add a docker fetch script for conveniently downloading the compose project files

docker/compose/zrok-instance/README.md

@@ -5,7 +5,7 @@
 
 The quickstart makes these assumptions about your global DNS configuration.
 
-1. A Caddy DNS plugin is available for your DNS provider (see [github.com/caddy-dns](https://github.com/caddy-dns))
+1. A Caddy DNS plugin is available for your DNS provider (see [github.com/caddy-dns](https://github.com/orgs/caddy-dns/repositories?type=all&q=sort%3Aname-asc))
 1. You have designated A DNS zone for zrok, e.g. `example.com` or `share.example.com` and created (and delegated, if necessary) the zone on your DNS provider's platform.
 1. A wildcard record exists for the IP address where the zrok instance will run, e.g. if your DNS zone is `share.example.com`, then your wildcard record is `*.share.example.com`.
 1. You have created an API token in your DNS provider's platform and the token has permission to create DNS records in the DNS zone.
@@ -14,7 +14,23 @@ The quickstart makes these assumptions about your global DNS configuration.
 
 Create a working directory on your Docker host and save these Docker Compose project files. A OpenZiti network is provided by the "quickstart" container and is managed exclusively by zrok.
 
-1. Get the ziti quickstart Compose file.
+#### Shortcut option
+
+1. Run this script to download the files.
+
+    ```bash
+    curl https://get.openziti.io/zrok-docker/fetch.bash | bash
+    ```
+
+    Optionally, customize the install path instead of using the current directory.
+    
+    ```bash
+    curl https://get.openziti.io/zrok-docker/fetch.bash | bash -s /path/to/install
+    ```
+
+#### Do it Yourself
+
+1. Fetch the ziti quickstart Compose file.
 
     ```bash
     wget https://get.openziti.io/dock/all-in-one/compose.yml

docker/compose/zrok-instance/fetch.bash

@@ -0,0 +1,86 @@
+#!/usr/bin/env bash
+
+set -o errexit
+set -o nounset
+set -o pipefail
+set -o xtrace
+
+requireBashVersion() {
+    if (( "${BASH_VERSION%%.*}" < 4 )); then
+        echo "This script requires Bash major version 4 or greater."
+        echo "Detected version: $BASH_VERSION"
+        exit 1;
+    fi
+}
+
+fetchFile() {
+
+    local url="${1}"
+    local path="${2}"
+
+    if [[ -s "$path" ]]; then
+        echo "ERROR: file already exists: $path" >&2
+        return 1
+    fi
+
+    if { command -v curl > /dev/null; } 2>&1; then
+        curl -fLsS --output "${path}" "${url}"
+    elif { command -v wget > /dev/null; } 2>&1; then
+        wget --output-document "${path}" "${url}"
+    else
+        echo "ERROR: need one of curl or wget to fetch the artifact." >&2
+        return 1
+    fi
+}
+
+
+requireCommand() {
+    if ! command -v "$1" &>/dev/null; then
+        logError "this script requires command '$1'. Please install on the search PATH and try again."
+        $1
+    fi
+}
+
+setWorkingDir() {
+    workdir="${1}"
+
+    cd "${workdir}"
+
+    # Count non-hidden files
+    non_hidden_files=$(find . -maxdepth 1 -not -name '.*' | wc -l)
+    # Count hidden files
+    if ls -ld .[^.]* 2> /dev/null; then
+        hidden_files=0
+        for file in .[^.]*; do
+            if [[ -f "$file" ]]; then
+                hidden_files=$((hidden_files + 1))
+            fi
+        done
+    else
+        hidden_files=0
+    fi
+    # Calculate total number of files
+    total_files=$((non_hidden_files + hidden_files))
+    if (( total_files > 0 )); then
+        echo "WARN: working directory is not empty: ${workdir}" >&2
+        return 1
+    fi
+}
+
+main() {
+    requireBashVersion
+    declare -a BINS=(unzip find)
+    for BIN in "${BINS[@]}"; do
+        requireCommand "$BIN"
+    done
+    setWorkingDir "${1:-$PWD}" || {
+        echo "WARN: installing anyway in a few seconds...press Ctrl-C to abort" >&2
+        sleep 9
+    }
+    fetchFile "${ZITI_QUICK_COMPOSE:-"https://get.openziti.io/dock/all-in-one/compose.yml"}" "compose.yml"
+    fetchFile "${ZROK_REPO_ZIP:-"https://github.com/openziti/zrok/archive/refs/heads/main.zip"}" "zrok.zip"
+    unzip -j -d . zrok.zip '*/docker/compose/zrok-instance/*'
+    rm zrok.zip .gitignore fetch.bash
+}
+
+main "${@}"