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/copyfrom_internal.h

@@ -0,0 +1,164 @@
+/*-------------------------------------------------------------------------
+ *
+ * copyfrom_internal.h
+ *	  Internal definitions for COPY FROM command.
+ *
+ *
+ * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/include/commands/copyfrom_internal.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef COPYFROM_INTERNAL_H
+#define COPYFROM_INTERNAL_H
+
+#include "commands/copy.h"
+#include "commands/trigger.h"
+
+/*
+ * Represents the different source cases we need to worry about at
+ * the bottom level
+ */
+typedef enum CopySource
+{
+	COPY_FILE,					/* from file (or a piped program) */
+	COPY_OLD_FE,				/* from frontend (2.0 protocol) */
+	COPY_NEW_FE,				/* from frontend (3.0 protocol) */
+	COPY_CALLBACK				/* from callback function */
+} CopySource;
+
+/*
+ *	Represents the end-of-line terminator type of the input
+ */
+typedef enum EolType
+{
+	EOL_UNKNOWN,
+	EOL_NL,
+	EOL_CR,
+	EOL_CRNL
+} EolType;
+
+/*
+ * Represents the heap insert method to be used during COPY FROM.
+ */
+typedef enum CopyInsertMethod
+{
+	CIM_SINGLE,					/* use table_tuple_insert or fdw routine */
+	CIM_MULTI,					/* always use table_multi_insert */
+	CIM_MULTI_CONDITIONAL		/* use table_multi_insert only if valid */
+} CopyInsertMethod;
+
+/*
+ * This struct contains all the state variables used throughout a COPY FROM
+ * operation.
+ *
+ * Multi-byte encodings: all supported client-side encodings encode multi-byte
+ * characters by having the first byte's high bit set. Subsequent bytes of the
+ * character can have the high bit not set. When scanning data in such an
+ * encoding to look for a match to a single-byte (ie ASCII) character, we must
+ * use the full pg_encoding_mblen() machinery to skip over multibyte
+ * characters, else we might find a false match to a trailing byte. In
+ * supported server encodings, there is no possibility of a false match, and
+ * it's faster to make useless comparisons to trailing bytes than it is to
+ * invoke pg_encoding_mblen() to skip over them. encoding_embeds_ascii is true
+ * when we have to do it the hard way.
+ */
+typedef struct CopyFromStateData
+{
+	/* low-level state data */
+	CopySource	copy_src;		/* type of copy source */
+	FILE	   *copy_file;		/* used if copy_src == COPY_FILE */
+	StringInfo	fe_msgbuf;		/* used if copy_src == COPY_NEW_FE */
+	bool		reached_eof;	/* true if we read to end of copy data (not
+								 * all copy_src types maintain this) */
+
+	EolType		eol_type;		/* EOL type of input */
+	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 */
+	Relation	rel;			/* relation to copy from */
+	List	   *attnumlist;		/* integer list of attnums to copy */
+	char	   *filename;		/* filename, or NULL for STDIN */
+	bool		is_program;		/* is 'filename' a program to popen? */
+	copy_data_source_cb data_source_cb; /* function for reading data */
+
+	CopyFormatOptions opts;
+	bool	   *convert_select_flags;	/* per-column CSV/TEXT CS flags */
+	Node	   *whereClause;	/* WHERE condition (or NULL) */
+
+	/* these are just for error messages, see CopyFromErrorCallback */
+	const char *cur_relname;	/* table name for error messages */
+	uint64		cur_lineno;		/* line number for error messages */
+	const char *cur_attname;	/* current att for error messages */
+	const char *cur_attval;		/* current att value for error messages */
+
+	/*
+	 * Working state
+	 */
+	MemoryContext copycontext;	/* per-copy execution context */
+
+	AttrNumber	num_defaults;
+	FmgrInfo   *in_functions;	/* array of input functions for each attrs */
+	Oid		   *typioparams;	/* array of element types for in_functions */
+	int		   *defmap;			/* array of default att numbers */
+	ExprState **defexprs;		/* array of default att expressions */
+	bool		volatile_defexprs;	/* is any of defexprs volatile? */
+	List	   *range_table;
+	ExprState  *qualexpr;
+
+	TransitionCaptureState *transition_capture;
+
+	/*
+	 * These variables are used to reduce overhead in COPY FROM.
+	 *
+	 * attribute_buf holds the separated, de-escaped text for each field of
+	 * the current line.  The CopyReadAttributes functions return arrays of
+	 * pointers into this buffer.  We avoid palloc/pfree overhead by re-using
+	 * the buffer on each cycle.
+	 *
+	 * In binary COPY FROM, attribute_buf holds the binary data for the
+	 * current field, but the usage is otherwise similar.
+	 */
+	StringInfoData attribute_buf;
+
+	/* field raw data pointers found by COPY FROM */
+
+	int			max_fields;
+	char	  **raw_fields;
+
+	/*
+	 * Similarly, line_buf holds the whole input line being processed. The
+	 * input cycle is first to read the whole line into line_buf, convert it
+	 * to server encoding there, and then extract the individual attribute
+	 * fields into attribute_buf.  line_buf is preserved unmodified so that we
+	 * can display it in error messages if appropriate.  (In binary mode,
+	 * line_buf is not used.)
+	 */
+	StringInfoData line_buf;
+	bool		line_buf_converted; /* converted to server encoding? */
+	bool		line_buf_valid; /* contains the row being processed? */
+
+	/*
+	 * Finally, raw_buf holds raw data read from the data source (file or
+	 * client connection).  In text mode, CopyReadLine parses this data
+	 * sufficiently to locate line boundaries, then transfers the data to
+	 * line_buf and converts it.  In binary mode, CopyReadBinaryData fetches
+	 * appropriate amounts of data from this buffer.  In both modes, we
+	 * guarantee that there is a \0 at raw_buf[raw_buf_len].
+	 */
+#define RAW_BUF_SIZE 65536		/* we palloc RAW_BUF_SIZE+1 bytes */
+	char	   *raw_buf;
+	int			raw_buf_index;	/* next byte to process */
+	int			raw_buf_len;	/* total # of bytes stored */
+	/* Shorthand for number of unconsumed bytes available in raw_buf */
+#define RAW_BUF_BYTES(cstate) ((cstate)->raw_buf_len - (cstate)->raw_buf_index)
+} CopyFromStateData;
+
+extern void ReceiveCopyBegin(CopyFromState cstate);
+extern void ReceiveCopyBinaryHeader(CopyFromState cstate);
+
+#endif							/* COPYFROM_INTERNAL_H */