Refactor entrypoint script for improved flexibility

Change the shebang to use env, add helper functions to handle environment variables, and dynamically append command arguments. This improves script flexibility and ensures critical variables are set or loaded from files.

Dockerfile

@@ -1,5 +1,5 @@
 ARG ALPINE_VERSION=latest
-FROM alpine:${ALPINE_VERSION} as build
+FROM alpine:${ALPINE_VERSION} AS build
 
 ENV CXXFLAGS=""
 WORKDIR /usr/src/telegram-bot-api

docker-entrypoint.sh

@@ -1,87 +1,113 @@
-#!/bin/sh
+#!/usr/bin/env sh
 set -e
 
-file_env() {
-  local var_name="$1"
-  local file_var_name="$2"
+USERNAME="telegram-bot-api"
+GROUPNAME="telegram-bot-api"
 
-  var_value=$(printenv "$var_name") || var_value=""
-  file_path=$(printenv "$file_var_name") || file_path=""
+COMMAND="telegram-bot-api"
 
-  if [ -z "$var_value" ] && [ -z "$file_path" ]; then
-    echo "error: expected $var_name or $file_var_name env vars to be set"
-    exit 1
+# Appends an argument to the COMMAND variable.
+append_args() {
+  COMMAND="$COMMAND $1"
+}
 
-  elif [ -n "$var_value" ] && [ -n "$file_path" ]; then
-    echo "both and $var_name $file_var_name env vars are set, expected only one of them"
-    exit 1
+# Sets $env_var from $file_env_var content or directly from $env_var.
+# Usage: file_env <env_var> <file_env_var>
+# - If both or neither variables are set, exits with an error.
+# - If only $file_env_var is set, reads content from the file path and sets $env_var.
+# - Exits with an error if the file does not exist.
+file_env() {
+    env_var="$1"
+    file_env_var="$2"
+    env_value=$(printenv "$env_var") || env_value=""
+    file_path=$(printenv "$file_env_var") || file_path=""
 
-  else
-    if [ -n "$file_path" ] && [ "$file_path" != "" ]; then
-      if [ -f "$file_path" ]; then
-        file_content=$(cat "$file_path")
-        export "$var_name=$file_content"
-      else
-        echo "error: $var_name=$file_path: file '$file_path' does not exist"
+    if [ -z "$env_value" ] && [ -z "$file_path" ]; then
+        echo "error: expected $env_var or $file_env_var env vars to be set"
         exit 1
-      fi
+    elif [ -n "$env_value" ] && [ -n "$file_path" ]; then
+        echo "both $env_var and $file_env_var env vars are set, expected only one of them"
+        exit 1
+    elif [ -n "$file_path" ]; then
+        if [ -f "$file_path" ]; then
+            export "$env_var=$(cat "$file_path")"
+        else
+            echo "error: $env_var=$file_path: file '$file_path' does not exist"
+            exit 1
+        fi
     fi
+}
+
+# Checks if an environment variable is set.
+# Usage: check_required_env <var_name>
+# - Exits with an error if the variable is not set.
+check_required_env() {
+  var_name="$1"
+
+  if [ -z "$(printenv "$var_name")" ]; then
+    echo "error: environment variable $var_name is required"
+    exit 1
   fi
 }
 
-USERNAME=telegram-bot-api
-GROUPNAME=telegram-bot-api
+# Appends an argument to CUSTOM_ARGS based on the environment variable value.
+# Usage: append_arg_from_env <var_name> <arg_name> <default_value>
+# - If <var_name> is set, uses its value; otherwise, uses <default_value>.
+# - Appends "<arg_name>=<value>" to CUSTOM_ARGS if a value is found.
+append_arg_from_env() {
+    var_name="$1"
+    arg_name="$2"
+    default_value="$3"
+    env_value=$(printenv "$var_name") || env_value=""
 
-chown ${USERNAME}:${GROUPNAME} "${TELEGRAM_WORK_DIR}"
+    [ -n "$env_value" ] || env_value="$default_value"
+    if [ -n "$env_value" ]; then
+      append_args "${arg_name}=$env_value"
+    fi
+}
+
+# Appends a flag to CUSTOM_ARGS if the environment variable is set (non-empty).
+# Usage: append_flag_from_env <var_name> <flag_name>
+# - If <var_name> is set, appends <flag_name> to CUSTOM_ARGS.
+append_flag_from_env() {
+  var_name="$1"
+  flag_name="$2"
 
-if [ -n "${1}" ]; then
-  exec "${*}"
-fi
+  if [ -n "$(printenv "$var_name")" ]; then
+    append_args "$flag_name"
+  fi
+}
 
+check_required_env "TELEGRAM_WORK_DIR"
+chown "${USERNAME}:${GROUPNAME}" "${TELEGRAM_WORK_DIR}"
+
+# Telegram Bot API Server knows how to read the API ID and API Hash from a environment variable.
+# Is not needed to pass it as arguments.
 file_env "TELEGRAM_API_ID" "TELEGRAM_API_ID_FILE"
 file_env "TELEGRAM_API_HASH" "TELEGRAM_API_HASH_FILE"
 
-DEFAULT_ARGS="--dir=${TELEGRAM_WORK_DIR} --temp-dir=${TELEGRAM_TEMP_DIR} --username=${USERNAME} --groupname=${GROUPNAME}"
-CUSTOM_ARGS=""
-
-if [ -n "$TELEGRAM_LOG_FILE" ]; then
-  CUSTOM_ARGS=" --log=${TELEGRAM_LOG_FILE}"
-fi
-if [ -n "$TELEGRAM_STAT" ]; then
-  CUSTOM_ARGS="${CUSTOM_ARGS} --http-stat-port=8082"
-fi
-if [ -n "$TELEGRAM_FILTER" ]; then
-  CUSTOM_ARGS="${CUSTOM_ARGS} --filter=$TELEGRAM_FILTER"
-fi
-if [ -n "$TELEGRAM_MAX_WEBHOOK_CONNECTIONS" ]; then
-  CUSTOM_ARGS="${CUSTOM_ARGS} --max-webhook-connections=$TELEGRAM_MAX_WEBHOOK_CONNECTIONS"
-fi
-if [ -n "$TELEGRAM_VERBOSITY" ]; then
-  CUSTOM_ARGS="${CUSTOM_ARGS} --verbosity=$TELEGRAM_VERBOSITY"
-fi
-if [ -n "$TELEGRAM_MAX_CONNECTIONS" ]; then
-  CUSTOM_ARGS="${CUSTOM_ARGS} --max-connections=$TELEGRAM_MAX_CONNECTIONS"
-fi
-if [ -n "$TELEGRAM_PROXY" ]; then
-  CUSTOM_ARGS="${CUSTOM_ARGS} --proxy=$TELEGRAM_PROXY"
-fi
-if [ -n "$TELEGRAM_LOCAL" ]; then
-  CUSTOM_ARGS="${CUSTOM_ARGS} --local"
-fi
-if [ -n "$TELEGRAM_HTTP_IP_ADDRESS" ]; then
-  CUSTOM_ARGS="${CUSTOM_ARGS} --http-ip-address=$TELEGRAM_HTTP_IP_ADDRESS"
-fi
-
-# Set http-port arg
-if [ -n "$TELEGRAM_HTTP_PORT" ]; then
-  CUSTOM_ARGS="${CUSTOM_ARGS} --http-port=$TELEGRAM_HTTP_PORT"
-else
-  CUSTOM_ARGS="${CUSTOM_ARGS} --http-port=8081"
-fi
-
-COMMAND="telegram-bot-api ${DEFAULT_ARGS}${CUSTOM_ARGS}"
+# Default arguments, passed from the Dockerfile.
+# Potentially can be overwritten by environment variables, if needed, but is not recommended.
+append_arg_from_env "TELEGRAM_WORK_DIR" "--dir"
+check_required_env "TELEGRAM_TEMP_DIR"
+append_arg_from_env "TELEGRAM_TEMP_DIR" "--temp-dir"
+append_args "--username=${USERNAME}"
+append_args "--groupname=${GROUPNAME}"
 
-echo "$COMMAND"
+check_required_env "TELEGRAM_API_ID"
+check_required_env "TELEGRAM_API_HASH"
 
-# shellcheck disable=SC2086
+# Environment variables that can be passed as arguments from environment by administrator.
+append_arg_from_env "TELEGRAM_HTTP_PORT" "--http-port" "8081"
+append_flag_from_env "TELEGRAM_LOCAL" "--local"
+append_flag_from_env "TELEGRAM_STAT" "--http-stat-port=8082"  # maybe change it to dynamic variable in the future
+append_arg_from_env "TELEGRAM_LOG_FILE" "--log"
+append_arg_from_env "TELEGRAM_FILTER" "--filter"
+append_arg_from_env "TELEGRAM_MAX_WEBHOOK_CONNECTIONS" "--max-webhook-connections"
+append_arg_from_env "TELEGRAM_VERBOSITY" "--verbosity"
+append_arg_from_env "TELEGRAM_MAX_CONNECTIONS" "--max-connections"
+append_arg_from_env "TELEGRAM_PROXY" "--proxy"
+append_arg_from_env "TELEGRAM_HTTP_IP_ADDRESS" "--http-ip-address"
+
+echo "$COMMAND"
 exec $COMMAND