Templates can define custom Liquid filters

Signed-off-by: itowlson <ivan.towlson@fermyon.com>

crates/templates/Cargo.toml

@@ -35,3 +35,10 @@ tokio = { version = "1.10", features = [ "fs", "process", "rt", "macros" ] }
 toml = "0.5"
 url = "2.2.2"
 walkdir = "2"
+wasmtime = { version = "0.39.1", features = [ "async" ] }
+wasmtime-wasi = "0.39.1"
+
+[dependencies.wit-bindgen-wasmtime]
+git = "https://github.com/bytecodealliance/wit-bindgen"
+rev = "cb871cfa1ee460b51eb1d144b175b9aab9c50aba"
+features = ["async"]

crates/templates/src/custom_filters.rs

@@ -0,0 +1,166 @@
+use std::{
+    fmt::{Debug, Display},
+    path::Path,
+    sync::{Arc, RwLock},
+};
+
+use anyhow::Context;
+use liquid_core::{Filter, ParseFilter, Runtime, ValueView};
+use wasmtime::{Engine, Linker, Module, Store};
+use wasmtime_wasi::{WasiCtx, WasiCtxBuilder};
+
+wit_bindgen_wasmtime::import!({paths: ["./wit/custom-filter.wit"]});
+
+struct CustomFilterContext {
+    wasi: WasiCtx,
+    data: custom_filter::CustomFilterData,
+}
+
+impl CustomFilterContext {
+    fn new() -> Self {
+        Self {
+            wasi: WasiCtxBuilder::new().build(),
+            data: custom_filter::CustomFilterData {},
+        }
+    }
+}
+
+#[derive(Clone)]
+pub(crate) struct CustomFilterParser {
+    name: String,
+    wasm_store: Arc<RwLock<Store<CustomFilterContext>>>,
+    exec: Arc<custom_filter::CustomFilter<CustomFilterContext>>,
+}
+
+impl CustomFilterParser {
+    pub(crate) fn load(name: &str, wasm_path: &Path) -> anyhow::Result<Self> {
+        let wasm = std::fs::read(&wasm_path).with_context(|| {
+            format!("Failed loading custom filter from {}", wasm_path.display())
+        })?;
+
+        let ctx = CustomFilterContext::new();
+        let engine = Engine::default();
+        let mut store = Store::new(&engine, ctx);
+        let mut linker = Linker::new(&engine);
+        wasmtime_wasi::add_to_linker(&mut linker, |ctx: &mut CustomFilterContext| &mut ctx.wasi)
+            .with_context(|| format!("Setting up WASI for custom filter {}", name))?;
+        let module = Module::new(&engine, &wasm)
+            .with_context(|| format!("Creating Wasm module for custom filter {}", name))?;
+        let instance = linker
+            .instantiate(&mut store, &module)
+            .with_context(|| format!("Instantiating Wasm module for custom filter {}", name))?;
+        let filter_exec =
+            custom_filter::CustomFilter::new(&mut store, &instance, |ctx| &mut ctx.data)
+                .with_context(|| format!("Loading Wasm executor for custom filer {}", name))?;
+
+        Ok(Self {
+            name: name.to_owned(),
+            wasm_store: Arc::new(RwLock::new(store)),
+            exec: Arc::new(filter_exec),
+        })
+    }
+}
+
+impl Debug for CustomFilterParser {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("CustomFilterParser")
+            .field("name", &self.name)
+            .finish()
+    }
+}
+
+impl ParseFilter for CustomFilterParser {
+    fn parse(
+        &self,
+        _arguments: liquid_core::parser::FilterArguments,
+    ) -> liquid_core::Result<Box<dyn Filter>> {
+        Ok(Box::new(CustomFilter {
+            name: self.name.to_owned(),
+            wasm_store: self.wasm_store.clone(),
+            exec: self.exec.clone(),
+        }))
+    }
+
+    fn reflection(&self) -> &dyn liquid_core::FilterReflection {
+        self
+    }
+}
+
+const EMPTY: [liquid_core::parser::ParameterReflection; 0] = [];
+
+impl liquid_core::FilterReflection for CustomFilterParser {
+    fn name(&self) -> &str {
+        &self.name
+    }
+
+    fn description(&self) -> &str {
+        ""
+    }
+
+    fn positional_parameters(&self) -> &'static [liquid_core::parser::ParameterReflection] {
+        &EMPTY
+    }
+
+    fn keyword_parameters(&self) -> &'static [liquid_core::parser::ParameterReflection] {
+        &EMPTY
+    }
+}
+
+struct CustomFilter {
+    name: String,
+    wasm_store: Arc<RwLock<Store<CustomFilterContext>>>,
+    exec: Arc<custom_filter::CustomFilter<CustomFilterContext>>,
+}
+
+impl Debug for CustomFilter {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("CustomFilter")
+            .field("name", &self.name)
+            .finish()
+    }
+}
+
+impl Display for CustomFilter {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.write_str(&self.name)
+    }
+}
+
+impl Filter for CustomFilter {
+    fn evaluate(
+        &self,
+        input: &dyn ValueView,
+        _runtime: &dyn Runtime,
+    ) -> Result<liquid::model::Value, liquid_core::error::Error> {
+        let mut store = self
+            .wasm_store
+            .write()
+            .map_err(|e| liquid_err(format!("Failed to get custom filter Wasm store: {}", e)))?;
+        let input_str = self.liquid_value_as_string(input)?;
+        match self.exec.exec(&mut *store, &input_str) {
+            Ok(Ok(text)) => Ok(to_liquid_value(text)),
+            Ok(Err(s)) => Err(liquid_err(s)),
+            Err(trap) => Err(liquid_err(format!("{:?}", trap))),
+        }
+    }
+}
+
+impl CustomFilter {
+    fn liquid_value_as_string(&self, input: &dyn ValueView) -> Result<String, liquid::Error> {
+        let str = input.as_scalar().map(|s| s.into_cow_str()).ok_or_else(|| {
+            liquid_err(format!(
+                "Filter '{}': no input or input is not a string",
+                self.name
+            ))
+        })?;
+        Ok(str.to_string())
+    }
+}
+
+fn to_liquid_value(value: String) -> liquid::model::Value {
+    liquid::model::Value::Scalar(liquid::model::Scalar::from(value))
+}
+
+fn liquid_err(text: String) -> liquid_core::error::Error {
+    liquid_core::error::Error::with_msg(text)
+}

crates/templates/src/lib.rs

@@ -3,6 +3,7 @@
 #![deny(missing_docs)]
 
 mod constraints;
+mod custom_filters;
 mod directory;
 mod environment;
 mod filters;

crates/templates/src/manager.rs

@@ -409,6 +409,11 @@ mod tests {
         PathBuf::from(crate_dir).join("..").join("..")
     }
 
+    fn test_data_root() -> PathBuf {
+        let crate_dir = env!("CARGO_MANIFEST_DIR");
+        PathBuf::from(crate_dir).join("tests")
+    }
+
     const TPLS_IN_THIS: usize = 8;
 
     #[tokio::test]
@@ -687,4 +692,49 @@ mod tests {
             .unwrap();
         assert!(spin_toml.contains("route = \"/...\""));
     }
+
+    #[tokio::test]
+    async fn can_use_custom_filter_in_template() {
+        let temp_dir = tempdir().unwrap();
+        let store = TemplateStore::new(temp_dir.path());
+        let manager = TemplateManager { store };
+        let source = TemplateSource::File(test_data_root());
+
+        manager
+            .install(&source, &InstallOptions::default(), &DiscardingReporter)
+            .await
+            .unwrap();
+
+        let template = manager.get("testing-custom-filter").unwrap().unwrap();
+
+        let dest_temp_dir = tempdir().unwrap();
+        let output_dir = dest_temp_dir.path().join("myproj");
+        let values = [
+            ("p1".to_owned(), "biscuits".to_owned()),
+            ("p2".to_owned(), "nomnomnom".to_owned()),
+        ]
+        .into_iter()
+        .collect();
+        let options = RunOptions {
+            output_path: output_dir.clone(),
+            name: "custom-filter-test".to_owned(),
+            values,
+            accept_defaults: false,
+        };
+
+        template
+            .run(options)
+            .silent()
+            .await
+            .execute()
+            .await
+            .unwrap();
+
+        let message = tokio::fs::read_to_string(output_dir.join("test.txt"))
+            .await
+            .unwrap();
+        assert!(message.contains("p1/studly = bIsCuItS"));
+        assert!(message.contains("p2/studly = nOmNoMnOm"));
+        assert!(message.contains("p1/clappy = b👏i👏s👏c👏u👏i👏t👏s"));
+    }
 }

crates/templates/src/reader.rs

@@ -16,6 +16,7 @@ pub(crate) struct RawTemplateManifestV1 {
     pub id: String,
     pub description: Option<String>,
     pub parameters: Option<IndexMap<String, RawParameter>>,
+    pub custom_filters: Option<Vec<RawCustomFilter>>,
 }
 
 #[derive(Debug, Deserialize)]
@@ -29,6 +30,13 @@ pub(crate) struct RawParameter {
     pub pattern: Option<String>,
 }
 
+#[derive(Debug, Deserialize)]
+#[serde(deny_unknown_fields, rename_all = "snake_case")]
+pub(crate) struct RawCustomFilter {
+    pub name: String,
+    pub wasm: String,
+}
+
 pub(crate) fn parse_manifest_toml(text: impl AsRef<str>) -> anyhow::Result<RawTemplateManifest> {
     toml::from_str(text.as_ref()).context("Failed to parse template manifest TOML")
 }

crates/templates/src/run.rs

@@ -140,7 +140,7 @@ impl Run {
                 let template_content_files = Self::collect_all_content(&from)?;
                 // TODO: okay we do want to do *some* parsing here because we don't want
                 // to prompt if the template bodies are garbage
-                let template_contents = Self::read_all(template_content_files)?;
+                let template_contents = self.read_all(template_content_files)?;
                 Self::to_output_paths(&from, to, template_contents)
             }
         };
@@ -225,8 +225,8 @@ impl Run {
     }
 
     // TODO: async when we know where things sit
-    fn read_all(paths: Vec<PathBuf>) -> anyhow::Result<Vec<(PathBuf, TemplateContent)>> {
-        let template_parser = Self::template_parser();
+    fn read_all(&self, paths: Vec<PathBuf>) -> anyhow::Result<Vec<(PathBuf, TemplateContent)>> {
+        let template_parser = self.template_parser();
         let contents = paths
             .iter()
             .map(std::fs::read)
@@ -329,11 +329,15 @@ impl Run {
         pathdiff::diff_paths(source, src_dir).map(|rel| (dest_dir.join(rel), cont))
     }
 
-    fn template_parser() -> liquid::Parser {
-        liquid::ParserBuilder::with_stdlib()
+    fn template_parser(&self) -> liquid::Parser {
+        let mut builder = liquid::ParserBuilder::with_stdlib()
             .filter(crate::filters::KebabCaseFilterParser)
             .filter(crate::filters::PascalCaseFilterParser)
-            .filter(crate::filters::SnakeCaseFilterParser)
+            .filter(crate::filters::SnakeCaseFilterParser);
+        for filter in self.template.custom_filters() {
+            builder = builder.filter(filter);
+        }
+        builder
             .build()
             .expect("can't fail due to no partials support")
     }

crates/templates/src/store.rs

@@ -71,6 +71,7 @@ pub(crate) struct TemplateLayout {
 }
 
 const METADATA_DIR_NAME: &str = "metadata";
+const FILTERS_DIR_NAME: &str = "filters";
 const CONTENT_DIR_NAME: &str = "content";
 
 const MANIFEST_FILE_NAME: &str = "spin-template.toml";
@@ -86,6 +87,14 @@ impl TemplateLayout {
         self.template_dir.join(METADATA_DIR_NAME)
     }
 
+    pub fn filters_dir(&self) -> PathBuf {
+        self.metadata_dir().join(FILTERS_DIR_NAME)
+    }
+
+    pub fn filter_path(&self, filename: &str) -> PathBuf {
+        self.filters_dir().join(filename)
+    }
+
     pub fn manifest_path(&self) -> PathBuf {
         self.metadata_dir().join(MANIFEST_FILE_NAME)
     }