fidius_host/

host.rs

// Copyright 2026 Colliery, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

//! PluginHost builder and plugin discovery.

use std::path::{Path, PathBuf};
#[cfg(feature = "wasm")]
use std::sync::Arc;

use ed25519_dalek::VerifyingKey;
use fidius_core::descriptor::BufferStrategyKind;

use crate::error::LoadError;
use crate::loader::{self, LoadedPlugin};
use crate::signing;
use crate::types::{LoadPolicy, PluginInfo, PluginRuntimeKind};

/// Host for loading and managing plugins.
#[allow(dead_code)] // load_policy will be used for non-security validation (hash/version lenient)
pub struct PluginHost {
    search_paths: Vec<PathBuf>,
    load_policy: LoadPolicy,
    require_signature: bool,
    trusted_keys: Vec<VerifyingKey>,
    expected_hash: Option<u64>,
    expected_strategy: Option<BufferStrategyKind>,
    /// Host-wide default `wasi:http` egress policy (FIDIUS-I-0027). Applied to
    /// every `load_wasm`; `load_wasm_with_egress` overrides it per plugin. `None`
    /// → no egress (a guest importing `wasi:http` fails closed at load).
    #[cfg(feature = "wasm")]
    egress: Option<Arc<dyn crate::executor::wasm::EgressPolicy>>,
}

/// Builder for configuring a PluginHost.
pub struct PluginHostBuilder {
    search_paths: Vec<PathBuf>,
    load_policy: LoadPolicy,
    require_signature: bool,
    trusted_keys: Vec<VerifyingKey>,
    expected_hash: Option<u64>,
    expected_strategy: Option<BufferStrategyKind>,
    #[cfg(feature = "wasm")]
    egress: Option<Arc<dyn crate::executor::wasm::EgressPolicy>>,
}

impl PluginHostBuilder {
    fn new() -> Self {
        Self {
            search_paths: Vec::new(),
            load_policy: LoadPolicy::Strict,
            require_signature: false,
            trusted_keys: Vec::new(),
            expected_hash: None,
            expected_strategy: None,
            #[cfg(feature = "wasm")]
            egress: None,
        }
    }

    /// Set a host-wide default `wasi:http` egress policy (FIDIUS-I-0027). Every
    /// `load_wasm` then enables outbound HTTP for a guest that declares the
    /// `http` capability, routing each request through `policy`. Without this (and
    /// without a per-load policy), `wasi:http` is never linked and a guest that
    /// imports it fails closed. Available only with the `wasm` feature.
    #[cfg(feature = "wasm")]
    pub fn egress(mut self, policy: impl crate::executor::wasm::EgressPolicy) -> Self {
        self.egress = Some(Arc::new(policy));
        self
    }

    /// Like [`Self::egress`] but accepts an already-erased
    /// `Arc<dyn EgressPolicy>` — for a policy that is shared across hosts, or
    /// selected/constructed at runtime (where the concrete type isn't known at
    /// the call site). Threads through `load_wasm` exactly like `egress`.
    /// Available only with the `wasm` feature.
    #[cfg(feature = "wasm")]
    pub fn egress_policy(mut self, policy: Arc<dyn crate::executor::wasm::EgressPolicy>) -> Self {
        self.egress = Some(policy);
        self
    }

    /// Add a directory to search for plugin dylibs.
    pub fn search_path(mut self, path: impl Into<PathBuf>) -> Self {
        self.search_paths.push(path.into());
        self
    }

    /// Set the load policy (Strict or Lenient).
    pub fn load_policy(mut self, policy: LoadPolicy) -> Self {
        self.load_policy = policy;
        self
    }

    /// Require plugins to have valid signatures.
    pub fn require_signature(mut self, require: bool) -> Self {
        self.require_signature = require;
        self
    }

    /// Set trusted Ed25519 public keys for signature verification.
    pub fn trusted_keys(mut self, keys: &[VerifyingKey]) -> Self {
        self.trusted_keys = keys.to_vec();
        self
    }

    /// Set the expected interface hash for validation.
    pub fn interface_hash(mut self, hash: u64) -> Self {
        self.expected_hash = Some(hash);
        self
    }

    /// Set the expected buffer strategy for validation.
    pub fn buffer_strategy(mut self, strategy: BufferStrategyKind) -> Self {
        self.expected_strategy = Some(strategy);
        self
    }

    /// Build the PluginHost.
    pub fn build(self) -> Result<PluginHost, LoadError> {
        Ok(PluginHost {
            search_paths: self.search_paths,
            load_policy: self.load_policy,
            require_signature: self.require_signature,
            trusted_keys: self.trusted_keys,
            expected_hash: self.expected_hash,
            expected_strategy: self.expected_strategy,
            #[cfg(feature = "wasm")]
            egress: self.egress,
        })
    }
}

impl PluginHost {
    /// Create a new builder.
    pub fn builder() -> PluginHostBuilder {
        PluginHostBuilder::new()
    }

    /// Discover all valid plugins in the configured search paths.
    ///
    /// Scans each path for both:
    /// - dylib files (cdylib plugins, the existing path), and
    /// - subdirectories containing a `package.toml` with `runtime = "python"`
    ///   (when the `python` feature is enabled).
    ///
    /// Returns owned `PluginInfo` for every valid plugin found, with
    /// `PluginInfo::runtime` distinguishing the two kinds.
    pub fn discover(&self) -> Result<Vec<PluginInfo>, LoadError> {
        #[cfg(feature = "tracing")]
        tracing::info!(search_paths = ?self.search_paths, "discovering plugins");

        let mut plugins = Vec::new();

        for search_path in &self.search_paths {
            if !search_path.is_dir() {
                continue;
            }

            let entries = std::fs::read_dir(search_path)?;
            for entry in entries {
                let entry = entry?;
                let path = entry.path();

                if is_dylib(&path) {
                    self.discover_cdylib(&path, &mut plugins);
                } else if path.is_dir() && path.join("package.toml").exists() {
                    self.discover_package(&path, &mut plugins);
                }
            }
        }

        Ok(plugins)
    }

    fn discover_cdylib(&self, path: &Path, plugins: &mut Vec<PluginInfo>) {
        // Verify signature before dlopen to prevent code execution from untrusted dylibs
        if self.require_signature && signing::verify_signature(path, &self.trusted_keys).is_err() {
            return;
        }

        let Ok(loaded) = loader::load_library(path) else {
            return; // Skip invalid dylibs during discovery
        };
        for plugin in &loaded.plugins {
            if loader::validate_against_interface(
                plugin,
                self.expected_hash,
                self.expected_strategy,
            )
            .is_ok()
            {
                plugins.push(plugin.info.clone());
            }
        }
    }

    /// Discover a directory-based package (`package.toml`) and surface it by
    /// runtime. Rust source packages are discovered via their built dylib (the
    /// loadable artifact), not here, so they're skipped.
    fn discover_package(&self, dir: &Path, plugins: &mut Vec<PluginInfo>) {
        let Ok(manifest) = fidius_core::package::load_manifest_untyped(dir) else {
            return;
        };
        use fidius_core::package::PackageRuntime;
        let runtime = match manifest.package.runtime() {
            PackageRuntime::Python => PluginRuntimeKind::Python,
            PackageRuntime::Wasm => PluginRuntimeKind::Wasm,
            // The cdylib is the loadable artifact for a Rust package; the
            // source directory isn't discovered.
            PackageRuntime::Rust => return,
        };
        plugins.push(PluginInfo {
            name: manifest.package.name.clone(),
            interface_name: manifest.package.interface.clone(),
            // Hash is unknown until load (the host validates against the
            // descriptor at load time, not discovery). Surface 0 so callers
            // know discovery alone hasn't validated the package.
            interface_hash: 0,
            interface_version: manifest.package.interface_version,
            capabilities: 0,
            buffer_strategy: BufferStrategyKind::PluginAllocated,
            runtime,
        });
    }

    /// Load a specific plugin by name.
    ///
    /// Searches all configured paths for a dylib containing a plugin
    /// with the given name. Returns the loaded plugin ready for calling.
    pub fn load(&self, name: &str) -> Result<LoadedPlugin, LoadError> {
        #[cfg(feature = "tracing")]
        tracing::info!(plugin_name = name, "loading plugin");

        for search_path in &self.search_paths {
            if !search_path.is_dir() {
                continue;
            }

            let entries = std::fs::read_dir(search_path)?;
            for entry in entries {
                let entry = entry?;
                let path = entry.path();

                if !is_dylib(&path) {
                    continue;
                }

                // Verify signature if required — always enforced regardless of LoadPolicy
                if self.require_signature {
                    signing::verify_signature(&path, &self.trusted_keys)?;
                }

                match loader::load_library(&path) {
                    Ok(loaded) => {
                        for plugin in loaded.plugins {
                            if plugin.info.name == name {
                                loader::validate_against_interface(
                                    &plugin,
                                    self.expected_hash,
                                    self.expected_strategy,
                                )?;
                                return Ok(plugin);
                            }
                        }
                    }
                    Err(_) => continue,
                }
            }
        }

        Err(LoadError::PluginNotFound {
            name: name.to_string(),
        })
    }

    /// Find a python plugin package directory by name across the configured
    /// search paths. The plugin name is matched against `package.toml`'s
    /// `[package].name`. Returns the directory path on success.
    pub fn find_python_package(&self, name: &str) -> Result<PathBuf, LoadError> {
        for search_path in &self.search_paths {
            if !search_path.is_dir() {
                continue;
            }
            let entries = std::fs::read_dir(search_path)?;
            for entry in entries {
                let entry = entry?;
                let path = entry.path();
                if !path.is_dir() {
                    continue;
                }
                if !path.join("package.toml").exists() {
                    continue;
                }
                let Ok(manifest) = fidius_core::package::load_manifest_untyped(&path) else {
                    continue;
                };
                if matches!(
                    manifest.package.runtime(),
                    fidius_core::package::PackageRuntime::Python
                ) && manifest.package.name == name
                {
                    return Ok(path);
                }
            }
        }
        Err(LoadError::PluginNotFound {
            name: name.to_string(),
        })
    }

    /// Load a Python plugin package by name and validate it against the
    /// supplied interface descriptor.
    ///
    /// The caller passes the static `<TraitName>_PYTHON_DESCRIPTOR` emitted
    /// by the interface crate's `#[plugin_interface]` macro — that's the
    /// out-of-band hint the loader needs to map method names to vtable
    /// indices and to check the interface hash.
    ///
    /// Available only when fidius-host is built with the `python` feature.
    #[cfg(feature = "python")]
    pub fn load_python(
        &self,
        name: &str,
        descriptor: &'static fidius_core::python_descriptor::PythonInterfaceDescriptor,
    ) -> Result<crate::handle::PluginHandle, LoadError> {
        let dir = self.find_python_package(name)?;
        // Signature policy — enforced identically to cdylib/WASM loads.
        if self.require_signature {
            signing::verify_package_signature(&dir, &self.trusted_keys)?;
        }
        let manifest = fidius_core::package::load_manifest_untyped(&dir)
            .map_err(|e| LoadError::PythonLoad(e.to_string()))?;
        let py = fidius_python::load_python_plugin(&dir, descriptor)
            .map_err(|e| LoadError::PythonLoad(e.to_string()))?;
        // Build the host-facing metadata from the manifest header + the
        // interface descriptor. `capabilities`/`buffer_strategy` are cdylib
        // concepts and take their no-op defaults for Python.
        let info = crate::types::PluginInfo {
            name: manifest.package.name.clone(),
            interface_name: descriptor.interface_name.to_string(),
            interface_hash: descriptor.interface_hash,
            interface_version: manifest.package.interface_version,
            capabilities: 0,
            buffer_strategy: fidius_core::descriptor::BufferStrategyKind::PluginAllocated,
            runtime: crate::types::PluginRuntimeKind::Python,
        };
        Ok(crate::handle::PluginHandle::from_python(py, info))
    }

    /// Find a WASM package directory by name across the search paths (matches
    /// `package.toml` `[package].name` with `runtime = "wasm"`).
    #[cfg(feature = "wasm")]
    pub fn find_wasm_package(&self, name: &str) -> Result<PathBuf, LoadError> {
        for search_path in &self.search_paths {
            if !search_path.is_dir() {
                continue;
            }
            for entry in std::fs::read_dir(search_path)? {
                let entry = entry?;
                let path = entry.path();
                if !path.is_dir() || !path.join("package.toml").exists() {
                    continue;
                }
                let Ok(manifest) = fidius_core::package::load_manifest_untyped(&path) else {
                    continue;
                };
                if matches!(
                    manifest.package.runtime(),
                    fidius_core::package::PackageRuntime::Wasm
                ) && manifest.package.name == name
                {
                    return Ok(path);
                }
            }
        }
        Err(LoadError::PluginNotFound {
            name: name.to_string(),
        })
    }

    /// Load a WASM component plugin package by name and validate it against the
    /// supplied interface descriptor (the `<TraitName>_WASM_DESCRIPTOR` the
    /// interface crate emits). Returns a unified [`crate::handle::PluginHandle`].
    ///
    /// The component is sandboxed: WASI is wired into the `Linker` but the guest
    /// gets a zero-grant `WasiCtx` (no FS preopens, no env, no sockets). The
    /// capability allow-list in `[wasm].capabilities` is applied in T-0104.
    ///
    /// Outbound HTTP is governed by the host's egress policy: a guest that
    /// declares the `http` capability gets `wasi:http` only when the host was
    /// given a policy (via [`PluginHostBuilder::egress`] or
    /// [`Self::load_wasm_with_egress`]) — otherwise it fails closed.
    ///
    /// Available only with the `wasm` feature.
    #[cfg(feature = "wasm")]
    pub fn load_wasm(
        &self,
        name: &str,
        descriptor: &'static fidius_core::wasm_descriptor::WasmInterfaceDescriptor,
    ) -> Result<crate::handle::PluginHandle, LoadError> {
        self.load_wasm_impl(name, descriptor, self.egress.clone())
    }

    /// Like [`Self::load_wasm`] but with a **per-plugin** `wasi:http` egress
    /// policy that overrides any host-wide default (FIDIUS-I-0027). This is the
    /// right primitive for isolating connectors: a host-wide policy only sees the
    /// outbound *request*, not which plugin issued it, so per-plugin policies are
    /// how you bound connector A to one set of hosts and connector B to another.
    #[cfg(feature = "wasm")]
    pub fn load_wasm_with_egress(
        &self,
        name: &str,
        descriptor: &'static fidius_core::wasm_descriptor::WasmInterfaceDescriptor,
        egress: impl crate::executor::wasm::EgressPolicy,
    ) -> Result<crate::handle::PluginHandle, LoadError> {
        self.load_wasm_impl(name, descriptor, Some(Arc::new(egress)))
    }

    #[cfg(feature = "wasm")]
    fn load_wasm_impl(
        &self,
        name: &str,
        descriptor: &'static fidius_core::wasm_descriptor::WasmInterfaceDescriptor,
        egress: Option<Arc<dyn crate::executor::wasm::EgressPolicy>>,
    ) -> Result<crate::handle::PluginHandle, LoadError> {
        use crate::executor::wasm::{WasmComponentExecutor, WasmMethod};

        let dir = self.find_wasm_package(name)?;
        // Signature policy — enforced identically to cdylib/Python loads.
        if self.require_signature {
            signing::verify_package_signature(&dir, &self.trusted_keys)?;
        }
        let manifest = fidius_core::package::load_manifest_untyped(&dir)
            .map_err(|e| LoadError::WasmLoad(e.to_string()))?;
        let wasm_meta = manifest
            .wasm
            .as_ref()
            .ok_or_else(|| LoadError::WasmLoad("manifest is missing the [wasm] section".into()))?;

        let methods: Vec<WasmMethod> = descriptor
            .methods
            .iter()
            .map(|m| WasmMethod {
                name: m.name.to_string(),
                wire_raw: m.wire_raw,
                streaming: m.streaming,
            })
            .collect();
        let info = crate::types::PluginInfo {
            name: manifest.package.name.clone(),
            interface_name: descriptor.interface_name.to_string(),
            interface_hash: descriptor.interface_hash,
            interface_version: manifest.package.interface_version,
            capabilities: 0,
            buffer_strategy: fidius_core::descriptor::BufferStrategyKind::PluginAllocated,
            runtime: crate::types::PluginRuntimeKind::Wasm,
        };
        let interface = descriptor.interface_export.to_string();
        let capabilities = wasm_meta.capabilities.clone();

        // Resolve a precompiled .cwasm: explicit `[wasm].precompiled`, or an
        // auto-detected sibling `<component-stem>.cwasm`. The AOT path is purely
        // a load-latency optimization, so a stale/mismatched .cwasm (built by a
        // different wasmtime) is non-fatal — we log and JIT-compile the
        // component instead (FIDIUS-T-0107).
        let cwasm_path = wasm_meta
            .precompiled
            .as_ref()
            .map(|p| dir.join(p))
            .or_else(|| {
                let sibling = dir.join(&wasm_meta.component).with_extension("cwasm");
                sibling.exists().then_some(sibling)
            });

        let jit = |interface: String, methods, capabilities, info| -> Result<_, LoadError> {
            let bytes = std::fs::read(dir.join(&wasm_meta.component))?;
            WasmComponentExecutor::from_component_bytes_with_egress(
                &bytes,
                interface,
                methods,
                capabilities,
                egress.clone(),
                info,
            )
            .map_err(|e| LoadError::WasmLoad(e.to_string()))
        };

        let executor = match cwasm_path {
            Some(cwasm) if cwasm.exists() => {
                let bytes = std::fs::read(&cwasm)?;
                // SAFETY: .cwasm is produced by `fidius pack`
                // (Engine::precompile_component); wasmtime validates the header
                // and refuses a mismatched engine/version (→ Err → JIT fallback).
                let aot = unsafe {
                    WasmComponentExecutor::from_cwasm_with_egress(
                        &bytes,
                        interface.clone(),
                        methods.clone(),
                        capabilities.clone(),
                        egress.clone(),
                        info.clone(),
                    )
                };
                match aot {
                    Ok(e) => e,
                    Err(_err) => {
                        #[cfg(feature = "tracing")]
                        tracing::warn!(
                            cwasm = %cwasm.display(),
                            error = %_err,
                            "precompiled .cwasm rejected (likely engine/version mismatch); falling back to JIT"
                        );
                        jit(interface, methods, capabilities, info)?
                    }
                }
            }
            _ => jit(interface, methods, capabilities, info)?,
        };

        // Interface-hash integrity check (parity with cdylib/Python).
        let got = executor
            .interface_hash()
            .map_err(|e| LoadError::WasmLoad(e.to_string()))?;
        if got != descriptor.interface_hash {
            return Err(LoadError::InterfaceHashMismatch {
                got,
                expected: descriptor.interface_hash,
            });
        }

        Ok(crate::handle::PluginHandle::from_wasm(executor))
    }
}

/// Check if a path has a platform-appropriate dylib extension.
fn is_dylib(path: &Path) -> bool {
    let ext = path.extension().and_then(|e| e.to_str()).unwrap_or("");
    if cfg!(target_os = "macos") {
        ext == "dylib"
    } else if cfg!(target_os = "windows") {
        ext == "dll"
    } else {
        ext == "so"
    }
}