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  2. Flex Gateway Policy Development Kit (PDK) (1.2)
  3. Implementing Your Custom Policy Features in Rust

  4. Using Third-Party Libraries

Using Third-Party Libraries

To view an example policy project that uses third-party libraries, see Crypto Policy Example.

Proxy Wasm defines a low level binary application interface (abi), that limits the system calls a library can make. All third-party libraries included in your policy must be compatible with the wasm32-wasi Rust compilation target.

To define a library such as serde_urlencoded, add it to the dependency list in cargo.toml:

[dependencies]
...
serde_urlencoded = "0.7.0"

Defining libraries enables you to use functions in lib.rs such as:

serde_urlencoded::to_string([("token", "myToken")])

Libraries that interact with an external service like a database, or perform a system call like reading a file, are usually not compatible with the wasm32-wasi target.

If your policy interacts with external services, use the Flex Gateway exposed HttpClient. For more information about performing an HTTP call, see Performing an HTTP Call.

It is possible that some libraries compile properly to the wasm32-wasi target but don’t work properly when deployed to Flex Gateway. Example errors include:

  • Failed to load Wasm module due to a missing import: …​

  • Wasm VM failed to initialize Wasm code

  • Plugin configured to fail closed failed to load

In these cases, contact the owners of the third-party library, or use a different library.

See Also