Add ColumnsCSV filter

Adds a CSV aware columns filter that preserves quoted columns containing
the delimiter. The existing columns implementation does a simple split
with the delimiter meaning any columns containing the delimiter will be
incorrectly split. For many cases this is fine, but for more complex
scenarios proper parsing is required.

README.md

@@ -26,7 +26,7 @@ for a good list and examples). These tools do a single job well and have many
 powerful features to accomplish anything you might want to do.
 
 On the other hand there can be a bit of a learning curve to remember their
-names , flags, and usage - even for basic tasks.
+names, flags, and usage - even for basic tasks.
 
 Pipesore is intended to be a single command that covers the most useful use
 cases of these tools while being intuitive to even someone who has never seen
@@ -69,6 +69,8 @@ first line of the input and return all other lines.
 | Filter                                          |         |
 | ------                                          | ------- |
 | Columns(delimiter *string*, columns *string*)   | Returns the selected `columns` in order where `columns` is a 1-indexed comma separated list of column positions. Columns are defined by splitting with the 'delimiter'. |
+
+| ColumnsCSV(delimiter *string*, columns *string*)| Returns the selected `columns` in order where `columns` is a 1-indexed comma separated list of column positions. Parsing is CSV aware so quoted columns containing the `delimiter` when splitting are preserved. |
 | CountLines()                                    | Returns the line count. Lines are delimited by `\r?\n`. |
 | CountRunes()                                    | Returns the rune (Unicode code points) count. Erroneous and short encodings are treated as single runes of width 1 byte. |
 | CountWords()                                    | Returns the word count. Words are delimited by<br />`\t\|\n\|\v\|\f\|\r\| \|0x85\|0xA0`. |

go.mod

@@ -1,3 +1,3 @@
 module github.com/dyson/pipesore
 
-go 1.19
+go 1.21

pkg/pipeline/filters.go

@@ -3,6 +3,7 @@ package pipeline
 import (
 	"bufio"
 	"container/ring"
+	"encoding/csv"
 	"fmt"
 	"io"
 	"reflect"
@@ -16,6 +17,7 @@ import (
 var (
 	Filters = map[string]reflect.Value{
 		"columns":      reflect.ValueOf(Columns),
+		"columnscsv":   reflect.ValueOf(ColumnsCSV),
 		"countlines":   reflect.ValueOf(CountLines),
 		"countrunes":   reflect.ValueOf(CountRunes),
 		"countwords":   reflect.ValueOf(CountWords),
@@ -43,7 +45,7 @@ func Columns(delimiter string, columns string) func(io.Reader, io.Writer) error
 		for _, column := range strings.Split(columns, ",") {
 			index, err := strconv.Atoi(strings.TrimSpace(column))
 			if err != nil {
-				return fmt.Errorf("list of columns must be comma serarated list of ints, got: %v", columns)
+				return fmt.Errorf("list of columns must be comma separated list of ints, got: %v", columns)
 			}
 
 			order = append(order, index)
@@ -66,7 +68,69 @@ func Columns(delimiter string, columns string) func(io.Reader, io.Writer) error
 
 		return scanner.Err()
 	}
+}
+
+// ColumnsCSV returns a CSV aware filter that writes the selected 'columns' in
+// the order provided where 'columns' is a 1-indexed comma separated list of
+// column positions. Columns are defined by splitting with the 'delimiter'.
+func ColumnsCSV(delimiter string, columns string) func(io.Reader, io.Writer) error {
+	return func(r io.Reader, w io.Writer) error {
+		if utf8.RuneCount([]byte(delimiter)) > 1 {
+			return fmt.Errorf("delimeter must be a single rune, got: %s", delimiter)
+		}
+
+		order := []int{}
+		for _, column := range strings.Split(columns, ",") {
+			index, err := strconv.Atoi(strings.TrimSpace(column))
+			if err != nil {
+				return fmt.Errorf("list of columns must be comma separated list of ints, got: %v", columns)
+			}
+
+			order = append(order, index)
+		}
+
+		reader := csv.NewReader(r)
+		reader.Comma, _ = utf8.DecodeRuneInString(delimiter)
+		// We really shouldn't be tolerant of malformed CSV input (and should
+		// error) however we can set LazyQuotes to be less strict for commonly
+		// incorrect quoting.
+		//
+		// Unfortunately how incorrect quoting should be interpreted is highly
+		// dependent on how it was incorrectly implemented and so with LazyQuotes
+		// enabled we will in some cases silently parse malformed CSV in a possibly
+		// unexpected way to the user.
+		//
+		// On the other hand users don't always have control over the generation of
+		// the CSV input and so it is hoped that the trade-off in using LazyQuotes
+		// will allow for a better experience overall. If this is not that case we
+		// can disable LazyQuotes and only parse valid rfc4180
+		// (https://www.rfc-editor.org/rfc/rfc4180.html) csv.
+		reader.LazyQuotes = true
+
+		writer := csv.NewWriter(w)
+		defer writer.Flush()
+
+		for {
+			lineColumns, err := reader.Read()
+			if err == io.EOF {
+				break
+			}
+			if err != nil {
+				return err
+			}
+
+			output := []string{}
+			for _, v := range order {
+				if v-1 < len(lineColumns) {
+					output = append(output, lineColumns[v-1])
+				}
+			}
 
+			writer.Write(output)
+		}
+
+		return nil
+	}
 }
 
 // CountLines returns a filter that writes the number of lines read.

pkg/pipeline/filters_test.go

@@ -23,6 +23,9 @@ func TestFilters(t *testing.T) {
 		{Columns(",", "3,2,1"), "one\t\tthree\n", "one\t\tthree\n"},
 		{Columns("\t", "9"), "one\t\tthree\n", "\n"},
 		{Columns("\t", "3,2,1"), "one\t\tthree\n", "three\t\tone\n"},
+		{ColumnsCSV(",", "3,2,1"), "one\t\tthree\n", "one\t\tthree\n"},
+		{ColumnsCSV("\t", "9"), "one\t\tthree\n", "\n"},
+		{ColumnsCSV(",", "3,2,1"), "one,\"t,w,o\",\"th\"\"ree\"\n", "\"th\"\"ree\",\"t,w,o\",one\n"},
 		{CountLines(), "", "0\n"},
 		{CountLines(), input, "3\n"},
 		{CountRunes(), "", "0\n"},
@@ -69,7 +72,7 @@ func TestFilters(t *testing.T) {
 
 			err := tc.filter(strings.NewReader(tc.input), got)
 			if err != nil {
-				t.Fatalf("(test: %d) error executing filter: %v", k, err)
+				t.Fatalf("(test: %d) error executing filter: %v: input: %v", k, err, tc.input)
 			}
 
 			if tc.want != got.String() {

pkg/pipeline/pipeline.go

@@ -1,27 +1,3 @@
-// MIT License
-
-// Copyright (c) 2019 John Arundel, 2022 Dyson Simmons
-
-// Permission is hereby granted, free of charge, to any person obtaining a copy
-// of this software and associated documentation files (the "Software"), to deal
-// in the Software without restriction, including without limitation the rights
-// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
-// copies of the Software, and to permit persons to whom the Software is
-// furnished to do so, subject to the following conditions:
-
-// The above copyright notice and this permission notice shall be included in all
-// copies or substantial portions of the Software.
-
-// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
-// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
-// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
-// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
-// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
-// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
-// SOFTWARE.
-
-// MIT License
-
 package pipeline
 
 import (