState *pstate,
 			if (header_specified)
 				errorConflictingDefElem(defel, pstate);
 			header_specified = true;
-			opts_out->header_line = defGetBoolean(defel);
+			opts_out->header_line = defGetCopyHeaderChoice(defel);
 		}
 		else if (strcmp(defel->defname, "quote") == 0)
 		{

src/backend/commands/copyfromparse.c

@@ -72,6 +72,7 @@
 #include "miscadmin.h"
 #include "pgstat.h"
 #include "port/pg_bswap.h"
+#include "utils/builtins.h"
 #include "utils/memutils.h"
 #include "utils/rel.h"
 
@@ -758,12 +759,58 @@ NextCopyFromRawFields(CopyFromState cstate, char ***fields, int *nfields)
 	/* only available for text or csv input */
 	Assert(!cstate->opts.binary);
 
-	/* on input just throw the header line away */
+	/* on input check that the header line is correct if needed */
 	if (cstate->cur_lineno == 0 && cstate->opts.header_line)
 	{
+		ListCell   *cur;
+		TupleDesc	tupDesc;
+
+		tupDesc = RelationGetDescr(cstate->rel);
+
 		cstate->cur_lineno++;
-		if (CopyReadLine(cstate))
-			return false;		/* done */
+		done = CopyReadLine(cstate);
+
+		if (cstate->opts.header_line == COPY_HEADER_MATCH)
+		{
+			int			fldnum;
+
+			if (cstate->opts.csv_mode)
+				fldct = CopyReadAttributesCSV(cstate);
+			else
+				fldct = CopyReadAttributesText(cstate);
+
+			if (fldct != list_length(cstate->attnumlist))
+				ereport(ERROR,
+						(errcode(ERRCODE_BAD_COPY_FILE_FORMAT),
+						 errmsg("wrong number of fields in header line: field count is %d, expected %d",
+								fldct, list_length(cstate->attnumlist))));
+
+			fldnum = 0;
+			foreach(cur, cstate->attnumlist)
+			{
+				int			attnum = lfirst_int(cur);
+				char	   *colName = cstate->raw_fields[attnum - 1];
+				Form_pg_attribute attr = TupleDescAttr(tupDesc, attnum - 1);
+
+				fldnum++;
+
+				if (colName == NULL)
+					ereport(ERROR,
+							(errcode(ERRCODE_BAD_COPY_FILE_FORMAT),
+							 errmsg("column name mismatch in header line field %d: got null value (\"%s\"), expected \"%s\"",
+									fldnum, cstate->opts.null_print, NameStr(attr->attname))));
+
+				if (namestrcmp(&attr->attname, colName) != 0) {
+					ereport(ERROR,
+							(errcode(ERRCODE_BAD_COPY_FILE_FORMAT),
+							 errmsg("column name mismatch in header line field %d: got \"%s\", expected \"%s\"",
+									fldnum, colName, NameStr(attr->attname))));
+				}
+			}
+		}
+
+		if (done)
+			return false;
 	}
 
 	cstate->cur_lineno++;

src/include/commands/copy.h

@@ -19,6 +19,17 @@
 #include "parser/parse_node.h"
 #include "tcop/dest.h"
 
+/*
+ * Represents whether a header line should be present, and whether it must
+ * match the actual names (which implies "true").
+ */
+typedef enum CopyHeaderChoice
+{
+	COPY_HEADER_FALSE = 0,
+	COPY_HEADER_TRUE,
+	COPY_HEADER_MATCH,
+} CopyHeaderChoice;
+
 /*
  * A struct to hold COPY options, in a parsed form. All of these are related
  * to formatting, except for 'freeze', which doesn't really belong here, but
@@ -32,7 +43,7 @@ typedef struct CopyFormatOptions
 	bool		binary;			/* binary format? */
 	bool		freeze;			/* freeze rows on loading? */
 	bool		csv_mode;		/* Comma Separated Value format? */
-	bool		header_line;	/* header line? */
+	CopyHeaderChoice 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

@@ -176,3 +176,26 @@ INFO:  progress: {"type": "FILE", "command": "COPY FROM", "relname": "tab_progre
 drop trigger check_after_tab_progress_reporting on tab_progress_reporting;
 drop function notice_after_tab_progress_reporting();
 drop table tab_progress_reporting;
+-- Test header matching feature
+create table header_copytest (
+	a int,
+	b int,
+	c text
+);
+copy header_copytest from stdin with (header wrong_choice);
+ERROR:  header requires a Boolean value or "match"
+copy header_copytest from stdin with (header match);
+copy header_copytest from stdin with (header match);
+ERROR:  column name mismatch in header line field 3: got null value ("\N"), expected "c"
+CONTEXT:  COPY header_copytest, line 1: "a	b	\N"
+copy header_copytest from stdin with (header match);
+ERROR:  wrong number of fields in header line: field count is 2, expected 3
+CONTEXT:  COPY header_copytest, line 1: "a	b"
+copy header_copytest from stdin with (header match);
+ERROR:  wrong number of fields in header line: field count is 4, expected 3
+CONTEXT:  COPY header_copytest, line 1: "a	b	c	d"
+copy header_copytest from stdin with (header match);
+ERROR:  column name mismatch in header line field 3: got "d", expected "c"
+CONTEXT:  COPY header_copytest, line 1: "a	b	d"
+copy header_copytest from stdin with (header match, format csv);
+drop table header_copytest;

src/test/regress/sql/copy.sql

@@ -197,3 +197,36 @@ copy tab_progress_reporting from :'filename'
 drop trigger check_after_tab_progress_reporting on tab_progress_reporting;
 drop function notice_after_tab_progress_reporting();
 drop table tab_progress_reporting;
+
+-- Test header matching feature
+create table header_copytest (
+	a int,
+	b int,
+	c text
+);
+copy header_copytest from stdin with (header wrong_choice);
+copy header_copytest from stdin with (header match);
+a	b	c
+1	2	foo
+\.
+copy header_copytest from stdin with (header match);
+a	b	\N
+1	2	foo
+\.
+copy header_copytest from stdin with (header match);
+a	b
+1	2
+\.
+copy header_copytest from stdin with (header match);
+a	b	c	d
+1	2	foo	bar
+\.
+copy header_copytest from stdin with (header match);
+a	b	d
+1	2	foo
+\.
+copy header_copytest from stdin with (header match, format csv);
+a,b,c
+1,2,foo
+\.
+drop table header_copytest;