Send numpy array as bytes from python to JS through Flask

A numpy array should be sent from python to JS through flask. I don't want to jsonify it and send as it would increase the size of the response and eventually the response time. So I thought I could convert numpy into bytes using tobytes(), send the bytes to JS through flask and convert the bytes back to float in JS and found Converting a string of packed bytes into an array of floats in Javascript answer helpful.

The list of operations are

byte_arr = np.array([5.6], dtype=np.float32).tobytes()  # Used one value just to make it simple
return byte_arr  # Bytes can be directly sent from flask as response

In JS,

str = response.text
bytes = Uint8Array.from(str, c => c.charCodeAt(0))
floats = new Float32Array(bytes.buffer)

But when converting to float in JS, I am not getting the correct values. When debugging I found that in JS some values in Uint8 array are not matching with the byte values that are sent from python.

JS: console.log(bytes)  // [51, 51, 255, 64]
Python: for val in byte_arr: print(val, end=" ")  // 51, 51, 179, 64

Just to verify, I created another client in python, made the same request and converted the response bytes to float. I encountered the same issue here also. So I narrowed down that the problem is on the server side not on the client side. One more interesting thing I found when playing with multiple values are, only the numbers which are greater than 127 (I guess so) are getting converted to 255.

While trying some random hacks, I tried to convert the byte integer to character using chr() method of python before sending the response and the conversion on the client side worked.

byte_arr = np.array([5.6], dtype=np.float32).tobytes()
byte_arr_char = "".join([chr(i) for i in byte_arr])
return byte_arr_char

But the question I have is, Is this an ideal solution or am I doing some hack here to make it work? Can anyone help me to understand why sending plain bytes without chr() doesn't work?

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