59 lines
1.6 KiB
TypeScript
59 lines
1.6 KiB
TypeScript
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import { Transform, TransformCallback } from 'stream'
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// Thanks: https://stackoverflow.com/a/45126242
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class StreamReplacer extends Transform {
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private pendingChunk: Buffer
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constructor (private readonly replacer: (line: string) => string) {
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super()
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}
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_transform (chunk: Buffer, _encoding: BufferEncoding, done: TransformCallback) {
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try {
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this.pendingChunk = this.pendingChunk?.length
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? Buffer.concat([ this.pendingChunk, chunk ])
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: chunk
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let index: number
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// As long as we keep finding newlines, keep making slices of the buffer and push them to the
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// readable side of the transform stream
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while ((index = this.pendingChunk.indexOf('\n')) !== -1) {
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// The `end` parameter is non-inclusive, so increase it to include the newline we found
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const line = this.pendingChunk.slice(0, ++index)
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// `start` is inclusive, but we are already one char ahead of the newline -> all good
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this.pendingChunk = this.pendingChunk.slice(index)
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// We have a single line here! Prepend the string we want
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this.push(this.doReplace(line))
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}
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return done()
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} catch (err) {
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return done(err)
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}
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}
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_flush (done: TransformCallback) {
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// If we have any remaining data in the cache, send it out
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if (!this.pendingChunk?.length) return done()
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try {
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return done(null, this.doReplace(this.pendingChunk))
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} catch (err) {
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return done(err)
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}
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}
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private doReplace (buffer: Buffer) {
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const line = this.replacer(buffer.toString('utf8'))
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return Buffer.from(line, 'utf8')
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}
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}
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export {
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StreamReplacer
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}
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