fix: enhance binary download flow with robust error handling (#394)

- Define specific error codes for common failure scenarios
- Improve platform and architecture error handling by using error codes
- Add check to reuse cached binary if already downloaded
- Enhance download process with better error handling and validation of the downloaded file
- Add post-download version check with error if binary execution fails

Signed-off-by: appleboy <appleboy.tw@gmail.com>

entrypoint.sh

@@ -8,6 +8,13 @@ GITHUB_ACTION_PATH="${GITHUB_ACTION_PATH%/}"
 DRONE_SSH_RELEASE_URL="${DRONE_SSH_RELEASE_URL:-https://github.com/appleboy/drone-ssh/releases/download}"
 DRONE_SSH_VERSION="${DRONE_SSH_VERSION:-1.8.1}"
 
+# Error codes
+readonly ERR_UNKNOWN_PLATFORM=2
+readonly ERR_UNKNOWN_ARCH=3
+readonly ERR_DOWNLOAD_FAILED=4
+readonly ERR_INVALID_BINARY=5
+readonly ERR_VERSION_CHECK_FAILED=6
+
 function log_error() {
   echo "$1" >&2
   exit "$2"
@@ -19,13 +26,13 @@ function detect_client_info() {
 
   case "${CLIENT_PLATFORM}" in
   darwin | linux | windows) ;;
-  *) log_error "Unknown or unsupported platform: ${CLIENT_PLATFORM}. Supported platforms are Linux, Darwin, and Windows." 2 ;;
+  *) log_error "Unknown or unsupported platform: ${CLIENT_PLATFORM}. Supported platforms are Linux, Darwin, and Windows." "${ERR_UNKNOWN_PLATFORM}" ;;
   esac
 
   case "${CLIENT_ARCH}" in
   x86_64* | i?86_64* | amd64*) CLIENT_ARCH="amd64" ;;
   aarch64* | arm64*) CLIENT_ARCH="arm64" ;;
-  *) log_error "Unknown or unsupported architecture: ${CLIENT_ARCH}. Supported architectures are x86_64, i686, and arm64." 3 ;;
+  *) log_error "Unknown or unsupported architecture: ${CLIENT_ARCH}. Supported architectures are x86_64, i686, and arm64." "${ERR_UNKNOWN_ARCH}" ;;
   esac
 }
 
@@ -33,17 +40,35 @@ detect_client_info
 DOWNLOAD_URL_PREFIX="${DRONE_SSH_RELEASE_URL}/v${DRONE_SSH_VERSION}"
 CLIENT_BINARY="drone-ssh-${DRONE_SSH_VERSION}-${CLIENT_PLATFORM}-${CLIENT_ARCH}"
 TARGET="${GITHUB_ACTION_PATH}/${CLIENT_BINARY}"
-echo "Downloading ${CLIENT_BINARY} from ${DOWNLOAD_URL_PREFIX}"
+
-INSECURE_OPTION=""
+# Check if binary already exists and is executable (caching)
-if [[ "${INPUT_CURL_INSECURE}" == 'true' ]]; then
+if [[ -f "${TARGET}" ]] && [[ -x "${TARGET}" ]]; then
+  echo "Binary ${CLIENT_BINARY} already exists, skipping download"
+else
+  echo "Downloading ${CLIENT_BINARY} from ${DOWNLOAD_URL_PREFIX}"
+  INSECURE_OPTION=""
+  if [[ "${INPUT_CURL_INSECURE}" == 'true' ]]; then
     INSECURE_OPTION="--insecure"
+  fi
+
+  # Download with better error handling
+  if ! curl -fsSL --retry 5 --keepalive-time 2 --location ${INSECURE_OPTION} \
+    "${DOWNLOAD_URL_PREFIX}/${CLIENT_BINARY}" -o "${TARGET}"; then
+    log_error "Failed to download ${CLIENT_BINARY} from ${DOWNLOAD_URL_PREFIX}. Please check the URL and your network connection." "${ERR_DOWNLOAD_FAILED}"
+  fi
+
+  # Validate downloaded file
+  if [[ ! -f "${TARGET}" ]] || [[ ! -s "${TARGET}" ]]; then
+    log_error "Downloaded file is missing or empty: ${TARGET}" "${ERR_INVALID_BINARY}"
+  fi
+
+  chmod +x "${TARGET}"
 fi
 
-curl -fsSL --retry 5 --keepalive-time 2 ${INSECURE_OPTION} "${DOWNLOAD_URL_PREFIX}/${CLIENT_BINARY}" -o "${TARGET}"
-chmod +x "${TARGET}"
-
 echo "======= CLI Version Information ======="
-"${TARGET}" --version
+if ! "${TARGET}" --version; then
+  log_error "Failed to execute ${TARGET} --version. The binary may be corrupted." "${ERR_VERSION_CHECK_FAILED}"
+fi
 echo "======================================="
 if [[ "${INPUT_CAPTURE_STDOUT}" == 'true' ]]; then
   {