Implement pack importing/exporting for downloaded Curseforge packs

Abstract out hash implementations
Implement file saving/downloading

curseforge/packinterop/disk.go

@@ -0,0 +1,81 @@
+package packinterop
+
+import (
+	"bufio"
+	"io"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+)
+
+type diskFile struct {
+	NameInternal string
+	Path         string
+}
+
+func (f diskFile) Name() string {
+	return f.NameInternal
+}
+
+func (f diskFile) Open() (io.ReadCloser, error) {
+	return os.Open(f.Path)
+}
+
+type readerFile struct {
+	NameInternal string
+	Reader       *io.ReadCloser
+}
+
+func (f readerFile) Name() string {
+	return f.NameInternal
+}
+
+func (f readerFile) Open() (io.ReadCloser, error) {
+	return *f.Reader, nil
+}
+
+type diskPackSource struct {
+	MetaSource *bufio.Reader
+	MetaName   string
+	BasePath   string
+}
+
+func (s diskPackSource) GetFile(path string) (ImportPackFile, error) {
+	return diskFile{path, filepath.Join(s.BasePath, filepath.FromSlash(path))}, nil
+}
+
+func (s diskPackSource) GetFileList() ([]ImportPackFile, error) {
+	list := make([]ImportPackFile, 0)
+	err := filepath.Walk(s.BasePath, func(path string, info os.FileInfo, err error) error {
+		if err != nil {
+			return err
+		}
+		if info.IsDir() {
+			return nil
+		}
+		// Get the name of the file, relative to the pack folder
+		name, err := filepath.Rel(s.BasePath, path)
+		if err != nil {
+			return err
+		}
+		list = append(list, diskFile{filepath.ToSlash(name), path})
+		return nil
+	})
+	if err != nil {
+		return nil, err
+	}
+	return list, nil
+}
+
+func (s diskPackSource) GetPackFile() ImportPackFile {
+	rc := ioutil.NopCloser(s.MetaSource)
+	return readerFile{s.MetaName, &rc}
+}
+
+func GetDiskPackSource(metaSource *bufio.Reader, metaName string, basePath string) ImportPackSource {
+	return diskPackSource{
+		MetaSource: metaSource,
+		MetaName:   metaName,
+		BasePath:   basePath,
+	}
+}