Better source_install_lib: add retries and print checksum

buildscripts/kokoro/psm-interop-test-java.sh

@@ -7,6 +7,19 @@ readonly GITHUB_REPOSITORY_NAME="grpc-java"
 readonly TEST_DRIVER_INSTALL_SCRIPT_URL="https://raw.githubusercontent.com/${TEST_DRIVER_REPO_OWNER:-grpc}/psm-interop/${TEST_DRIVER_BRANCH:-main}/.kokoro/psm_interop_kokoro_lib.sh"
 readonly BUILD_SCRIPT_DIR="$(dirname "$0")"
 
-echo "Sourcing test driver install script from: ${TEST_DRIVER_INSTALL_SCRIPT_URL}"
-source /dev/stdin <<< "$(curl -s "${TEST_DRIVER_INSTALL_SCRIPT_URL}")"
+psm::lang::source_install_lib() {
+  echo "Sourcing test driver install script from: ${TEST_DRIVER_INSTALL_SCRIPT_URL}"
+  local install_lib
+  # Download to a tmp file.
+  install_lib="$(mktemp -d)/psm_interop_kokoro_lib.sh"
+  curl -s --retry-connrefused --retry 5 -o "${install_lib}" "${TEST_DRIVER_INSTALL_SCRIPT_URL}"
+  # Checksum.
+  if command -v sha256sum &> /dev/null; then
+    echo "Install script checksum:"
+    sha256sum "${install_lib}"
+  fi
+  source "${install_lib}"
+}
+
+psm::lang::source_install_lib
 psm::run "${PSM_TEST_SUITE}"