Add ENCODING option to COPY TO/FROM and file_fdw.

File encodings can be specified separately from client encoding.
If not specified, client encoding is used for backward compatibility.

Cases when the encoding doesn't match client encoding are slower
than matched cases because we don't have conversion procs for other
encodings. Performance improvement would be be a future work.

Original patch by Hitoshi Harada, and modified by me.

src/backend/commands/copy.c

@@ -95,8 +95,8 @@ typedef struct CopyStateData
 								 * dest == COPY_NEW_FE in COPY FROM */
 	bool		fe_eof;			/* true if detected end of copy data */
 	EolType		eol_type;		/* EOL type of input */
-	int			client_encoding;	/* remote side's character encoding */
-	bool		need_transcoding;		/* client encoding diff from server? */
+	int			file_encoding;	/* file or remote side's character encoding */
+	bool		need_transcoding;		/* file encoding diff from server? */
 	bool		encoding_embeds_ascii;	/* ASCII can be non-first byte? */
 
 	/* parameters from the COPY command */
@@ -110,7 +110,7 @@ typedef struct CopyStateData
 	bool		header_line;	/* CSV header line? */
 	char	   *null_print;		/* NULL marker string (server encoding!) */
 	int			null_print_len; /* length of same */
-	char	   *null_print_client;		/* same converted to client encoding */
+	char	   *null_print_client;		/* same converted to file encoding */
 	char	   *delim;			/* column delimiter (must be 1 byte) */
 	char	   *quote;			/* CSV quote char (must be 1 byte) */
 	char	   *escape;			/* CSV escape char (must be 1 byte) */
@@ -845,6 +845,8 @@ ProcessCopyOptions(CopyState cstate,
 	if (cstate == NULL)
 		cstate = (CopyStateData *) palloc0(sizeof(CopyStateData));
 
+	cstate->file_encoding = -1;
+
 	/* Extract options from the statement node tree */
 	foreach(option, options)
 	{
@@ -948,6 +950,19 @@ ProcessCopyOptions(CopyState cstate,
 						 errmsg("argument to option \"%s\" must be a list of column names",
 								defel->defname)));
 		}
+		else if (strcmp(defel->defname, "encoding") == 0)
+		{
+			if (cstate->file_encoding >= 0)
+				ereport(ERROR,
+						(errcode(ERRCODE_SYNTAX_ERROR),
+						 errmsg("conflicting or redundant options")));
+			cstate->file_encoding = pg_char_to_encoding(defGetString(defel));
+			if (cstate->file_encoding < 0)
+				ereport(ERROR,
+						(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+						 errmsg("argument to option \"%s\" must be a valid encoding name",
+								defel->defname)));
+		}
 		else
 			ereport(ERROR,
 					(errcode(ERRCODE_SYNTAX_ERROR),
@@ -1278,17 +1293,20 @@ BeginCopy(bool is_from,
 		}
 	}
 
+	/* Use client encoding when ENCODING option is not specified. */
+	if (cstate->file_encoding < 0)
+		cstate->file_encoding = pg_get_client_encoding();
+
 	/*
-	 * Set up encoding conversion info.  Even if the client and server
-	 * encodings are the same, we must apply pg_client_to_server() to validate
+	 * Set up encoding conversion info.  Even if the file and server
+	 * encodings are the same, we must apply pg_any_to_server() to validate
 	 * data in multibyte encodings.
 	 */
-	cstate->client_encoding = pg_get_client_encoding();
 	cstate->need_transcoding =
-		(cstate->client_encoding != GetDatabaseEncoding() ||
+		(cstate->file_encoding != GetDatabaseEncoding() ||
 		 pg_database_encoding_max_length() > 1);
 	/* See Multibyte encoding comment above */
-	cstate->encoding_embeds_ascii = PG_ENCODING_IS_CLIENT_ONLY(cstate->client_encoding);
+	cstate->encoding_embeds_ascii = PG_ENCODING_IS_CLIENT_ONLY(cstate->file_encoding);
 
 	cstate->copy_dest = COPY_FILE;		/* default */
 
@@ -1526,12 +1544,13 @@ CopyTo(CopyState cstate)
 	else
 	{
 		/*
-		 * For non-binary copy, we need to convert null_print to client
+		 * For non-binary copy, we need to convert null_print to file
 		 * encoding, because it will be sent directly with CopySendString.
 		 */
 		if (cstate->need_transcoding)
-			cstate->null_print_client = pg_server_to_client(cstate->null_print,
-													 cstate->null_print_len);
+			cstate->null_print_client = pg_server_to_any(cstate->null_print,
+														 cstate->null_print_len,
+														 cstate->file_encoding);
 
 		/* if a header has been requested send the line */
 		if (cstate->header_line)
@@ -2608,8 +2627,9 @@ CopyReadLine(CopyState cstate)
 	{
 		char	   *cvt;
 
-		cvt = pg_client_to_server(cstate->line_buf.data,
-								  cstate->line_buf.len);
+		cvt = pg_any_to_server(cstate->line_buf.data,
+							   cstate->line_buf.len,
+							   cstate->file_encoding);
 		if (cvt != cstate->line_buf.data)
 		{
 			/* transfer converted data back to line_buf */
@@ -2854,7 +2874,7 @@ CopyReadLineText(CopyState cstate)
 			/* -----
 			 * get next character
 			 * Note: we do not change c so if it isn't \., we can fall
-			 * through and continue processing for client encoding.
+			 * through and continue processing for file encoding.
 			 * -----
 			 */
 			c2 = copy_raw_buf[raw_buf_ptr];
@@ -2968,7 +2988,7 @@ not_end_of_copy:
 
 			mblen_str[0] = c;
 			/* All our encodings only read the first byte to get the length */
-			mblen = pg_encoding_mblen(cstate->client_encoding, mblen_str);
+			mblen = pg_encoding_mblen(cstate->file_encoding, mblen_str);
 			IF_NEED_REFILL_AND_NOT_EOF_CONTINUE(mblen - 1);
 			IF_NEED_REFILL_AND_EOF_BREAK(mblen - 1);
 			raw_buf_ptr += mblen - 1;
@@ -3467,7 +3487,7 @@ CopyAttributeOutText(CopyState cstate, char *string)
 	char		delimc = cstate->delim[0];
 
 	if (cstate->need_transcoding)
-		ptr = pg_server_to_client(string, strlen(string));
+		ptr = pg_server_to_any(string, strlen(string), cstate->file_encoding);
 	else
 		ptr = string;
 
@@ -3540,7 +3560,7 @@ CopyAttributeOutText(CopyState cstate, char *string)
 				start = ptr++;	/* we include char in next run */
 			}
 			else if (IS_HIGHBIT_SET(c))
-				ptr += pg_encoding_mblen(cstate->client_encoding, ptr);
+				ptr += pg_encoding_mblen(cstate->file_encoding, ptr);
 			else
 				ptr++;
 		}
@@ -3627,7 +3647,7 @@ CopyAttributeOutCSV(CopyState cstate, char *string,
 		use_quote = true;
 
 	if (cstate->need_transcoding)
-		ptr = pg_server_to_client(string, strlen(string));
+		ptr = pg_server_to_any(string, strlen(string), cstate->file_encoding);
 	else
 		ptr = string;
 
@@ -3654,7 +3674,7 @@ CopyAttributeOutCSV(CopyState cstate, char *string,
 					break;
 				}
 				if (IS_HIGHBIT_SET(c) && cstate->encoding_embeds_ascii)
-					tptr += pg_encoding_mblen(cstate->client_encoding, tptr);
+					tptr += pg_encoding_mblen(cstate->file_encoding, tptr);
 				else
 					tptr++;
 			}
@@ -3678,7 +3698,7 @@ CopyAttributeOutCSV(CopyState cstate, char *string,
 				start = ptr;	/* we include char in next run */
 			}
 			if (IS_HIGHBIT_SET(c) && cstate->encoding_embeds_ascii)
-				ptr += pg_encoding_mblen(cstate->client_encoding, ptr);
+				ptr += pg_encoding_mblen(cstate->file_encoding, ptr);
 			else
 				ptr++;
 		}

src/backend/parser/gram.y

@@ -2236,6 +2236,10 @@ copy_opt_item:
 				{
 					$$ = makeDefElem("force_not_null", (Node *)$4);
 				}
+			| ENCODING Sconst
+				{
+					$$ = makeDefElem("encoding", (Node *)makeString($2));
+				}
 		;
 
 /* The following exist for backward compatibility with very old versions */

src/backend/utils/mb/mbutils.c

@@ -496,6 +496,17 @@ pg_encoding_max_length_sql(PG_FUNCTION_ARGS)
  */
 char *
 pg_client_to_server(const char *s, int len)
+{
+	Assert(ClientEncoding);
+
+	return pg_any_to_server(s, len, ClientEncoding->encoding);
+}
+
+/*
+ * convert any encoding to server encoding.
+ */
+char *
+pg_any_to_server(const char *s, int len, int encoding)
 {
 	Assert(DatabaseEncoding);
 	Assert(ClientEncoding);
@@ -503,8 +514,8 @@ pg_client_to_server(const char *s, int len)
 	if (len <= 0)
 		return (char *) s;
 
-	if (ClientEncoding->encoding == DatabaseEncoding->encoding ||
-		ClientEncoding->encoding == PG_SQL_ASCII)
+	if (encoding == DatabaseEncoding->encoding ||
+		encoding == PG_SQL_ASCII)
 	{
 		/*
 		 * No conversion is needed, but we must still validate the data.
@@ -524,8 +535,8 @@ pg_client_to_server(const char *s, int len)
 		 * to the parser but we have no way to convert it.	We compromise by
 		 * rejecting the data if it contains any non-ASCII characters.
 		 */
-		if (PG_VALID_BE_ENCODING(ClientEncoding->encoding))
-			(void) pg_verify_mbstr(ClientEncoding->encoding, s, len, false);
+		if (PG_VALID_BE_ENCODING(encoding))
+			(void) pg_verify_mbstr(encoding, s, len, false);
 		else
 		{
 			int			i;
@@ -543,7 +554,11 @@ pg_client_to_server(const char *s, int len)
 		return (char *) s;
 	}
 
-	return perform_default_encoding_conversion(s, len, true);
+	if (ClientEncoding->encoding == encoding)
+		return perform_default_encoding_conversion(s, len, true);
+	else
+		return (char *) pg_do_encoding_conversion(
+			(unsigned char *) s, len, encoding, DatabaseEncoding->encoding);
 }
 
 /*
@@ -551,6 +566,17 @@ pg_client_to_server(const char *s, int len)
  */
 char *
 pg_server_to_client(const char *s, int len)
+{
+	Assert(ClientEncoding);
+
+	return pg_any_to_server(s, len, ClientEncoding->encoding);
+}
+
+/*
+ * convert server encoding to any encoding.
+ */
+char *
+pg_server_to_any(const char *s, int len, int encoding)
 {
 	Assert(DatabaseEncoding);
 	Assert(ClientEncoding);
@@ -558,12 +584,16 @@ pg_server_to_client(const char *s, int len)
 	if (len <= 0)
 		return (char *) s;
 
-	if (ClientEncoding->encoding == DatabaseEncoding->encoding ||
-		ClientEncoding->encoding == PG_SQL_ASCII ||
+	if (encoding == DatabaseEncoding->encoding ||
+		encoding == PG_SQL_ASCII ||
 		DatabaseEncoding->encoding == PG_SQL_ASCII)
 		return (char *) s;		/* assume data is valid */
 
-	return perform_default_encoding_conversion(s, len, false);
+	if (ClientEncoding->encoding == encoding)
+		return perform_default_encoding_conversion(s, len, false);
+	else
+		return (char *) pg_do_encoding_conversion(
+			(unsigned char *) s, len, DatabaseEncoding->encoding, encoding);
 }
 
 /*