feat(ruby-sdk): create Extism module / namespace (#5)

I noticed when calling set_log_file that it's on the top-level namespace.
And so is the rest of the gem. It's not a good idea to do this as it
pollutes the user's application. Best practice is to wrap all code in a
module which by convention is the gem name.

I was also getting `Uninitialized constant FFI:NIL` and in the
set_log_file method and I could not tell why it was needed. I changed it
to a regular ruby nil. If it's needed for some reason I'll change it
back or move to another PR.

ruby/example.rb

@@ -4,7 +4,7 @@ require 'json'
 manifest = {
   :wasm => [{:path => "../wasm/code.wasm"}]
 }
-plugin = Plugin.new(manifest)
+plugin = Extism::Plugin.new(manifest)
 res = JSON.parse(plugin.call("count_vowels", ARGV[0] || "this is a test"))
 puts res['count']
 

ruby/lib/extism.rb

@@ -1,57 +1,59 @@
 require 'ffi'
 require 'json'
 
-module C
-  extend FFI::Library
-  ffi_lib "extism"
-  attach_function :extism_plugin_register, [:pointer, :uint64, :bool], :int32
-  attach_function :extism_error, [:int32], :string
-  attach_function :extism_call, [:int32, :string, :pointer, :uint64], :int32
-  attach_function :extism_output_length, [:int32], :uint64
-  attach_function :extism_output_get, [:int32, :pointer, :uint64], :void
-  attach_function :extism_log_file, [:string, :pointer], :void
-end
-
-class Error < StandardError
-end
-
-def set_log_file(name, level=FFI::NIL)
-  if level != FFI::NIL then
-    level = FFI::MemoryPointer::from_string(level)
-  end
-  C.extism_log_file(name, level)
-end
-
-
-class Plugin
-  def initialize(wasm, wasi=false, config=nil)
-    if wasm.class == Hash then
-      wasm = JSON.generate(wasm)
-    end
-    code = FFI::MemoryPointer.new(:char, wasm.bytesize)
-    code.put_bytes(0, wasm)
-    @plugin = C.extism_plugin_register(code, wasm.bytesize, wasi)
-
-    if config != nil and @plugin >= 0 then
-      s = JSON.generate(config)
-      ptr = FFI::MemoryPointer::from_string(s)
-      C.extism_plugin_config(@plugin, ptr, s.bytesize)
-    end
+module Extism
+  module C
+    extend FFI::Library
+    ffi_lib "extism"
+    attach_function :extism_plugin_register, [:pointer, :uint64, :bool], :int32
+    attach_function :extism_error, [:int32], :string
+    attach_function :extism_call, [:int32, :string, :pointer, :uint64], :int32
+    attach_function :extism_output_length, [:int32], :uint64
+    attach_function :extism_output_get, [:int32, :pointer, :uint64], :void
+    attach_function :extism_log_file, [:string, :pointer], :void
   end
 
-  def call(name, data)
-    input = FFI::MemoryPointer::from_string(data)
-    rc = C.extism_call(@plugin, name, input, data.bytesize)
-    if rc != 0 then
-      err = C.extism_error(@plugin)
-      if err&.empty? then
-        raise Error.new "extism_call failed"
-      else raise Error.new err
+
+  class Error < StandardError
+  end
+
+  def self.set_log_file(name, level=nil)
+    if level then
+      level = FFI::MemoryPointer::from_string(level)
+    end
+    C.extism_log_file(name, level)
+  end
+
+  class Plugin
+    def initialize(wasm, wasi=false, config=nil)
+      if wasm.class == Hash then
+        wasm = JSON.generate(wasm)
+      end
+      code = FFI::MemoryPointer.new(:char, wasm.bytesize)
+      code.put_bytes(0, wasm)
+      @plugin = C.extism_plugin_register(code, wasm.bytesize, wasi)
+
+      if config != nil and @plugin >= 0 then
+        s = JSON.generate(config)
+        ptr = FFI::MemoryPointer::from_string(s)
+        C.extism_plugin_config(@plugin, ptr, s.bytesize)
       end
     end
-    out_len = C.extism_output_length(@plugin)
-    buf = FFI::MemoryPointer.new(:char, out_len)
-    C.extism_output_get(@plugin, buf, out_len)
-    return buf.read_string()
+
+    def call(name, data)
+      input = FFI::MemoryPointer::from_string(data)
+      rc = C.extism_call(@plugin, name, input, data.bytesize)
+      if rc != 0 then
+        err = C.extism_error(@plugin)
+        if err&.empty? then
+          raise Error.new "extism_call failed"
+        else raise Error.new err
+        end
+      end
+      out_len = C.extism_output_length(@plugin)
+      buf = FFI::MemoryPointer.new(:char, out_len)
+      C.extism_output_get(@plugin, buf, out_len)
+      return buf.read_string()
+    end
   end
 end