Add HTTP restricted artifact reader

2026-07-28 00:40:25 +00:00
parent a74c03bd9b
commit 45c2644b9d
5 changed files with 359 additions and 154 deletions
--- a/internal/adapter/http/artifact_reader.go
+++ b/internal/adapter/http/artifact_reader.go
@@ -0,0 +1,165 @@
+package httpadapter
+
+import (
+	"context"
+	"crypto/sha256"
+	"errors"
+	"fmt"
+	"io"
+	"mime"
+	"os"
+	"path/filepath"
+	"strings"
+
+	"gitea.maximumdirect.net/eric/scriptorium"
+)
+
+var (
+	ErrFileNotAllowed  = errors.New("file artifact references are not allowed")
+	ErrFileOutsideRoot = errors.New("file artifact path is outside artifact root")
+	ErrFileTooLarge    = errors.New("file artifact exceeds size limit")
+)
+
+const fallbackArtifactContentType = "text/plain"
+
+// NewRestrictedArtifactReader creates the HTTP artifact reader for a rooted
+// filesystem and optional byte limit. An empty root permits inline artifacts
+// but denies file references; a zero limit permits artifacts of any size.
+func NewRestrictedArtifactReader(root string, maxBytes int64) (scriptorium.ArtifactReader, error) {
+	if maxBytes < 0 {
+		return nil, fmt.Errorf("artifact size limit must be greater than or equal to 0")
+	}
+
+	cleanRoot := strings.TrimSpace(root)
+	if cleanRoot == "" {
+		return &restrictedArtifactReader{maxBytes: maxBytes}, nil
+	}
+	absRoot, err := filepath.Abs(filepath.Clean(cleanRoot))
+	if err != nil {
+		return nil, fmt.Errorf("resolve artifact root: %w", err)
+	}
+	return &restrictedArtifactReader{root: absRoot, maxBytes: maxBytes}, nil
+}
+
+type restrictedArtifactReader struct {
+	root     string
+	maxBytes int64
+}
+
+var _ scriptorium.ArtifactReader = (*restrictedArtifactReader)(nil)
+
+func (r *restrictedArtifactReader) Read(ctx context.Context, ref scriptorium.ArtifactRef) (*scriptorium.Artifact, error) {
+	select {
+	case <-ctx.Done():
+		return nil, ctx.Err()
+	default:
+	}
+
+	switch ref.Type {
+	case scriptorium.ArtifactRefInline:
+		return readInlineArtifact(ref)
+	case scriptorium.ArtifactRefFile:
+		return r.readFileArtifact(ref)
+	default:
+		return nil, fmt.Errorf("unsupported artifact reference type %q", ref.Type)
+	}
+}
+
+func readInlineArtifact(ref scriptorium.ArtifactRef) (*scriptorium.Artifact, error) {
+	if ref.Body == "" {
+		return nil, errors.New("inline artifact body is required")
+	}
+
+	body := []byte(ref.Body)
+	return &scriptorium.Artifact{
+		ContentType: fallbackArtifactContentType,
+		Body:        body,
+		Size:        int64(len(body)),
+		Hash:        artifactHash(body),
+		URI:         ref.URI,
+	}, nil
+}
+
+func (r *restrictedArtifactReader) readFileArtifact(ref scriptorium.ArtifactRef) (*scriptorium.Artifact, error) {
+	if ref.URI == "" {
+		return nil, errors.New("file artifact path is required")
+	}
+	if r.root == "" {
+		return nil, ErrFileNotAllowed
+	}
+
+	path, err := r.resolveLexicalPath(ref.URI)
+	if err != nil {
+		return nil, err
+	}
+	return readArtifactFile(path, r.maxBytes)
+}
+
+// resolveLexicalPath checks cleaned path containment without resolving symlinks.
+func (r *restrictedArtifactReader) resolveLexicalPath(rawPath string) (string, error) {
+	cleanPath := filepath.Clean(strings.TrimSpace(rawPath))
+	candidate := cleanPath
+	if !filepath.IsAbs(cleanPath) {
+		candidate = filepath.Join(r.root, cleanPath)
+	}
+
+	absCandidate, err := filepath.Abs(candidate)
+	if err != nil {
+		return "", fmt.Errorf("resolve artifact path: %w", err)
+	}
+	absCandidate = filepath.Clean(absCandidate)
+
+	rel, err := filepath.Rel(r.root, absCandidate)
+	if err != nil {
+		return "", fmt.Errorf("compare artifact path to root: %w", err)
+	}
+	if rel == ".." || strings.HasPrefix(rel, ".."+string(filepath.Separator)) || filepath.IsAbs(rel) {
+		return "", ErrFileOutsideRoot
+	}
+	return absCandidate, nil
+}
+
+func readArtifactFile(path string, maxBytes int64) (*scriptorium.Artifact, error) {
+	file, err := os.Open(path)
+	if err != nil {
+		return nil, fmt.Errorf("failed to read file %s: %w", path, err)
+	}
+	defer file.Close()
+
+	info, err := file.Stat()
+	if err != nil {
+		return nil, fmt.Errorf("failed to stat file %s: %w", path, err)
+	}
+	if maxBytes > 0 && info.Size() > maxBytes {
+		return nil, ErrFileTooLarge
+	}
+
+	var reader io.Reader = file
+	if maxBytes > 0 {
+		reader = io.LimitReader(file, maxBytes+1)
+	}
+	body, err := io.ReadAll(reader)
+	if err != nil {
+		return nil, fmt.Errorf("failed to read file %s: %w", path, err)
+	}
+	if maxBytes > 0 && int64(len(body)) > maxBytes {
+		return nil, ErrFileTooLarge
+	}
+
+	contentType := mime.TypeByExtension(filepath.Ext(path))
+	if contentType == "" {
+		contentType = fallbackArtifactContentType
+	}
+	return &scriptorium.Artifact{
+		Name:        filepath.Base(path),
+		ContentType: contentType,
+		Body:        body,
+		URI:         path,
+		Size:        int64(len(body)),
+		Hash:        artifactHash(body),
+	}, nil
+}
+
+func artifactHash(body []byte) string {
+	return fmt.Sprintf("%x", sha256.Sum256(body))
+}