WASIp2 component support for wasmtime

docs/wasm-wasi-example.md

@@ -40,7 +40,7 @@ This is from a main function from a wasm module
  ```Containerfile
  FROM scratch
 COPY hello.wasm /
-CMD ["/hello.wasm"]
+ENTRYPOINT ["/hello.wasm"]
  ```
 * Build wasm image using buildah
 ```console

src/libcrun/handlers/handler-utils.c

@@ -19,6 +19,7 @@
 #define _GNU_SOURCE
 
 #include <config.h>
+#include <string.h>
 #include "../container.h"
 #include "../utils.h"
 #include "handler-utils.h"
@@ -69,3 +70,25 @@ wasm_can_handle_container (libcrun_container_t *container, libcrun_error_t *err
 
   return 0;
 }
+
+wasm_encoding_t
+wasm_interpete_header (const char *header)
+{
+  // Check for the WebAssembly magic bytes
+  // See: https://webassembly.github.io/spec/core/binary/modules.html#binary-module
+  if (strncmp (header, "\0asm", 4))
+    return WASM_ENC_INVALID;
+
+  /* The next four bytes are the WebAssembly version.
+     We don't care for the specific WebAssembly version
+     so we only read the value of the `layer` field which
+     was defined by the component spec.
+     See: https://github.com/WebAssembly/component-model/blob/main/design/mvp/Binary.md#component-definitions
+  */
+  if (header[6] == '\0' && header[7] == '\0')
+    return WASM_ENC_MODULE;
+
+  // `layer` does not equal `0x00 0x00` so we are working
+  // with a component.
+  return WASM_ENC_COMPONENT;
+}

src/libcrun/handlers/handler-utils.h

@@ -21,6 +21,15 @@
 #include "../container.h"
 #include <unistd.h>
 
+typedef enum
+{
+  WASM_ENC_INVALID,
+  WASM_ENC_MODULE,
+  WASM_ENC_COMPONENT
+} wasm_encoding_t;
+
 int wasm_can_handle_container (libcrun_container_t *container, libcrun_error_t *err);
 
+wasm_encoding_t wasm_interpete_header (const char *header);
+
 #endif