feat: initial goget release — modern IPv6-first download utility

internal/output/resume.go

@@ -0,0 +1,154 @@
+//go:build linux || freebsd
+// +build linux freebsd
+
+package output
+
+import (
+	"encoding/json"
+	"fmt"
+	"os"
+	"time"
+
+	"codeberg.org/petrbalvin/goget/internal/core"
+)
+
+// ResumeMetaFileSuffix is the file suffix used for resume metadata files.
+const ResumeMetaFileSuffix = ".goget.meta"
+
+// ResumeMetadata holds metadata for resuming interrupted downloads.
+type ResumeMetadata struct {
+	URL          string        `json:"url"`
+	ETag         string        `json:"etag,omitempty"`
+	LastModified string        `json:"last_modified,omitempty"`
+	Downloaded   int64         `json:"downloaded"`
+	Total        int64         `json:"total,omitempty"`
+	LastWrite    time.Time     `json:"last_write"`
+	Version      string        `json:"version"`
+	Chunks       map[int]int64 `json:"chunks,omitempty"` // per-chunk progress for parallel downloads
+}
+
+// NewResumeMetadata creates a new ResumeMetadata instance with the given parameters.
+func NewResumeMetadata(url, etag, lastModified string, downloaded, total int64) *ResumeMetadata {
+	return &ResumeMetadata{
+		URL:          url,
+		ETag:         etag,
+		LastModified: lastModified,
+		Downloaded:   downloaded,
+		Total:        total,
+		LastWrite:    time.Now(),
+		Version:      "1.0",
+	}
+}
+
+// Save writes the metadata to a JSON file alongside the downloaded file.
+func (rm *ResumeMetadata) Save(outputPath string) error {
+	metaPath := outputPath + ResumeMetaFileSuffix
+	data, err := json.MarshalIndent(rm, "", "  ")
+	if err != nil {
+		return fmt.Errorf("failed to marshal meta: %w", err)
+	}
+	return os.WriteFile(metaPath, data, 0600)
+}
+
+// LoadResumeMetadata reads resume metadata from the associated JSON file.
+func LoadResumeMetadata(outputPath string) (*ResumeMetadata, error) {
+	metaPath := outputPath + ResumeMetaFileSuffix
+	data, err := os.ReadFile(metaPath)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return nil, nil
+		}
+		return nil, fmt.Errorf("failed to read meta: %w", err)
+	}
+
+	var rm ResumeMetadata
+	if err := json.Unmarshal(data, &rm); err != nil {
+		return nil, fmt.Errorf("failed to parse metadata: %w", err)
+	}
+
+	return &rm, nil
+}
+
+// DeleteResumeMetadata removes the metadata file associated with the given output path.
+func DeleteResumeMetadata(outputPath string) error {
+	metaPath := outputPath + ResumeMetaFileSuffix
+	if err := os.Remove(metaPath); err != nil && !os.IsNotExist(err) {
+		return err
+	}
+	return nil
+}
+
+// CanResume checks whether a download can be resumed by validating the metadata file.
+// It returns true only if valid metadata exists and matches the requested URL.
+func CanResume(outputPath string, reqURL string) (bool, *ResumeMetadata, error) {
+	// Check if output file exists
+	info, err := os.Stat(outputPath)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return false, nil, nil
+		}
+		return false, nil, err
+	}
+
+	// Load metadata
+	meta, err := LoadResumeMetadata(outputPath)
+	if err != nil {
+		return false, nil, err
+	}
+
+	// Without valid metadata, resume is not safe (file may be from another download or corrupted)
+	if meta == nil {
+		return false, nil, nil
+	}
+
+	// Verify URL matches
+	if meta.URL != reqURL {
+		return false, nil, fmt.Errorf("url mismatch: metadata for %s, requested %s", meta.URL, reqURL)
+	}
+
+	// Verify file size matches
+	if info.Size() != meta.Downloaded {
+		return false, nil, fmt.Errorf("size mismatch: file has %d bytes, metadata expects %d", info.Size(), meta.Downloaded)
+	}
+
+	return true, meta, nil
+}
+
+// GetResumeInfo creates a ResumeInfo from the metadata for use in download resumption.
+func GetResumeInfo(meta *ResumeMetadata, outputPath string) (*core.ResumeInfo, error) {
+	info, err := os.Stat(outputPath)
+	if err != nil {
+		return nil, err
+	}
+
+	return &core.ResumeInfo{
+		DownloadedBytes: meta.Downloaded,
+		ETag:            meta.ETag,
+		LastModified:    meta.LastModified,
+		URL:             meta.URL,
+		LastWrite:       info.ModTime(),
+	}, nil
+}
+
+// FileExists checks whether a file exists at the given path.
+func FileExists(path string) bool {
+	_, err := os.Stat(path)
+	return err == nil
+}
+
+// GetFileSize returns the size of the file at the given path.
+func GetFileSize(path string) (int64, error) {
+	info, err := os.Stat(path)
+	if err != nil {
+		return 0, err
+	}
+	return info.Size(), nil
+}
+
+// CleanupResumeFiles removes the downloaded file and its associated metadata file.
+func CleanupResumeFiles(outputPath string) error {
+	if err := os.Remove(outputPath); err != nil && !os.IsNotExist(err) {
+		return err
+	}
+	return DeleteResumeMetadata(outputPath)
+}