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_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")
+	})
+})