Added support to diff two images "on the fly" (also partially)

Author: oderwat

cmd/docker-inspector/diff.go

@@ -0,0 +1,179 @@
+// Package diff provides functionality for comparing Docker image contents
+package main
+
+import (
+	"fmt"
+	"strings"
+	"time"
+)
+
+// Mode specifies what attributes to compare
+type Mode int
+
+const (
+	// CompareAll includes all attributes including modification times
+	CompareAll Mode = iota
+	// CompareNoTimes excludes modification time comparisons
+	CompareNoTimes
+)
+
+// Change represents the type of difference found
+type Change string
+
+const (
+	Added    Change = "added"
+	Removed  Change = "removed"
+	Modified Change = "modified"
+)
+
+// FileDiff represents a difference between two versions of a file
+type FileDiff struct {
+	Path    string   `json:"path"`
+	Type    Change   `json:"type"`
+	OldFile FileInfo `json:"oldFile,omitempty"`
+	NewFile FileInfo `json:"newFile,omitempty"`
+	// Details contains human-readable descriptions of the changes
+	Details []string `json:"details,omitempty"`
+}
+
+// Summary contains statistical information about the differences
+type Summary struct {
+	TotalDifferences int `json:"totalDifferences"`
+	AddedFiles       int `json:"addedFiles"`
+	RemovedFiles     int `json:"removedFiles"`
+	ModifiedFiles    int `json:"modifiedFiles"`
+}
+
+// Result contains the complete diff information
+type Result struct {
+	Differences []FileDiff `json:"differences"`
+	Summary     Summary    `json:"summary"`
+}
+
+// FileInfo mirrors the internal inspector's FileInfo structure
+type FileInfo struct {
+	Path      string     `json:"path"`
+	Size      int64      `json:"size"`
+	Mode      string     `json:"mode"`
+	ModTime   *time.Time `json:"modTime,omitempty"`
+	IsDir     bool       `json:"isDir"`
+	SymlinkTo string     `json:"symlinkTo,omitempty"`
+	User      string     `json:"user"`
+	Group     string     `json:"group"`
+	MD5       string     `json:"md5,omitempty"`
+}
+
+// Compare performs a comparison of two sets of FileInfo records
+func Compare(old, new []FileInfo, mode Mode) (*Result, error) {
+	result := &Result{}
+
+	// Create maps for faster lookups
+	oldFiles := make(map[string]FileInfo)
+	newFiles := make(map[string]FileInfo)
+
+	// Skip special files and populate maps
+	for _, f := range old {
+		if !isSpecialFile(f.Path) {
+			oldFiles[f.Path] = f
+		}
+	}
+	for _, f := range new {
+		if !isSpecialFile(f.Path) {
+			newFiles[f.Path] = f
+		}
+	}
+
+	// Find removed files
+	for path, oldFile := range oldFiles {
+		if _, exists := newFiles[path]; !exists {
+			diff := FileDiff{
+				Path:    path,
+				Type:    Removed,
+				OldFile: oldFile,
+			}
+			result.Differences = append(result.Differences, diff)
+			result.Summary.RemovedFiles++
+		}
+	}
+
+	// Find added and modified files
+	for path, newFile := range newFiles {
+		oldFile, exists := oldFiles[path]
+		if !exists {
+			diff := FileDiff{
+				Path:    path,
+				Type:    Added,
+				NewFile: newFile,
+			}
+			result.Differences = append(result.Differences, diff)
+			result.Summary.AddedFiles++
+			continue
+		}
+
+		// Check for modifications
+		if differences := compareFiles(oldFile, newFile, mode); len(differences) > 0 {
+			diff := FileDiff{
+				Path:    path,
+				Type:    Modified,
+				OldFile: oldFile,
+				NewFile: newFile,
+				Details: differences,
+			}
+			result.Differences = append(result.Differences, diff)
+			result.Summary.ModifiedFiles++
+		}
+	}
+
+	result.Summary.TotalDifferences = result.Summary.AddedFiles +
+		result.Summary.RemovedFiles +
+		result.Summary.ModifiedFiles
+
+	return result, nil
+}
+
+// compareFiles returns a list of differences between two files
+func compareFiles(old, new FileInfo, mode Mode) []string {
+	var differences []string
+
+	// Compare basic attributes
+	if old.Size != new.Size {
+		differences = append(differences,
+			fmt.Sprintf("size changed: %d -> %d", old.Size, new.Size))
+	}
+	if old.Mode != new.Mode {
+		differences = append(differences,
+			fmt.Sprintf("permissions changed: %s -> %s", old.Mode, new.Mode))
+	}
+	if old.User != new.User || old.Group != new.Group {
+		differences = append(differences,
+			fmt.Sprintf("ownership changed: %s:%s -> %s:%s",
+				old.User, old.Group, new.User, new.Group))
+	}
+
+	// Compare modification times if requested
+	if mode == CompareAll && old.ModTime != nil && new.ModTime != nil {
+		if !old.ModTime.Equal(*new.ModTime) {
+			differences = append(differences,
+				fmt.Sprintf("modification time changed: %s -> %s",
+					old.ModTime.Format(time.RFC3339),
+					new.ModTime.Format(time.RFC3339)))
+		}
+	}
+
+	// Compare MD5 if available
+	if old.MD5 != "" && new.MD5 != "" && old.MD5 != new.MD5 {
+		differences = append(differences, "content changed (different MD5)")
+	}
+
+	return differences
+}
+
+// isSpecialFile returns true for files we want to ignore
+func isSpecialFile(path string) bool {
+	return strings.HasPrefix(path, "/proc/") ||
+		strings.HasPrefix(path, "/sys/") ||
+		strings.HasPrefix(path, "/dev/") ||
+		path == "/etc/resolv.conf" ||
+		path == "/etc/hostname" ||
+		path == "/etc/hosts"
+}