wavetermdev/waveterm · info · ErrBOF

beginning of file

Error message

beginning of file

What it means

ErrBOF ("beginning of file") is a sentinel error in the logview multibuf package. Backward-scanning APIs (PrevLinePtr, Move, PrevLine) return it when the caller asks to move before offset 0 of the file, i.e. there is no earlier line to read. It is a normal, expected signal — not a failure — that the scan has hit the start of the file.

Source

Thrown at pkg/util/logview/multibuf.go:20

// SPDX-License-Identifier: Apache-2.0

package logview

import (
	"errors"
	"io"
	"os"
)

type MultiBufferByteGetter struct {
	File    *os.File
	Offset  int64
	EOF     bool
	Buffers [][]byte
	BufSize int64
}

var ErrBOF = errors.New("beginning of file")

func MakeMultiBufferByteGetter(file *os.File, bufSize int64) *MultiBufferByteGetter {
	return &MultiBufferByteGetter{
		File:    file,
		Offset:  0,
		EOF:     false,
		Buffers: [][]byte{},
		BufSize: bufSize,
	}
}

func (mb *MultiBufferByteGetter) readFromBuffer(offset int64) (byte, bool) {
	if offset < mb.Offset || offset >= mb.Offset+int64(mb.bufSize()) {
		return 0, false
	}
	bufIdx := int((offset - mb.Offset) / mb.BufSize)
	bufOffset := (offset - mb.Offset) % mb.BufSize
	return mb.Buffers[bufIdx][bufOffset], true

View on GitHub (pinned to a4447c1563)

Solutions

1. Check for errors.Is(err, logview.ErrBOF) after each backward step and treat it as the stop condition of your scan loop, not as a failure.
2. Clamp or validate the target offset before calling Move/PrevLinePtr so it never goes below 0.
3. Ensure the *os.File passed to MakeMultiBufferByteGetter is valid and opened for reading so offsets behave as expected.

Example fix

// before
line, err := mb.PrevLinePtr(off)
if err != nil {
    return err
}
// after
line, err := mb.PrevLinePtr(off)
if errors.Is(err, logview.ErrBOF) {
    return nil // reached start of file; stop scanning
}
if err != nil {
    return err
}

if targetOffset < 0 {
    // skip backward scan; already at start of file
}

func isBOF(err error) bool { return errors.Is(err, logview.ErrBOF) }

line, err := mb.PrevLinePtr(off)
if errors.Is(err, logview.ErrBOF) {
    return io.EOF // normalize to standard end/edge-of-input signal
}
if err != nil {
    return err
}

When it happens

Trigger: Calling PrevLinePtr/PrevLine repeatedly until the iterator is already at offset 0, or calling Move with a negative target offset below 0 on a MultiBufferByteGetter reading a log file.

Common situations: Tail/grep-style log viewers that page backwards through a log and read past the first line; scanning a small file where the requested lookback window exceeds the file size.

Related errors

• procinfo: process not found
• failed to copy from file: %v
• no window found with workspace ${data.workspaceid}
• missing zone file info for ${zoneId}:${fileName}
• integer overflow

AI-assisted analysis of wavetermdev/waveterm@a4447c1563 (2026-09-01). Data as JSON: /api/errors/a96d8ca82147cba3. Report an issue: GitHub.