Add boot image management with ISO extraction and serving

Upload Proxmox ISOs via API or dashboard UI, extract kernel+initrd
using pure-Go iso9660 library, store on disk, and serve over HTTP
for PXE booting. Dynamic kernel/initrd filenames per image replace
the previous hardcoded paths.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/image/extract.go

@@ -0,0 +1,125 @@
+package image
+
+import (
+	"fmt"
+	"io"
+	"os"
+	"path/filepath"
+	"strings"
+
+	"github.com/kdomanski/iso9660"
+)
+
+type ExtractResult struct {
+	KernelFilename string
+	InitrdFilename string
+}
+
+var kernelCandidates = []string{"linux26", "vmlinuz", "bzImage"}
+var initrdCandidates = []string{"initrd.img", "initrd", "initrd.gz"}
+
+func ExtractFromISO(r io.Reader, destDir string) (*ExtractResult, error) {
+	tmp, err := os.CreateTemp(filepath.Dir(destDir), "iso-upload-*.tmp")
+	if err != nil {
+		return nil, fmt.Errorf("create temp file: %w", err)
+	}
+	tmpPath := tmp.Name()
+	defer os.Remove(tmpPath)
+
+	if _, err := io.Copy(tmp, r); err != nil {
+		tmp.Close()
+		return nil, fmt.Errorf("write ISO to temp file: %w", err)
+	}
+	tmp.Close()
+
+	f, err := os.Open(tmpPath)
+	if err != nil {
+		return nil, fmt.Errorf("open temp ISO: %w", err)
+	}
+	defer f.Close()
+
+	img, err := iso9660.OpenImage(f)
+	if err != nil {
+		return nil, fmt.Errorf("parse ISO: %w", err)
+	}
+
+	root, err := img.RootDir()
+	if err != nil {
+		return nil, fmt.Errorf("read ISO root: %w", err)
+	}
+
+	candidateSet := make(map[string]bool)
+	for _, c := range kernelCandidates {
+		candidateSet[strings.ToLower(c)] = true
+	}
+	for _, c := range initrdCandidates {
+		candidateSet[strings.ToLower(c)] = true
+	}
+
+	found := make(map[string]*iso9660.File)
+	walkDir(root, candidateSet, found)
+
+	kernelFile, kernelName := matchFirst(found, kernelCandidates)
+	initrdFile, initrdName := matchFirst(found, initrdCandidates)
+
+	if kernelFile == nil {
+		return nil, fmt.Errorf("no kernel found in ISO (looked for %s)", strings.Join(kernelCandidates, ", "))
+	}
+	if initrdFile == nil {
+		return nil, fmt.Errorf("no initrd found in ISO (looked for %s)", strings.Join(initrdCandidates, ", "))
+	}
+
+	if err := extractFile(kernelFile, filepath.Join(destDir, kernelName)); err != nil {
+		return nil, fmt.Errorf("extract kernel: %w", err)
+	}
+	if err := extractFile(initrdFile, filepath.Join(destDir, initrdName)); err != nil {
+		return nil, fmt.Errorf("extract initrd: %w", err)
+	}
+
+	return &ExtractResult{
+		KernelFilename: kernelName,
+		InitrdFilename: initrdName,
+	}, nil
+}
+
+func walkDir(dir *iso9660.File, candidates map[string]bool, found map[string]*iso9660.File) {
+	children, err := dir.GetChildren()
+	if err != nil {
+		return
+	}
+	for _, child := range children {
+		name := strings.ToLower(child.Name())
+		if child.IsDir() {
+			walkDir(child, candidates, found)
+		} else if candidates[name] {
+			if _, exists := found[name]; !exists {
+				found[name] = child
+			}
+		}
+	}
+}
+
+func matchFirst(found map[string]*iso9660.File, candidates []string) (*iso9660.File, string) {
+	for _, c := range candidates {
+		lower := strings.ToLower(c)
+		if f, ok := found[lower]; ok {
+			return f, f.Name()
+		}
+	}
+	return nil, ""
+}
+
+func extractFile(isoFile *iso9660.File, destPath string) error {
+	out, err := os.Create(destPath)
+	if err != nil {
+		return err
+	}
+	defer out.Close()
+
+	reader := isoFile.Reader()
+	if reader == nil {
+		return fmt.Errorf("cannot read %s from ISO", isoFile.Name())
+	}
+	_, err = io.Copy(out, reader)
+	return err
+}