PHP Get Content of HTTP 400 Response

You have to define custom stream context (3rd argument of function file_get_contents) with ignore_errors option on.

You are calling recv() in a loop until the socket disconnects or fails (and writing the received data to your stream the wrong way), storing all of the raw data into your char* buffer. That is not the correct way to read an HTTP response, especially if HTTP keep-alives are used (in which case no disconnect will occur at the end of the response). You must follow the rules outlined in RFC 2616. Namely:

1. Read until the "rnrn" sequence is encountered. This terminates the response headers. Do not read any more bytes past that yet.

2. Analyze the received headers, per the rules in RFC 2616 Section 4.4. They tell you the actual format of the remaining response data.

3. Read the remaining data, if any, per the format discovered in #2.

4. Check the received headers for the presence of a Connection: close header if the response is using HTTP 1.1, or the lack of a Connection: keep-alive header if the response is using HTTP 0.9 or 1.0. If detected, close your end of the socket connection because the server is closing its end. Otherwise, keep the connection open and re-use it for subsequent requests (unless you are done using the connection, in which case do close it).

5. Process the received data as needed.

In short, you need to do something more like this instead (pseudo code):

string headers[];
byte data[];

string statusLine = read a CRLF-delimited line;
int statusCode = extract from status line;
string responseVersion = extract from status line;

do
{
    string header = read a CRLF-delimited line;
    if (header == "") break;
    add header to headers list;
}
while (true);

if ( !((statusCode in [1xx, 204, 304]) || (request was "HEAD")) )
{
    if (headers["Transfer-Encoding"] ends with "chunked")
    {
        do
        {
            string chunk = read a CRLF delimited line;
            int chunkSize = extract from chunk line;
            if (chunkSize == 0) break;

            read exactly chunkSize number of bytes into data storage;

            read and discard until a CRLF has been read;
        }
        while (true);

        do
        {
            string header = read a CRLF-delimited line;
            if (header == "") break;
            add header to headers list;
        }
        while (true);
    }
    else if (headers["Content-Length"] is present)
    {
        read exactly Content-Length number of bytes into data storage;
    }
    else if (headers["Content-Type"] begins with "multipart/")
    {
        string boundary = extract from Content-Type header;
        read into data storage until terminating boundary has been read;
    }
    else
    {
        read bytes into data storage until disconnected;
    }
}

if (!disconnected)
{
    if (responseVersion == "HTTP/1.1")
    {
        if (headers["Connection"] == "close")
            close connection;
    }
    else
    {
        if (headers["Connection"] != "keep-alive")
            close connection;
    }
}

check statusCode for errors;
process data contents, per info in headers list;

Triggers:

First of all, you need to set up an onFormSubmit trigger.

Mogsdad has a great answer for this:

1. Choose Edit > Current project's triggers. You see a panel with the message No triggers set up. Click here to add one now.
2. Click the link.
3. Under Run, select the function you want executed by the trigger. (That's getResponse(), in this case.)
4. Under Events, select From Spreadsheet.
5. From the next drop-down list, select On form submit.
6. Click Save.

Note: The trigger needs to be set up on the spreadsheet for this.

Get Response Values:

Once you have your trigger set up properly, all you need is:

function getResponse(e) {
  var response = e.values;
}

Here we're using event objects to get the values submitted in the form response. This returns the array of values being submitted to the spreadsheet, in the example I tested, the array looks like this:

[25/07/2019 10:02:36, Option 1, Answer 2, Option 3]

References:

• Setting up an onFormSubmit trigger
• Installable Triggers
• Event Objects