csv reader: fix EOF on quotes

This commit fixes an with the csv reader where and EOF occurring on a
quoted field would cause a parsing error.

Closes #4732

zio/csvio/preprocess.go

@@ -73,15 +73,21 @@ func (p *preprocess) parseField() ([]byte, error) {
 		}
 		if c == '"' {
 			hasstr = true
-			str, err := p.parseString()
+			var str []byte
+			str, err = p.parseString()
 			p.scratch = append(p.scratch, str...)
-			if err != nil {
+			if err == nil {
+				continue
+			}
+			if err != io.EOF {
 				return p.scratch, err
 			}
-			continue
 		}
-		if rune(c) == p.delimiter || c == '\n' {
-			ending := []byte{c}
+		if rune(c) == p.delimiter || c == '\n' || err == io.EOF {
+			var ending []byte
+			if err != io.EOF {
+				ending = []byte{c}
+			}
 			if hasstr {
 				// If field had quotes wrap entire field in quotes.
 				if last := len(p.scratch) - 1; last > 0 && p.scratch[last] == '\r' {
@@ -92,7 +98,7 @@ func (p *preprocess) parseField() ([]byte, error) {
 				p.scratch = append([]byte{'"'}, bytes.TrimSpace(p.scratch)...)
 			}
 			p.scratch = append(p.scratch, ending...)
-			return p.scratch, nil
+			return p.scratch, err
 		}
 		p.scratch = append(p.scratch, c)
 	}
@@ -108,7 +114,6 @@ func (p *preprocess) parseString() ([]byte, error) {
 		if c == '"' {
 			next, err := p.scanner.ReadByte()
 			if err != nil {
-				str = append(str, c)
 				return str, err
 			}
 			if next == '"' {

zio/csvio/preprocess_test.go

@@ -19,7 +19,8 @@ field1,"field"2,field"3" my friend
 field4,"field"5 with "multiple" quotes "to" escape,field6
 """,""",""" has a couple "" embedded quotes and a , comma",""" """
 x,"hello,
-"" world , " foo,y`
+"" world , " foo,y
+field1,field2,"test eof with quotes"`
 	const expected = `
 ,,
 "","",""
@@ -28,7 +29,8 @@ field1,"field2","field3 my friend"
 field4,"field5 with multiple quotes to escape",field6
 """,""",""" has a couple "" embedded quotes and a , comma",""" """
 x,"hello,
-"" world ,  foo",y`
+"" world ,  foo",y
+field1,field2,"test eof with quotes"`
 
 	p := newPreprocess(strings.NewReader(input), ',')
 	var buf bytes.Buffer