Continued work on download system (cache + cf meta now implemented)

core/download.go

@@ -2,19 +2,21 @@ package core
 
 import (
 	"encoding/json"
+	"errors"
 	"fmt"
 	"golang.org/x/exp/slices"
 	"io"
 	"io/ioutil"
+	"net/http"
 	"os"
 	"path/filepath"
 	"strings"
-	"sync"
 )
 
 type DownloadSession interface {
 	GetManualDownloads() []ManualDownload
-	StartDownloads(workers int) chan CompletedDownload
+	StartDownloads() chan CompletedDownload
+	SaveIndex() error
 }
 
 type CompletedDownload struct {
@@ -23,8 +25,8 @@ type CompletedDownload struct {
 	Hashes       map[string]string
 	// Error indicates if/why downloading this file failed
 	Error error
-	// Warning indicates a message to show to the user regarding this file (download was successful, but had a problem)
+	// Warnings indicates messages to show to the user regarding this file (download was successful, but had a problem)
-	Warning error
+	Warnings []error
 }
 
 type downloadSessionInternal struct {
@@ -43,207 +45,333 @@ type downloadTask struct {
 	hash               string
 }
 
-func (d downloadSessionInternal) GetManualDownloads() []ManualDownload {
+func (d *downloadSessionInternal) GetManualDownloads() []ManualDownload {
+	// TODO: set destpaths
 	return d.manualDownloads
 }
 
-func (d downloadSessionInternal) StartDownloads(workers int) chan CompletedDownload {
+func (d *downloadSessionInternal) StartDownloads() chan CompletedDownload {
-	tasks := make(chan downloadTask)
 	downloads := make(chan CompletedDownload)
-	var indexLock sync.RWMutex
+	for _, task := range d.downloadTasks {
-	for i := 0; i < workers; i++ {
+		// Get handle for mod
-		go func() {
+		cacheHandle := d.cacheIndex.GetHandleFromHash(task.hashFormat, task.hash)
-			for task := range tasks {
+		if cacheHandle != nil {
-				// Lookup file in index
+			download, err := reuseExistingFile(cacheHandle, d.hashesToObtain, task.destFilePath)
-				indexLock.RLock()
+			if err != nil {
-				// Map hash stored in mod to cache hash format
-				storedHashFmtList, hasStoredHashFmt := d.cacheIndex.Hashes[task.hashFormat]
-				cacheHashFmtList := d.cacheIndex.Hashes[cacheHashFormat]
-				if hasStoredHashFmt {
-					hashIdx := slices.Index(storedHashFmtList, task.hash)
-					if hashIdx > -1 {
-						// Found in index; try using it!
-						cacheFileHash := cacheHashFmtList[hashIdx]
-						cacheFilePath := filepath.Join(d.cacheFolder, cacheFileHash[:2], cacheFileHash[2:])
-
-						// Find hashes already stored in the index
-						hashes := make(map[string]string)
-						hashesToObtain := slices.Clone(d.hashesToObtain)
-						for hashFormat, hashList := range d.cacheIndex.Hashes {
-							if len(hashList) > hashIdx {
-								hashes[hashFormat] = hashList[hashIdx]
-							}
-						}
-
-						indexLock.RUnlock()
-
-						// Assuming the file already exists, attempt to open it
-						file, err := os.Open(cacheFilePath)
-						if err == nil {
-							// Calculate hashes
-							if len(hashesToObtain) > 0 {
-								// TODO: this code needs to add more hashes to the index
-								err = teeHashes(cacheFileHash, cacheHashFormat, d.hashesToObtain, hashes, io.Discard, file)
-								if err != nil {
-									downloads <- CompletedDownload{
-										Error: fmt.Errorf("failed to read hashes of file %s from cache: %w", cacheFilePath, err),
-									}
-									continue
-								}
-							}
-
-							downloads <- CompletedDownload{
-								File:         file,
-								DestFilePath: task.destFilePath,
-								Hashes:       hashes,
-							}
-							continue
-						} else if !os.IsNotExist(err) {
-							// Some other error trying to open the file!
-							downloads <- CompletedDownload{
-								Error: fmt.Errorf("failed to read file %s from cache: %w", cacheFilePath, err),
-							}
-							continue
-						}
-					}
-				}
-				indexLock.RUnlock()
-
-				// Create temp file to download to
-				tempFile, err := ioutil.TempFile(filepath.Join(d.cacheFolder, "temp"), "download-tmp")
-				if err != nil {
-					downloads <- CompletedDownload{
-						Error: fmt.Errorf("failed to create temporary file for download: %w", err),
-					}
-					continue
-				}
-
-				hashes := make(map[string]string)
-				hashes[task.hashFormat] = task.hash
-
-				// TODO: do download
-				var file *os.File
-				indexLock.Lock()
-				// Update hashes in the index and open file
-				hashIdx := slices.Index(cacheHashFmtList, hashes[cacheHashFormat])
-				if hashIdx < 0 {
-					// Doesn't exist in the index; add as a new value
-					hashIdx = len(cacheHashFmtList)
-
-					cacheFileHash := cacheHashFmtList[hashIdx]
-					cacheFilePath := filepath.Join(d.cacheFolder, cacheFileHash[:2], cacheFileHash[2:])
-					// Create the containing directory
-					err = os.MkdirAll(filepath.Dir(cacheFilePath), 0755)
-					if err != nil {
-						_ = tempFile.Close()
-						indexLock.Unlock()
-						downloads <- CompletedDownload{
-							Error: fmt.Errorf("failed to create directories for file %s in cache: %w", cacheFilePath, err),
-						}
-						continue
-					}
-					// Create destination file
-					file, err = os.Create(cacheFilePath)
-					if err != nil {
-						_ = tempFile.Close()
-						indexLock.Unlock()
-						downloads <- CompletedDownload{
-							Error: fmt.Errorf("failed to write file %s to cache: %w", cacheFilePath, err),
-						}
-						continue
-					}
-					// Seek back to start of temp file
-					_, err = tempFile.Seek(0, 0)
-					if err != nil {
-						_ = file.Close()
-						_ = tempFile.Close()
-						indexLock.Unlock()
-						downloads <- CompletedDownload{
-							Error: fmt.Errorf("failed to seek temp file %s in cache: %w", tempFile.Name(), err),
-						}
-						continue
-					}
-					// Copy temporary file to cache
-					_, err = io.Copy(file, tempFile)
-					if err != nil {
-						_ = file.Close()
-						_ = tempFile.Close()
-						indexLock.Unlock()
-						downloads <- CompletedDownload{
-							Error: fmt.Errorf("failed to seek temp file %s in cache: %w", tempFile.Name(), err),
-						}
-						continue
-					}
-				} else {
-					// Exists in the index and should exist on disk; open for reading
-					cacheFileHash := cacheHashFmtList[hashIdx]
-					cacheFilePath := filepath.Join(d.cacheFolder, cacheFileHash[:2], cacheFileHash[2:])
-					file, err = os.Open(cacheFilePath)
-					if err != nil {
-						_ = tempFile.Close()
-						indexLock.Unlock()
-						downloads <- CompletedDownload{
-							Error: fmt.Errorf("failed to write file %s to cache: %w", cacheFilePath, err),
-						}
-						continue
-					}
-				}
-				// Close temporary file, as we are done with it
-				err = tempFile.Close()
-				if err != nil {
-					_ = file.Close()
-					indexLock.Unlock()
-					downloads <- CompletedDownload{
-						Error: fmt.Errorf("failed to close temporary file for download: %w", err),
-					}
-					continue
-				}
-				var warning error
-				for hashFormat, hashList := range d.cacheIndex.Hashes {
-					if hashIdx >= len(hashList) {
-						// Add empty values to make hashList fit hashIdx
-						hashList = append(hashList, make([]string, (hashIdx-len(hashList))+1)...)
-						d.cacheIndex.Hashes[hashFormat] = hashList
-					}
-					// Replace if it doesn't already exist
-					if hashList[hashIdx] == "" {
-						hashList[hashIdx] = hashes[hashFormat]
-					} else if hash, ok := hashes[hashFormat]; ok && hashList[hashIdx] != hash {
-						// Warn if the existing hash is inconsistent!
-						warning = fmt.Errorf("inconsistent %s hash for %s overwritten - value %s (expected %s)", hashFormat,
-							file.Name(), hashList[hashIdx], hash)
-						hashList[hashIdx] = hashes[hashFormat]
-					}
-				}
-				indexLock.Unlock()
-
 				downloads <- CompletedDownload{
-					File:         file,
+					Error: err,
-					DestFilePath: task.destFilePath,
-					Hashes:       hashes,
-					Warning:      warning,
 				}
+			} else {
+				downloads <- download
 			}
-		}()
+			continue
-	}
-	go func() {
-		for _, v := range d.downloadTasks {
-			tasks <- v
 		}
-	}()
+
+		download, err := downloadNewFile(&task, d.cacheFolder, d.hashesToObtain, &d.cacheIndex)
+		if err != nil {
+			downloads <- CompletedDownload{
+				Error: err,
+			}
+		} else {
+			downloads <- download
+		}
+	}
 	return downloads
 }
 
-func teeHashes(validateHash string, validateHashFormat string, hashesToObtain []string, hashes map[string]string,
+func (d *downloadSessionInternal) SaveIndex() error {
+	data, err := json.Marshal(d.cacheIndex)
+	if err != nil {
+		return fmt.Errorf("failed to serialise index: %w", err)
+	}
+	err = ioutil.WriteFile(filepath.Join(d.cacheFolder, "index.json"), data, 0644)
+	if err != nil {
+		return fmt.Errorf("failed to write index: %w", err)
+	}
+	return nil
+}
+
+func reuseExistingFile(cacheHandle *CacheIndexHandle, hashesToObtain []string, destFilePath string) (CompletedDownload, error) {
+	// Already stored; try using it!
+	file, err := cacheHandle.Open()
+	if err == nil {
+		remainingHashes := cacheHandle.GetRemainingHashes(hashesToObtain)
+		if len(remainingHashes) > 0 {
+			err = teeHashes(remainingHashes, cacheHandle.Hashes, io.Discard, file)
+			if err != nil {
+				_ = file.Close()
+				return CompletedDownload{}, fmt.Errorf("failed to read hashes of file %s from cache: %w", cacheHandle.Path(), err)
+			}
+			_, err := file.Seek(0, 0)
+			if err != nil {
+				_ = file.Close()
+				return CompletedDownload{}, fmt.Errorf("failed to seek file %s in cache: %w", cacheHandle.Path(), err)
+			}
+			cacheHandle.UpdateIndex()
+		}
+
+		return CompletedDownload{
+			File:         file,
+			DestFilePath: destFilePath,
+			Hashes:       cacheHandle.Hashes,
+		}, nil
+	} else {
+		return CompletedDownload{}, fmt.Errorf("failed to read file %s from cache: %w", cacheHandle.Path(), err)
+	}
+}
+
+func downloadNewFile(task *downloadTask, cacheFolder string, hashesToObtain []string, index *CacheIndex) (CompletedDownload, error) {
+	// Create temp file to download to
+	tempFile, err := ioutil.TempFile(filepath.Join(cacheFolder, "temp"), "download-tmp")
+	if err != nil {
+		return CompletedDownload{}, fmt.Errorf("failed to create temporary file for download: %w", err)
+	}
+
+	hashesToObtain, hashes := getHashListsForDownload(hashesToObtain, task.hashFormat, task.hash)
+	if len(hashesToObtain) > 0 {
+		var data io.ReadCloser
+		if task.url != "" {
+			resp, err := http.Get(task.url)
+			// TODO: content type, user-agent?
+			if err != nil {
+				return CompletedDownload{}, fmt.Errorf("failed to download %s: %w", task.url, err)
+			}
+			if resp.StatusCode != 200 {
+				_ = resp.Body.Close()
+				return CompletedDownload{}, fmt.Errorf("failed to download %s: invalid status code %v", task.url, resp.StatusCode)
+			}
+			data = resp.Body
+		} else {
+			data, err = task.metaDownloaderData.DownloadFile()
+			if err != nil {
+				return CompletedDownload{}, err
+			}
+		}
+
+		err = teeHashes(hashesToObtain, hashes, tempFile, data)
+		_ = data.Close()
+		if err != nil {
+			return CompletedDownload{}, fmt.Errorf("failed to download file for %s: %w", task.destFilePath, err)
+		}
+	}
+
+	// Create handle with calculated hashes
+	cacheHandle, alreadyExists := index.NewHandleFromHashes(hashes)
+	// Update index stored hashes
+	warnings := cacheHandle.UpdateIndex()
+
+	var file *os.File
+	if alreadyExists {
+		err = tempFile.Close()
+		if err != nil {
+			return CompletedDownload{}, fmt.Errorf("failed to close temporary file %s: %w", tempFile.Name(), err)
+		}
+		file, err = cacheHandle.Open()
+		if err != nil {
+			return CompletedDownload{}, fmt.Errorf("failed to read file %s from cache: %w", cacheHandle.Path(), err)
+		}
+	} else {
+		// Automatically closes tempFile
+		file, err = cacheHandle.CreateFromTemp(tempFile)
+		if err != nil {
+			_ = tempFile.Close()
+			return CompletedDownload{}, fmt.Errorf("failed to move file %s to cache: %w", cacheHandle.Path(), err)
+		}
+	}
+
+	return CompletedDownload{
+		File:         file,
+		DestFilePath: task.destFilePath,
+		Hashes:       hashes,
+		Warnings:     warnings,
+	}, nil
+}
+
+func selectPreferredHash(hashes map[string]string) (currHash string, currHashFormat string) {
+	for _, hashFormat := range preferredHashList {
+		if hash, ok := hashes[hashFormat]; ok {
+			currHashFormat = hashFormat
+			currHash = hash
+		}
+	}
+	return
+}
+
+// getHashListsForDownload creates a hashes map with the given validate hash+format,
+// ensures cacheHashFormat is in hashesToObtain (cloned+returned) and validateHashFormat isn't
+func getHashListsForDownload(hashesToObtain []string, validateHashFormat string, validateHash string) ([]string, map[string]string) {
+	hashes := make(map[string]string)
+	hashes[validateHashFormat] = validateHash
+
+	cl := []string{cacheHashFormat}
+	for _, v := range hashesToObtain {
+		if v != validateHashFormat && v != cacheHashFormat {
+			cl = append(cl, v)
+		}
+	}
+	return cl, hashes
+}
+
+func teeHashes(hashesToObtain []string, hashes map[string]string,
 	dst io.Writer, src io.Reader) error {
-	// TODO: implement
+	// Select the best hash from the hashes map to validate against
+	validateHashFormat, validateHash := selectPreferredHash(hashes)
+	if validateHashFormat == "" {
+		return errors.New("failed to find preferred hash for file")
+	}
+
+	// Create writers for all the hashers
+	mainHasher, err := GetHashImpl(validateHashFormat)
+	if err != nil {
+		return fmt.Errorf("failed to get hash format %s", validateHashFormat)
+	}
+	hashers := make(map[string]HashStringer, len(hashesToObtain))
+	allWriters := make([]io.Writer, len(hashers))
+	for i, v := range hashesToObtain {
+		hashers[v], err = GetHashImpl(v)
+		if err != nil {
+			return fmt.Errorf("failed to get hash format %s", v)
+		}
+		allWriters[i] = hashers[v]
+	}
+	allWriters = append(allWriters, mainHasher, dst)
+
+	// Copy source to all writers (all hashers and dst)
+	w := io.MultiWriter(allWriters...)
+	_, err = io.Copy(w, src)
+	if err != nil {
+		return fmt.Errorf("failed to read file: %w", err)
+	}
+
+	calculatedHash := mainHasher.HashToString(mainHasher.Sum(nil))
+
+	// Check if the hash of the downloaded file matches the expected hash
+	if calculatedHash != validateHash {
+		return fmt.Errorf(
+			"%s hash of downloaded file does not match with expected hash!\n download hash: %s\n expected hash: %s\n",
+			validateHashFormat, calculatedHash, validateHash)
+	}
+
+	for hashFormat, v := range hashers {
+		hashes[hashFormat] = v.HashToString(v.Sum(nil))
+	}
+
+	return nil
 }
 
 const cacheHashFormat = "sha256"
 
 type CacheIndex struct {
-	Version uint32
+	Version     uint32
-	Hashes  map[string][]string
+	Hashes      map[string][]string
+	cachePath   string
+	nextHashIdx int
+}
+
+type CacheIndexHandle struct {
+	index   *CacheIndex
+	hashIdx int
+	Hashes  map[string]string
+}
+
+func (c *CacheIndex) GetHandleFromHash(hashFormat string, hash string) *CacheIndexHandle {
+	storedHashFmtList, hasStoredHashFmt := c.Hashes[hashFormat]
+	if hasStoredHashFmt {
+		hashIdx := slices.Index(storedHashFmtList, hash)
+		if hashIdx > -1 {
+			hashes := make(map[string]string)
+			for curHashFormat, hashList := range c.Hashes {
+				if hashIdx < len(hashList) && hashList[hashIdx] != "" {
+					hashes[curHashFormat] = hashList[hashIdx]
+				}
+			}
+			return &CacheIndexHandle{
+				index:   c,
+				hashIdx: hashIdx,
+				Hashes:  hashes,
+			}
+		}
+	}
+	return nil
+}
+
+func (c *CacheIndex) NewHandleFromHashes(hashes map[string]string) (*CacheIndexHandle, bool) {
+	for hashFormat, hash := range hashes {
+		handle := c.GetHandleFromHash(hashFormat, hash)
+		if handle != nil {
+			// Add hashes to handle
+			for hashFormat2, hash2 := range hashes {
+				handle.Hashes[hashFormat2] = hash2
+			}
+			return handle, true
+		}
+	}
+	i := c.nextHashIdx
+	c.nextHashIdx += 1
+	return &CacheIndexHandle{
+		index:   c,
+		hashIdx: i,
+		Hashes:  hashes,
+	}, false
+}
+
+func (h *CacheIndexHandle) GetRemainingHashes(hashesToObtain []string) []string {
+	var remaining []string
+	for _, hashFormat := range hashesToObtain {
+		if _, ok := h.Hashes[hashFormat]; !ok {
+			remaining = append(remaining, hashFormat)
+		}
+	}
+	return remaining
+}
+
+func (h *CacheIndexHandle) Path() string {
+	cacheFileHash := h.index.Hashes[cacheHashFormat][h.hashIdx]
+	cacheFilePath := filepath.Join(h.index.cachePath, cacheFileHash[:2], cacheFileHash[2:])
+	return cacheFilePath
+}
+
+func (h *CacheIndexHandle) Open() (*os.File, error) {
+	return os.Open(h.Path())
+}
+
+func (h *CacheIndexHandle) CreateFromTemp(temp *os.File) (*os.File, error) {
+	err := os.MkdirAll(filepath.Dir(h.Path()), 0755)
+	if err != nil {
+		return nil, err
+	}
+	err = os.Rename(temp.Name(), h.Path())
+	if err != nil {
+		return nil, err
+	}
+	err = temp.Close()
+	if err != nil {
+		return nil, err
+	}
+	return os.Open(h.Path())
+}
+
+func (h *CacheIndexHandle) UpdateIndex() (warnings []error) {
+	// Add hashes to index
+	for hashFormat, hash := range h.Hashes {
+		hashList := h.index.Hashes[hashFormat]
+		if h.hashIdx >= len(hashList) {
+			// Add empty values to make hashList fit hashIdx
+			hashList = append(hashList, make([]string, (h.hashIdx-len(hashList))+1)...)
+			h.index.Hashes[hashFormat] = hashList
+		}
+
+		// Replace if it doesn't already exist
+		if hashList[h.hashIdx] == "" {
+			hashList[h.hashIdx] = h.Hashes[hashFormat]
+		} else if hashList[h.hashIdx] != hash {
+			// Warn if the existing hash is inconsistent!
+			warnings = append(warnings, fmt.Errorf("inconsistent %s hash for %s overwritten - value %s (expected %s)",
+				hashFormat, h.Path(), hashList[h.hashIdx], hash))
+			hashList[h.hashIdx] = h.Hashes[hashFormat]
+		}
+	}
+	return
 }
 
 func CreateDownloadSession(mods []*Mod, hashesToObtain []string) (DownloadSession, error) {
@@ -281,6 +409,8 @@ func CreateDownloadSession(mods []*Mod, hashesToObtain []string) (DownloadSessio
 	if !hasCacheHashFmt {
 		cacheIndex.Hashes[cacheHashFormat] = make([]string, 0)
 	}
+	cacheIndex.cachePath = cachePath
+	cacheIndex.nextHashIdx = len(cacheIndex.Hashes[cacheHashFormat])
 
 	// TODO: move in/ files?
 
@@ -336,5 +466,5 @@ func CreateDownloadSession(mods []*Mod, hashesToObtain []string) (DownloadSessio
 
 	// TODO: index housekeeping? i.e. remove deleted files, remove old files (LRU?)
 
-	return downloadSession, nil
+	return &downloadSession, nil
 }

core/hash.go

@@ -33,6 +33,14 @@ func GetHashImpl(hashType string) (HashStringer, error) {
 	return nil, fmt.Errorf("hash implementation %s not found", hashType)
 }
 
+var preferredHashList = []string{
+	"murmur2",
+	"md5",
+	"sha1",
+	"sha256",
+	"sha512",
+}
+
 type HashStringer interface {
 	hash.Hash
 	HashToString([]byte) string

core/interfaces.go

@@ -45,7 +45,7 @@ type MetaDownloader interface {
 // MetaDownloaderData specifies the per-Mod metadata retrieved for downloading
 type MetaDownloaderData interface {
 	GetManualDownload() (bool, ManualDownload)
-	DownloadFile(io.Writer) error
+	DownloadFile() (io.ReadCloser, error)
 }
 
 type ManualDownload struct {

curseforge/curseforge.go

@@ -2,9 +2,11 @@ package curseforge
 
 import (
 	"errors"
+	"fmt"
 	"github.com/spf13/viper"
 	"golang.org/x/exp/slices"
 	"io"
+	"net/http"
 	"path/filepath"
 	"regexp"
 	"strconv"
@@ -448,20 +450,116 @@ func parseExportData(from map[string]interface{}) (cfExportData, error) {
 type cfDownloader struct{}
 
 func (c cfDownloader) GetFilesMetadata(mods []*core.Mod) ([]core.MetaDownloaderData, error) {
-	// TODO implement me
+	if len(mods) == 0 {
-	panic("implement me")
+		return []core.MetaDownloaderData{}, nil
+	}
+
+	downloaderData := make([]core.MetaDownloaderData, len(mods))
+	indexMap := make(map[int]int)
+	projectMetadata := make([]cfUpdateData, len(mods))
+	modIDs := make([]int, len(mods))
+	for i, v := range mods {
+		updateData, ok := v.GetParsedUpdateData("curseforge")
+		if !ok {
+			return nil, fmt.Errorf("failed to read CurseForge update metadata from %s", v.Name)
+		}
+		project := updateData.(cfUpdateData)
+		indexMap[project.ProjectID] = i
+		projectMetadata[i] = project
+		modIDs[i] = project.ProjectID
+	}
+
+	modData, err := cfDefaultClient.getModInfoMultiple(modIDs)
+	if err != nil {
+		return nil, fmt.Errorf("failed to get CurseForge mod metadata: %w", err)
+	}
+
+	handleFileInfo := func(modID int, fileInfo modFileInfo) {
+		// If metadata already exists (i.e. opted-out) update it with more metadata
+		if meta, ok := downloaderData[indexMap[modID]].(*cfDownloadMetadata); ok {
+			if meta.noDistribution {
+				meta.websiteUrl = meta.websiteUrl + "/files/" + strconv.Itoa(fileInfo.ID)
+				meta.fileName = fileInfo.FileName
+			}
+		}
+		downloaderData[indexMap[modID]] = &cfDownloadMetadata{
+			url: fileInfo.DownloadURL,
+		}
+	}
+
+	fileIDsToLookup := make([]int, 0)
+	for _, mod := range modData {
+		if _, ok := indexMap[mod.ID]; !ok {
+			return nil, fmt.Errorf("unknown mod ID in response: %v (for %v)", mod.ID, mod.Name)
+		}
+		if !mod.AllowModDistribution {
+			downloaderData[indexMap[mod.ID]] = &cfDownloadMetadata{
+				noDistribution: true, // Inverted so the default value is not this (probably doesn't matter)
+				name:           mod.Name,
+				websiteUrl:     mod.Links.WebsiteURL,
+			}
+		}
+
+		fileID := projectMetadata[indexMap[mod.ID]].FileID
+		fileInfoFound := false
+		// First look in latest files
+		for _, fileInfo := range mod.LatestFiles {
+			if fileInfo.ID == fileID {
+				fileInfoFound = true
+				handleFileInfo(mod.ID, fileInfo)
+				break
+			}
+		}
+
+		if !fileInfoFound {
+			fileIDsToLookup = append(fileIDsToLookup, fileID)
+		}
+	}
+
+	if len(fileIDsToLookup) > 0 {
+		fileData, err := cfDefaultClient.getFileInfoMultiple(fileIDsToLookup)
+		if err != nil {
+			return nil, fmt.Errorf("failed to get CurseForge file metadata: %w", err)
+		}
+		for _, fileInfo := range fileData {
+			if _, ok := indexMap[fileInfo.ModID]; !ok {
+				return nil, fmt.Errorf("unknown mod ID in response: %v from file %v (for %v)", fileInfo.ModID, fileInfo.ID, fileInfo.FileName)
+			}
+			handleFileInfo(fileInfo.ModID, fileInfo)
+		}
+	}
+
+	return downloaderData, nil
 }
 
 type cfDownloadMetadata struct {
-	url                string
+	url            string
-	allowsDistribution bool
+	noDistribution bool
+	name           string
+	fileName       string
+	websiteUrl     string
 }
 
-func (m *cfDownloadMetadata) RequiresManualDownload() bool {
+func (m *cfDownloadMetadata) GetManualDownload() (bool, core.ManualDownload) {
-	return !m.allowsDistribution
+	if !m.noDistribution {
+		return false, core.ManualDownload{}
+	}
+	return true, core.ManualDownload{
+		Name:     m.name,
+		FileName: m.fileName,
+		URL:      m.websiteUrl,
+	}
 }
 
-func (m *cfDownloadMetadata) DownloadFile(writer io.Writer) error {
+func (m *cfDownloadMetadata) DownloadFile() (io.ReadCloser, error) {
-	// TODO implement me
+	resp, err := http.Get(m.url)
-	panic("implement me")
+	// TODO: content type, user-agent?
+	if err != nil {
+		return nil, fmt.Errorf("failed to download %s: %w", m.url, err)
+	}
+	if resp.StatusCode != 200 {
+		_ = resp.Body.Close()
+		return nil, fmt.Errorf("failed to download %s: invalid status code %v", m.url, resp.StatusCode)
+	}
+	return resp.Body, nil
 }

curseforge/request.go

@@ -147,7 +147,11 @@ type modInfo struct {
 		FileType    int    `json:"releaseType"`
 		Modloader   int    `json:"modLoader"`
 	} `json:"latestFilesIndexes"`
-	ModLoaders []string `json:"modLoaders"`
+	ModLoaders           []string `json:"modLoaders"`
+	AllowModDistribution bool     `json:"allowModDistribution"`
+	Links                struct {
+		WebsiteURL string `json:"websiteUrl"`
+	} `json:"links"`
 }
 
 func (c *cfApiClient) getModInfo(modID int) (modInfo, error) {
@@ -203,6 +207,7 @@ func (c *cfApiClient) getModInfoMultiple(modIDs []int) ([]modInfo, error) {
 // modFileInfo is a subset of the deserialised JSON response from the Curse API for mod files
 type modFileInfo struct {
 	ID           int       `json:"id"`
+	ModID        int       `json:"modId"`
 	FileName     string    `json:"fileName"`
 	FriendlyName string    `json:"displayName"`
 	Date         time.Time `json:"fileDate"`