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148 lines
3.8 KiB
JavaScript
148 lines
3.8 KiB
JavaScript
const { Stream } = require('pdfjs-dist/lib/core/stream')
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const { MissingDataException } = require('pdfjs-dist/lib/core/core_utils')
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const BUF_SIZE = 1024 // read from the file in 1024 byte pages
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class FSStream extends Stream {
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constructor(fh, start, length, dict, cachedBytes, checkDeadline) {
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const nonEmptyDummyBuffer = Buffer.alloc(1, 0)
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super(nonEmptyDummyBuffer, start, length, dict)
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delete this.bytes
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this.fh = fh
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this.checkDeadline = checkDeadline
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this.cachedBytes = cachedBytes || []
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}
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get length() {
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return this.end - this.start
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}
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get isEmpty() {
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return this.length === 0
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}
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// Manage cached reads from the file
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requestRange(begin, end) {
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this.checkDeadline(`request range ${begin} - ${end}`)
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// expand small ranges to read a larger amount
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if (end - begin < BUF_SIZE) {
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end = begin + BUF_SIZE
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}
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end = Math.min(end, this.length)
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// keep a cache of previous reads with {begin,end,buffer} values
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const result = {
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begin: begin,
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end: end,
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buffer: Buffer.alloc(end - begin, 0),
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}
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this.cachedBytes.push(result)
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return this.fh.read(result.buffer, 0, end - begin, begin)
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}
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_ensureGetPos(pos) {
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const found = this.cachedBytes.find(x => {
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return x.begin <= pos && pos < x.end
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})
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if (!found) {
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throw new MissingDataException(pos, pos + 1)
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}
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return found
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}
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_ensureGetRange(begin, end) {
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end = Math.min(end, this.length) // BG: handle overflow case
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const found = this.cachedBytes.find(x => {
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return x.begin <= begin && end <= x.end
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})
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if (!found) {
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throw new MissingDataException(begin, end)
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}
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return found
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}
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_readByte(found, pos) {
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return found.buffer[pos - found.begin]
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}
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_readBytes(found, pos, end) {
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return found.buffer.subarray(pos - found.begin, end - found.begin)
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}
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// handle accesses to the bytes
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ensureByte(pos) {
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this._ensureGetPos(pos) // may throw a MissingDataException
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}
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getByte() {
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const pos = this.pos
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if (this.pos >= this.end) {
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return -1
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}
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const found = this._ensureGetPos(pos)
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return this._readByte(found, this.pos++)
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}
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// BG: for a range, end is not included (see Buffer.subarray for example)
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ensureBytes(length, forceClamped = false) {
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const pos = this.pos
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this._ensureGetRange(pos, pos + length)
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}
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getBytes(length, forceClamped = false) {
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const pos = this.pos
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const strEnd = this.end
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const found = this._ensureGetRange(pos, pos + length)
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if (!length) {
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const subarray = this._readBytes(found, pos, strEnd)
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// `this.bytes` is always a `Uint8Array` here.
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return forceClamped ? new Uint8ClampedArray(subarray) : subarray
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}
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let end = pos + length
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if (end > strEnd) {
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end = strEnd
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}
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this.pos = end
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const subarray = this._readBytes(found, pos, end)
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// `this.bytes` is always a `Uint8Array` here.
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return forceClamped ? new Uint8ClampedArray(subarray) : subarray
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}
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getByteRange() {
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// BG: this isn't needed as far as I can tell
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throw new Error('not implemented')
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}
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reset() {
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this.pos = this.start
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}
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moveStart() {
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this.start = this.pos
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}
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makeSubStream(start, length, dict = null) {
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this.checkDeadline(`make sub stream start=${start}/length=${length}`)
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// BG: had to add this check for null length, it is being called with only
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// the start value at one point in the xref decoding. The intent is clear
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// enough
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// - a null length means "to the end of the file" -- not sure how it is
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// working in the existing pdfjs code without this.
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if (!length) {
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length = this.end - start
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}
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return new FSStream(
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this.fh,
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start,
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length,
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dict,
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this.cachedBytes,
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this.checkDeadline
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)
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}
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}
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module.exports = { FSStream }
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