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Change to avoid overwriting data length bytes #22

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Change to avoid overwriting data length bytes #22

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11 changes: 5 additions & 6 deletions frame/recoverable.js
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Original file line number Diff line number Diff line change
Expand Up @@ -84,20 +84,19 @@ module.exports = function (blocks, blockSize, offsetCodec) {
/**
* Overwrites an item at `offset` with null bytes.
*
* The only bytes we need to change are the actual data bytes, so we can skip
* the book-end bytes that record the length of the data and *only* touch the
* data bytes themselves.
*
* @param {number} offset - the offset of the item to overwrite
* @param {function} cb - callback that returns any error as an argument
*/
const overwrite = (offset, cb) => {
blocks.readUInt32BE(offset, function (err, len) {
if (err) return cb(err)

const bookend = Buffer.alloc(4)
bookend.writeUInt32BE(len, 0)

const nullBytes = Buffer.alloc(len)
const full = Buffer.concat([bookend, nullBytes, bookend])

blocks.write(full, offset, cb)
blocks.write(nullBytes, offset + 4, cb)
})
}

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