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

3 files changed, 40 insertions, 21 deletions

diff --git a/src/backend/commands/copy.c b/src/backend/commands/copy.c
index 74ae42b19a7..fae9c41db65 100644
--- a/src/backend/commands/copy.c
+++ b/src/backend/commands/copy.c
@@ -322,11 +322,13 @@ DoCopy(ParseState *pstate, const CopyStmt *stmt,
 }
 
 /*
- * Extract a CopyHeaderChoice value from a DefElem.  This is like
- * defGetBoolean() but also accepts the special value "match".
+ * Extract the CopyFormatOptions.header_line value from a DefElem.
+ *
+ * Parses the HEADER option for COPY, which can be a boolean, a non-negative
+ * integer (number of lines to skip), or the special value "match".
  */
-static CopyHeaderChoice
-defGetCopyHeaderChoice(DefElem *def, bool is_from)
+static int
+defGetCopyHeaderOption(DefElem *def, bool is_from)
 {
 	/*
 	 * If no parameter value given, assume "true" is meant.
@@ -335,20 +337,27 @@ defGetCopyHeaderChoice(DefElem *def, bool is_from)
 		return COPY_HEADER_TRUE;
 
 	/*
-	 * Allow 0, 1, "true", "false", "on", "off", or "match".
+	 * Allow 0, 1, "true", "false", "on", "off", a non-negative integer, 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;
+				int			ival = intVal(def->arg);
+
+				if (ival < 0)
+					ereport(ERROR,
+							(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+							 errmsg("a negative integer value cannot be "
+									"specified for %s", def->defname)));
+
+				if (!is_from && ival > 1)
+					ereport(ERROR,
+							(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+							 errmsg("cannot use multi-line header in COPY TO")));
+
+				return ival;
 			}
 			break;
 		default:
@@ -381,7 +390,8 @@ defGetCopyHeaderChoice(DefElem *def, bool is_from)
 	}
 	ereport(ERROR,
 			(errcode(ERRCODE_SYNTAX_ERROR),
-			 errmsg("%s requires a Boolean value or \"match\"",
+			 errmsg("%s requires a Boolean value, a non-negative integer, "
+					"or the string \"match\"",
 					def->defname)));
 	return COPY_HEADER_FALSE;	/* keep compiler quiet */
 }
@@ -566,7 +576,7 @@ ProcessCopyOptions(ParseState *pstate,
 			if (header_specified)
 				errorConflictingDefElem(defel, pstate);
 			header_specified = true;
-			opts_out->header_line = defGetCopyHeaderChoice(defel, is_from);
+			opts_out->header_line = defGetCopyHeaderOption(defel, is_from);
 		}
 		else if (strcmp(defel->defname, "quote") == 0)
 		{
@@ -769,7 +779,7 @@ ProcessCopyOptions(ParseState *pstate,
 				 errmsg("COPY delimiter cannot be \"%s\"", opts_out->delim)));
 
 	/* Check header */
-	if (opts_out->binary && opts_out->header_line)
+	if (opts_out->binary && opts_out->header_line != COPY_HEADER_FALSE)
 		ereport(ERROR,
 				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 		/*- translator: %s is the name of a COPY option, e.g. ON_ERROR */
diff --git a/src/backend/commands/copyfromparse.c b/src/backend/commands/copyfromparse.c
index f52f2477df1..b1ae97b833d 100644
--- a/src/backend/commands/copyfromparse.c
+++ b/src/backend/commands/copyfromparse.c
@@ -771,21 +771,30 @@ static pg_attribute_always_inline bool
 NextCopyFromRawFieldsInternal(CopyFromState cstate, char ***fields, int *nfields, bool is_csv)
 {
 	int			fldct;
-	bool		done;
+	bool		done = false;
 
 	/* only available for text or csv input */
 	Assert(!cstate->opts.binary);
 
 	/* on input check that the header line is correct if needed */
-	if (cstate->cur_lineno == 0 && cstate->opts.header_line)
+	if (cstate->cur_lineno == 0 && cstate->opts.header_line != COPY_HEADER_FALSE)
 	{
 		ListCell   *cur;
 		TupleDesc	tupDesc;
+		int			lines_to_skip = cstate->opts.header_line;
+
+		/* If set to "match", one header line is skipped */
+		if (cstate->opts.header_line == COPY_HEADER_MATCH)
+			lines_to_skip = 1;
 
 		tupDesc = RelationGetDescr(cstate->rel);
 
-		cstate->cur_lineno++;
-		done = CopyReadLine(cstate, is_csv);
+		for (int i = 0; i < lines_to_skip; i++)
+		{
+			cstate->cur_lineno++;
+			if ((done = CopyReadLine(cstate, is_csv)))
+				break;
+		}
 
 		if (cstate->opts.header_line == COPY_HEADER_MATCH)
 		{
diff --git a/src/backend/commands/copyto.c b/src/backend/commands/copyto.c
index ea6f18f2c80..67b94b91cae 100644
--- a/src/backend/commands/copyto.c
+++ b/src/backend/commands/copyto.c
@@ -199,7 +199,7 @@ CopyToTextLikeStart(CopyToState cstate, TupleDesc tupDesc)
 														  cstate->file_encoding);
 
 	/* if a header has been requested send the line */
-	if (cstate->opts.header_line)
+	if (cstate->opts.header_line == COPY_HEADER_TRUE)
 	{
 		ListCell   *cur;
 		bool		hdr_delim = false;