doc: move example to README

README.md

@@ -21,19 +21,93 @@ cmake ..
 make
 ```
 
-or just:
+or:
 
 ```bash
 make
 ```
 
-## Example
-
-See [extism-wamr.c](bin/extism-wamr.c)
-
-## Notes
+## Getting started
 
 - `extism_runtime_init` should always be called before creating any plugins, and there
   is only a single global runtime that host functions can be loaded into
 - The plugins listed in `ExtismManifest` that depend on other Wasm modules must have all 
   dependencies listed first in the manifest with module names specified.
+
+### Creating and calling a plugin
+
+```c
+#include <stdio.h>
+#include <stdlib.h>
+#include <extism-wamr.h>
+
+// Read a file from disk - an implementation of `read_file` can be found 
+// in `bin/extism-wamr.c`
+uint8_t *read_file(const char *, size_t *);
+
+// Return the input as-is
+uint64_t host_reflect(ExtismExecEnv *env, uint64_t x) { return x; }
+
+// Run an Extism plugin and print the output
+ExtismStatus run_wasm(const char *wasm_file, const char *func_name, const char *input, size_t input_len){
+  char errbuf[1024];
+  size_t datalen = 0, len = 0;
+  uint8_t *data = read_file(wasm_file, &datalen);
+  if (data == NULL) {
+    return ExtismStatusErr;
+  }
+
+  // Initialize the runtime, this must be done before anything else 
+  extism_runtime_init();
+
+  // Specify the modules to be loaded, setting `name` to `NULL` marks a module
+  // at the main module
+  ExtismWasm wasm = {
+      .data = data,
+      .length = datalen,
+      .name = NULL,
+  };
+  ExtismManifest manifest;
+  extism_manifest_init(&manifest, &wasm, 1, NULL, 0, NULL);
+
+  // Define a host function
+  extism_host_function("extism:host/user", "host_reflect", "(I)I", host_reflect,
+                       NULL);
+
+  // Create the plugin instance
+  ExtismPlugin *plugin = extism_plugin_new(&manifest, errbuf, 1024);
+  if (plugin == NULL) {
+    fputs("ERROR: ", stderr);
+    fputs(errbuf, stderr);
+    fputs("\n", stderr);
+    free(data);
+    extism_runtime_cleanup();
+    return ExtismStatusErr;
+  }
+
+  // Call `func_name`
+  if ((status = extism_plugin_call(plugin, func_name, (const void *)input,
+                                   input_len)) != ExtismStatusOk) {
+    // Print error if it fails
+    const char *s = extism_plugin_error(plugin, &len);
+    fprintf(stderr, "ERROR(%d): ", status);
+    fwrite(s, len, 1, stderr);
+    fputc('\n', stderr);
+  } else {
+    // Otherwise print the output
+    uint8_t *output = extism_plugin_output(plugin, &len);
+    if (len > 0) {
+      fwrite(output, len, 1, stdout);
+      fputc('\n', stdout);
+    }
+  }
+
+  // Cleanup
+  extism_plugin_free(plugin);
+  extism_runtime_cleanup();
+  free(data);
+  return ExtismStatusOk;
+}
+
+```
+

bin/extism-wamr.c

@@ -74,14 +74,15 @@ int main(int argc, char *argv[]) {
     fputs(errbuf, stderr);
     fputs("\n", stderr);
     free(data);
+    extism_runtime_cleanup();
     return 1;
   }
 
   const char *input = argc > 3 ? argv[3] : "";
   size_t input_len = argc > 3 ? strlen(argv[3]) : 0;
 
   for (int i = 0; i < loop; i++) {
-    // Call `count_vowels` function
+    // Call a function
     if ((status = extism_plugin_call(plugin, argv[2], (const void *)input,
                                      input_len)) != ExtismStatusOk) {
       // Print error if it fails