FCLauncher/fclauncher/minecraft.go

package main

import (
	"crypto/sha1"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"os"
	"path/filepath"
	"time"
)

type McVersionManifestEntry struct {
	Id string
	Type string
	Url string
	Time time.Time
	ReleaseTime time.Time
	Sha1 string
	ComplianceLevel int
}

type McLatestEntry struct {
	Release string
	Snapshot string
}

type McVersionManifest struct {
	Latest McLatestEntry
	Versions []McVersionManifestEntry
}

type McArguments struct {
	Game []string
	Jvm []string
}

type McAssetIndex struct {
	Id string
	Sha1 string
	Size int
	TotalSize int
	Url string
}

type McJavaVersion struct {
	Component string
	MajorVersion int
}

type McLibraryArtifact struct {
	Path string
	Sha1 string
	Size int
	Url string
}

type McLibraryDownload struct {
	Artifact McLibraryArtifact
}

type McRuleOs struct {
	Name string
	Version string
	ARch string
}

type McRule struct {
	Action string
	Features map[string]bool
	Os McRuleOs
}

type McLibrary struct {
	Downloads McLibraryDownload
	Name string
	Rules []McRule
}

type McDownload struct {
	Sha1 string
	Size int
	Url string
}

type McMetadata struct {
	Arguments McArguments
	AssetIndex McAssetIndex
	Assets string
	ComplianceLevel int
	Downloads map[string]McDownload
	Id string
	JavaVersion	McJavaVersion
	Libraries []McLibrary
	Logging interface{}
	MainClass string
	MinimumLauncherVersion int
	ReleaseTime time.Time
	Time time.Time
	Type string
}

func GetVersionManifest() (McVersionManifest, error) {
	resp, err := http.Get("https://piston-meta.mojang.com/mc/game/version_manifest_v2.json")
	var returnError error = nil
	if err == nil {
		defer resp.Body.Close()
		data, err := io.ReadAll(resp.Body)
		if err == nil {
			versionManifest := McVersionManifest{}	
			err = json.Unmarshal(data, &versionManifest)
			if err == nil {
				dir, err := os.UserConfigDir()
				if err != nil {
					return versionManifest, nil
				}
				err = os.MkdirAll(filepath.Join(dir, "FCLauncher", "cache"), 0755)
				f, err := os.OpenFile(filepath.Join(dir, "FCLauncher", "cache", "versionManifest.json"), os.O_CREATE|os.O_RDWR, 0755)
				defer f.Close()
				f.Write(data)
				return versionManifest, nil
			} else {
				returnError = fmt.Errorf("Unable to parse Json: %e\n", err)
			}
		} else {
			returnError = fmt.Errorf("Unable to read version manifest: %e\n", err)
		}
	} else {
		returnError = fmt.Errorf("Unable to download version manifest: %e\n", err)
	}

	dir, err := os.UserConfigDir()
	if err != nil {
		return McVersionManifest{}, returnError
	}
	path := filepath.Join(dir, "FCLauncher", "cache", "versionManifest.json")
	if _, err = os.Stat(path); err != nil {
		return McVersionManifest{}, returnError
	}
	f, err := os.OpenFile(path, os.O_RDONLY, 0755)
	if err != nil {
		return McVersionManifest{}, returnError
	}
	data, _ := io.ReadAll(f)
	if err != nil {
		return McVersionManifest{}, returnError
	}
	versionManifest := McVersionManifest{}
	err = json.Unmarshal(data, &versionManifest)
	if err != nil {
		return McVersionManifest{}, returnError
	}
	return versionManifest, nil

}

func GetVersionMetadata(wantedVersion string) (McMetadata, error) {
	manifest, err := GetVersionManifest()
	if err != nil {
		return McMetadata{}, fmt.Errorf("GetVersionMetadata: %e\n", err)
	}

	for _, version := range manifest.Versions {
		if wantedVersion == version.Id {
			//found it
			dir, err := os.UserConfigDir()
			if err == nil {
				path := filepath.Join(dir, "FCLauncher", "cache", "versionMetadata", wantedVersion+".json")
				if _, err := os.Stat(path); err == nil {
					if f, err := os.OpenFile(path, os.O_RDONLY, 0755); err == nil {
						defer f.Close()
						if data, err := io.ReadAll(f); err == nil {
							sha := sha1.Sum(data)
							if hex.EncodeToString(sha[:20]) == version.Sha1{
								metadata := McMetadata{}
								json.Unmarshal(data, &metadata)
								fmt.Printf("Found cache!\n")
								return metadata, nil
							}
						}
					}
				}
			}
			resp, err := http.Get(version.Url)
			if err != nil {
				return McMetadata{}, fmt.Errorf("Unable to download metadata: %e\n", err)
			}
			defer resp.Body.Close()
			data, err := io.ReadAll(resp.Body)
			if err != nil {
				return McMetadata{}, fmt.Errorf("Unable to download metadata: %e\n", err)
			}
			sha := sha1.Sum(data)
			if hex.EncodeToString(sha[:20]) != version.Sha1 {
				return McMetadata{}, fmt.Errorf("GetMetadata: Sha1 hash does not match\n")
			}
			metadata := McMetadata{}
			err = json.Unmarshal(data, &metadata)
			dir, err = os.UserConfigDir()
			if err == nil {
				path := filepath.Join(dir, "FCLauncher", "cache", "versionMetadata")
				if os.MkdirAll(path, 0755) == nil {
					if f, err := os.OpenFile(filepath.Join(path, wantedVersion+".json"), os.O_CREATE|os.O_RDWR, 0755); err == nil {
						defer f.Close()
						f.Write(data)
					}
				}
			}
			return metadata, nil
			
		}
	}
	return McMetadata{}, fmt.Errorf("Unable to find version %s\n", wantedVersion)
}