1. A method for identifying a network application, comprising: analyzing, by a processor of a computer system, a source code of a network application, among a plurality of network applications, to extract a plurality of source code tokens; generating an index document of the network application based on the plurality of source code tokens, wherein the index document is included in a plurality of index documents corresponding to the plurality of network applications, the plurality of index documents being loaded as a corpus into a search engine; extracting, by the processor, a plurality of packet header tokens from a packet header of a packet in a flow to generate one or more query documents; comparing, by the processor using the search engine, the plurality of packet header tokens of the one or more query documents to the plurality of index documents to generate a plurality of match scores, wherein each of the plurality of match scores represents a similarity measure between the plurality of packet header tokens and one of the plurality of index documents; and determining, based at least on a match score of the plurality of match scores and corresponding to the network application, that the flow is generated by the network application.