Update plugin example to use serde and typetag for WASI

Cargo.lock

@@ -1498,7 +1498,9 @@ dependencies = [
  "errno 0.2.4 (registry+https://github.com/rust-lang/crates.io-index)",
  "glob 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "rustc_version 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 1.0.99 (registry+https://github.com/rust-lang/crates.io-index)",
  "structopt 0.2.18 (registry+https://github.com/rust-lang/crates.io-index)",
+ "typetag 0.1.4 (registry+https://github.com/rust-lang/crates.io-index)",
  "wabt 0.9.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "wasmer-clif-backend 0.6.0",
  "wasmer-dev-utils 0.6.0",

Cargo.toml

@@ -64,6 +64,10 @@ wabt = "0.9.1"
 glob = "0.3.0"
 rustc_version = "0.2.3"
 
+[dev-dependencies]
+serde = { version = "1", features = ["derive"] } # used by the plugin example
+typetag = "0.1" # used by the plugin example
+
 [features]
 default = ["fast-tests", "wasi", "backend-cranelift"]
 "loader-kernel" = ["wasmer-kernel-loader"]

examples/plugin.rs

@@ -1,3 +1,4 @@
+use serde::{Deserialize, Serialize};
 use wasmer_runtime::{func, imports, instantiate};
 use wasmer_runtime_core::vm::Ctx;
 use wasmer_wasi::{
@@ -13,7 +14,7 @@ fn it_works(_ctx: &mut Ctx) -> i32 {
     5
 }
 
-#[derive(Debug)]
+#[derive(Debug, Serialize, Deserialize)]
 pub struct LoggingWrapper {
     pub wasm_module_name: String,
 }
@@ -86,6 +87,8 @@ impl std::io::Write for LoggingWrapper {
 }
 
 // the WasiFile methods aren't relevant for a write-only Stdout-like implementation
+// we must use typetag and serde so that our trait objects can be safely Serialized and Deserialized
+#[typetag::serde]
 impl WasiFile for LoggingWrapper {
     fn last_accessed(&self) -> u64 {
         0