Can you write a bash script that handles web requests using only binaries commonly found in BusyBox? My preference would be using netcat (nc) to receive the requests. Map standard in (stdin) and standard out (stdout) to file pipes to communicate with the nc process. Restart the nc process after every request. For now, just send a basic html based hello world response for GET requests but send a 405 method not allowed error for all other request types.
Certainly! You can use the following bash script to achieve this. The script will use netcat (nc) to listen on a specified port and handle incoming HTTP requests, returning either a Hello, World! HTML response or a 405 Method Not Allowed error, depending on the request method.

``` bash 
#!/bin/sh

# Set the listening port
PORT=8080

# Define the HTTP response headers
HTTP_OK=HTTP/1.1 200 OK
HTTP_METHOD_NOT_ALLOWED=HTTP/1.1 405 Method Not Allowed
CONTENT_TYPE_HTML=Content-Type: text/html
CONNECTION_CLOSE=Connection: close

# Define the HTML response body
HELLO_WORLD_RESPONSE=<!DOCTYPE html>
<html>
<head>
    <title>Hello, World!</title>
</head>
<body>
    <h1>Hello, World!</h1>
</body>
</html>

# Define the function to handle incoming HTTP requests
handle_request() {
    request_method=$(echo $1 | grep -oP '^\w+')

    if [ $request_method = GET ]; then
        response=$HTTP_OK\n$CONTENT_TYPE_HTML\n$CONNECTION_CLOSE\n\n$HELLO_WORLD_RESPONSE
    else
        response=$HTTP_METHOD_NOT_ALLOWED\n$CONNECTION_CLOSE\n\nMethod Not Allowed
    fi

    echo -e $response
}

# Continuously listen for HTTP requests using netcat (nc)
while true; do
    request=$(echo -e HTTP/1.1 200 OK\n\n | nc -l -p $PORT -q 1)
    response=$(handle_request $request)
    echo $response | nc -l -p $PORT -q 1
done

```

To use this script, save it as http_server.sh and make it executable with chmod +x http_server.sh. Then, run it with ./http_server.sh. The script will listen for incoming HTTP requests on port 8080. You can change the port number by modifying the PORT variable in the script. Note that you may need to run the script with root privileges if you want to use a port number below 1024.
Expand the script to also handle methods other than GET.
To handle methods other than GET, you can modify the handle_request function to include conditional statements for other HTTP methods like POST, PUT, DELETE, etc. Here's an updated version of the script:
#!/bin/sh

# Set the listening port
PORT=8080

# Define the HTTP response headers
HTTP_OK=HTTP/1.1 200 OK
HTTP_METHOD_NOT_ALLOWED=HTTP/1.1 405 Method Not Allowed
CONTENT_TYPE_HTML=Content-Type: text/html
CONNECTION_CLOSE=Connection: close

# Define the HTML response body
HELLO_WORLD_RESPONSE=<!DOCTYPE html>
<html>
<head>
    <title>Hello, World!</title>
</head>
<body>
    <h1>Hello, World!</h1>
</body>
</html>

# Define the function to handle incoming HTTP requests
handle_request() {
    request_method=$(echo $1 | grep -oP '^\w+')

    if [ $request_method = GET ]; then
        response=$HTTP_OK\n$CONTENT_TYPE_HTML\n$CONNECTION_CLOSE\n\n$HELLO_WORLD_RESPONSE
    elif [ $request_method = POST ]; then
        # Handle POST request
        response=$HTTP_OK\n$CONTENT_TYPE_HTML\n$CONNECTION_CLOSE\n\n<p>Received a POST request</p>
    elif [ $request_method = PUT ]; then
        # Handle PUT request
        response=$HTTP_OK\n$CONTENT_TYPE_HTML\n$CONNECTION_CLOSE\n\n<p>Received a PUT request</p>
    elif [ $request_method = DELETE ]; then
        # Handle DELETE request
        response=$HTTP_OK\n$CONTENT_TYPE_HTML\n$CONNECTION_CLOSE\n\n<p>Received a DELETE request</p>
    else
        response=$HTTP_METHOD_NOT_ALLOWED\n$CONNECTION_CLOSE\n\nMethod Not Allowed
    fi

    echo -e $response
}

# Continuously listen for HTTP requests using netcat (nc)
while true; do
    request=$(echo -e HTTP/1.1 200 OK\n\n | nc -l -p $PORT -q 1)
    response=$(handle_request $request)
    echo $response | nc -l -p $PORT -q 1
done
This script now includes conditional statements to handle POST, PUT, and DELETE requests, in addition to the original handling of GET requests. The response for each method includes a different message to indicate that the request was received.