Split copy.c into four files.

Copy.c has grown really large. Split it into more manageable parts:

- copy.c now contains only a few functions that are common to COPY FROM
  and COPY TO.

- copyto.c contains code for COPY TO.

- copyfrom.c contains code for initializing COPY FROM, and inserting the
  tuples to the correct table.

- copyfromparse.c contains code for reading from the client/file/program,
  and parsing the input text/CSV/binary format into tuples.

All of these parts are fairly complicated, and fairly independent of each
other. There is a patch being discussed to implement parallel COPY FROM,
which will add a lot of new code to the COPY FROM path, and another patch
which would allow INSERTs to use the same multi-insert machinery as COPY
FROM, both of which will require refactoring that code. With those two
patches, there's going to be a lot of code churn in copy.c anyway, so now
seems like a good time to do this refactoring.

The CopyStateData struct is also split. All the formatting options, like
FORMAT, QUOTE, ESCAPE, are put in a new CopyFormatOption struct, which
is used by both COPY FROM and TO. Other state data are kept in separate
CopyFromStateData and CopyToStateData structs.

Reviewed-by: Soumyadeep Chakraborty, Erik Rijkers, Vignesh C, Andres Freund
Discussion: https://www.postgresql.org/message-id/8e15b560-f387-7acc-ac90-763986617bfb%40iki.fi

src/include/commands/copy.h

@@ -19,26 +19,71 @@
 #include "parser/parse_node.h"
 #include "tcop/dest.h"
 
-/* CopyStateData is private in commands/copy.c */
-typedef struct CopyStateData *CopyState;
+/*
+ * 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
+ * it's expedient to parse it along with all the other options.
+ */
+typedef struct CopyFormatOptions
+{
+	/* parameters from the COPY command */
+	int			file_encoding;	/* file or remote side's character encoding,
+								 * -1 if not specified */
+	bool		binary;			/* binary format? */
+	bool		freeze;			/* freeze rows on loading? */
+	bool		csv_mode;		/* Comma Separated Value format? */
+	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 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) */
+	List	   *force_quote;	/* list of column names */
+	bool		force_quote_all;	/* FORCE_QUOTE *? */
+	bool	   *force_quote_flags;	/* per-column CSV FQ flags */
+	List	   *force_notnull;	/* list of column names */
+	bool	   *force_notnull_flags;	/* per-column CSV FNN flags */
+	List	   *force_null;		/* list of column names */
+	bool	   *force_null_flags;	/* per-column CSV FN flags */
+	bool		convert_selectively;	/* do selective binary conversion? */
+	List	   *convert_select; /* list of column names (can be NIL) */
+} CopyFormatOptions;
+
+/* These are private in commands/copy[from|to].c */
+typedef struct CopyFromStateData *CopyFromState;
+typedef struct CopyToStateData *CopyToState;
+
 typedef int (*copy_data_source_cb) (void *outbuf, int minread, int maxread);
 
 extern void DoCopy(ParseState *state, const CopyStmt *stmt,
 				   int stmt_location, int stmt_len,
 				   uint64 *processed);
 
-extern void ProcessCopyOptions(ParseState *pstate, CopyState cstate, bool is_from, List *options);
-extern CopyState BeginCopyFrom(ParseState *pstate, Relation rel, const char *filename,
+extern void ProcessCopyOptions(ParseState *pstate, CopyFormatOptions *ops_out, bool is_from, List *options);
+extern CopyFromState BeginCopyFrom(ParseState *pstate, Relation rel, Node *whereClause,
+							   const char *filename,
 							   bool is_program, copy_data_source_cb data_source_cb, List *attnamelist, List *options);
-extern void EndCopyFrom(CopyState cstate);
-extern bool NextCopyFrom(CopyState cstate, ExprContext *econtext,
+extern void EndCopyFrom(CopyFromState cstate);
+extern bool NextCopyFrom(CopyFromState cstate, ExprContext *econtext,
 						 Datum *values, bool *nulls);
-extern bool NextCopyFromRawFields(CopyState cstate,
+extern bool NextCopyFromRawFields(CopyFromState cstate,
 								  char ***fields, int *nfields);
 extern void CopyFromErrorCallback(void *arg);
 
-extern uint64 CopyFrom(CopyState cstate);
+extern uint64 CopyFrom(CopyFromState cstate);
 
 extern DestReceiver *CreateCopyDestReceiver(void);
 
+/*
+ * internal prototypes
+ */
+extern CopyToState BeginCopyTo(ParseState *pstate, Relation rel, RawStmt *query,
+							   Oid queryRelId, const char *filename, bool is_program,
+							   List *attnamelist, List *options);
+extern void EndCopyTo(CopyToState cstate);
+extern uint64 DoCopyTo(CopyToState cstate);
+extern List *CopyGetAttnums(TupleDesc tupDesc, Relation rel,
+							List *attnamelist);
+
 #endif							/* COPY_H */