Bash HTTP Server (using socat)

http_server.sh

#!/usr/bin/env bash
set -o errexit
set -o nounset

function server() {
  echo "Starting TCP server at http://localhost:8000..."
  socat TCP-LISTEN:8000,pktinfo,reuseaddr,fork SYSTEM:"'${SHELL}' '${BASH_SOURCE[0]}' request"
}

function request() {
  read -r first_line
  export HTTP_METHOD="$(cut -d' ' -f 1 - <<< "${first_line}")"
  export HTTP_PATH="$(cut -d' ' -f 2 - <<< "${first_line}")"

  log "Received HTTP request"
  write_http "HTTP/1.1 200 OK"
  write_http "Content-Type: text/plain"
  write_http "Server: Shell Script"
  write_http
  write_http 'Hello, World!'
  write_http
  log "Sent HTTP response"
}

function log() {
  {
    echo -en "\e[1;32m[$(date) ${HTTP_METHOD} ${SOCAT_PEERADDR}:${SOCAT_PEERPORT}${HTTP_PATH}] "
    echo -en "\e[0m"
    echo "${@}"
  } >&2
}

function write_http() {
  printf $"%s\r\n" "${1:-}"
}

operation="${1:-help}"
shift 1
case "${operation}" in
  server)  server "${@}" ;;
  request) request "${@}" ;;
  help|-h|--help)
    echo "USAGE: ${BASH_SOURCE[0]} <operation> [flags...]"
    echo "Operations:"
    echo "  - help    - Show this message."
    echo "  - server  - run a webserver."
    echo "  - request - handle a request on stdin, dump the response to stdout."
    exit 0
    ;;
  *)
    echo "ERROR: Invalid operation ${operation@Q}."
    echo "Run '${BASH_SOURCE[0]} --help' for script usage."
    exit 1
    ;;
esac

output.txt

$ ./http_server.sh server & sleep 2; curl -vvv http://localhost:8000/foo/bar; wait < <(jobs -p)
[1] 20471
Starting TCP server at http://localhost:8000...
*   Trying 127.0.0.1:8000...
* Connected to localhost (127.0.0.1) port 8000 (#0)                                                  > GET /foo/bar HTTP/1.1
> Host: localhost:8000
> User-Agent: curl/8.1.2
> Accept: */*
>
[Sun Jun 18 10:00:42 BST 2023 GET 127.0.0.1:45522/foo/bar] Received HTTP request
< HTTP/1.1 200 OK
< Content-Type: text/plain
< Server: Shell Script
* no chunk, no close, no size. Assume close to signal end
<
Hello, World!

[Sun Jun 18 10:00:42 BST 2023 GET 127.0.0.1:45522/foo/bar] Sent HTTP response
* Closing connection 0