Serialization

For some applications, compiling Hyperscan pattern databases immediately prior to use is not an appropriate design. Some users may wish to:

  • Compile pattern databases on a different host;
  • Persist compiled databases to storage and only re-compile pattern databases when the patterns change;
  • Control the region of memory in which the compiled database is located.

Hyperscan pattern databases are not completely flat in memory: they contain pointers and have specific alignment requirements. Therefore, they cannot be copied (or otherwise relocated) directly. To enable these use cases, Hyperscan provides functionality for serializing and deserializing compiled pattern databases.

The API provides the following functions:

  1. hs_serialize_database(): serializes a pattern database into a flat relocatable buffer of bytes.
  2. hs_deserialize_database(): reconstructs a newly allocated pattern database from the output of hs_serialize_database().
  3. hs_deserialize_database_at(): reconstructs a pattern database at a given memory location from the output of hs_serialize_database().
  4. hs_serialized_database_size(): given a serialized pattern database, returns the size of the memory block required by the database when deserialized.
  5. hs_serialized_database_info(): given a serialized pattern database, returns a string containing information about the database. This call is analogous to hs_database_info().

Note

Hyperscan performs both version and platform compatibility checks upon deserialization. The hs_deserialize_database() and hs_deserialize_database_at() functions will only permit the deserialization of databases compiled with (a) the same version of Hyperscan and (b) platform features supported by the current host platform. See Instruction Set Specialization for more information on platform specialization.

The Runtime Library

The main Hyperscan library (libhs) contains both the compiler and runtime portions of the library. This means that in order to support the Hyperscan compiler, which is written in C++, it requires C++ linkage and has a dependency on the C++ standard library.

Many embedded applications require only the scanning (“runtime”) portion of the Hyperscan library. In these cases, pattern compilation generally takes place on another host, and serialized pattern databases are delivered to the application for use.

To support these applications without requiring the C++ dependency, a runtime-only version of the Hyperscan library, called libhs_runtime, is also distributed. This library does not depend on the C++ standard library and provides all Hyperscan functions other that those used to compile databases.