Add a component model example

This adds the 'Hello World' example from here[0]. The runtime is in Rust
and the component is in C.

This requires some new tools

  - https://github.com/bytecodealliance/wit-bindgen
  - https://github.com/bytecodealliance/wasm-tools

You can use the pre-built packages, once downloaded and untar'd, edit

  rust/hello_world/component/Makefile

and adjust the paths for the above tools.

To build the component with make you may need to specify where the WASI
sysroot is

  $ make WASI_SYSROOT=/path/to/wasi-sysroot

[0]: <https://docs.rs/wasmtime/latest/wasmtime/component/macro.bindgen.html>

Signed-off-by: Andrew Clayton <a.clayton@nginx.com>

3 files changed, 42 insertions, 0 deletions

diff --git a/rust/hello_world/component/.gitignore b/rust/hello_world/component/.gitignore
new file mode 100644
index 0000000..5e4f2b2
--- /dev/null
+++ b/rust/hello_world/component/.gitignore
@@ -0,0 +1 @@
+hello_world*
diff --git a/rust/hello_world/component/Makefile b/rust/hello_world/component/Makefile
new file mode 100644
index 0000000..a7f3f85
--- /dev/null
+++ b/rust/hello_world/component/Makefile
@@ -0,0 +1,27 @@
+# Look for wasi-sysroot in some common places, falling back
+# to provided WASI_SYSROOT
+ifneq ("$(wildcard /usr/wasm32-wasi)", "")
+        # Fedora
+        WASI_SYSROOT ?= /usr/wasm32-wasi
+else ifneq ("$(wildcard /usr/local/share/wasi-sysroot)", "")
+        # FreeBSD
+        WASI_SYSROOT ?= /usr/local/share/wasi-sysroot
+endif
+
+export WASI_SYSROOT
+
+CC      = clang
+CFLAGS  = -Wall -Wextra --target=wasm32-wasi --sysroot=$(WASI_SYSROOT)
+LDFLAGS = -Wl,--no-entry -mexec-model=reactor --rtlib=compiler-rt
+
+all: hello_world.wasm
+
+bindgen:
+	/home/andrew/src/c/wasm/wit-bindgen-v0.13.0-x86_64-linux/wit-bindgen c ../wit
+
+hello_world.wasm: bindgen my-component.c
+	$(CC) $(CFLAGS) $(LDFLAGS) -o $@ hello_world.c hello_world_component_type.o my-component.c
+	/home/andrew/src/c/wasm/wasm-tools-1.0.48-x86_64-linux/wasm-tools component new hello_world.wasm -o hello_world-component.wasm
+
+clean:
+	rm -f hello_world*
diff --git a/rust/hello_world/component/my-component.c b/rust/hello_world/component/my-component.c
new file mode 100644
index 0000000..fe09975
--- /dev/null
+++ b/rust/hello_world/component/my-component.c
@@ -0,0 +1,14 @@
+/*
+ * my-component.c
+ */
+
+#include "hello_world.h"
+
+void hello_world_greet(void)
+{
+	hello_world_string_t my_string;
+
+	hello_world_string_set(&my_string, "Hello, world!");
+
+	hello_world_name(&my_string);
+}