feat(workspace): add text editing and image previews

internal/api/workspace_image.go

@@ -0,0 +1,117 @@
+package api
+
+import (
+	"bytes"
+	"encoding/xml"
+	"io"
+	"mime"
+	"net/http"
+	"os"
+	"path"
+	"strconv"
+	"strings"
+	"syscall"
+)
+
+const maxImageBytes = 16 << 20
+
+func (a *API) wsImage(w http.ResponseWriter, r *http.Request, root *os.Root) {
+	if r.Method != http.MethodGet {
+		fail(w, 405, "method not allowed")
+		return
+	}
+	p := r.URL.Query().Get("path")
+	if p == "" || path.IsAbs(p) || p == "." || p == ".." || strings.HasPrefix(p, "../") || path.Clean(p) != p || strings.ContainsRune(p, 0) {
+		fail(w, 400, "invalid path")
+		return
+	}
+	anchor, err := root.Open(".")
+	if err != nil {
+		fail(w, 500, "storage unavailable")
+		return
+	}
+	defer anchor.Close()
+	f, err := openDownload(anchor, p)
+	if err != nil {
+		fail(w, 404, "image unavailable")
+		return
+	}
+	defer f.Close()
+	st, err := f.Stat()
+	if err != nil || !st.Mode().IsRegular() {
+		fail(w, 415, "unsupported image")
+		return
+	}
+	if st.Size() > maxImageBytes {
+		fail(w, 413, "image too large")
+		return
+	}
+	b, err := io.ReadAll(io.LimitReader(f, maxImageBytes+1))
+	if err != nil {
+		fail(w, 500, "image read failed")
+		return
+	}
+	if len(b) > maxImageBytes {
+		fail(w, 413, "image too large")
+		return
+	}
+	after, err := f.Stat()
+	if err != nil || int64(len(b)) != st.Size() || st.Size() != after.Size() || !st.ModTime().Equal(after.ModTime()) || st.Sys().(*syscall.Stat_t).Ctim != after.Sys().(*syscall.Stat_t).Ctim {
+		fail(w, 409, "image changed; reload")
+		return
+	}
+	mimeType := workspaceImageType(p, b)
+	if mimeType == "" {
+		fail(w, 415, "unsupported image")
+		return
+	}
+	w.Header().Set("Content-Type", mimeType)
+	w.Header().Set("X-Content-Type-Options", "nosniff")
+	w.Header().Set("Content-Security-Policy", "sandbox; default-src 'none'; style-src 'unsafe-inline'")
+	w.Header().Set("Content-Disposition", mime.FormatMediaType("attachment", map[string]string{"filename": path.Base(p)}))
+	w.Header().Set("Cache-Control", "no-store")
+	w.Header().Set("Content-Length", strconv.Itoa(len(b)))
+	w.Write(b)
+}
+
+func workspaceImageType(name string, b []byte) string {
+	switch mimeType := http.DetectContentType(b); mimeType {
+	case "image/png", "image/jpeg", "image/gif", "image/webp":
+		return mimeType
+	}
+	if !strings.EqualFold(path.Ext(name), ".svg") {
+		return ""
+	}
+	d := xml.NewDecoder(bytes.NewReader(bytes.TrimPrefix(b, []byte{0xef, 0xbb, 0xbf})))
+	depth, roots := 0, 0
+	for {
+		token, err := d.Token()
+		if err == io.EOF {
+			if roots == 1 && depth == 0 {
+				return "image/svg+xml"
+			}
+			return ""
+		}
+		if err != nil {
+			return ""
+		}
+		switch t := token.(type) {
+		case xml.StartElement:
+			if depth == 0 {
+				roots++
+				if roots != 1 || t.Name.Local != "svg" || t.Name.Space != "http://www.w3.org/2000/svg" {
+					return ""
+				}
+			}
+			depth++
+		case xml.EndElement:
+			depth--
+		case xml.CharData:
+			if depth == 0 && len(bytes.TrimSpace(t)) != 0 {
+				return ""
+			}
+		case xml.Directive:
+			return ""
+		}
+	}
+}