Google already successfully argued in court that creating an online search index of books constitutes fair use: https://en.wikipedia.org/wiki/Authors_Guild,_Inc._v._Google,....
The index isn't the full content. The OP search is about indexing the entire contents of the book for verbatim information retrieval.
The index isn't the full content. The OP search is about indexing the entire contents of the book for verbatim information retrieval.