faucet-transform-wasm 1.0.2

//! Config types for the WASM transform. No I/O or wasmtime here.

use schemars::JsonSchema;
use serde::{Deserialize, Serialize};

/// Configuration for the `wasm` transform.
#[derive(Debug, Clone, Serialize, Deserialize, JsonSchema)]
pub struct WasmTransformConfig {
    /// Filesystem path to the precompiled `.wasm` module (absolute, or relative
    /// to the working directory). URLs are not supported in v1.
    pub module: String,
    /// Name of the exported transform function. Default `"transform"`.
    #[serde(default = "default_function")]
    pub function: String,
    /// Linear-memory cap for the module, in mebibytes. A record that grows
    /// memory past this limit fails that record (routed by `on_error`).
    /// Default `16`. The practical lower bound for ~1 KB JSON records is ~8 MB.
    #[serde(default = "default_memory_limit_mb")]
    pub memory_limit_mb: u32,
    /// wasmtime fuel budget per record — a deterministic CPU bound. A record
    /// that exhausts its fuel fails (routed by `on_error`). Default
    /// `10_000_000`. Fuel is the effective CPU limit in v1 (there are no
    /// blocking host calls, so a wall-clock timeout would be redundant).
    #[serde(default = "default_fuel_limit")]
    pub fuel_limit: u64,
    /// What to do when a record fails inside the module (trap, fuel/memory
    /// exhaustion, ABI violation, or non-JSON output). Default `fail`.
    #[serde(default)]
    pub on_error: WasmOnError,
    /// Re-stat the module file's mtime before each page; recompile and swap in
    /// the new module atomically at the page boundary if it changed. In-flight
    /// records within a page always use one module. Default `false`.
    #[serde(default)]
    pub reload_on_change: bool,
}

/// Policy for a per-record module failure.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Default, Serialize, Deserialize, JsonSchema)]
#[serde(rename_all = "snake_case")]
pub enum WasmOnError {
    /// Abort the whole run with a [`faucet_core::FaucetError::Transform`]
    /// (the default; matches every other transform's fail-fast behaviour).
    #[default]
    Fail,
    /// Drop the failing record and continue (a warning + metric is emitted).
    Skip,
    /// Emit the record unchanged and continue (a warning + metric is emitted).
    Passthrough,
}

fn default_function() -> String {
    "transform".to_owned()
}

fn default_memory_limit_mb() -> u32 {
    16
}

fn default_fuel_limit() -> u64 {
    10_000_000
}

impl WasmTransformConfig {
    /// The low-cardinality metric label for this module — the file basename.
    pub(crate) fn module_label(&self) -> String {
        std::path::Path::new(&self.module)
            .file_name()
            .map(|s| s.to_string_lossy().into_owned())
            .unwrap_or_else(|| self.module.clone())
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use serde_json::json;

    #[test]
    fn decodes_minimal_config_with_defaults() {
        let cfg: WasmTransformConfig =
            serde_json::from_value(json!({"module": "./t.wasm"})).unwrap();
        assert_eq!(cfg.module, "./t.wasm");
        assert_eq!(cfg.function, "transform");
        assert_eq!(cfg.memory_limit_mb, 16);
        assert_eq!(cfg.fuel_limit, 10_000_000);
        assert_eq!(cfg.on_error, WasmOnError::Fail);
        assert!(!cfg.reload_on_change);
    }

    #[test]
    fn decodes_full_config() {
        let cfg: WasmTransformConfig = serde_json::from_value(json!({
            "module": "/abs/redact.wasm",
            "function": "run",
            "memory_limit_mb": 32,
            "fuel_limit": 5000,
            "on_error": "skip",
            "reload_on_change": true
        }))
        .unwrap();
        assert_eq!(cfg.function, "run");
        assert_eq!(cfg.memory_limit_mb, 32);
        assert_eq!(cfg.fuel_limit, 5000);
        assert_eq!(cfg.on_error, WasmOnError::Skip);
        assert!(cfg.reload_on_change);
    }

    #[test]
    fn rejects_missing_module() {
        let err = serde_json::from_value::<WasmTransformConfig>(json!({})).unwrap_err();
        assert!(err.to_string().contains("module"), "{err}");
    }

    #[test]
    fn rejects_unknown_on_error() {
        let err = serde_json::from_value::<WasmTransformConfig>(
            json!({"module": "t.wasm", "on_error": "explode"}),
        )
        .unwrap_err();
        assert!(
            err.to_string().to_lowercase().contains("on_error")
                || err.to_string().contains("explode"),
            "{err}"
        );
    }

    #[test]
    fn module_label_is_basename() {
        let cfg: WasmTransformConfig =
            serde_json::from_value(json!({"module": "/a/b/redact_email.wasm"})).unwrap();
        assert_eq!(cfg.module_label(), "redact_email.wasm");
        let bare: WasmTransformConfig =
            serde_json::from_value(json!({"module": "x.wasm"})).unwrap();
        assert_eq!(bare.module_label(), "x.wasm");
    }

    #[test]
    fn schema_builds_with_module_property() {
        let schema = schemars::schema_for!(WasmTransformConfig);
        let json = serde_json::to_value(&schema).unwrap();
        assert!(
            json.get("properties")
                .and_then(|p| p.get("module"))
                .is_some()
        );
    }
}