Proof of concept C host

component-model/examples/example-c-host/.gitignore

@@ -0,0 +1 @@
+host

component-model/examples/example-c-host/Dockerfile

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+FROM ubuntu:24.04 AS build
+
+ARG WASMTIME_VERSION=42.0.1
+ARG WASI_SDK_VERSION=27
+
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    gcc libc6-dev curl xz-utils ca-certificates \
+    && rm -rf /var/lib/apt/lists/*
+
+# Install wasmtime C API
+RUN curl -sL https://github.com/bytecodealliance/wasmtime/releases/download/v${WASMTIME_VERSION}/wasmtime-v${WASMTIME_VERSION}-x86_64-linux-c-api.tar.xz \
+    | tar xJ --strip-components=1 -C /usr/local \
+    && ldconfig
+
+# Install wasi-sdk (for building the guest component)
+RUN curl -sLO https://github.com/WebAssembly/wasi-sdk/releases/download/wasi-sdk-${WASI_SDK_VERSION}/wasi-sdk-${WASI_SDK_VERSION}.0-x86_64-linux.deb \
+    && dpkg -i wasi-sdk-${WASI_SDK_VERSION}.0-x86_64-linux.deb \
+    && rm wasi-sdk-${WASI_SDK_VERSION}.0-x86_64-linux.deb
+
+# Install wit-bindgen and wasm-tools (pin versions)
+ARG WIT_BINDGEN_VERSION=0.53.1
+ARG WASM_TOOLS_VERSION=1.245.1
+RUN curl -sL https://github.com/bytecodealliance/wit-bindgen/releases/download/v${WIT_BINDGEN_VERSION}/wit-bindgen-${WIT_BINDGEN_VERSION}-x86_64-linux.tar.gz \
+    | tar xz --strip-components=1 -C /usr/local/bin --wildcards '*/wit-bindgen' \
+    && curl -sL https://github.com/bytecodealliance/wasm-tools/releases/download/v${WASM_TOOLS_VERSION}/wasm-tools-${WASM_TOOLS_VERSION}-x86_64-linux.tar.gz \
+    | tar xz --strip-components=1 -C /usr/local/bin --wildcards '*/wasm-tools'
+
+WORKDIR /src
+
+# Fetch guest source from upstream component-docs
+ARG COMPONENT_DOCS_REV=7c1b5a9
+RUN curl -sL -o world.wit \
+      https://raw.githubusercontent.com/bytecodealliance/component-docs/${COMPONENT_DOCS_REV}/component-model/examples/tutorial/wit/adder/world.wit \
+    && mkdir -p wit/adder && mv world.wit wit/adder/world.wit
+RUN curl -sL -o component.c \
+      https://raw.githubusercontent.com/bytecodealliance/component-docs/${COMPONENT_DOCS_REV}/component-model/examples/tutorial/c/adder/component.c
+
+# Build the guest component
+RUN wit-bindgen c wit/adder/world.wit
+RUN /opt/wasi-sdk/bin/wasm32-wasip2-clang \
+    -o adder.wasm \
+    -mexec-model=reactor \
+    component.c adder.c adder_component_type.o
+
+# Build the host
+COPY host.c .
+RUN gcc -o /usr/local/bin/adder-host host.c -lwasmtime
+
+# Runtime image
+FROM ubuntu:24.04
+
+COPY --from=build /usr/local/lib/libwasmtime.so /usr/local/lib/
+RUN ldconfig
+COPY --from=build /usr/local/bin/adder-host /usr/local/bin/adder-host
+COPY --from=build /src/adder.wasm /opt/adder.wasm
+
+ENTRYPOINT ["adder-host"]
+CMD ["1", "2", "/opt/adder.wasm"]

component-model/examples/example-c-host/adder.wasm

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+../example-host/add.wasm

component-model/examples/example-c-host/host.c

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+/**
+ * C host for the adder WebAssembly component.
+ *
+ * Uses the Wasmtime C API's component model support to load and run
+ * a component that exports: docs:adder/add.add(u32, u32) -> u32
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <wasmtime.h>
+
+static void exit_if_error(const char *step, wasmtime_error_t *error) {
+  if (error == NULL)
+    return;
+  wasm_byte_vec_t error_message;
+  wasmtime_error_message(error, &error_message);
+  wasmtime_error_delete(error);
+  fprintf(stderr, "error: failed to %s\n%.*s\n", step, (int)error_message.size,
+          error_message.data);
+  wasm_byte_vec_delete(&error_message);
+  exit(1);
+}
+
+int main(int argc, char *argv[]) {
+  if (argc != 4) {
+    fprintf(stderr, "Usage: %s <x> <y> <component.wasm>\n", argv[0]);
+    return 1;
+  }
+
+  uint32_t x = (uint32_t)atoi(argv[1]);
+  uint32_t y = (uint32_t)atoi(argv[2]);
+  const char *path = argv[3];
+
+  // 1. Create engine with component model enabled
+  wasm_config_t *config = wasm_config_new();
+  wasmtime_config_wasm_component_model_set(config, true);
+  wasm_engine_t *engine = wasm_engine_new_with_config(config);
+
+  // 2. Read the component file
+  FILE *f = fopen(path, "rb");
+  if (!f) {
+    fprintf(stderr, "error: could not open %s\n", path);
+    return 1;
+  }
+  fseek(f, 0, SEEK_END);
+  long fsize = ftell(f);
+  fseek(f, 0, SEEK_SET);
+  uint8_t *wasm_bytes = malloc(fsize);
+  fread(wasm_bytes, 1, fsize, f);
+  fclose(f);
+
+  // 3. Compile the component
+  wasmtime_component_t *component = NULL;
+  exit_if_error("compile component",
+      wasmtime_component_new(engine, wasm_bytes, fsize, &component));
+  free(wasm_bytes);
+
+  // 4. Create linker and add WASI P2
+  wasmtime_component_linker_t *linker =
+      wasmtime_component_linker_new(engine);
+  exit_if_error("add WASI to linker",
+      wasmtime_component_linker_add_wasip2(linker));
+
+  // 5. Create store with WASI config
+  wasmtime_store_t *store = wasmtime_store_new(engine, NULL, NULL);
+  wasmtime_context_t *context = wasmtime_store_context(store);
+  exit_if_error("set WASI config",
+      wasmtime_context_set_wasi(context, wasi_config_new()));
+
+  // 6. Instantiate
+  wasmtime_component_instance_t instance;
+  exit_if_error("instantiate component",
+      wasmtime_component_linker_instantiate(linker, context, component, &instance));
+
+  // 7. Look up the exported "add" function.
+  //    The export is nested: first find the "docs:adder/add@0.1.0" instance,
+  //    then the "add" function within it.
+  wasmtime_component_export_index_t *iface_idx =
+      wasmtime_component_instance_get_export_index(
+          &instance, context, NULL,
+          "docs:adder/add@0.1.0", strlen("docs:adder/add@0.1.0"));
+  if (iface_idx == NULL) {
+    fprintf(stderr, "error: could not find export 'docs:adder/add@0.1.0'\n");
+    return 1;
+  }
+
+  wasmtime_component_export_index_t *func_idx =
+      wasmtime_component_instance_get_export_index(
+          &instance, context, iface_idx,
+          "add", strlen("add"));
+  wasmtime_component_export_index_delete(iface_idx);
+  if (func_idx == NULL) {
+    fprintf(stderr, "error: could not find function 'add'\n");
+    return 1;
+  }
+
+  wasmtime_component_func_t func;
+  bool found = wasmtime_component_instance_get_func(
+      &instance, context, func_idx, &func);
+  wasmtime_component_export_index_delete(func_idx);
+  if (!found) {
+    fprintf(stderr, "error: could not get function handle for 'add'\n");
+    return 1;
+  }
+
+  // 8. Call the function: add(x, y) -> u32
+  wasmtime_component_val_t args[2] = {
+      {.kind = WASMTIME_COMPONENT_U32, .of.u32 = x},
+      {.kind = WASMTIME_COMPONENT_U32, .of.u32 = y},
+  };
+  wasmtime_component_val_t results[1] = {0};
+
+  exit_if_error("call 'add'",
+      wasmtime_component_func_call(&func, context, args, 2, results, 1));
+
+  printf("%u + %u = %u\n", x, y, results[0].of.u32);
+
+  // 9. Cleanup
+  wasmtime_component_val_delete(&results[0]);
+  wasmtime_store_delete(store);
+  wasmtime_component_linker_delete(linker);
+  wasmtime_component_delete(component);
+  wasm_engine_delete(engine);
+
+  return 0;
+}

component-model/examples/example-c-host/justfile

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+@_default:
+  echo "TODO"; exit 1

component-model/src/language-support/building-a-simple-component/c.md

@@ -323,20 +323,19 @@ if you followed the manual instructions above):
 
 {{#include ../example-host-part2.md}}
 
-## 7. Run the component from C/C++ Applications
+## 7. Run the component from the example C host
 
-It is not yet possible to run a WebAssembly Component using the `wasmtime` C API.
-See [`wasmtime` issue #6987](https://github.com/bytecodealliance/wasmtime/issues/6987) for more details.
-The C API is preferred over directly using the example host Rust crate in C++.
+After setting up the wasmtime toolchain 
+*TODO: somehow,* 
+the `example-c-host` project can be built, and run our `adder` much like the rust one.
 
-However, C/C++ language guest components can be composed with components written in any other language
-and run by their toolchains,
-or even composed with a C language command component and run via the `wasmtime` CLI
-or any other host.
+*TODO: the C++ API is nicer and may be more appropriate for example code*
 
-See the [Rust Tooling guide](./rust.md#running-a-component-from-rust-applications)
-for instructions on how to run this component from the Rust `example-host`
-(replacing the path to `add.wasm` with your `adder.wasm` or `adder.component.wasm` above).
+C/C++ language guest components can also be composed with components written in any other language
+and run by their toolchains, or even composed with a C language command component and run via the
+`wasmtime` CLI or any other host.
+
+*TODO: work in `wasmtime --invoke 'add(2,2)' adder.wasm`*
 
 [!NOTE]: #
 [!WARNING]: #