feat: DTail fork — server/client feature development

Squashed development of the snonux/dtail fork's product code (internal/, cmd/)
since diverging from mimecast/dtail. Major areas:

- Read/output path: the former "turbo" channel-less path is now the single,
  default server-side read/output path for cat/grep/tail and MapReduce; the old
  channel-based path and its config/env toggles were removed.
- MapReduce: single aggregate implementation (server + serverless) fed directly
  by a processor pipeline, with input-exhausted finalization via the shutdown
  coordinator; high-concurrency and data-race fixes.
- Journal source reads (journal:unit.service) via journalctl, Linux-gated behind
  a journal-v1 capability.
- Auth-key fast reconnect: in-memory per-user public-key cache with TTL/max-keys,
  registered over an authenticated session (AUTHKEY), checked before
  authorized_keys.
- Interactive query reload (--interactive-query) with SESSION START/UPDATE
  generation boundaries and capability negotiation.
- Client-side deadlines: --timeout / --shutdownAfter as context deadlines;
  follow shutdown handling.
- Client logging: diagnostics-only daily log by default, opt-in payload tee via
  --log-payload.
- Numerous correctness fixes (buffer-pool double-recycle races, EOF-sentinel
  leaks, glob-expansion cap, TOCTOU in CSV parsing) with accompanying unit tests.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

1 files changed, 52 insertions, 186 deletions

diff --git a/internal/io/fs/readfile.go b/internal/io/fs/readfile.go
index dc1d8ea..7969cf0 100644
--- a/internal/io/fs/readfile.go
+++ b/internal/io/fs/readfile.go
@@ -2,7 +2,6 @@ package fs
 
 import (
 	"bufio"
-	"bytes"
 	"compress/gzip"
 	"context"
 	"errors"
@@ -10,25 +9,18 @@ import (
 	"io"
 	"os"
 	"strings"
-	"sync"
 	"time"
 
-	"github.com/mimecast/dtail/internal/config"
 	"github.com/mimecast/dtail/internal/io/dlog"
-	"github.com/mimecast/dtail/internal/io/line"
-	"github.com/mimecast/dtail/internal/io/pool"
-	"github.com/mimecast/dtail/internal/lcontext"
-	"github.com/mimecast/dtail/internal/regex"
-
-	"github.com/DataDog/zstd"
 )
 
 type readStatus int
 
 const (
-	nothing         readStatus = iota
-	abortReading    readStatus = iota
-	continueReading readStatus = iota
+	nothing              readStatus = iota
+	abortReading         readStatus = iota
+	continueReading      readStatus = iota
+	defaultMaxLineLength            = 1024 * 1024
 )
 
 // Used to tail and filter a local log file.
@@ -37,6 +29,8 @@ type readFile struct {
 	stats
 	// Path of log file to tail.
 	filePath string
+	// Rooted target used for validated server-side re-opens.
+	validatedTarget *ValidatedReadTarget
 	// The glob identifier of the file.
 	globID string
 	// Channel to send a server message to the dtail client
@@ -49,6 +43,8 @@ type readFile struct {
 	seekEOF bool
 	// Warned already about a long line.
 	warnedAboutLongLine bool
+	// Maximum line length before a line is split.
+	maxLineLength int
 }
 
 // String returns the string representation of the readFile
@@ -72,52 +68,42 @@ func (f readFile) Retry() bool {
 	return f.retry
 }
 
-// Start tailing a log file.
-func (f readFile) Start(ctx context.Context, ltx lcontext.LContext,
-	lines chan<- *line.Line, re regex.Regex) error {
-
-	reader, fd, err := f.makeReader()
-	if fd != nil {
-		defer fd.Close()
+func (f *readFile) lineLimit() int {
+	if f.maxLineLength <= 0 {
+		return defaultMaxLineLength
 	}
-	if err != nil {
-		return err
-	}
-
-	rawLines := make(chan *bytes.Buffer, 100)
-	truncate := make(chan struct{})
-
-	readCtx, readCancel := context.WithCancel(ctx)
-	var filterWg sync.WaitGroup
-	filterWg.Add(1)
+	return f.maxLineLength
+}
 
-	go f.periodicTruncateCheck(ctx, truncate)
-	go func() {
-		f.filter(ctx, ltx, rawLines, lines, re)
-		filterWg.Done()
-		// If the filter stopped, make the reader stop too, no need to read
-		// more data if there is nothing more the filter wants to filter for!
-		// E.g. it could be that we only want to filter N matches but not more.
-		readCancel()
-	}()
+func (f *readFile) warnAboutLongLine(ctx context.Context) bool {
+	if f.warnedAboutLongLine {
+		return true
+	}
 
-	err = f.read(readCtx, fd, reader, rawLines, truncate)
-	close(rawLines)
-	// Filter may sends some data still. So wait until it is done here.
-	filterWg.Wait()
+	if f.serverMessages == nil {
+		f.warnedAboutLongLine = true
+		return true
+	}
 
-	return err
+	select {
+	case f.serverMessages <- dlog.Common.Warn(f.filePath,
+		"Long log line, splitting into multiple lines") + "\n":
+		f.warnedAboutLongLine = true
+		return true
+	case <-ctx.Done():
+		return false
+	}
 }
 
-func (f *readFile) makeReader() (*bufio.Reader, *os.File, error) {
+func (f *readFile) makeReader() (*bufio.Reader, *os.File, io.Closer, error) {
 	if f.filePath == "" && f.globID == "-" {
 		return f.makePipeReader()
 	}
 	return f.makeFileReader()
 }
 
-func (f *readFile) makeFileReader() (reader *bufio.Reader, fd *os.File, err error) {
-	if fd, err = os.Open(f.filePath); err != nil {
+func (f *readFile) makeFileReader() (reader *bufio.Reader, fd *os.File, decompressor io.Closer, err error) {
+	if fd, err = f.openFile(); err != nil {
 		return
 	}
 
@@ -127,21 +113,32 @@ func (f *readFile) makeFileReader() (reader *bufio.Reader, fd *os.File, err erro
 		}
 	}
 
-	reader, err = f.makeCompressedFileReader(fd)
+	reader, decompressor, err = f.makeCompressedFileReader(fd)
 	return
 }
 
-func (f *readFile) makePipeReader() (*bufio.Reader, *os.File, error) {
-	return bufio.NewReader(os.Stdin), nil, nil
+func (f *readFile) openFile() (*os.File, error) {
+	if f.validatedTarget != nil {
+		return f.validatedTarget.Open()
+	}
+	return os.Open(f.filePath)
 }
 
-func (f *readFile) periodicTruncateCheck(ctx context.Context, truncate chan struct{}) {
+func (f *readFile) makePipeReader() (*bufio.Reader, *os.File, io.Closer, error) {
+	return bufio.NewReader(os.Stdin), nil, nil, nil
+}
+
+func (f *readFile) periodicTruncateCheck(ctx context.Context, truncate chan<- struct{}) {
+	ticker := time.NewTicker(time.Second * 3)
+	defer ticker.Stop()
+
 	for {
 		select {
-		case <-time.After(time.Second * 3):
+		case <-ticker.C:
 			select {
 			case truncate <- struct{}{}:
 			case <-ctx.Done():
+				return
 			}
 		case <-ctx.Done():
 			return
@@ -149,7 +146,7 @@ func (f *readFile) periodicTruncateCheck(ctx context.Context, truncate chan stru
 	}
 }
 
-func (f *readFile) makeCompressedFileReader(fd *os.File) (reader *bufio.Reader, err error) {
+func (f *readFile) makeCompressedFileReader(fd *os.File) (reader *bufio.Reader, decompressor io.Closer, err error) {
 	switch {
 	case strings.HasSuffix(f.FilePath(), ".gz"):
 		fallthrough
@@ -160,82 +157,16 @@ func (f *readFile) makeCompressedFileReader(fd *os.File) (reader *bufio.Reader,
 		if err != nil {
 			return
 		}
+		decompressor = gzipReader
 		reader = bufio.NewReader(gzipReader)
 	case strings.HasSuffix(f.FilePath(), ".zst"):
-		dlog.Common.Info(f.FilePath(), "Detected zstd compression format")
-		reader = bufio.NewReader(zstd.NewReader(fd))
+		return f.makeZstdReader(fd)
 	default:
 		reader = bufio.NewReader(fd)
 	}
 	return
 }
 
-func (f *readFile) read(ctx context.Context, fd *os.File, reader *bufio.Reader,
-	rawLines chan *bytes.Buffer, truncate <-chan struct{}) error {
-
-	var offset uint64
-	message := pool.BytesBuffer.Get().(*bytes.Buffer)
-
-	for {
-		b, err := reader.ReadByte()
-		if err != nil {
-			status, err := f.handleReadError(ctx, err, fd, rawLines, truncate, message)
-			if abortReading == status {
-				return err
-			}
-			time.Sleep(time.Millisecond * 100)
-			continue
-		}
-
-		offset++
-		message.WriteByte(b)
-
-		status, newMessage := f.handleReadByte(ctx, b, rawLines, message)
-		if status == abortReading {
-			return nil
-		}
-		message = newMessage
-	}
-}
-
-// Filter log lines matching a given regular expression.
-func (f *readFile) filter(ctx context.Context, ltx lcontext.LContext,
-	rawLines <-chan *bytes.Buffer, lines chan<- *line.Line, re regex.Regex) {
-
-	// Do we have any kind of local context settings? If so then run the more complex
-	// filterWithLContext method.
-	if ltx.Has() {
-		// We can not skip transmitting any lines to the client with a local
-		// grep context specified.
-		f.canSkipLines = false
-		f.filterWithLContext(ctx, ltx, rawLines, lines, re)
-		return
-	}
-
-	f.filterWithoutLContext(ctx, rawLines, lines, re)
-}
-
-func (f *readFile) transmittable(rawLine *bytes.Buffer, length, capacity int,
-	re regex.Regex) (*line.Line, bool) {
-
-	newLine := line.Null()
-	if !re.Match(rawLine.Bytes()) {
-		f.updateLineNotMatched()
-		f.updateLineNotTransmitted()
-		return newLine, false
-	}
-	f.updateLineMatched()
-
-	// Can we actually send more messages, channel capacity reached?
-	if f.canSkipLines && length >= capacity {
-		f.updateLineNotTransmitted()
-		return newLine, false
-	}
-	f.updateLineTransmitted()
-
-	return line.New(rawLine, f.totalLineCount(), f.transmittedPerc(), f.globID), true
-}
-
 // Check wether log file is truncated. Returns nil if not.
 func (f *readFile) truncated(fd *os.File) (bool, error) {
 	if fd == nil {
@@ -250,7 +181,7 @@ func (f *readFile) truncated(fd *os.File) (bool, error) {
 		return true, err
 	}
 	// Can not open file at original path.
-	pathFd, err := os.Open(f.filePath)
+	pathFd, err := f.openFile()
 	if err != nil {
 		return true, err
 	}
@@ -267,68 +198,3 @@ func (f *readFile) truncated(fd *os.File) (bool, error) {
 	return false, nil
 }
 
-// Deal with the scenario that nothing could be read from the fd.
-func (f *readFile) handleReadError(ctx context.Context, err error, fd *os.File,
-	rawLines chan *bytes.Buffer, truncate <-chan struct{},
-	message *bytes.Buffer) (readStatus, error) {
-
-	if err != io.EOF {
-		return abortReading, err
-	}
-
-	select {
-	case <-truncate:
-		if isTruncated, err := f.truncated(fd); isTruncated {
-			return abortReading, err
-		}
-	case <-ctx.Done():
-		return abortReading, nil
-	default:
-	}
-
-	if !f.seekEOF {
-		dlog.Common.Info(f.FilePath(), "End of file reached")
-		if len(message.Bytes()) > 0 {
-			select {
-			case rawLines <- message:
-			case <-ctx.Done():
-			}
-		}
-		return abortReading, nil
-	}
-
-	return nothing, nil
-}
-
-// Now process the byte we just read from the fd.
-func (f *readFile) handleReadByte(ctx context.Context, b byte,
-	rawLines chan *bytes.Buffer, message *bytes.Buffer) (readStatus, *bytes.Buffer) {
-
-	switch b {
-	case '\n':
-		select {
-		case rawLines <- message:
-			message = pool.BytesBuffer.Get().(*bytes.Buffer)
-			f.warnedAboutLongLine = false
-		case <-ctx.Done():
-			return abortReading, message
-		}
-	default:
-		if message.Len() >= config.Server.MaxLineLength {
-			if !f.warnedAboutLongLine {
-				f.serverMessages <- dlog.Common.Warn(f.filePath,
-					"Long log line, splitting into multiple lines") + "\n"
-				f.warnedAboutLongLine = true
-			}
-			message.WriteByte('\n')
-			select {
-			case rawLines <- message:
-				message = pool.BytesBuffer.Get().(*bytes.Buffer)
-			case <-ctx.Done():
-				return abortReading, message
-			}
-		}
-	}
-
-	return nothing, message
-}