| 1 | package agent |
| 2 | |
| 3 | import ( |
| 4 | "bytes" |
| 5 | "encoding/json" |
| 6 | "fmt" |
| 7 | "io" |
| 8 | "log/slog" |
| 9 | "os" |
| 10 | "path/filepath" |
| 11 | "time" |
| 12 | |
| 13 | "reasonix/internal/fileutil" |
| 14 | "reasonix/internal/store" |
| 15 | ) |
| 16 | |
| 17 | // sessionDAGTailRepairMinAge keeps tail repair from truncating a line another |
| 18 | // writer is still appending: a torn tail is only cut once the log has been |
| 19 | // quiet for this long. |
| 20 | const sessionDAGTailRepairMinAge = 2 * time.Second |
| 21 | |
| 22 | type sessionDAGHeader struct { |
| 23 | generation int64 |
| 24 | upgradedFrom int |
| 25 | } |
| 26 | |
| 27 | // encodeSessionDAGEntries serializes entries one per line, filling in the |
| 28 | // schema version and the default writer/timestamp. |
| 29 | func encodeSessionDAGEntries(entries []sessionDAGEntry, now time.Time) ([]byte, error) { |
| 30 | var buf bytes.Buffer |
| 31 | for i := range entries { |
| 32 | e := &entries[i] |
| 33 | e.SchemaVersion = sessionDAGSchemaVersion |
| 34 | if e.At.IsZero() { |
| 35 | e.At = now |
| 36 | } |
| 37 | if e.Writer == "" { |
| 38 | e.Writer = SessionWriterID() |
| 39 | } |
| 40 | b, err := json.Marshal(e) |
| 41 | if err != nil { |
| 42 | return nil, fmt.Errorf("encode session entry: %w", err) |
| 43 | } |
| 44 | buf.Write(b) |
| 45 | buf.WriteByte('\n') |
| 46 | } |
| 47 | return buf.Bytes(), nil |
| 48 | } |
| 49 | |
| 50 | // appendSessionDAGEntries writes entries as one contiguous batch and returns |
| 51 | // the log size afterwards. Callers hold the session file lock: JSON lines |
| 52 | // exceed PIPE_BUF, so the flock, not O_APPEND, is what keeps two writers' |
| 53 | // batches from interleaving. |
| 54 | func appendSessionDAGEntries(sessionPath string, entries []sessionDAGEntry, sync bool) (int64, error) { |
| 55 | path := store.SessionEventLog(sessionPath) |
| 56 | if path == "" { |
| 57 | return 0, fmt.Errorf("empty session event log path") |
| 58 | } |
| 59 | if len(entries) == 0 { |
| 60 | info, err := os.Stat(path) |
| 61 | if err != nil { |
| 62 | return 0, err |
| 63 | } |
| 64 | return info.Size(), nil |
| 65 | } |
| 66 | fileutil.Crash("dag-append", path) |
| 67 | if err := os.MkdirAll(filepath.Dir(path), 0o755); err != nil { |
| 68 | return 0, err |
| 69 | } |
| 70 | data, err := encodeSessionDAGEntries(entries, time.Now().UTC()) |
| 71 | if err != nil { |
| 72 | return 0, err |
| 73 | } |
| 74 | f, err := os.OpenFile(path, os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0o600) |
| 75 | if err != nil { |
| 76 | return 0, fmt.Errorf("open session event log: %w", err) |
| 77 | } |
| 78 | if err := f.Chmod(0o600); err != nil { |
| 79 | _ = f.Close() |
| 80 | return 0, fmt.Errorf("protect session event log: %w", err) |
| 81 | } |
| 82 | if _, err := f.Write(data); err != nil { |
| 83 | _ = f.Close() |
| 84 | return 0, fmt.Errorf("append session entries: %w", err) |
| 85 | } |
| 86 | if sync { |
| 87 | if err := f.Sync(); err != nil { |
| 88 | _ = f.Close() |
| 89 | return 0, err |
| 90 | } |
| 91 | } |
| 92 | info, err := f.Stat() |
| 93 | if err != nil { |
| 94 | _ = f.Close() |
| 95 | return 0, err |
| 96 | } |
| 97 | return info.Size(), f.Close() |
| 98 | } |
| 99 | |
| 100 | // readSessionDAGHeader decodes the leading log entry without reading the rest |
| 101 | // of the file, so a writer can notice a rotation (new generation) cheaply. |
| 102 | func readSessionDAGHeader(sessionPath string) (sessionDAGHeader, bool, error) { |
| 103 | path := store.SessionEventLog(sessionPath) |
| 104 | if path == "" { |
| 105 | return sessionDAGHeader{}, false, nil |
| 106 | } |
| 107 | f, err := os.Open(path) |
| 108 | if err != nil { |
| 109 | if os.IsNotExist(err) { |
| 110 | return sessionDAGHeader{}, false, nil |
| 111 | } |
| 112 | return sessionDAGHeader{}, false, err |
| 113 | } |
| 114 | defer f.Close() |
| 115 | var e sessionDAGEntry |
| 116 | if err := json.NewDecoder(io.LimitReader(f, sessionEventProbeMaxBytes)).Decode(&e); err != nil { |
| 117 | return sessionDAGHeader{}, false, nil |
| 118 | } |
| 119 | if e.SchemaVersion != sessionDAGSchemaVersion || e.Type != sessionDAGTypeLog { |
| 120 | return sessionDAGHeader{}, false, nil |
| 121 | } |
| 122 | return sessionDAGHeader{generation: e.Generation, upgradedFrom: e.UpgradedFrom}, true, nil |
| 123 | } |
| 124 | |
| 125 | // repairSessionDAGTail truncates a torn tail found by replay once the log has |
| 126 | // been quiet long enough that no writer can still be finishing that line. The |
| 127 | // discarded bytes go to the .damaged sidecar first. Callers hold the file lock. |
| 128 | func repairSessionDAGTail(sessionPath string, st *sessionDAGState, now time.Time) (bool, error) { |
| 129 | if st == nil || !st.damaged || st.lastGoodEnd >= st.size { |
| 130 | return false, nil |
| 131 | } |
| 132 | path := store.SessionEventLog(sessionPath) |
| 133 | info, err := os.Stat(path) |
| 134 | if err != nil { |
| 135 | return false, err |
| 136 | } |
| 137 | if info.Size() != st.size || now.Sub(info.ModTime()) < sessionDAGTailRepairMinAge { |
| 138 | return false, nil |
| 139 | } |
| 140 | if preserveErr := preserveDamagedEventLogTail(sessionPath, path, st.lastGoodEnd, st.size); preserveErr != nil { |
| 141 | slog.Warn("session: could not preserve damaged log tail; truncating anyway", |
| 142 | "path", path, "from", st.lastGoodEnd, "size", st.size, "err", preserveErr) |
| 143 | } |
| 144 | if err := os.Truncate(path, st.lastGoodEnd); err != nil { |
| 145 | return false, err |
| 146 | } |
| 147 | if st.lastGoodEnd > 0 { |
| 148 | f, err := os.OpenFile(path, os.O_WRONLY|os.O_APPEND, 0o600) |
| 149 | if err != nil { |
| 150 | return false, err |
| 151 | } |
| 152 | if _, err := f.Write([]byte{'\n'}); err != nil { |
| 153 | _ = f.Close() |
| 154 | return false, err |
| 155 | } |
| 156 | if err := f.Close(); err != nil { |
| 157 | return false, err |
| 158 | } |
| 159 | } |
| 160 | st.size = st.lastGoodEnd |
| 161 | if st.lastGoodEnd > 0 { |
| 162 | st.size++ |
| 163 | } |
| 164 | st.damaged = false |
| 165 | return true, nil |
| 166 | } |
| 167 |