sql: fix COPY CSV so it handles multiple records at a time

This was broken since the golang csv reader reads the entire input all
at once, so the underlying buffer is consumed. This caused the loop that
reads each record to terminate early.

Release note (bug fix): Fixed the COPY CSV command so that it handles
multiple records separated by newline characters.

pkg/sql/copy.go

@@ -323,17 +323,25 @@ func (c *copyMachine) processCopyData(ctx context.Context, data string, final bo
 	}
 	c.buf.WriteString(data)
 	var readFn func(ctx context.Context, final bool) (brk bool, err error)
+	var checkLoopFn func() bool
 	switch c.format {
 	case tree.CopyFormatText:
 		readFn = c.readTextData
+		checkLoopFn = func() bool { return c.buf.Len() > 0 }
 	case tree.CopyFormatBinary:
 		readFn = c.readBinaryData
+		checkLoopFn = func() bool { return c.buf.Len() > 0 }
 	case tree.CopyFormatCSV:
 		readFn = c.readCSVData
+		// Never exit the loop from this check. Instead, it's up to the readCSVData
+		// function to break when it's done reading. This is because the csv.Reader
+		// consumes all of c.buf in one shot, so checking if c.buf is empty would
+		// cause us to exit the loop early.
+		checkLoopFn = func() bool { return true }
 	default:
 		panic("unknown copy format")
 	}
-	for c.buf.Len() > 0 {
+	for checkLoopFn() {
 		brk, err := readFn(ctx, final)
 		if err != nil {
 			return err
@@ -378,6 +386,9 @@ func (c *copyMachine) readCSVData(ctx context.Context, final bool) (brk bool, er
 	record, err := c.csvReader.Read()
 	// Look for end of data before checking for errors, since a field count
 	// error will still return record data.
+	if record == nil && err == io.EOF {
+		return true, nil
+	}
 	if len(record) == 1 && record[0] == endOfData && c.buf.Len() == 0 {
 		return true, nil
 	}

pkg/sql/pgwire/testdata/pgtest/copy

@@ -262,3 +262,51 @@ ReadyForQuery
 {"Type":"CopyInResponse","ColumnFormatCodes":[0,0]}
 {"Type":"ErrorResponse","Code":"22P04"}
 {"Type":"ReadyForQuery","TxStatus":"I"}
+
+send
+Query {"String": "DELETE FROM t"}
+Query {"String": "COPY t FROM STDIN CSV"}
+CopyData {"Data": "1,one\n2,two\n3,three"}
+CopyDone
+Query {"String": "SELECT * FROM t ORDER BY i"}
+----
+
+until ignore=RowDescription
+ReadyForQuery
+ReadyForQuery
+ReadyForQuery
+----
+{"Type":"CommandComplete","CommandTag":"DELETE 3"}
+{"Type":"ReadyForQuery","TxStatus":"I"}
+{"Type":"CopyInResponse","ColumnFormatCodes":[0,0]}
+{"Type":"CommandComplete","CommandTag":"COPY 3"}
+{"Type":"ReadyForQuery","TxStatus":"I"}
+{"Type":"DataRow","Values":[{"text":"1"},{"text":"one"}]}
+{"Type":"DataRow","Values":[{"text":"2"},{"text":"two"}]}
+{"Type":"DataRow","Values":[{"text":"3"},{"text":"three"}]}
+{"Type":"CommandComplete","CommandTag":"SELECT 3"}
+{"Type":"ReadyForQuery","TxStatus":"I"}
+
+send
+Query {"String": "DELETE FROM t"}
+Query {"String": "COPY t FROM STDIN DELIMITER ',' NULL ''"}
+CopyData {"Data": "1,one\n2,two\n3,three"}
+CopyDone
+Query {"String": "SELECT * FROM t ORDER BY i"}
+----
+
+until ignore=RowDescription
+ReadyForQuery
+ReadyForQuery
+ReadyForQuery
+----
+{"Type":"CommandComplete","CommandTag":"DELETE 3"}
+{"Type":"ReadyForQuery","TxStatus":"I"}
+{"Type":"CopyInResponse","ColumnFormatCodes":[0,0]}
+{"Type":"CommandComplete","CommandTag":"COPY 3"}
+{"Type":"ReadyForQuery","TxStatus":"I"}
+{"Type":"DataRow","Values":[{"text":"1"},{"text":"one"}]}
+{"Type":"DataRow","Values":[{"text":"2"},{"text":"two"}]}
+{"Type":"DataRow","Values":[{"text":"3"},{"text":"three"}]}
+{"Type":"CommandComplete","CommandTag":"SELECT 3"}
+{"Type":"ReadyForQuery","TxStatus":"I"}