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feat: Adds begin/end byte slices to exporter (#207)
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,104 @@ | ||
| 'use strict' | ||
|
|
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| const CID = require('cids') | ||
| const pull = require('pull-stream') | ||
| const asyncValues = require('pull-async-values') | ||
| const asyncMap = require('pull-stream/throughs/async-map') | ||
| const map = require('pull-stream/throughs/map') | ||
| const UnixFS = require('ipfs-unixfs') | ||
| const waterfall = require('async/waterfall') | ||
|
|
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| module.exports = (fileNode, dag, begin = 0, end) => { | ||
| let streamPosition = 0 | ||
|
|
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| return pull( | ||
| asyncValues((cb) => { | ||
| const meta = UnixFS.unmarshal(fileNode.data) | ||
|
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| if (meta.type !== 'file') { | ||
| return cb(new Error(`Node ${fileNode} was not a file (was ${meta.type}), can only read files`)) | ||
| } | ||
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| const fileSize = meta.fileSize() | ||
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| if (!end || end > fileSize) { | ||
| end = fileSize | ||
| } | ||
|
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| if (begin < 0) { | ||
| begin = fileSize + begin | ||
| } | ||
|
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| if (end < 0) { | ||
| end = fileSize + end | ||
| } | ||
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| const links = fileNode.links | ||
|
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| if (!links || !links.length) { | ||
| if (meta.data && meta.data.length) { | ||
| // file was small enough to fit in one DAGNode so has no links | ||
| return cb(null, [(done) => done(null, meta.data)]) | ||
| } | ||
|
|
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| return cb(new Error(`Path ${fileNode} had no links or data`)) | ||
| } | ||
|
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| const linkedDataSize = links.reduce((acc, curr) => acc + curr.size, 0) | ||
| const overhead = (linkedDataSize - meta.fileSize()) / links.length | ||
|
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| // create an array of functions to fetch link data | ||
| cb(null, links.map((link) => (done) => { | ||
| // DAGNode Links report unixfs object data sizes $overhead bytes (typically 14) | ||
| // larger than they actually are due to the protobuf wrapper | ||
| const bytesInLinkedObjectData = link.size - overhead | ||
|
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| if (begin > (streamPosition + bytesInLinkedObjectData)) { | ||
| // Start byte is after this block so skip it | ||
| streamPosition += bytesInLinkedObjectData | ||
|
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| return done() | ||
| } | ||
|
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| if (end < streamPosition) { | ||
| // End byte was before this block so skip it | ||
| streamPosition += bytesInLinkedObjectData | ||
|
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| return done() | ||
| } | ||
|
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| // transform the multihash to a cid, the cid to a node and the node to some data | ||
| waterfall([ | ||
| (next) => dag.get(new CID(link.multihash), next), | ||
| (node, next) => next(null, node.value.data), | ||
| (data, next) => next(null, UnixFS.unmarshal(data).data) | ||
| ], done) | ||
| })) | ||
| }), | ||
| asyncMap((loadLinkData, cb) => loadLinkData(cb)), | ||
| pull.filter(Boolean), | ||
| map((data) => { | ||
| const block = extractDataFromBlock(data, streamPosition, begin, end) | ||
|
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| streamPosition += data.length | ||
|
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| return block | ||
| }) | ||
| ) | ||
| } | ||
|
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| function extractDataFromBlock (block, streamPosition, begin, end) { | ||
| const blockLength = block.length | ||
|
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| if (end - streamPosition < blockLength) { | ||
| // If the end byte is in the current block, truncate the block to the end byte | ||
| block = block.slice(0, end - streamPosition) | ||
| } | ||
|
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| if (begin > streamPosition && begin < (streamPosition + blockLength)) { | ||
| // If the start byte is in the current block, skip to the start byte | ||
| block = block.slice(begin - streamPosition) | ||
| } | ||
|
|
||
| return block | ||
| } |
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