A picture from ComfyUI loses the workflow written into it

ComfyUI saves the whole workflow — prompt, checkpoint, nodes — as PNG text
chunks in every picture. They are taken out before the picture is sent.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

internal/comfy/comfy.go

@@ -14,6 +14,7 @@ import (
 	"context"
 	"crypto/rand"
 	"embed"
+	"encoding/binary"
 	"encoding/hex"
 	"encoding/json"
 	"errors"
@@ -444,9 +445,43 @@ func (c *Client) get(ctx context.Context, u, apiKey string) (Image, error) {
 	if ct == "" || ct == "application/octet-stream" {
 		ct = http.DetectContentType(b)
 	}
+	if ct == "image/png" {
+		b = withoutPNGText(b)
+	}
 	return Image{Data: b, ContentType: ct}, nil
 }
 
+// withoutPNGText is a PNG without its text chunks. ComfyUI writes the whole
+// workflow into every picture it saves — the prompt, and the checkpoint and
+// nodes behind it — and what a picture says about how it was made is the
+// operator's to publish, not something to hand every client. A file that is
+// not a well-formed PNG is returned as it came.
+func withoutPNGText(b []byte) []byte {
+	const sig = "\x89PNG\r\n\x1a\n"
+	if len(b) < len(sig) || string(b[:len(sig)]) != sig {
+		return b
+	}
+	out := make([]byte, 0, len(b))
+	out = append(out, b[:len(sig)]...)
+	for i := len(sig); i < len(b); {
+		if i+12 > len(b) {
+			return b
+		}
+		n := int(binary.BigEndian.Uint32(b[i:]))
+		end := i + 12 + n
+		if n < 0 || end > len(b) {
+			return b
+		}
+		switch string(b[i+4 : i+8]) {
+		case "tEXt", "iTXt", "zTXt":
+		default:
+			out = append(out, b[i:end]...)
+		}
+		i = end
+	}
+	return out
+}
+
 // refusal is what /prompt said when it would not queue a workflow.
 func refusal(e, nodes json.RawMessage) string {
 	var top struct {

internal/comfy/comfy_test.go

@@ -2,6 +2,7 @@ package comfy
 
 import (
 	"context"
+	"encoding/binary"
 	"encoding/json"
 	"fmt"
 	"net/http"
@@ -196,3 +197,31 @@ func TestAClientThatLeavesTakesItsWorkflowOffTheCard(t *testing.T) {
 		t.Errorf("deleted %v, interrupted %v", f.deleted, f.interrupted)
 	}
 }
+
+func TestAPictureLosesTheWorkflowComfyUIWroteIntoIt(t *testing.T) {
+	chunk := func(kind, data string) []byte {
+		b := make([]byte, 0, 12+len(data))
+		b = binary.BigEndian.AppendUint32(b, uint32(len(data)))
+		b = append(b, kind...)
+		b = append(b, data...)
+		return append(b, 0, 0, 0, 0) // a CRC nobody here checks
+	}
+	png := []byte("\x89PNG\r\n\x1a\n")
+	png = append(png, chunk("IHDR", "0123456789abc")...)
+	png = append(png, chunk("tEXt", "prompt\x00{\"1\":...}")...)
+	png = append(png, chunk("IDAT", "pixels")...)
+	png = append(png, chunk("iTXt", "workflow\x00...")...)
+	png = append(png, chunk("IEND", "")...)
+	got := string(withoutPNGText(png))
+	if strings.Contains(got, "prompt") || strings.Contains(got, "workflow") {
+		t.Errorf("text left in: %q", got)
+	}
+	for _, kind := range []string{"IHDR", "IDAT", "pixels", "IEND"} {
+		if !strings.Contains(got, kind) {
+			t.Errorf("%s gone: %q", kind, got)
+		}
+	}
+	if broken := png[:30]; string(withoutPNGText(broken)) != string(broken) {
+		t.Error("a truncated PNG was changed")
+	}
+}