Refactor CopyReadAttributes{CSV,Text}() to use a callback in COPY FROM

CopyReadAttributes{CSV,Text}() are used to parse lines for text and CSV
format.  This reduces the number of "if" branches that need to be
checked when parsing fields in CSV and text mode when dealing with a
COPY FROM, something that can become more noticeable with more
attributes and more lines to process.

Extracted from a larger patch by the same author.

Author: Sutou Kouhei
Discussion: https://postgr.es/m/20231204.153548.2126325458835528809.kou@clear-code.com

Author: michaelpq

src/backend/commands/copyfrom.c

@@ -1776,6 +1776,11 @@ BeginCopyFrom(ParseState *pstate,
 
 		cstate->max_fields = attr_count;
 		cstate->raw_fields = (char **) palloc(attr_count * sizeof(char *));
+
+		if (cstate->opts.csv_mode)
+			cstate->copy_read_attributes = CopyReadAttributesCSV;
+		else
+			cstate->copy_read_attributes = CopyReadAttributesText;
 	}
 
 	MemoryContextSwitchTo(oldcontext);

src/backend/commands/copyfromparse.c

@@ -25,10 +25,10 @@
  *    is copied into 'line_buf', with quotes and escape characters still
  *    intact.
  *
- * 4. CopyReadAttributesText/CSV() function takes the input line from
- *    'line_buf', and splits it into fields, unescaping the data as required.
- *    The fields are stored in 'attribute_buf', and 'raw_fields' array holds
- *    pointers to each field.
+ * 4. CopyReadAttributesText/CSV() function (via copy_read_attribute) takes
+ *    the input line from 'line_buf', and splits it into fields, unescaping
+ *    the data as required.  The fields are stored in 'attribute_buf', and
+ *    'raw_fields' array holds pointers to each field.
  *
  * If encoding conversion is not required, a shortcut is taken in step 2 to
  * avoid copying the data unnecessarily.  The 'input_buf' pointer is set to
@@ -152,8 +152,6 @@ static const char BinarySignature[11] = "PGCOPY\n\377\r\n\0";
 /* non-export function prototypes */
 static bool CopyReadLine(CopyFromState cstate);
 static bool CopyReadLineText(CopyFromState cstate);
-static int	CopyReadAttributesText(CopyFromState cstate);
-static int	CopyReadAttributesCSV(CopyFromState cstate);
 static Datum CopyReadBinaryAttribute(CopyFromState cstate, FmgrInfo *flinfo,
 									 Oid typioparam, int32 typmod,
 									 bool *isnull);
@@ -775,10 +773,7 @@ NextCopyFromRawFields(CopyFromState cstate, char ***fields, int *nfields)
 		{
 			int			fldnum;
 
-			if (cstate->opts.csv_mode)
-				fldct = CopyReadAttributesCSV(cstate);
-			else
-				fldct = CopyReadAttributesText(cstate);
+			fldct = cstate->copy_read_attributes(cstate);
 
 			if (fldct != list_length(cstate->attnumlist))
 				ereport(ERROR,
@@ -830,10 +825,7 @@ NextCopyFromRawFields(CopyFromState cstate, char ***fields, int *nfields)
 		return false;
 
 	/* Parse the line into de-escaped field values */
-	if (cstate->opts.csv_mode)
-		fldct = CopyReadAttributesCSV(cstate);
-	else
-		fldct = CopyReadAttributesText(cstate);
+	fldct = cstate->copy_read_attributes(cstate);
 
 	*fields = cstate->raw_fields;
 	*nfields = fldct;
@@ -1502,7 +1494,7 @@ GetDecimalFromHex(char hex)
  *
  * The return value is the number of fields actually read.
  */
-static int
+int
 CopyReadAttributesText(CopyFromState cstate)
 {
 	char		delimc = cstate->opts.delim[0];
@@ -1756,7 +1748,7 @@ CopyReadAttributesText(CopyFromState cstate)
  * CopyReadAttributesText, except we parse the fields according to
  * "standard" (i.e. common) CSV usage.
  */
-static int
+int
 CopyReadAttributesCSV(CopyFromState cstate)
 {
 	char		delimc = cstate->opts.delim[0];

src/include/commands/copyfrom_internal.h

@@ -52,6 +52,13 @@ typedef enum CopyInsertMethod
 								 * ExecForeignBatchInsert only if valid */
 } CopyInsertMethod;
 
+/*
+ * Per-format callback to parse a line into separate fields.
+ *
+ * Returns the number of fields read.
+ */
+typedef int (*CopyReadAttributes) (CopyFromState cstate);
+
 /*
  * This struct contains all the state variables used throughout a COPY FROM
  * operation.
@@ -130,6 +137,12 @@ typedef struct CopyFromStateData
 	int			max_fields;
 	char	  **raw_fields;
 
+	/*
+	 * Per-format callback to parse lines, then fill raw_fields and
+	 * attribute_buf.
+	 */
+	CopyReadAttributes copy_read_attributes;
+
 	/*
 	 * Similarly, line_buf holds the whole input line being processed. The
 	 * input cycle is first to read the whole line into line_buf, and then
@@ -183,4 +196,8 @@ typedef struct CopyFromStateData
 extern void ReceiveCopyBegin(CopyFromState cstate);
 extern void ReceiveCopyBinaryHeader(CopyFromState cstate);
 
+/* Callbacks for copy_read_attributes */
+extern int	CopyReadAttributesCSV(CopyFromState cstate);
+extern int	CopyReadAttributesText(CopyFromState cstate);
+
 #endif							/* COPYFROM_INTERNAL_H */