add greet exmaple: passing strings back and forth (c)

examples/wasm/greet.pl

@@ -0,0 +1,7 @@
+use strict;
+use warnings;
+use Path::Tiny qw( path );
+use lib path(__FILE__)->parent->child('lib')->stringify;
+use Greet;
+
+print greet("Perl!"), "\n";

examples/wasm/lib/Greet.c

@@ -0,0 +1,23 @@
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+
+#define EXPORT __attribute__ ((visibility ("default")))
+
+EXPORT void *
+_allocate(size_t size) {
+  return malloc(size);
+}
+
+EXPORT void
+_deallocate(void* ptr) {
+  free(ptr);
+}
+
+EXPORT char *
+_greet(const char *subject) {
+  int len = strlen(subject) + strlen("Hello, ") + 1;
+  char *greeting = malloc(len);
+  snprintf(greeting, len, "Hello, %s", subject);
+  return greeting;
+}

examples/wasm/lib/Greet.pm

@@ -0,0 +1,31 @@
+package Greet;
+
+use strict;
+use warnings;
+use FFI::Platypus;
+use FFI::Platypus::Memory qw( strcpy );
+use base qw( Exporter );
+use Wasm
+  -api => 0,
+  -self
+;
+
+our @EXPORT = qw( greet );
+
+sub greet
+{
+  my($subject) = @_;
+
+  my $input_offset = _allocate(length($subject) + 1);
+  strcpy( $memory->address + $input_offset, $subject );
+
+  my $output_offset = _greet($input_offset);
+  my $greeting      = FFI::Platypus->new->cast('opaque', 'string', $memory->address + $output_offset);
+
+  _deallocate($input_offset);
+  _deallocate($output_offset);
+
+  return $greeting;
+}
+
+1;