Implement pack importing/exporting for downloaded Curseforge packs

Abstract out hash implementations
Implement file saving/downloading

core/hash.go

@@ -0,0 +1,23 @@
+package core
+
+import (
+	"crypto/md5"
+	"crypto/sha256"
+	"crypto/sha512"
+	"errors"
+	"hash"
+)
+
+// GetHashImpl gets an implementation of hash.Hash for the given hash type string
+func GetHashImpl(hashType string) (hash.Hash, error) {
+	switch hashType {
+	case "sha256":
+		return sha256.New(), nil
+	case "sha512":
+		return sha512.New(), nil
+	case "md5":
+		return md5.New(), nil
+	}
+	// TODO: implement murmur2
+	return nil, errors.New("hash implementation not found")
+}

core/index.go

@@ -1,8 +1,8 @@
 package core
 
 import (
-	"crypto/sha256"
 	"encoding/hex"
+	"errors"
 	"io"
 	"os"
 	"path/filepath"
@@ -130,7 +130,10 @@ func (in *Index) updateFile(path string) error {
 	// Hash usage strategy (may change):
 	// Just use SHA256, overwrite existing hash regardless of what it is
 	// May update later to continue using the same hash that was already being used
-	h := sha256.New()
+	h, err := GetHashImpl("sha256")
+	if err != nil {
+		return err
+	}
 	if _, err := io.Copy(h, f); err != nil {
 		return err
 	}
@@ -310,3 +313,37 @@ func (in Index) GetAllMods() []string {
 	}
 	return list
 }
+
+// GetFilePath attempts to get the path of the destination index file as it is stored on disk
+func (in Index) GetFilePath(f IndexFile) string {
+	return filepath.Join(filepath.Dir(in.indexFile), filepath.FromSlash(f.File))
+}
+
+// SaveFile attempts to read the file from disk
+func (in Index) SaveFile(f IndexFile, dest io.Writer) error {
+	hashFormat := f.HashFormat
+	if hashFormat == "" {
+		hashFormat = in.HashFormat
+	}
+	src, err := os.Open(in.GetFilePath(f))
+	if err != nil {
+		return err
+	}
+	h, err := GetHashImpl(hashFormat)
+	if err != nil {
+		return err
+	}
+
+	w := io.MultiWriter(h, dest)
+	_, err = io.Copy(w, src)
+	if err != nil {
+		return err
+	}
+
+	calculatedHash := hex.EncodeToString(h.Sum(nil))
+	if calculatedHash != f.Hash {
+		return errors.New("hash of saved file is invalid")
+	}
+
+	return nil
+}

core/mod.go

@@ -1,12 +1,13 @@
 package core
 
 import (
-	"crypto/sha256"
 	"encoding/hex"
 	"errors"
 	"io"
+	"net/http"
 	"os"
 	"path/filepath"
+	"strconv"
 
 	"github.com/BurntSushi/toml"
 )
@@ -37,6 +38,7 @@ type ModDownload struct {
 }
 
 // The three possible values of Side (the side that the mod is on) are "server", "client", and "both".
+//noinspection GoUnusedConst
 const (
 	ServerSide    = "server"
 	ClientSide    = "client"
@@ -88,7 +90,10 @@ func (m Mod) Write() (string, string, error) {
 	}
 	defer f.Close()
 
-	h := sha256.New()
+	h, err := GetHashImpl("sha256")
+	if err != nil {
+		return "", "", err
+	}
 	w := io.MultiWriter(h, f)
 
 	enc := toml.NewEncoder(w)
@@ -109,3 +114,36 @@ func (m Mod) GetParsedUpdateData(updaterName string) (interface{}, bool) {
 func (m Mod) GetFilePath() string {
 	return m.metaFile
 }
+
+// GetDestFilePath returns the path of the destination file of the mod
+func (m Mod) GetDestFilePath() string {
+	return filepath.Join(filepath.Dir(m.metaFile), filepath.FromSlash(m.FileName))
+}
+
+// DownloadFile attempts to resolve and download the file
+func (m Mod) DownloadFile(dest io.Writer) error {
+	resp, err := http.Get(m.Download.URL)
+	if err != nil {
+		return err
+	}
+	if resp.StatusCode != 200 {
+		_ = resp.Body.Close()
+		return errors.New("invalid status code " + strconv.Itoa(resp.StatusCode))
+	}
+	h, err := GetHashImpl(m.Download.HashFormat)
+	if err != nil {
+		return err
+	}
+
+	w := io.MultiWriter(h, dest)
+	_, err = io.Copy(w, resp.Body)
+	if err != nil {
+		return err
+	}
+
+	calculatedHash := hex.EncodeToString(h.Sum(nil))
+	if calculatedHash != m.Download.Hash {
+		return errors.New("hash of saved file is invalid")
+	}
+	return nil
+}

core/pack.go

@@ -1,7 +1,6 @@
 package core
 
 import (
-	"crypto/sha256"
 	"encoding/hex"
 	"errors"
 	"io"
@@ -65,7 +64,10 @@ func (pack *Pack) UpdateIndexHash() error {
 	// Hash usage strategy (may change):
 	// Just use SHA256, overwrite existing hash regardless of what it is
 	// May update later to continue using the same hash that was already being used
-	h := sha256.New()
+	h, err := GetHashImpl("sha256")
+	if err != nil {
+		return err
+	}
 	if _, err := io.Copy(h, f); err != nil {
 		return err
 	}