  A key prediction of the standard cosmological model -- which relies on the
assumption that dark matter is cold, i.e. non-relativistic at the epoch of
structure formation -- is the existence of a large number of dark matter
substructures on sub-galactic scales. This assumption can be tested by studying
the perturbations induced by dark matter substructures on cold stellar streams.
Here, we study the prospects for discriminating cold from warm dark matter by
generating mock data for upcoming astronomical surveys such as the Large
Synoptic Survey Telescope (LSST), and reconstructing the properties of the dark
matter particle from the perturbations induced on the stellar density profile
of a stream. We discuss the statistical and systematic uncertainties, and show
that the method should allow to set stringent constraints on the mass of
thermal dark matter relics, and possibly to yield an actual measurement of the
dark matter particle mass if it is in the $\mathcal{O}(1)$ keV range.
