// useModifiedFiles augments the provided build.Context by the
// mapping from file names to alternative contents.
func useModifiedFiles(orig *build.Context, modified map[string][]byte) *build.Context {
rc := func(data []byte) (io.ReadCloser, error) {
return ioutil.NopCloser(bytes.NewBuffer(data)), nil
}
copy := *orig // make a copy
ctxt := ©
ctxt.OpenFile = func(path string) (io.ReadCloser, error) {
// Fast path: names match exactly.
if content, ok := modified[path]; ok {
return rc(content)
}
// Slow path: check for same file under a different
// alias, perhaps due to a symbolic link.
for filename, content := range modified {
if sameFile(path, filename) {
return rc(content)
}
}
return buildutil.OpenFile(orig, path)
}
return ctxt
}
// readFile is like ioutil.ReadFile, but
// it goes through the virtualized build.Context.
func readFile(ctxt *build.Context, filename string) ([]byte, error) {
rc, err := buildutil.OpenFile(ctxt, filename)
if err != nil {
return nil, err
}
defer rc.Close()
var buf bytes.Buffer
if _, err := io.Copy(&buf, rc); err != nil {
return nil, err
}
return buf.Bytes(), nil
}
func TestOverlay(t *testing.T) {
ctx := &build.Default
ov := map[string][]byte{
"/somewhere/a.go": []byte("file contents"),
}
names := []string{"/somewhere/a.go", "/somewhere//a.go"}
ctx = buildutil.OverlayContext(ctx, ov)
for _, name := range names {
f, err := buildutil.OpenFile(ctx, name)
if err != nil {
t.Errorf("unexpected error %v", err)
}
b, err := ioutil.ReadAll(f)
if err != nil {
t.Errorf("unexpected error %v", err)
}
if got, expected := string(b), string(ov["/somewhere/a.go"]); got != expected {
t.Errorf("read %q, expected %q", got, expected)
}
}
}