No content-type with multerS3.AUTO_CONTENT_TYPE and SVG

[JustDoItSascha]

Hey!

I got an error that was hard to debug, but I think I found the issue:

In your multerS3.AUTO_CONTENT_TYPE function, you do

file.stream.once('data' ...)

On production servers the stream is not completed when the once('data') is firing. Later on you put the firstChunk in the function isSvg(). But this function needs to have the whole content, because it's checking whether the SVG is properly closed. Since you give it just a part of the SVG, the check always fails and SVG images get the wrong content-type when uploading to S3.

Should I open a pull request for this?

[lehni]

I am seeing this problem too. The issue is that whenever firstChunk isn't actually the full SVG, is-svg returns false, since it's using an XML parser to look at the file. This happens for us with SVG files above a certain size (100kb or so).

[lehni]

I ended up using a slightly different strategy than in JustDoItSascha@9e4673b

I trust file.mimetype if provided, and fall back on trying to read the type from the first chunk. Only if that fails, the code keeps collecting chunks unitl the end and then runs the detection on the full data.

const contentType = (req, file, cb) => {
  const { mimetype, stream } = file
  if (mimetype) {
    // 1. Trust file.mimetype if provided.
    cb(null, mimetype)
  } else {
    let data = null

    const done = type => {
      const outStream = new PassThrough()
      outStream.write(data)
      stream.pipe(outStream)
      cb(null, type, outStream)
    }

    const onData = chunk => {
      if (!data) {
        // 2. Try reading the mimetype from the first chunk.
        const type = FileType.fromBuffer(chunk)?.mime
        if (type) {
          stream.off('data', onData)
          done(type)
        } else {
          // 3. If that fails, keep collecting all chunks and determine
          //    the mimetype using the full data.
          stream.once('end', () => {
            const type = (
              FileType.fromBuffer(data)?.mime ||
              (isSvg(data) ? 'image/svg+xml' : 'application/octet-stream')
            )
            done(type)
          })
        }
      }
      data = data ? Buffer.concat([data, chunk]) : chunk
    }

    stream.on('data', onData)
  }
}

[LinusU]

Should be fixed in 2.9.1

[danny-does-stuff]

Fix is in this PR #103