wasm: implement imports

Updates #40.

wasm/imports.go

@@ -95,6 +95,7 @@ func (module *Module) resolveImports(resolve ResolveFunc) error {
 
 	modules := make(map[string]*Module)
 
+	var funcs uint32
 	for _, importEntry := range module.Import.Entries {
 		importedModule, ok := modules[importEntry.ModuleName]
 		if !ok {
@@ -134,6 +135,9 @@ func (module *Module) resolveImports(resolve ResolveFunc) error {
 				return InvalidFunctionIndexError(index)
 			}
 			module.FunctionIndexSpace = append(module.FunctionIndexSpace, *fn)
+			module.Code.Bodies = append(module.Code.Bodies, *fn.Body)
+			module.imports.Funcs = append(module.imports.Funcs, funcs)
+			funcs++
 		case ExternalGlobal:
 			glb := importedModule.GetGlobal(int(index))
 			if glb == nil {
@@ -143,6 +147,7 @@ func (module *Module) resolveImports(resolve ResolveFunc) error {
 				return ErrImportMutGlobal
 			}
 			module.GlobalIndexSpace = append(module.GlobalIndexSpace, *glb)
+			module.imports.Globals++
 
 			// In both cases below, index should be always 0 (according to the MVP)
 			// We check it against the length of the index space anyway.
@@ -151,16 +156,16 @@ func (module *Module) resolveImports(resolve ResolveFunc) error {
 				return InvalidTableIndexError(index)
 			}
 			module.TableIndexSpace[0] = importedModule.TableIndexSpace[0]
+			module.imports.Tables++
 		case ExternalMemory:
 			if int(index) >= len(importedModule.LinearMemoryIndexSpace) {
 				return InvalidLinearMemoryIndexError(index)
 			}
 			module.LinearMemoryIndexSpace[0] = importedModule.LinearMemoryIndexSpace[0]
+			module.imports.Memories++
 		default:
 			return InvalidExternalError(exportEntry.Kind)
 		}
-
 	}
-
 	return nil
 }

wasm/index.go

@@ -51,6 +51,10 @@ func (m *Module) populateFunctions() error {
 		m.FunctionIndexSpace = append(m.FunctionIndexSpace, fn)
 	}
 
+	funcs := make([]uint32, 0, len(m.Function.Types)+len(m.imports.Funcs))
+	funcs = append(funcs, m.imports.Funcs...)
+	funcs = append(funcs, m.Function.Types...)
+	m.Function.Types = funcs
 	return nil
 }
 

wasm/module.go

@@ -50,6 +50,13 @@ type Module struct {
 	LinearMemoryIndexSpace [][]byte
 
 	Other []Section // Other holds the custom sections if any
+
+	imports struct {
+		Funcs    []uint32
+		Globals  int
+		Tables   int
+		Memories int
+	}
 }
 
 // ResolveFunc is a function that takes a module name and
@@ -90,7 +97,13 @@ func ReadModule(r io.Reader, resolvePath ResolveFunc) (*Module, error) {
 	}
 
 	if m.Import != nil {
-		return nil, errors.New("Imports aren't supported")
+		if resolvePath == nil {
+			return nil, errors.New("wasm: no module importer provided")
+		}
+		err := m.resolveImports(resolvePath)
+		if err != nil {
+			return nil, err
+		}
 	}
 
 	for _, fn := range []func() error{