Publish a gs://kubernetes-release/release/latest.txt when we publish a build

Adds a kube::release::gcs::publish_latest_official that checks the
current contents of this file in GCS, verifies that we're pushing a
newer build, and updates it if so. (i.e. it handles the case of
pushing a 0.13.1 and then later pushing a 0.12.3.) This follows the
pattern of the ci/ build, which Jenkins just updates unconditionally.

I already updated the file for 0.13.1. After this we can update the
get-k8s script, so we don't have to keep updating it.

build/common.sh

@@ -833,3 +833,53 @@ function kube::release::gcs::publish_latest() {
   echo "+++ gsutil cat ${latest_file_dst}:"
   gsutil cat ${latest_file_dst}
 }
+
+# Publish a new latest.txt, but only if the release we're dealing with
+# is newer than the contents in GCS.
+function kube::release::gcs::publish_latest_official() {
+  local -r new_version=${KUBE_GCS_LATEST_CONTENTS}
+  local -r latest_file_dst="gs://${KUBE_GCS_RELEASE_BUCKET}/${KUBE_GCS_LATEST_FILE}"
+
+  local -r version_regex="^v(0|[1-9][0-9]*)\\.(0|[1-9][0-9]*)\\.(0|[1-9][0-9]*)$"
+  [[ ${new_version} =~ ${version_regex} ]] || {
+    echo "!!! publish_latest_official passed bogus value: '${new_version}'" >&2
+    return 1
+  }
+
+  local -r version_major="${BASH_REMATCH[1]}"
+  local -r version_minor="${BASH_REMATCH[2]}"
+  local -r version_patch="${BASH_REMATCH[3]}"
+
+  local gcs_version
+  gcs_version=$(gsutil cat "${latest_file_dst}")
+
+  [[ ${gcs_version} =~ ${version_regex} ]] || {
+    echo "!!! ${latest_file_dst} contains invalid release version, can't compare: '${gcs_version}'" >&2
+    return 1
+  }
+
+  local -r gcs_version_major="${BASH_REMATCH[1]}"
+  local -r gcs_version_minor="${BASH_REMATCH[2]}"
+  local -r gcs_version_patch="${BASH_REMATCH[3]}"
+
+  local greater=true
+  if [[ "${gcs_version_major}" -gt "${version_major}" ]]; then
+    greater=false
+  elif [[ "${gcs_version_major}" -lt "${version_major}" ]]; then
+    : # fall out
+  elif [[ "${gcs_version_minor}" -gt "${version_minor}" ]]; then
+    greater=false
+  elif [[ "${gcs_version_minor}" -lt "${version_minor}" ]]; then
+    : # fall out
+  elif [[ "${gcs_version_patch}" -ge "${version_patch}" ]]; then
+    greater=false
+  fi
+
+  if [[ "${greater}" != "true" ]]; then
+    echo "+++ ${gcs_version} (latest on GCS) >= ${new_version} (just uploaded), not updating ${latest_file_dst}"
+    return 0
+  fi
+
+  echo "+++ ${new_version} (just uploaded) > ${gcs_version} (latest on GCS), updating ${latest_file_dst}"
+  kube::release::gcs::publish_latest
+}

build/push-official-release.sh

@@ -22,7 +22,7 @@ set -o pipefail
 
 KUBE_RELEASE_VERSION=${1-}
 
-VERSION_REGEX="v[0-9]+.[0-9]+(.[0-9]+)?"
+VERSION_REGEX="^v(0|[1-9][0-9]*)\\.(0|[1-9][0-9]*)\\.(0|[1-9][0-9]*)$"
 [[ ${KUBE_RELEASE_VERSION} =~ $VERSION_REGEX ]] || {
   echo "!!! You must specify the version you are releasing in the form of '$VERSION_REGEX'" >&2
   exit 1
@@ -34,9 +34,11 @@ KUBE_GCS_UPLOAD_RELEASE=y
 KUBE_GCS_RELEASE_BUCKET=kubernetes-release
 KUBE_GCS_PROJECT=google-containers
 KUBE_GCS_RELEASE_PREFIX=release/${KUBE_RELEASE_VERSION}
+KUBE_GCS_LATEST_FILE="release/latest.txt"
+KUBE_GCS_LATEST_CONTENTS=${KUBE_RELEASE_VERSION}
 
 KUBE_ROOT=$(dirname "${BASH_SOURCE}")/..
 source "$KUBE_ROOT/build/common.sh"
 
-
 kube::release::gcs::release
+kube::release::gcs::publish_latest_official