blog | ~wheresalice

#!/bin/bash
# setup:
# 1. chmod a+x this file
# 2. mkdir ~/webmentions && chmod a+w ~/webmentions
# 3. sqlite3 ~/webmentions/webmention.db "CREATE TABLE webmentions(published TEXT NOT NULL DEFAULT CURRENT_TIMESTAMP,source TEXT NOT NULL,target TEXT NOT NULL,UNIQUE(source, target));"
# 4. change DB_DIR to point to the full path to your webmentions directory
#
# test:
# curl -i -d source="https://www.example.com" -d target="https://wheresalice.info" https://wheresalice.envs.net/cgi-bin/webmention.sh
#
# references
# https://devtut.github.io/bash/cgi-scripts.html#request-method-get
# https://gist.github.com/dam2k/5df0d8d3fdabc41e8ce2c799734f65d4
set -euo pipefail
readonly DB_DIR="/home/wheresalice/webmentions"
: "${FILTER_PATTERN:=^[A-Za-z0-9_]+$}"
function urldecode() {
  : "${*//+/ }"
  echo -e "${_//%/\\x}"
}
filter() {
  echo "$1" | tr -d \' | tr -d \` | tr -d \$ | tr -d \;
}
sendstatus() {
  printf 'Content-Type: text/plain\n'
  printf 'Status: %s\n' "$1"
  printf '\n'
}
main() {
  export REQUEST_METHOD=${REQUEST_METHOD:-}
  export CONTENT_TYPE=${CONTENT_TYPE:-}
  if [ "${REQUEST_METHOD}" != "POST" ]; then
    sendstatus '400 Bad Request'
    printf 'Only POST is supported'
    exit 0
  fi
  if [ -z "${CONTENT_TYPE##*x-www-form-urlencoded*}" ]; then
    true
  else
    sendstatus '400 Bad Request'
    printf 'Unsupported Media Type\n'
    printf 'Expected application/x-www-form-urlencoded'
    exit 0
  fi
  read -r -n "$CONTENT_LENGTH" QUERY_STRING_POST
  local source target
  source=$(echo "${QUERY_STRING_POST}" | awk 'match($0, /source=([^&]+)/, a) { print a[1] }')
  target=$(echo "${QUERY_STRING_POST}" | awk 'match($0, /target=([^&]+)/, a) { print a[1] }')
  source=$(urldecode "${source}")
  target=$(urldecode "${target}")
  source=$(filter "${source}")
  target=$(filter "${target}")
  if [ -z "${source}" ] || [ -z "${target}" ]; then
    sendstatus '400 Bad Request'
    printf 'source and target are required\n'
    printf "%s -> %s\n" "${source}" "${target}"
    echo "${QUERY_STRING_POST}"
    exit 0
  fi
  (printf "PRAGMA journal_mode = WAL; INSERT INTO webmentions (source,target) VALUES('%s','%s');" "${source}" "${target}") | sqlite3 "${DB_DIR}/webmention.db" >/dev/null
  sendstatus '202 Accepted'
  printf "%s -> %s\n" "${source}" "${target}"
}
main "$@"