Research papers disseminate the knowledge produced by the scientific community. Access to this literature is crucial for researchers and the general public. Apparently 'bibliogifts' are available online for free from text-sharing platforms. However, little is known about such platforms. What is the size of the underlying digital libraries? What are the topics covered? Where do these documents originally come from? This paper reports a study of the Library Genesis platform (LibGen). The 25 million documents (42 terabytes) it hosts and distributes for free are mostly research papers, textbooks, and books in English. The paper collection stems from isolated but massive paper uploads (71%) in line with a 'biblioleaks' scenario, as well as from daily crowdsourcing (29%) by worldwide users of platforms such as Reddit Scholar and Sci-Hub. By relating the DOIs registered at CrossRef and those cached at LibGen, this study reveals that 36% of all DOI papers are available for free at LibGen. This figure is even higher (68%) for three major publishers: Elsevier, Springer, and Wiley. More research is needed to understand to what extent researchers and the general public have recourse to such text-sharing platforms, and why.