git.giacomolli.uk - onechat/blob - journal.go

   1 package main
   2
   3 import (
   4         "bufio"
   5         "context"
   6         "errors"
   7         "fmt"
   8         "io"
   9         "os"
  10         "path/filepath"
  11         "slices"
  12         "strconv"
  13         "strings"
  14 )
  15
  16 // Position names one line of a day file: the day as YYYYMMDD, the byte offset
  17 // of the line, and its length with the newline.
  18 type Position struct {
  19         day    uint32
  20         offset uint64
  21         length uint32
  22 }
  23
  24 // Journal appends JSON lines to one file for each day in dir, named
  25 // YYYY-MM-DD.jsonl, and reads them back by their position. It keeps the file of
  26 // the last day open for writes and each file that it read open for reads.
  27 type Journal struct {
  28         dir     string
  29         file    *os.File
  30         day     uint32
  31         size    uint64
  32         readers map[uint32]*os.File
  33 }
  34
  35 // Write appends line to the file of day, YYYY-MM-DD, with one write to the
  36 // operating system, without a buffer. A crash of the process then loses
  37 // nothing. It returns the position of the line.
  38 func (j *Journal) Write(day string, line []byte) (Position, error) {
  39         number, err := journalDayNumber(day)
  40         if err != nil {
  41                 return Position{}, err
  42         }
  43
  44         if number != j.day {
  45                 err = j.closeWriter()
  46                 if err != nil {
  47                         return Position{}, err
  48                 }
  49
  50                 j.file, err = os.OpenFile(filepath.Join(j.dir, day+".jsonl"), os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0o600)
  51                 if err != nil {
  52                         return Position{}, fmt.Errorf("open day file: %w", err)
  53                 }
  54
  55                 info, err := j.file.Stat()
  56                 if err != nil {
  57                         return Position{}, fmt.Errorf("read day file size: %w", err)
  58                 }
  59
  60                 j.day = number
  61                 j.size = uint64(info.Size())
  62         }
  63
  64         _, err = j.file.Write(line)
  65         if err != nil {
  66                 return Position{}, fmt.Errorf("write line: %w", err)
  67         }
  68
  69         place := Position{
  70                 day:    number,
  71                 offset: j.size,
  72                 length: uint32(len(line)),
  73         }
  74
  75         j.size += uint64(len(line))
  76
  77         return place, nil
  78 }
  79
  80 // Read returns the line at place without its newline.
  81 func (j *Journal) Read(place Position) ([]byte, error) {
  82         reader, open := j.readers[place.day]
  83         if !open {
  84                 var err error
  85
  86                 reader, err = os.Open(filepath.Join(j.dir, journalDayName(place.day)+".jsonl"))
  87                 if err != nil {
  88                         return nil, fmt.Errorf("open day file: %w", err)
  89                 }
  90
  91                 if j.readers == nil {
  92                         j.readers = make(map[uint32]*os.File)
  93                 }
  94
  95                 j.readers[place.day] = reader
  96         }
  97
  98         line := make([]byte, place.length)
  99         _, err := reader.ReadAt(line, int64(place.offset))
 100         if err != nil {
 101                 return nil, fmt.Errorf("read line of %s: %w", journalDayName(place.day), err)
 102         }
 103
 104         if len(line) == 0 || line[len(line)-1] != '\n' {
 105                 return nil, fmt.Errorf("line of %s at %d does not end its record", journalDayName(place.day), place.offset)
 106         }
 107
 108         return line[:len(line)-1], nil
 109 }
 110
 111 // Close closes the open day files.
 112 func (j *Journal) Close() error {
 113         err := j.closeWriter()
 114         for day, reader := range j.readers {
 115                 err = errors.Join(err, reader.Close())
 116
 117                 delete(j.readers, day)
 118         }
 119
 120         return err
 121 }
 122
 123 // Scan gives each line of the day files from place on to add, with its
 124 // position, oldest day first. The zero position starts at the first line. A
 125 // crash during a write can leave a part of a line at the end of the last day
 126 // file. Its write never returned, so Scan cuts it off.
 127 func (j *Journal) Scan(ctx context.Context, place Position, add func([]byte, Position) error) error {
 128         paths, err := filepath.Glob(filepath.Join(j.dir, "*.jsonl"))
 129         if err != nil {
 130                 return fmt.Errorf("list day files: %w", err)
 131         }
 132
 133         slices.Sort(paths)
 134
 135         for n, path := range paths {
 136                 day, err := journalDayNumber(strings.TrimSuffix(filepath.Base(path), ".jsonl"))
 137                 if err != nil {
 138                         return err
 139                 }
 140
 141                 if day < place.day {
 142                         continue
 143                 }
 144
 145                 offset := uint64(0)
 146                 if day == place.day {
 147                         offset = place.offset
 148                 }
 149
 150                 err = journalScanFile(ctx, path, day, offset, n == len(paths)-1, add)
 151                 if err != nil {
 152                         return err
 153                 }
 154         }
 155
 156         return nil
 157 }
 158
 159 func (j *Journal) closeWriter() error {
 160         if j.file == nil {
 161                 return nil
 162         }
 163
 164         err := j.file.Close()
 165         j.file = nil
 166         j.day = 0
 167         if err != nil {
 168                 return fmt.Errorf("close day file: %w", err)
 169         }
 170
 171         return nil
 172 }
 173
 174 // journalDayNumber returns the day YYYY-MM-DD as the number YYYYMMDD.
 175 func journalDayNumber(day string) (uint32, error) {
 176         number, err := strconv.ParseUint(strings.ReplaceAll(day, "-", ""), 10, 32)
 177         if err != nil || len(day) != len("2006-01-02") {
 178                 return 0, fmt.Errorf("invalid day %q", day)
 179         }
 180
 181         return uint32(number), nil
 182 }
 183
 184 // journalDayName returns the day number YYYYMMDD as YYYY-MM-DD.
 185 func journalDayName(day uint32) string {
 186         return fmt.Sprintf("%04d-%02d-%02d", day/10000, day/100%100, day%100)
 187 }
 188
 189 // journalScanFile gives each line of the day file at path from offset on to
 190 // add. In the last day file, it cuts a part of a line at the end.
 191 func journalScanFile(ctx context.Context, path string, day uint32, offset uint64, last bool, add func([]byte, Position) error) (err error) {
 192         file, err := os.Open(path)
 193         if err != nil {
 194                 return fmt.Errorf("open day file: %w", err)
 195         }
 196
 197         defer func() {
 198                 err = errors.Join(err, file.Close())
 199         }()
 200
 201         _, err = file.Seek(int64(offset), io.SeekStart)
 202         if err != nil {
 203                 return fmt.Errorf("seek day file: %w", err)
 204         }
 205
 206         reader := bufio.NewReader(file)
 207         for {
 208                 if ctx.Err() != nil {
 209                         return ctx.Err()
 210                 }
 211
 212                 line, err := reader.ReadBytes('\n')
 213                 if errors.Is(err, io.EOF) && len(line) == 0 {
 214                         return nil
 215                 }
 216
 217                 if errors.Is(err, io.EOF) && last {
 218                         return journalCutFile(path, offset)
 219                 }
 220
 221                 if errors.Is(err, io.EOF) {
 222                         return fmt.Errorf("%s ends in an incomplete line at %d", filepath.Base(path), offset)
 223                 }
 224
 225                 if err != nil {
 226                         return fmt.Errorf("read %s: %w", filepath.Base(path), err)
 227                 }
 228
 229                 place := Position{
 230                         day:    day,
 231                         offset: offset,
 232                         length: uint32(len(line)),
 233                 }
 234
 235                 err = add(line[:len(line)-1], place)
 236                 if err != nil {
 237                         return fmt.Errorf("%s at %d: %w", filepath.Base(path), offset, err)
 238                 }
 239
 240                 offset += uint64(len(line))
 241         }
 242 }
 243
 244 // journalCutFile cuts the file at path to size bytes.
 245 func journalCutFile(path string, size uint64) error {
 246         err := os.Truncate(path, int64(size))
 247         if err != nil {
 248                 return fmt.Errorf("cut incomplete line: %w", err)
 249         }
 250
 251         return nil
 252 }