Separate out ILineReader abstraction (#1504)

* Split up pkg/input/record_reader.go

* new ILineReader/TLineReader

pkg/input/constants.go

@@ -0,0 +1,3 @@
+package input
+
+const CSV_BOM = "\xef\xbb\xbf"

pkg/input/line_reader.go

@@ -0,0 +1,126 @@
+// This file contains the interface for file-format-specific record-readers, as
+// well as a collection of utility functions.
+
+package input
+
+import (
+	"bufio"
+	"container/list"
+	"io"
+)
+
+type ILineReader interface {
+	Scan() bool
+	Text() string
+}
+
+type TLineReader struct {
+	scanner *bufio.Scanner
+}
+
+// NewLineReader handles reading lines which may be delimited by multi-line separators,
+// e.g. "\xe2\x90\x9e" for USV.
+func NewLineReader(handle io.Reader, irs string) *TLineReader {
+	scanner := bufio.NewScanner(handle)
+
+	if irs == "\n" || irs == "\r\n" {
+		// Handled by default scanner.
+	} else {
+		irsbytes := []byte(irs)
+		irslen := len(irsbytes)
+
+		// Custom splitter
+		recordSplitter := func(
+			data []byte,
+			atEOF bool,
+		) (
+			advance int,
+			token []byte,
+			err error,
+		) {
+			datalen := len(data)
+			end := datalen - irslen
+			for i := 0; i <= end; i++ {
+				if data[i] == irsbytes[0] {
+					match := true
+					for j := 1; j < irslen; j++ {
+						if data[i+j] != irsbytes[j] {
+							match = false
+							break
+						}
+					}
+					if match {
+						return i + irslen, data[:i], nil
+					}
+				}
+			}
+			if !atEOF {
+				return 0, nil, nil
+			}
+			// There is one final token to be delivered, which may be the empty string.
+			// Returning bufio.ErrFinalToken here tells Scan there are no more tokens after this
+			// but does not trigger an error to be returned from Scan itself.
+			return 0, data, bufio.ErrFinalToken
+		}
+
+		scanner.Split(recordSplitter)
+	}
+
+	return &TLineReader{
+		scanner: scanner,
+	}
+}
+
+func (r *TLineReader) Scan() bool {
+	return r.scanner.Scan()
+}
+
+func (r *TLineReader) Text() string {
+	return r.scanner.Text()
+}
+
+// TODO: comment copiously
+//
+// Lines are written to the channel with their trailing newline (or whatever
+// IRS) stripped off. So, callers get "a=1,b=2" rather than "a=1,b=2\n".
+func channelizedLineReader(
+	lineReader ILineReader,
+	linesChannel chan<- *list.List,
+	downstreamDoneChannel <-chan bool, // for mlr head
+	recordsPerBatch int64,
+) {
+	i := int64(0)
+	done := false
+
+	lines := list.New()
+
+	for lineReader.Scan() {
+		i++
+
+		lines.PushBack(lineReader.Text())
+
+		// See if downstream processors will be ignoring further data (e.g. mlr
+		// head).  If so, stop reading. This makes 'mlr head hugefile' exit
+		// quickly, as it should.
+		if i%recordsPerBatch == 0 {
+			select {
+			case _ = <-downstreamDoneChannel:
+				done = true
+				break
+			default:
+				break
+			}
+			if done {
+				break
+			}
+			linesChannel <- lines
+			lines = list.New()
+		}
+
+		if done {
+			break
+		}
+	}
+	linesChannel <- lines
+	close(linesChannel) // end-of-stream marker
+}

pkg/input/record_reader.go

@@ -4,19 +4,11 @@
 package input
 
 import (
-	"bufio"
 	"container/list"
-	"io"
-	"regexp"
-	"strings"
 
-	"github.com/johnkerl/miller/pkg/cli"
-	"github.com/johnkerl/miller/pkg/lib"
 	"github.com/johnkerl/miller/pkg/types"
 )
 
-const CSV_BOM = "\xef\xbb\xbf"
-
 // Since Go is concurrent, the context struct (AWK-like variables such as
 // FILENAME, NF, NF, FNR, etc.) needs to be duplicated and passed through the
 // channels along with each record. Hence the initial context, which readers
@@ -32,166 +24,3 @@ type IRecordReader interface {
 		downstreamDoneChannel <-chan bool, // for mlr head
 	)
 }
-
-// NewLineScanner handles read lines which may be delimited by multi-line separators,
-// e.g. "\xe2\x90\x9e" for USV.
-func NewLineScanner(handle io.Reader, irs string) *bufio.Scanner {
-	scanner := bufio.NewScanner(handle)
-
-	// Handled by default scanner.
-	if irs == "\n" || irs == "\r\n" {
-		return scanner
-	}
-
-	irsbytes := []byte(irs)
-	irslen := len(irsbytes)
-
-	// Custom splitter
-	recordSplitter := func(
-		data []byte,
-		atEOF bool,
-	) (
-		advance int,
-		token []byte,
-		err error,
-	) {
-		datalen := len(data)
-		end := datalen - irslen
-		for i := 0; i <= end; i++ {
-			if data[i] == irsbytes[0] {
-				match := true
-				for j := 1; j < irslen; j++ {
-					if data[i+j] != irsbytes[j] {
-						match = false
-						break
-					}
-				}
-				if match {
-					return i + irslen, data[:i], nil
-				}
-			}
-		}
-		if !atEOF {
-			return 0, nil, nil
-		}
-		// There is one final token to be delivered, which may be the empty string.
-		// Returning bufio.ErrFinalToken here tells Scan there are no more tokens after this
-		// but does not trigger an error to be returned from Scan itself.
-		return 0, data, bufio.ErrFinalToken
-	}
-
-	scanner.Split(recordSplitter)
-
-	return scanner
-}
-
-// TODO: comment copiously
-//
-// Lines are written to the channel with their trailing newline (or whatever
-// IRS) stripped off. So, callers get "a=1,b=2" rather than "a=1,b=2\n".
-func channelizedLineScanner(
-	lineScanner *bufio.Scanner,
-	linesChannel chan<- *list.List,
-	downstreamDoneChannel <-chan bool, // for mlr head
-	recordsPerBatch int64,
-) {
-	i := int64(0)
-	done := false
-
-	lines := list.New()
-
-	for lineScanner.Scan() {
-		i++
-
-		lines.PushBack(lineScanner.Text())
-
-		// See if downstream processors will be ignoring further data (e.g. mlr
-		// head).  If so, stop reading. This makes 'mlr head hugefile' exit
-		// quickly, as it should.
-		if i%recordsPerBatch == 0 {
-			select {
-			case _ = <-downstreamDoneChannel:
-				done = true
-				break
-			default:
-				break
-			}
-			if done {
-				break
-			}
-			linesChannel <- lines
-			lines = list.New()
-		}
-
-		if done {
-			break
-		}
-	}
-	linesChannel <- lines
-	close(linesChannel) // end-of-stream marker
-}
-
-// IPairSplitter splits a string into left and right, e.g. for IPS.
-// This helps us reuse code for splitting by IPS string, or IPS regex.
-type iPairSplitter interface {
-	Split(input string) []string
-}
-
-func newPairSplitter(options *cli.TReaderOptions) iPairSplitter {
-	if options.IPSRegex == nil {
-		return &tIPSSplitter{ips: options.IPS}
-	} else {
-		return &tIPSRegexSplitter{ipsRegex: options.IPSRegex}
-	}
-}
-
-type tIPSSplitter struct {
-	ips string
-}
-
-func (s *tIPSSplitter) Split(input string) []string {
-	return strings.SplitN(input, s.ips, 2)
-}
-
-type tIPSRegexSplitter struct {
-	ipsRegex *regexp.Regexp
-}
-
-func (s *tIPSRegexSplitter) Split(input string) []string {
-	return lib.RegexCompiledSplitString(s.ipsRegex, input, 2)
-}
-
-// IFieldSplitter splits a string into pieces, e.g. for IFS.
-// This helps us reuse code for splitting by IFS string, or IFS regex.
-type iFieldSplitter interface {
-	Split(input string) []string
-}
-
-func newFieldSplitter(options *cli.TReaderOptions) iFieldSplitter {
-	if options.IFSRegex == nil {
-		return &tIFSSplitter{ifs: options.IFS, allowRepeatIFS: options.AllowRepeatIFS}
-	} else {
-		return &tIFSRegexSplitter{ifsRegex: options.IFSRegex}
-	}
-}
-
-type tIFSSplitter struct {
-	ifs            string
-	allowRepeatIFS bool
-}
-
-func (s *tIFSSplitter) Split(input string) []string {
-	fields := lib.SplitString(input, s.ifs)
-	if s.allowRepeatIFS {
-		fields = lib.StripEmpties(fields) // left/right trim
-	}
-	return fields
-}
-
-type tIFSRegexSplitter struct {
-	ifsRegex *regexp.Regexp
-}
-
-func (s *tIFSRegexSplitter) Split(input string) []string {
-	return lib.RegexCompiledSplitString(s.ifsRegex, input, -1)
-}

pkg/input/record_reader_csvlite.go

@@ -144,9 +144,9 @@ func (reader *RecordReaderCSVLite) processHandle(
 	reader.headerStrings = nil
 
 	recordsPerBatch := reader.recordsPerBatch
-	lineScanner := NewLineScanner(handle, reader.readerOptions.IRS)
+	lineReader := NewLineReader(handle, reader.readerOptions.IRS)
 	linesChannel := make(chan *list.List, recordsPerBatch)
-	go channelizedLineScanner(lineScanner, linesChannel, downstreamDoneChannel, recordsPerBatch)
+	go channelizedLineReader(lineReader, linesChannel, downstreamDoneChannel, recordsPerBatch)
 
 	for {
 		recordsAndContexts, eof := reader.recordBatchGetter(reader, linesChannel, filename, context, errorChannel)

pkg/input/record_reader_dkvp_nidx.go

@@ -101,9 +101,9 @@ func (reader *RecordReaderDKVPNIDX) processHandle(
 	context.UpdateForStartOfFile(filename)
 	recordsPerBatch := reader.recordsPerBatch
 
-	lineScanner := NewLineScanner(handle, reader.readerOptions.IRS)
+	lineReader := NewLineReader(handle, reader.readerOptions.IRS)
 	linesChannel := make(chan *list.List, recordsPerBatch)
-	go channelizedLineScanner(lineScanner, linesChannel, downstreamDoneChannel, recordsPerBatch)
+	go channelizedLineReader(lineReader, linesChannel, downstreamDoneChannel, recordsPerBatch)
 
 	for {
 		recordsAndContexts, eof := reader.getRecordBatch(linesChannel, errorChannel, context)

pkg/input/record_reader_json.go

@@ -1,7 +1,6 @@
 package input
 
 import (
-	"bufio"
 	"container/list"
 	"fmt"
 	"io"
@@ -203,7 +202,7 @@ func (reader *RecordReaderJSON) processHandle(
 // JSONCommentEnabledReader implements io.Reader to strip comment lines
 // off of CSV data.
 type JSONCommentEnabledReader struct {
-	lineScanner   *bufio.Scanner
+	lineReader    ILineReader
 	readerOptions *cli.TReaderOptions
 	context       *types.Context    // Needed for channelized stdout-printing logic
 	readerChannel chan<- *list.List // list of *types.RecordAndContext
@@ -220,7 +219,7 @@ func NewJSONCommentEnabledReader(
 	readerChannel chan<- *list.List, // list of *types.RecordAndContext
 ) *JSONCommentEnabledReader {
 	return &JSONCommentEnabledReader{
-		lineScanner:   bufio.NewScanner(underlying),
+		lineReader:    NewLineReader(underlying, "\n"),
 		readerOptions: readerOptions,
 		context:       types.NewNilContext(),
 		readerChannel: readerChannel,
@@ -237,10 +236,10 @@ func (bsr *JSONCommentEnabledReader) Read(p []byte) (n int, err error) {
 	// Loop until we can get a non-comment line to pass on, or end of file.
 	for {
 		// EOF
-		if !bsr.lineScanner.Scan() {
+		if !bsr.lineReader.Scan() {
 			return 0, io.EOF
 		}
-		line := bsr.lineScanner.Text()
+		line := bsr.lineReader.Text()
 
 		// Non-comment line
 		if !strings.HasPrefix(line, bsr.readerOptions.CommentString) {

pkg/input/record_reader_pprint.go

@@ -148,9 +148,9 @@ func (reader *RecordReaderPprintBarredOrMarkdown) processHandle(
 	reader.headerStrings = nil
 
 	recordsPerBatch := reader.recordsPerBatch
-	lineScanner := NewLineScanner(handle, reader.readerOptions.IRS)
+	lineReader := NewLineReader(handle, reader.readerOptions.IRS)
 	linesChannel := make(chan *list.List, recordsPerBatch)
-	go channelizedLineScanner(lineScanner, linesChannel, downstreamDoneChannel, recordsPerBatch)
+	go channelizedLineReader(lineReader, linesChannel, downstreamDoneChannel, recordsPerBatch)
 
 	for {
 		recordsAndContexts, eof := reader.recordBatchGetter(reader, linesChannel, filename, context, errorChannel)