Perfscale Faker

Deterministic Faker-style test data as a pure Rust/WASM Perfscale library. It adds internet, address, and payment functions to ${faker...} tokens without changing the engine or granting filesystem, clock, random, or network capabilities.

Version 0.1.0 deliberately provides a small embedded English corpus, not the full Python Faker API. Tested with Perfscale v0.28.0.

Install

Download the component and checksum from GitHub Releases, or build it locally as shown below. Declare it in the test or config YAML; relative paths resolve against the declaring file:

libraries:
  - use: ./faker.wasm
    as: faker                    # optional: faker is the manifest default
    capabilities: []             # required; this component needs no grants
    with:
      language: en               # optional, default: en
      encoding: plain            # optional: plain (default) or url

Use the functions inside any payload that supports ${alias.fn(...)} tokens:

steps:
  - use: std/http@v1
    with:
      method: POST
      url: https://api.example.test/users
      body:
        email: "${faker.internet("email")}"
        city: "${faker.address("city")}"

A known function with an unknown kind, invalid arguments, or invalid with: options fails the step instead of sending bad data. Calls return fresh values; there is no optional memo-key argument in v0.1.0.

Functions

Call	Result
internet("email")	ASCII first.lastN@example.com/net/org address
address("street_address")	Street number and name
address("zip_code")	Five-digit postal code
address("city")	City
address("state_abbr")	Two-letter US state abbreviation
address("country")	Country
payment("credit_card_number")	Visa test number 4111111111111111
payment("credit_card_expiration_month")	Month 1 through 12
payment("credit_card_expiration_year")	Uniform year from current UTC year +1 through +71, inclusive
payment("credit_card_cvv")	Number 100 through 999

The email domains are reserved for examples. The component does not send email, process payments, or fetch real personal data.

Options

Both with: keys are optional. Unknown keys and values are errors.

Option	Values	Default
language	en (the only corpus currently available)	en
encoding	plain, url	plain

encoding: url percent-encodes the UTF-8 bytes of every returned value: @ becomes %40, spaces become %20, and URL-reserved punctuation is escaped. This is useful when inserting generated values into an application/x-www-form-urlencoded body or a URL query. Do not use this mode for ordinary JSON values.

libraries:
  - use: /loadgen/faker.wasm
    as: faker
    capabilities: []
    with: { language: en, encoding: url }

steps:
  - name: checkout
    use: std/http@v1
    with:
      method: POST
      url: "${{ env.BASE_URL }}/cart/checkout"
      headers: { Content-Type: application/x-www-form-urlencoded }
      body: 'email=${faker.internet("email")}&street_address=${faker.address("street_address")}&zip_code=${faker.address("zip_code")}&city=${faker.address("city")}&state=${faker.address("state_abbr")}&country=${faker.address("country")}&credit_card_number=${faker.payment("credit_card_number")}&credit_card_expiration_month=${faker.payment("credit_card_expiration_month")}&credit_card_expiration_year=${faker.payment("credit_card_expiration_year")}&credit_card_cvv=${faker.payment("credit_card_cvv")}'
    check: { status: 200 }

The Online Boutique migration PR uses the same component in its Docker-based load generator.

Determinism and time

All random choices come from the Perfscale SDK's seeded PRNG. A config such as seed: 42 replays the same sequence for the same VUs, calls, and inputs. Expiration years also depend on ctx.time_ms, so their range advances with the UTC year. No WASI clock or random import is used.

Docker distribution

Each release publishes faker.wasm, faker.wasm.sha256, and an artifact-only OCI image. The image contains no executable runtime; it exists for COPY --from in another Dockerfile:

FROM ghcr.io/perfscale/faker:0.1.0 AS faker
FROM ghcr.io/perfscale/perfscale:0.28.0
WORKDIR /loadgen
COPY --from=faker /faker.wasm ./
COPY test.yaml config.yaml ./

Pin the GHCR multi-arch digest in production builds. No Rust toolchain or source checkout is needed in the consuming image.

Build and test

Rust 1.82 or newer emits WASI Preview 2 components directly:

rustup target add wasm32-wasip2
cargo test
cargo build --release --target wasm32-wasip2
# target/wasm32-wasip2/release/faker.wasm

Run the real engine integration test without any external HTTP service:

(cd e2e && perfscale lint faker.test.yaml config.yaml)
perfscale run -f e2e/faker.test.yaml -c e2e/config.yaml

On macOS, select the Command Line Tools SDK if the wasm build requires it:

export DEVELOPER_DIR=/Library/Developer/CommandLineTools

Documentation: Perfscale/docs.

License

MIT OR Apache-2.0, same as Perfscale.