Add make publish: build the image on the Docker host and push it to the registry

script/publish runs script/docker with DOCKER_HOST set to the Docker
host (ssh://root@fsn1app1 unless set) and pushes the image to
git.eeqj.de/sneak/smallwebwaf under four tags: the UTC date as
YYYY-MM-DD, the short commit hash, the branch name and latest. It
refuses a working tree with uncommitted changes, since the hash tag
names a commit.

Makefile

@@ -1,11 +1,12 @@
-.PHONY: bootstrap setup test lint fmt fmt-check tidy check docker hooks build \
-	run example-app
+.PHONY: bootstrap setup test lint fmt fmt-check tidy check docker publish \
+	hooks build run example-app
 
 # Makefile targets are thin shims; the implementations live in script/
 # per the scripts-to-rule-them-all pattern (see the Entrypoints section
 # of README.md). tidy writes go.mod and go.sum as `go mod tidy` does,
 # which test checks. build and run are for working on the code by hand;
-# example-app checks the image with an app built on it.
+# example-app checks the image with an app built on it; publish builds
+# the image on the Docker host and pushes it to the registry.
 
 bootstrap:
 	@script/bootstrap
@@ -34,6 +35,9 @@ check:
 docker:
 	@script/docker
 
+publish:
+	@script/publish
+
 hooks:
 	@script/install-precommit
 

README.md

@@ -68,8 +68,9 @@ Not built, and not planned:
 
 ### The image
 
-No image is published. Build it from a clone. `make docker` runs the tests and
-the linter, then builds the image, tagged `smallwebwaf`.
+The image is published at `git.eeqj.de/sneak/smallwebwaf`. You can also build it
+from a clone. `make docker` runs the tests and the linter, then builds the
+image, tagged `smallwebwaf`.
 
 ```sh
 git clone https://git.eeqj.de/sneak/smallwebwaf.git
@@ -665,6 +666,15 @@ on the host.
   `make check`.
 - `script/docker`: builds the image, whose build runs the tests and the linter
   first. `make docker`.
+- `script/publish`: runs `script/docker`, whose build happens on the Docker host
+  named by `DOCKER_HOST` (`ssh://root@fsn1app1` unless set). It then pushes the
+  image to `PUBLISH_IMAGE` (`git.eeqj.de/sneak/smallwebwaf` unless set). It
+  refuses a working tree with uncommitted changes. `make publish`. It pushes
+  four tags:
+    - the UTC date as `YYYY-MM-DD`;
+    - the short commit hash;
+    - the branch name;
+    - `latest`.
 - `script/cibuild`: what CI runs: `script/bootstrap`, `script/check`, then the
   image build.
 - `script/precommit`: run by the git pre-commit hook; runs `script/check`.

script/publish

@@ -0,0 +1,54 @@
+#!/bin/sh
+# script/publish: build the image on the Docker host and push it to the
+# registry under four tags: the UTC date (YYYY-MM-DD), the short commit
+# hash, the branch name and latest. The build is script/docker's, so the
+# tests and the linter run first. The host and the registry name are
+# environment variables with defaults, for running it against another.
+#
+# The working tree must be clean: the hash tag names a commit, and an
+# image built from uncommitted changes would carry a hash that does not
+# describe it.
+set -eu
+
+SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd -P)"
+ROOT="$(cd "$SCRIPT_DIR/.." && pwd -P)"
+
+: "${DOCKER_HOST:=ssh://root@fsn1app1}"
+: "${PUBLISH_IMAGE:=git.eeqj.de/sneak/smallwebwaf}"
+export DOCKER_HOST
+
+main() {
+    cd "$ROOT"
+
+    # Own line: a failing command substitution inside an argument does
+    # not trip `set -e`.
+    changes="$(git status --porcelain)"
+    if [ -n "$changes" ]; then
+        echo "script/publish: the working tree is not clean; commit or stash first" >&2
+        exit 1
+    fi
+
+    date="$(date -u +%Y-%m-%d)"
+    hash="$(git rev-parse --short HEAD)"
+    branch="$(git rev-parse --abbrev-ref HEAD)"
+    if [ "$branch" = "HEAD" ]; then
+        echo "script/publish: detached HEAD; check out a branch first" >&2
+        exit 1
+    fi
+    # A tag is [A-Za-z0-9_.-]; a branch name such as feature/x is not.
+    branch="$(printf '%s' "$branch" | tr -c 'A-Za-z0-9_.-' '-')"
+
+    local_tag="$("$SCRIPT_DIR/projectname")"
+    "$SCRIPT_DIR/docker"
+
+    for tag in "$date" "$hash" "$branch" latest; do
+        docker tag "$local_tag" "$PUBLISH_IMAGE:$tag"
+    done
+    for tag in "$date" "$hash" "$branch" latest; do
+        docker push "$PUBLISH_IMAGE:$tag"
+    done
+
+    echo "pushed $PUBLISH_IMAGE with tags: $date $hash $branch latest"
+}
+
+main "$@"