From d24c2fe48c4e72dc4e17cd23bc317c0c7236b808 Mon Sep 17 00:00:00 2001
From: Alex Crichton <alex@alexcrichton.com>
Date: Wed, 18 Jan 2023 18:39:35 -0600
Subject: [PATCH] Detect components in `wasmtime compile` more robustly (#5592)

The binary version of component is going to change over time so use a
more robust method than checking for a fixed 8 bytes.
---
 Cargo.lock              |  1 +
 Cargo.toml              |  1 +
 src/commands/compile.rs | 10 +++++++++-
 3 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/Cargo.lock b/Cargo.lock
index 2ae1764cff..9de93d645b 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -3491,6 +3491,7 @@ dependencies = [
  "tempfile",
  "test-programs",
  "tokio",
+ "wasmparser",
  "wasmtime",
  "wasmtime-cache",
  "wasmtime-cli-flags",
diff --git a/Cargo.toml b/Cargo.toml
index 55e238f042..b2b44636ed 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -41,6 +41,7 @@ listenfd = "1.0.0"
 wat = { workspace = true }
 serde = "1.0.94"
 serde_json = "1.0.26"
+wasmparser = { workspace = true }
 
 [target.'cfg(unix)'.dependencies]
 rustix = { workspace = true, features = ["mm", "param"] }
diff --git a/src/commands/compile.rs b/src/commands/compile.rs
index e7562447a5..2ee93eb033 100644
--- a/src/commands/compile.rs
+++ b/src/commands/compile.rs
@@ -90,7 +90,15 @@ impl CompileCommand {
         // bytes with the current component model proposal.
         #[cfg(feature = "component-model")]
         {
-            if input.starts_with(b"\0asm\x0a\0\x01\0") {
+            if let Ok(wasmparser::Chunk::Parsed {
+                payload:
+                    wasmparser::Payload::Version {
+                        encoding: wasmparser::Encoding::Component,
+                        ..
+                    },
+                ..
+            }) = wasmparser::Parser::new(0).parse(&input, true)
+            {
                 fs::write(output, engine.precompile_component(&input)?)?;
                 return Ok(());
             }