I didn't necessarily mean for you to change your line oriented input to something else, I just wanted you to know that the read will block and accumulate pieces of the message until it encounters a newline.

You can treat a socket as if it were a file. Ideally, amazon would close the socket after sending the message, which would send an eof signal into the socket, and just like when reading a file, your while loop would end. But based on what you say about the input you are receiving, amazon doesn't do that. You could read the whole file in one go, but then you would get the duplicated message in the retry and any subsequent retrys until amazon closed the socket.

So, you need to examine the input to see what characters lie between the end of the message and the retry. You should inspect() the string to see all the hidden characters. It may be as simple as testing for a line that contains only a closing brace and no whitespace, i.e. the final closing brace of the JSON message, and then breaking out of your while loop.

I just checked the JSON spec here, json, and whitespace before or after a brace is ignored, so valid JSON could look like this:

{
    "glossary": {
        "title": "example glossary"
}
    "book": {
        "name": "Hello World"
}
}
[download]

...which means a closing brace on a line by itself would not signal the end of the message. Whether amazon actually does that is another thing entirely.