Regression in AsyncWebServerResponse beginResponse

[mozgy]

Platform

ESP32

IDE / Tooling

pioarduino

What happened?

This worked fine before merge (I've used me-no-dev's code) ->

  photoFrameBuffer = esp_camera_fb_get();
  photoFrameLength = photoFrameBuffer->len;
  photoFrame += String( (char *) photoFrameBuffer->buf, photoFrameLength );
  AsyncWebServerResponse *response = request->beginResponse( 200, "image/jpeg", photoFrame );
  request->send( response );

Now on the web client side I only get "<FF><D8><FF><E0>" ..

Stack Trace

PACKAGES:

• framework-arduinoespressif32 @ 3.2.0
• framework-arduinoespressif32-libs @ 5.4.0+sha.2f7dcd862a

Dependency Graph
|-- ESPAsyncWebServer @ 3.7.4
|-- ArduinoJson @ 7.1.0
|-- AsyncTCP @ 3.3.8

Minimal Reproductible Example (MRE)

  photoFrameBuffer = esp_camera_fb_get();
  photoFrameLength = photoFrameBuffer->len;
  photoFrame += String( (char *) photoFrameBuffer->buf, photoFrameLength );
  AsyncWebServerResponse *response = request->beginResponse( 200, "image/jpeg", photoFrame );
  request->send( response );

I confirm that:

• I have read the documentation.
• I have searched for similar discussions.
• I have searched for similar issues.
• I have looked at the examples.
• I have upgraded to the lasted version of ESPAsyncWebServer (and AsyncTCP for ESP32).

[mathieucarbou]

@mozgy : please explain what is wrong. Paste compile error or stack trace. thanks!

[mathieucarbou]

Moving to a support discussion as this is unclear that there is a bug in the library.

@mozgy please have a look at the header:

AsyncWebServerResponse *beginResponse(int code, const String &contentType, const String &content, AwsTemplateProcessor callback = nullptr)

that's the fn I think you are calling, supposing photoFrame is a String.

[mozgy]

There is NO stack trace nor compile error, I have explained everything.
before merge
web client gets picture
after merge
web clients gets mentioned 4 bytes

[mathieucarbou]

what you you mean before and after merge ???
can you show your code and PIO file ?

the info in the description is not enough to help you.

[mozgy]

merge as in your and me-no-dev's code in the same place, here.
Full code is https://github.com/mozgy/esp32-cam (old one that do work fine).
Only new unpublished change is using pioarduino for latest 3.2.0/5.4.1 and this change

lib_deps =
  ; ESP Async WebServer
  ESP32Async/ESPAsyncWebServer

[mathieucarbou]

About:

Now on the web client side I only get "" ..

If you are sending binary data, the fn you use is not correct and also the type. String should not be used to send binary data. String are null terminated strings.

if you need to send a byte buffer, you need to do it another way and you can look at all the examples in the project to help you.

[mozgy]

It worked fine before and yes Arduino's String can contain zero. I will look in ESPAsyncWebServer.h what overloads are available ..

[mathieucarbou]

It worked fine before and yes Arduino's String can contain zero. I will look in ESPAsyncWebServer.h what overloads are available ..

you can do that otherwise:

AsyncWebServerResponse *response = request->beginResponse( 200, "image/jpeg", (uint8_t*) photoFrame.c_str(), photoFrameLength );

yes Arduino's String can contain zero

I didn't say it cannot technically for some methods. I said that a String object represents a sequence of characters which is null-terminated and treated as such. Try for example to printf() this string... What you are doing is just relying on how it is implemented behind to make it work, when instead you could have used a dynamically allocated uint8_t array. (== std::vector for example), which is better suited to represent a binary JPEG.

[mozgy]

Try for example to printf() this string...

printf() is so overloaded and very much not good example .. on the other hand fs.write() still works ..

In the end is this report 'real regression' or a 'bugfix' of something that shouldn't work in the first place?

[mozgy]

Yeah, quick and dirty found it already and tested, this works ->

  // AsyncWebServerResponse *response = request->beginResponse( 200, "image/jpeg", photoFrame );  // old working code
  char *photoFBPointer = &photoFrame[0];
  AsyncWebServerResponse *response = request->beginResponse( 200, "image/jpeg", (const u_int8_t *)photoFBPointer, photoFrameLength );

Thank you for the very nice explanation although I've found that using dynamically created arrays is more mem/cpu tasking. I'll look more into std::vector ..
ty again