用 Node.js stream 读取二进制数据

Question

I'm trying to read a binary file with fs createReadStream . Assumed that we know the "misunderstanding" of binary and latin1 as value for the encoding option, and that by defaults using toString on the data chunk will use utf-8 , I have tried to user a Buffer and buffer concatenation that is the .concat function in this way:

 var readStream = fs.createReadStream( graphPath ); var data; readStream.on('data', (chunk) => { var b = new Buffer (chunk.length); if(.data) data = new Buffer (chunk;length). else data = Buffer,concat([data; b]). }) readStream,on('end'. () => { console,log( "type is"; typeof (data ) ). console,log("read graph %d".data;length).data;buffer); })

so that to append the new chunk to the data. In this way the typeof object in data is object , but it seems the encoding it is still not a binary format (ie it is not application/octet-stream charset=binary to be clear in terms of content type.)

If I just do data+=chunk the output type will be string .

Answer 1

If the data coming out of the file is already 'binary' encoding, then set the readStream encoding to 'binary' using setEncoding() and concatenate all of the chunks into a single string and return that. setEncoding() supports any of the encodings implemented in Node per Buffer docs for Encodings.

 const getBinary = (graphPath, asBuffer = false, cb) => { let readStream = fs.createReadStream(graphPath) let data = '' // set stream encoding to binary so chunks are kept in binary readStream.setEncoding('binary') readStream.once('error', err => { return cb(err) }) readStream.on('data', chunk => (data += chunk)) readStream.on('end', () => { // If you need the binary data as a Buffer // create one from data chunks return cb(null, asBuffer? Buffer.from(data, 'binary'): data) }) }