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fix(gnoweb): In serveEval, use MaxBytesReader to cap the JSON size #5897

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fix(gnoweb): In serveEval, use MaxBytesReader to cap the JSON size #5897

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fix(gnoweb): In serveEval, use MaxBytesReader to cap the JSON size
jefft0 Jul 3, 2026
39cc04f
fix(gnoweb): In serveEval, limit the size of req.PkgPath and req.Expr…
jefft0 Jul 3, 2026
ee9f7e0
Rerun tests
jefft0 Jul 3, 2026
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17 changes: 17 additions & 0 deletions gno.land/pkg/gnoweb/feature/playground/handler.go
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Original file line number Diff line number Diff line change
Expand Up @@ -32,6 +32,16 @@ const (
// against memory exhaustion from large or numerous on-chain package files.
maxForkCodeSize = 1 << 20 // 1 MiB

// maxEvalBodyBytes caps the eval request body to guard against memory
// exhaustion from oversized JSON payloads.
maxEvalBodyBytes = 1 << 20 // 1 MiB

// maxEvalPkgPathLen and maxEvalExpressionLen bound the eval request fields
// well below maxEvalBodyBytes, rejecting oversized requests before they are
// forwarded to the RPC node. Legitimate values are far smaller.
maxEvalPkgPathLen = 1024
maxEvalExpressionLen = 64 * 1024

// defaultCode defines the default code displayed in the code editor.
defaultCode = `package main

Expand Down Expand Up @@ -212,6 +222,8 @@ func (h *Handler) serveEval(w http.ResponseWriter, r *http.Request) {
return
}

r.Body = http.MaxBytesReader(w, r.Body, maxEvalBodyBytes)

@davd-gzl davd-gzl Jul 3, 2026

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Missing test: the three new caps have no coverage. Add to TestHandlerPlaygroundEval:

test cases 
{
	name:       "oversized body",
	method:     http.MethodPost,
	body:       `{"pkg_path":"r/x","expression":"` + strings.Repeat("a", maxEvalBodyBytes+1) + `"}`,
	wantStatus: http.StatusBadRequest,
	wantError:  "invalid request body",
},
{
	name:       "oversized pkg_path",
	method:     http.MethodPost,
	body:       `{"pkg_path":"` + strings.Repeat("a", maxEvalPkgPathLen+1) + `","expression":"Render(\"\")"}`,
	wantStatus: http.StatusBadRequest,
	wantError:  "too long",
},
{
	name:       "oversized expression",
	method:     http.MethodPost,
	body:       `{"pkg_path":"r/x","expression":"` + strings.Repeat("a", maxEvalExpressionLen+1) + `"}`,
	wantStatus: http.StatusBadRequest,
	wantError:  "too long",
},


var req evalRequest
if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
writeJSON(w, http.StatusBadRequest, evalResponse{Error: "invalid request body"})
Expand All @@ -223,6 +235,11 @@ func (h *Handler) serveEval(w http.ResponseWriter, r *http.Request) {
return
}

if len(req.PkgPath) > maxEvalPkgPathLen || len(req.Expression) > maxEvalExpressionLen {
writeJSON(w, http.StatusBadRequest, evalResponse{Error: "pkg_path or expression is too long"})
return
}

// Clean the pkg path.
pkgPath := strings.TrimPrefix(req.PkgPath, h.deps.Domain+"/")
pkgPath = strings.TrimPrefix(pkgPath, h.deps.Domain)
Expand Down