125 lines
3.1 KiB
Go
125 lines
3.1 KiB
Go
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package assets
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import (
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"crypto/sha1"
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"encoding/hex"
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"encoding/json"
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"errors"
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"fmt"
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"io"
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"mccl/pkg/retriever"
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"net/http"
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"os"
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"path"
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)
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// assetDownloadUrl is a base URL for an asset to be retrieved from, first %s
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// is a directory which name is first two characters of a hash that goes
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// under the second %s.
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const assetDownloadUrl = "https://resources.download.minecraft.net/%s/%s"
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// Asset represents a single asset file, that is some resource like a texture,
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// or a sound, and so on.
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type Asset struct {
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Hash string `json:"hash"`
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Size int64 `json:"size"`
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}
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// url forms a full URL to an asset.
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func (a *Asset) url() string {
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return fmt.Sprintf(assetDownloadUrl, a.Hash[:2], a.Hash)
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}
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// path forms a relative path to an asset.
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func (a *Asset) path() string {
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return path.Join(a.Hash[:2], a.Hash)
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}
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// Retrieve is a method of a Retrievable interface that is used to download
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// an asset from Mojang's server. It performs the checks for a valid size
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// and hash. Returns a slice of bytes an asset consists of or an error
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// if something gone wrong.
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func (a Asset) Retrieve() ([]byte, error) {
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resp, err := http.Get(a.url())
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if err != nil {
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return nil, err
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}
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defer resp.Body.Close()
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if resp.StatusCode != http.StatusOK {
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return nil, fmt.Errorf("failed to download a file. Status code is %d", resp.StatusCode)
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} else if resp.ContentLength != a.Size {
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return nil, fmt.Errorf("response size mismatch. %d != %d", resp.ContentLength, a.Size)
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}
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buf, err := io.ReadAll(resp.Body)
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if err != nil {
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return nil, err
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}
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if l := len(buf); l != int(a.Size) {
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return nil, fmt.Errorf("file size mismatch. %d != %d", l, a.Size)
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}
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h := sha1.New()
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if _, err := h.Write(buf); err != nil {
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return nil, err
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}
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if hex.EncodeToString(h.Sum(nil)) != a.Hash {
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return nil, errors.New("hash mismatch")
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}
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return buf, nil
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}
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// Assets represents an asset index file.
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type Assets struct {
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Objects map[string]Asset `json:"objects"`
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}
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// New returns a new Assets that is being unmarshaled from a JSON data.
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func New(data []byte) (*Assets, error) {
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a := &Assets{}
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if err := json.Unmarshal(data, a); err != nil {
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return nil, err
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}
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return a, nil
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}
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// RetrieveAsset is a special retriever.WorkerFunc function that is used to
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// check for an existency of an asset, and, if not, to retrieve it and write
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// it to an actual file.
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func RetrieveAsset(item retriever.Retrievable, basePath string) (int, error) {
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asset := item.(Asset)
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p := path.Join(basePath, asset.path())
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if s, err := os.Stat(p); err == nil && s.Size() == asset.Size {
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return int(s.Size()), nil
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}
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data, err := item.Retrieve()
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if err != nil {
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return 0, err
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}
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if err := os.MkdirAll(path.Dir(p), 0777); err != nil {
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return 0, err
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}
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tf, err := os.Create(p)
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if err != nil {
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return 0, err
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}
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defer tf.Close()
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written, err := tf.Write(data)
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if err != nil {
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return 0, err
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} else if written != len(data) {
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return 0, fmt.Errorf("written bytes length mismatch. %d != %d", written, len(data))
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}
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return written, nil
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}
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