Solution
import io
filedata = request.files['file'].read()
data = io.BytesIO(filedata)
tmp_mesh = mesh.Mesh.from_file("tmp.stl", fh=data)
import io
filedata = request.files['file'].read()
data = io.BytesIO(filedata)
tmp_mesh = mesh.Mesh.from_file("tmp.stl", fh=data)