feat(dowloader): resume partial downloads (#4537)

* feat(resume downloads): add basic tests

Signed-off-by: Saarthak Verma <saarthakverma739@gmail.com>

* test(resume downloads): implement file download tc

Signed-off-by: Saarthak Verma <saarthakverma739@gmail.com>

* test(resume downloads): add resume partial download test

Signed-off-by: Saarthak Verma <saarthakverma739@gmail.com>

* feat(resume downloads): implement resumable downloads for interrupted transfers

- Adds support for resuming partially downloaded files
- Uses HTTP Range header to continue from last byte position
- Maintains download progress across interruptions
- Preserves partial downloads with .partial extension
- Validates SHA256 checksum after completion

Signed-off-by: Saarthak Verma <saarthakverma739@gmail.com>

* fix(resume downloads): incorrect download percent on front end

Signed-off-by: Saarthak Verma <saarthakverma739@gmail.com>

* feat(resume download): add range header check tc

Signed-off-by: Saarthak Verma <saarthakverma739@gmail.com>

* feat(resume download): implement range header check

Signed-off-by: Saarthak Verma <saarthakverma739@gmail.com>

---------

Signed-off-by: Saarthak Verma <saarthakverma739@gmail.com>

pkg/downloader/uri.go

@@ -2,7 +2,9 @@ package downloader
 
 import (
 	"crypto/sha256"
+	"errors"
 	"fmt"
+	"hash"
 	"io"
 	"net/http"
 	"net/url"
@@ -204,6 +206,25 @@ func removePartialFile(tmpFilePath string) error {
 	return nil
 }
 
+func calculateHashForPartialFile(file *os.File) (hash.Hash, error) {
+	hash := sha256.New()
+	_, err := io.Copy(hash, file)
+	if err != nil {
+		return nil, err
+	}
+	return hash, nil
+}
+
+func (uri URI) checkSeverSupportsRangeHeader() (bool, error) {
+	url := uri.ResolveURL()
+	resp, err := http.Head(url)
+	if err != nil {
+		return false, err
+	}
+	defer resp.Body.Close()
+	return resp.Header.Get("Accept-Ranges") == "bytes", nil
+}
+
 func (uri URI) DownloadFile(filePath, sha string, fileN, total int, downloadStatus func(string, string, string, float64)) error {
 	url := uri.ResolveURL()
 	if uri.LooksLikeOCI() {
@@ -266,8 +287,34 @@ func (uri URI) DownloadFile(filePath, sha string, fileN, total int, downloadStat
 
 	log.Info().Msgf("Downloading %q", url)
 
-	// Download file
-	resp, err := http.Get(url)
+	req, err := http.NewRequest("GET", url, nil)
+	if err != nil {
+		return fmt.Errorf("failed to create request for %q: %v", filePath, err)
+	}
+
+	// save partial download to dedicated file
+	tmpFilePath := filePath + ".partial"
+	tmpFileInfo, err := os.Stat(tmpFilePath)
+	if err == nil {
+		support, err := uri.checkSeverSupportsRangeHeader()
+		if err != nil {
+			return fmt.Errorf("failed to check if uri server supports range header: %v", err)
+		}
+		if support {
+			startPos := tmpFileInfo.Size()
+			req.Header.Set("Range", fmt.Sprintf("bytes=%d-", startPos))
+		} else {
+			err := removePartialFile(tmpFilePath)
+			if err != nil {
+				return err
+			}
+		}
+	} else if !errors.Is(err, os.ErrNotExist) {
+		return fmt.Errorf("failed to check file %q existence: %v", filePath, err)
+	}
+
+	// Start the request
+	resp, err := http.DefaultClient.Do(req)
 	if err != nil {
 		return fmt.Errorf("failed to download file %q: %v", filePath, err)
 	}
@@ -283,26 +330,20 @@ func (uri URI) DownloadFile(filePath, sha string, fileN, total int, downloadStat
 		return fmt.Errorf("failed to create parent directory for file %q: %v", filePath, err)
 	}
 
-	// save partial download to dedicated file
-	tmpFilePath := filePath + ".partial"
-
-	// remove tmp file
-	err = removePartialFile(tmpFilePath)
+	// Create and write file
+	outFile, err := os.OpenFile(tmpFilePath, os.O_APPEND|os.O_RDWR|os.O_CREATE, 0644)
 	if err != nil {
-		return err
-	}
-
-	// Create and write file content
-	outFile, err := os.Create(tmpFilePath)
-	if err != nil {
-		return fmt.Errorf("failed to create file %q: %v", tmpFilePath, err)
+		return fmt.Errorf("failed to create / open file %q: %v", tmpFilePath, err)
 	}
 	defer outFile.Close()
-
+	hash, err := calculateHashForPartialFile(outFile)
+	if err != nil {
+		return fmt.Errorf("failed to calculate hash for partial file")
+	}
 	progress := &progressWriter{
 		fileName:       tmpFilePath,
 		total:          resp.ContentLength,
-		hash:           sha256.New(),
+		hash:           hash,
 		fileNo:         fileN,
 		totalFiles:     total,
 		downloadStatus: downloadStatus,

pkg/downloader/uri_test.go

@@ -1,6 +1,15 @@
 package downloader_test
 
 import (
+	"crypto/rand"
+	"crypto/sha256"
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"regexp"
+	"strconv"
+
 	. "github.com/mudler/LocalAI/pkg/downloader"
 	. "github.com/onsi/ginkgo/v2"
 	. "github.com/onsi/gomega"
@@ -38,3 +47,139 @@ var _ = Describe("Gallery API tests", func() {
 		})
 	})
 })
+
+type RangeHeaderError struct {
+	msg string
+}
+
+func (e *RangeHeaderError) Error() string { return e.msg }
+
+var _ = Describe("Download Test", func() {
+	var mockData []byte
+	var mockDataSha string
+	var filePath string
+
+	extractRangeHeader := func(rangeString string) (int, int, error) {
+		regex := regexp.MustCompile(`^bytes=(\d+)-(\d+|)$`)
+		matches := regex.FindStringSubmatch(rangeString)
+		rangeErr := RangeHeaderError{msg: "invalid / ill-formatted range"}
+		if matches == nil {
+			return -1, -1, &rangeErr
+		}
+		startPos, err := strconv.Atoi(matches[1])
+		if err != nil {
+			return -1, -1, err
+		}
+
+		endPos := -1
+		if matches[2] != "" {
+			endPos, err = strconv.Atoi(matches[2])
+			if err != nil {
+				return -1, -1, err
+			}
+			endPos += 1 // because range is inclusive in rangeString
+		}
+		return startPos, endPos, nil
+	}
+
+	getMockServer := func(supportsRangeHeader bool) *httptest.Server {
+		mockServer := httptest.NewUnstartedServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			if r.Method != "HEAD" && r.Method != "GET" {
+				w.WriteHeader(http.StatusNotFound)
+				return
+			}
+			if r.Method == "HEAD" {
+				if supportsRangeHeader {
+					w.Header().Add("Accept-Ranges", "bytes")
+				}
+				w.WriteHeader(http.StatusOK)
+				return
+			}
+			// GET method
+			startPos := 0
+			endPos := len(mockData)
+			var err error
+			var respData []byte
+			rangeString := r.Header.Get("Range")
+			if rangeString != "" {
+				startPos, endPos, err = extractRangeHeader(rangeString)
+				if err != nil {
+					if _, ok := err.(*RangeHeaderError); ok {
+						w.WriteHeader(http.StatusBadRequest)
+						return
+					}
+					Expect(err).ToNot(HaveOccurred())
+				}
+				if endPos == -1 {
+					endPos = len(mockData)
+				}
+				if startPos < 0 || startPos >= len(mockData) || endPos < 0 || endPos > len(mockData) || startPos > endPos {
+					w.WriteHeader(http.StatusBadRequest)
+					return
+				}
+			}
+			respData = mockData[startPos:endPos]
+			w.WriteHeader(http.StatusOK)
+			w.Write(respData)
+		}))
+		mockServer.EnableHTTP2 = true
+		mockServer.Start()
+		return mockServer
+	}
+
+	BeforeEach(func() {
+		mockData = make([]byte, 20000)
+		_, err := rand.Read(mockData)
+		Expect(err).ToNot(HaveOccurred())
+		_mockDataSha := sha256.New()
+		_, err = _mockDataSha.Write(mockData)
+		Expect(err).ToNot(HaveOccurred())
+		mockDataSha = fmt.Sprintf("%x", _mockDataSha.Sum(nil))
+		dir, err := os.Getwd()
+		filePath = dir + "/my_supercool_model"
+		Expect(err).NotTo(HaveOccurred())
+	})
+
+	Context("URI DownloadFile", func() {
+		It("fetches files from mock server", func() {
+			mockServer := getMockServer(true)
+			defer mockServer.Close()
+			uri := URI(mockServer.URL)
+			err := uri.DownloadFile(filePath, mockDataSha, 1, 1, func(s1, s2, s3 string, f float64) {})
+			Expect(err).ToNot(HaveOccurred())
+		})
+
+		It("resumes partially downloaded files", func() {
+			mockServer := getMockServer(true)
+			defer mockServer.Close()
+			uri := URI(mockServer.URL)
+			// Create a partial file
+			tmpFilePath := filePath + ".partial"
+			file, err := os.OpenFile(tmpFilePath, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0644)
+			Expect(err).ToNot(HaveOccurred())
+			_, err = file.Write(mockData[0:10000])
+			Expect(err).ToNot(HaveOccurred())
+			err = uri.DownloadFile(filePath, mockDataSha, 1, 1, func(s1, s2, s3 string, f float64) {})
+			Expect(err).ToNot(HaveOccurred())
+		})
+
+		It("restarts download from 0 if server doesn't support Range header", func() {
+			mockServer := getMockServer(false)
+			defer mockServer.Close()
+			uri := URI(mockServer.URL)
+			// Create a partial file
+			tmpFilePath := filePath + ".partial"
+			file, err := os.OpenFile(tmpFilePath, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0644)
+			Expect(err).ToNot(HaveOccurred())
+			_, err = file.Write(mockData[0:10000])
+			Expect(err).ToNot(HaveOccurred())
+			err = uri.DownloadFile(filePath, mockDataSha, 1, 1, func(s1, s2, s3 string, f float64) {})
+			Expect(err).ToNot(HaveOccurred())
+		})
+	})
+
+	AfterEach(func() {
+		os.Remove(filePath) // cleanup, also checks existance of filePath`
+		os.Remove(filePath + ".partial")
+	})
+})