Function ReadPage

internal/guts_cli/guts_cli.go:21–70

ReadPage reads Page info & full Page data from a path. This is not transactionally safe.

(path string, pageID uint64)

// ReadPage reads Page info & full Page data from a path.
// This is not transactionally safe.
func ReadPage(path string, pageID uint64) (*common.Page, []byte, error) {
	// Find Page size.
	pageSize, hwm, err := ReadPageAndHWMSize(path)
	if err != nil {
		return nil, nil, fmt.Errorf("read Page size: %s", err)
	}

	// Open database file.
	f, err := os.Open(path)
	if err != nil {
		return nil, nil, err
	}
	defer f.Close()

	// Read one block into buffer.
	buf := make([]byte, pageSize)
	if n, err := f.ReadAt(buf, int64(pageID*pageSize)); err != nil {
		return nil, nil, err
	} else if n != len(buf) {
		return nil, nil, io.ErrUnexpectedEOF
	}

	// Determine total number of blocks.
	p := common.LoadPage(buf)
	if p.Id() != common.Pgid(pageID) {
		return nil, nil, fmt.Errorf("error: %w due to unexpected Page id: %d != %d", ErrCorrupt, p.Id(), pageID)
	}
	overflowN := p.Overflow()
	if overflowN >= uint32(hwm)-3 { // we exclude 2 Meta pages and the current Page.
		return nil, nil, fmt.Errorf("error: %w, Page claims to have %d overflow pages (>=hwm=%d). Interrupting to avoid risky OOM", ErrCorrupt, overflowN, hwm)
	}

	if overflowN == 0 {
		return p, buf, nil
	}

	// Re-read entire Page (with overflow) into buffer.
	buf = make([]byte, (uint64(overflowN)+1)*pageSize)
	if n, err := f.ReadAt(buf, int64(pageID*pageSize)); err != nil {
		return nil, nil, err
	} else if n != len(buf) {
		return nil, nil, io.ErrUnexpectedEOF
	}
	p = common.LoadPage(buf)
	if p.Id() != common.Pgid(pageID) {
		return nil, nil, fmt.Errorf("error: %w due to unexpected Page id: %d != %d", ErrCorrupt, p.Id(), pageID)
	}

	return p, buf, nil
}

func WritePage(path string, pageBuf []byte) error {
	page := common.LoadPage(pageBuf)