release: 3.3.3

- now seems to need linux-headers, see https://github.com/socketry/nio4r/issues/225

.editorconfig

@@ -0,0 +1,9 @@
+root = true
+
+[*]
+indent_style = space
+indent_size = 2
+end_of_line = lf
+charset = utf-8
+trim_trailing_whitespace = true
+insert_final_newline = true

.github/workflows/cd.yml

@@ -0,0 +1,35 @@
+---
+name: cd
+
+on:
+  push:
+    tags:
+    - 'v*.*.*'
+
+jobs:
+  release-dockerimage:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v2
+    - name: Extract dyndnsd version from tag name
+      run: |
+        echo "DYNDNSD_VERSION=${GITHUB_REF#refs/*/v}" >> $GITHUB_ENV
+
+    # https://github.com/marketplace/actions/build-and-push-docker-images
+    - name: Set up Docker Buildx
+      uses: docker/setup-buildx-action@v1
+
+    - name: Login to Docker Hub
+      uses: docker/login-action@v1
+      with:
+        username: cmur2
+        password: ${{ secrets.DOCKER_TOKEN }}
+
+    - name: Build and push Docker image for dyndnsd ${{ env.DYNDNSD_VERSION }}
+      uses: docker/build-push-action@v2
+      with:
+        context: docker
+        build-args: |
+          DYNDNSD_VERSION=${{ env.DYNDNSD_VERSION }}
+        push: true
+        tags: cmur2/dyndnsd:v${{ env.DYNDNSD_VERSION }}

.github/workflows/ci.yml

@@ -0,0 +1,32 @@
+---
+name: ci
+
+on:
+  push:
+    branches: [master]
+  pull_request:
+    branches: [master]
+  workflow_dispatch:
+  schedule:
+  - cron: '35 4 * * 4'  # weekly on thursday morning
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        ruby-version:
+        - '2.5'
+        - '2.6'
+        - '2.7'
+        - '3.0'
+    steps:
+    - uses: actions/checkout@v2
+    - name: Set up Ruby ${{ matrix.ruby-version }}
+      uses: ruby/setup-ruby@v1
+      with:
+        ruby-version: ${{ matrix.ruby-version }}
+        bundler-cache: true  # runs 'bundle install' and caches installed gems automatically
+    - name: Lint and Test
+      run: |
+        bundle exec rake ci

.github/workflows/dockerhub.yml

@@ -0,0 +1,19 @@
+---
+name: dockerhub
+
+on:
+  schedule:
+  - cron: '7 4 * * 4'  # weekly on thursday morning
+  workflow_dispatch:
+
+jobs:
+  pull-released-dockerimages:
+    runs-on: ubuntu-latest
+    steps:
+    - name: Avoid stale tags by pulling
+      run: |
+        ALL_IMAGES="$(curl -s https://hub.docker.com/v2/repositories/cmur2/dyndnsd/tags?page_size=1000 | jq -r '.results[].name | "cmur2/dyndnsd:" + .' | grep -e 'cmur2/dyndnsd:v')"
+        for image in $ALL_IMAGES; do
+          echo "Pulling $image to avoid staleness..."
+          docker pull "$image"
+        done

.github/workflows/vulnscan.yml

@@ -0,0 +1,46 @@
+---
+name: vulnscan
+
+on:
+  schedule:
+  - cron: '7 4 * * 4'  # weekly on thursday morning
+  workflow_dispatch:
+
+jobs:
+  scan-released-dockerimages:
+    runs-on: ubuntu-latest
+    env:
+      TRIVY_LIGHT: 'true'
+      TRIVY_IGNORE_UNFIXED: 'true'
+      TRIVY_REMOVED_PKGS: 'true'
+    steps:
+    - name: Install Trivy
+      run: |
+        mkdir -p $GITHUB_WORKSPACE/bin
+        echo "$GITHUB_WORKSPACE/bin" >> "$GITHUB_PATH"
+        curl -sfL https://raw.githubusercontent.com/aquasecurity/trivy/master/contrib/install.sh | sh -s -- -b $GITHUB_WORKSPACE/bin
+    - name: Download Trivy DB
+      run: |
+        trivy image --download-db-only
+    - name: Scan vulnerabilities using Trivy
+      env:
+        TRIVY_SKIP_DIRS: 'usr/lib/ruby/gems/2.7.0/gems/jaeger-client-0.10.0/crossdock,usr/lib/ruby/gems/2.7.0/gems/jaeger-client-1.0.0/crossdock,usr/lib/ruby/gems/2.7.0/gems/jaeger-client-1.1.0/crossdock'
+      run: |
+        trivy --version
+
+        # semver sorting as per https://stackoverflow.com/a/40391207/2148786
+        ALL_IMAGES="$(curl -s https://hub.docker.com/v2/repositories/cmur2/dyndnsd/tags?page_size=1000 | jq -r '.results[].name | "cmur2/dyndnsd:" + .' | grep -e 'cmur2/dyndnsd:v' | sed '/-/!{s/$/_/}' | sort -r -V | sed 's/_$//')"
+        EXIT_CODE=0
+        set -e
+        for major_version in $(seq 1 10); do
+          for image in $ALL_IMAGES; do
+            if [[ "$image" = cmur2/dyndnsd:v$major_version.* ]]; then
+              echo -e "\nScanning newest patch release $image of major v$major_version...\n"
+              if ! trivy image --skip-update --exit-code 1 "$image"; then
+                EXIT_CODE=1
+              fi
+              break
+            fi
+          done
+        done
+        exit "$EXIT_CODE"

.gitignore

@@ -1,3 +1,4 @@
 .DS_Store
 *.lock
 pkg/*
+.yardoc

.rubocop.yml

@@ -1,15 +1,27 @@
-inherit_from: .rubocop_todo.yml
+require:
+- rubocop-rake
+- rubocop-rspec
 
 AllCops:
-  TargetRubyVersion: '2.3'
+  TargetRubyVersion: '2.5'
+  NewCops: enable
 
-Gemspec/OrderedDependencies:
+Layout/EmptyLineAfterGuardClause:
   Enabled: false
 
 # allows nicer usage of private_class_method
 Layout/EmptyLinesAroundArguments:
   Enabled: false
 
+Layout/HashAlignment:
+  Enabled: false
+
+Layout/LeadingEmptyLines:
+  Enabled: false
+
+Layout/LineLength:
+  Max: 200
+
 Layout/SpaceInsideHashLiteralBraces:
   Enabled: false
 
@@ -25,16 +37,13 @@ Metrics/ClassLength:
 Metrics/CyclomaticComplexity:
   Enabled: false
 
-Metrics/LineLength:
-  Max: 200
-
 Metrics/MethodLength:
   Enabled: false
 
 Metrics/PerceivedComplexity:
   Enabled: false
 
-Naming/UncommunicativeMethodParamName:
+Naming/MethodParameterName:
   Enabled: false
 
 Naming/MemoizedInstanceVariableName:
@@ -49,15 +58,24 @@ Style/Documentation:
 Style/FormatStringToken:
   Enabled: false
 
-Style/FrozenStringLiteralComment:
-  Enabled: false
-
 Style/GuardClause:
   Enabled: false
 
+Style/HashEachMethods:
+  Enabled: true
+
+Style/HashTransformKeys:
+  Enabled: true
+
+Style/HashTransformValues:
+  Enabled: true
+
 Style/IdenticalConditionalBranches:
   Enabled: false
 
+Style/IfUnlessModifier:
+  Enabled: false
+
 Style/InverseMethods:
   Enabled: false
 
@@ -69,3 +87,12 @@ Style/RescueModifier:
 
 Style/SymbolArray:
   Enabled: false
+
+Style/TrailingCommaInArrayLiteral:
+  Enabled: false
+
+RSpec/ExampleLength:
+  Max: 20
+
+RSpec/MultipleExpectations:
+  Max: 20

.rubocop_todo.yml

@@ -1,7 +0,0 @@
-# This configuration was generated by
-# `rubocop --auto-gen-config`
-# on 2018-02-23 12:54:10 +0100 using RuboCop version 0.52.1.
-# The point is for the user to remove these configuration records
-# one by one as the offenses are removed from the code base.
-# Note that changes in the inspected code, or installation of new
-# versions of RuboCop, may require this file to be generated again.

.solargraph.yml

@@ -0,0 +1,16 @@
+---
+include:
+- "**/*.rb"
+- "bin/dyndnsd"
+exclude:
+- spec/**/*
+- test/**/*
+- vendor/**/*
+- ".bundle/**/*"
+require: []
+domains: []
+reporters:
+- rubocop
+- require_not_found
+require_paths: []
+max_files: 5000

.travis.yml

@@ -1,7 +0,0 @@
----
-sudo: false
-language: ruby
-rvm:
-  - 2.5
-  - 2.4
-  - 2.3

CHANGELOG.md

@@ -1,6 +1,101 @@
 # Changelog
 
-## 2.0.0
+## 3.3.3 (April 1, 2021)
+
+OTHER:
+
+- update base of Docker image to Alpine 3.13.4 to fix security vulnerabilities
+
+## 3.3.2 (February 20, 2021)
+
+OTHER:
+
+- update to use `docker/build-push-action@v2` for releasing Docker image in GHA
+
+## 3.3.1 (February 18, 2021)
+
+OTHER:
+
+- update base of Docker image to Alpine 3.13.2 to fix security vulnerabilities
+
+## 3.3.0 (January 18, 2021)
+
+OTHER:
+
+- update base of Docker image to Alpine 3.13
+
+## 3.2.0 (January 14, 2021)
+
+IMPROVEMENTS:
+
+- Add Ruby 3.0 support
+
+## 3.1.3 (December 20, 2020)
+
+OTHER:
+
+- fix Docker image release process in Github Actions CI, 3.1.2 was not released as a Docker image
+
+## 3.1.2 (December 20, 2020)
+
+OTHER:
+
+- fixes vulnerabilities in Docker image by using updated Alpine base image
+- start using Github Actions CI for tests and drop Travis CI
+
+## 3.1.1 (October 3, 2020)
+
+IMPROVEMENTS:
+
+- Use webrick gem which contains fixes against [CVE-2020-25613](https://www.ruby-lang.org/en/news/2020/09/29/http-request-smuggling-cve-2020-25613/)
+
+## 3.1.0 (August 19, 2020)
+
+IMPROVEMENTS:
+
+- Add officially maintained [Docker image for dyndnsd](https://hub.docker.com/r/cmur2/dyndnsd)
+
+## 3.0.0 (July 29, 2020)
+
+IMPROVEMENTS:
+
+- Drop EOL Ruby 2.4 and lower support, now minimum version supported is Ruby 2.5
+
+## 2.3.1 (July 27, 2020)
+
+IMPROVEMENTS:
+
+- Fix annoying error message `log writing failed. can't be called from trap context` on shutdown by not attempting to log redundant information there
+
+## 2.3.0 (July 20, 2020)
+
+IMPROVEMENTS:
+
+- Allow enabling debug logging
+- Add updater that uses [DNS zone transfers via AXFR (RFC5936)](https://tools.ietf.org/html/rfc5936) to allow any secondary nameserver(s) to fetch the zone contents after (optionally) receiving a [DNS NOTIFY (RFC1996)](https://tools.ietf.org/html/rfc1996) request
+
+## 2.2.0 (March 6, 2020)
+
+IMPROVEMENTS:
+
+- Refactor gemspec based on [recommendations](https://piotrmurach.com/articles/writing-a-ruby-gem-specification/) so tests are now excluded from gem and binaries move to `./exe` directory
+- Adopt Ruby 2.3 frozen string literals for source code potentially reducing memory consumption
+
+## 2.1.1 (March 1, 2020)
+
+IMPROVEMENTS:
+
+- Fix potential `nil` cases detected by [Sorbet](https://sorbet.org) including refactorings
+
+## 2.1.0 (March 1, 2020)
+
+IMPROVEMENTS:
+
+- Add Ruby 2.7 support
+- Add [solargraph](https://github.com/castwide/solargraph) to dev tooling as Ruby Language Server usable e.g. for IDEs (used solargraph version not compatible with Ruby 2.7 as bundler-audit 0.6.x requires old `thor` gem)
+- Document code using YARD tags, e.g. for type information and better code completion
+
+## 2.0.0 (January 25, 2019)
 
 IMPROVEMENTS:
 
@@ -8,8 +103,8 @@ IMPROVEMENTS:
 - Better protocol compliance by returning `badauth` in response body on HTTP 401 errors
 - Better code maintainability by refactorings
 - Update dependencies, mainly `rack` to new major version 2
-- Add Ruby 2.5 support
-- Add experimental [OpenTracing](http://opentracing.io/) support with [CNCF Jaeger](https://github.com/jaegertracing/jaeger)
+- Add Ruby 2.5 and Ruby 2.6 support
+- Add experimental [OpenTracing](https://opentracing.io/) support with [CNCF Jaeger](https://github.com/jaegertracing/jaeger)
 - Support host offlining by deleting the associated DNS records
 - Add textfile reporter to write Graphite-style metrics (also compatible with [Prometheus](https://prometheus.io/)) into a file
 

Gemfile

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 source 'https://rubygems.org'
 
 gemspec

README.md

@@ -1,19 +1,23 @@
 # dyndnsd.rb
 
-[![Build Status](https://travis-ci.org/cmur2/dyndnsd.svg?branch=master)](https://travis-ci.org/cmur2/dyndnsd) [![Dependencies](https://badges.depfu.com/badges/4f25da8493f7a29f652ac892fbf9227b/overview.svg)](https://depfu.com/github/cmur2/dyndnsd)
+![ci](https://github.com/cmur2/dyndnsd/workflows/ci/badge.svg) [![Dependencies](https://badges.depfu.com/badges/4f25da8493f7a29f652ac892fbf9227b/overview.svg)](https://depfu.com/github/cmur2/dyndnsd)
 
 A small, lightweight and extensible DynDNS server written with Ruby and Rack.
 
+
 ## Description
 
-dyndnsd.rb aims to implement a small [DynDNS-compliant](https://help.dyn.com/remote-access-api/) server in Ruby supporting IPv4 and IPv6 addresses. It has an integrated user and hostname database in it's configuration file that is used for authentication and authorization. Besides talking the DynDNS protocol it is able to invoke a so-called *updater*, a small Ruby module that takes care of supplying the current hostname => ip mapping to a DNS server.
+dyndnsd.rb aims to implement a small [DynDNS-compliant](https://help.dyn.com/remote-access-api/) server in Ruby supporting IPv4 and IPv6 addresses. It has an integrated user and hostname database in its configuration file that is used for authentication and authorization. Besides talking the DynDNS protocol it is able to invoke a so-called *updater*, a small Ruby module that takes care of supplying the current hostname => ip mapping to a DNS server.
 
-There is currently one updater shipped with dyndnsd.rb `command_with_bind_zone` that writes out a zone file in BIND syntax onto the current system and invokes a user-supplied command afterwards that is assumed to trigger the DNS server (not necessarily BIND since it's zone files are read by other DNS servers, too) to reload it's zone configuration.
+There are currently two updaters shipped with dyndnsd.rb:
+- `zone_transfer_server` that uses [DNS zone transfers via AXFR (RFC5936)](https://tools.ietf.org/html/rfc5936) to allow any secondary nameserver(s) to fetch the zone contents after (optionally) receiving a [DNS NOTIFY (RFC1996)](https://tools.ietf.org/html/rfc1996) request
+- `command_with_bind_zone` that writes out a zone file in BIND syntax onto the current system and invokes a user-supplied command afterwards that is assumed to trigger the DNS server (not necessarily BIND since its zone files are read by other DNS servers, too) to reload its zone configuration
 
 Because of the mechanisms used, dyndnsd.rb is known to work only on \*nix systems.
 
 See the [changelog](CHANGELOG.md) before upgrading. The older version 1.x of dyndnsd.rb is still available on [branch dyndnsd-1.x](https://github.com/cmur2/dyndnsd/tree/dyndnsd-1.x).
 
+
 ## General Usage
 
 Install the gem:
@@ -25,14 +29,16 @@ Create a configuration file in YAML format somewhere:
 ```yaml
 # listen address and port
 host: "0.0.0.0"
-port: "80"
-# optional: drop priviliges in case you want to but you may need sudo for external commands
+port: 80
+# optional: drop privileges in case you want to but you may need sudo for external commands
 user: "nobody"
 group: "nogroup"
-# logfile is optional, logs to STDOUT else
+# logfile is optional, logs to STDOUT otherwise
 logfile: "dyndnsd.log"
-# interal database file
+# internal database file
 db: "db.json"
+# enable debug mode?
+debug: false
 # all hostnames are required to be cool-name.example.org
 domain: "example.org"
 # configure the updater, here we use command_with_bind_zone, params are updater-specific
@@ -58,17 +64,98 @@ users:
 
 Run dyndnsd.rb by:
 
-	dyndnsd /path/to/config.yaml
+```bash
+dyndnsd /path/to/config.yml
+```
 
-## Using dyndnsd.rb with [NSD](https://www.nlnetlabs.nl/nsd/)
 
-NSD is a nice opensource, authoritative-only, low-memory DNS server that reads BIND-style zone files (and converts them into it's own database) and has a simple config file.
+### Docker image
 
-A feature NSD is lacking is the [Dynamic DNS update](https://tools.ietf.org/html/rfc2136) functionality BIND offers but one can fake it using the following dyndnsd.rb config:
+There is an officially maintained [Docker image for dyndnsd](https://hub.docker.com/r/cmur2/dyndnsd) available at Dockerhub. The goal is to have a minimal secured image available (currently based on Alpine) that works well for the `zone_transfer_server` updater use case.
+
+Users can make extensions by deriving from the official Docker image or building their own.
+
+The Docker image consumes the same configuration file in YAML format as the gem, inside the container it needs to be mounted/available as `/etc/dyndnsd/config.yml`. the following YAML should be used as a base and extended with user's settings:
 
 ```yaml
 host: "0.0.0.0"
-port: "8245" # the DynDNS.com alternative HTTP port
+port: 8080
+# omit the logfile: option so logging to STDOUT will happen automatically
+db: "/var/lib/dyndnsd/db.json"
+
+# User's settings for updater and permissions follow here!
+```
+
+more ports might be needed depending on if DNS zone transfer is needed
+
+Run the Docker image exposing the DynDNS-API on host port 8080 via:
+
+```bash
+docker run -d --name dyndnsd \
+           -p 8080:8080 \
+           -v /host/path/to/dyndnsd/config.yml:/etc/dyndnsd/config.yml \
+           -v /host/ptherpath/to/dyndnsd/datadir:/var/lib/dyndnsd \
+           cmur2/dyndnsd:vX.Y.Z
+```
+
+*Note*: You may need to expose more then just port 8080 e.g. if you use the `zone_transfer_server` which can be done by appending additional `-p 5353:5353` flags to the `docker run` command.
+
+
+
+## Using dyndnsd.rb with any nameserver via DNS zone transfers (AXFR)
+
+By using [DNS zone transfers via AXFR (RFC5936)](https://tools.ietf.org/html/rfc5936) any secondary nameserver can retrieve the DNS zone contents from dyndnsd.rb and serve them to clients.
+To speedup propagation after changes dyndnsd.rb can issue a [DNS NOTIFY (RFC1996)](https://tools.ietf.org/html/rfc1996) to inform the nameserver that the DNS zone contents changed and should be fetched even before the time indicated in the SOA record is up.
+Currently dyndnsd.rb does not support any authentication for incoming DNS zone transfer requests so it should be isolated from the internet on these ports.
+
+This approach has several advantages:
+- dyndnsd.rb can be used in *hidden primary* fashion isolated from client's DNS traffic and does not need to implement full nameserver features
+- any existing, production-grade, caching, geo-replicated nameserver setup can be used to pull DNS zone contents from the *hidden primary* dyndnsd.rb and serve it to clients
+- any nameserver(s) and dyndnsd.rb do not need to be located on the same host
+
+Example dyndnsd.rb configuration:
+
+```yaml
+host: "0.0.0.0"
+port: 8245 # the DynDNS.com alternative HTTP port
+db: "/opt/dyndnsd/db.json"
+domain: "dyn.example.org"
+updater:
+  name: "zone_transfer_server"
+  params:
+    # endpoint(s) to listen for incoming zone transfer (AXFR) requests, default 0.0.0.0@53
+    server_listens:
+    - 127.0.0.1@5300
+    # where to send DNS NOTIFY request(s) to on zone content change
+    send_notifies:
+    - '127.0.0.1'
+    # TTL for all records in the zone (in seconds)
+    zone_ttl: 300  # 5m
+    # zone's NS record(s) (at least one)
+    zone_nameservers:
+    - "dns.example.org."
+    # info for zone's SOA record
+    zone_email_address: "admin.example.org."
+    # zone's additional A/AAAA records
+    zone_additional_ips:
+    - "127.0.0.1"
+users:
+  foo:
+    password: "secret"
+    hosts:
+      - foo.example.org
+```
+
+
+## Using dyndnsd.rb with [NSD](https://www.nlnetlabs.nl/projects/nsd/about/)
+
+NSD is a nice, open source, authoritative-only, low-memory DNS server that reads BIND-style zone files (and converts them into its own database) and has a simple configuration file.
+
+A feature NSD is lacking is the [Dynamic DNS update (RFC2136)](https://tools.ietf.org/html/rfc2136) functionality BIND offers but one can fake it using the following dyndnsd.rb configuration:
+
+```yaml
+host: "0.0.0.0"
+port: 8245 # the DynDNS.com alternative HTTP port
 db: "/opt/dyndnsd/db.json"
 domain: "dyn.example.org"
 updater:
@@ -93,12 +180,15 @@ users:
 
 Start dyndnsd.rb before NSD to make sure the zone file exists else NSD complains.
 
+
 ## Using dyndnsd.rb with X
 
 Please provide ideas if you are using dyndnsd.rb with other DNS servers :)
 
+
 ## Advanced topics
 
+
 ### Update URL
 
 The update URL you want to tell your clients (humans or scripts ^^) consists of the following
@@ -111,10 +201,11 @@ where:
 * USER and PASSWORD are needed for HTTP Basic Auth and valid combinations are defined in your config.yaml
 * DOMAIN should match what you defined in your config.yaml as domain but may be anything else when using a webserver as proxy
 * PORT depends on your (webserver/proxy) settings
-* HOSTNAMES is a required list of comma separated FQDNs (they all have to end with your config.yaml domain) the user wants to update
+* HOSTNAMES is a required list of comma-separated FQDNs (they all have to end with your config.yaml domain) the user wants to update
 * MYIP is optional and the HTTP client's IP address will be used if missing
 * MYIP6 is optional but if present also requires presence of MYIP
 
+
 ### IP address determination
 
 The following rules apply:
@@ -123,15 +214,20 @@ The following rules apply:
 * use any IP address provided via the X-Real-IP header e.g. when used behind HTTP reverse proxy such as nginx, or
 * use any IP address used by the connecting HTTP client
 
-If you want to provide an additional IPv6 address as myip6 parameter the myip parameter containing an IPv4 address has to be present, too! No automatism is applied then.
+If you want to provide an additional IPv6 address as myip6 parameter, the myip parameter containing an IPv4 address has to be present, too! No automatism is applied then.
+
 
 ### SSL, multiple listen ports
 
 Use a webserver as a proxy to handle SSL and/or multiple listen addresses and ports. DynDNS.com provides HTTP on port 80 and 8245 and HTTPS on port 443.
 
-### Init scripts
 
-The [Debian 6 init.d script](init.d/debian-6-dyndnsd) assumes that dyndnsd.rb is installed into the system ruby (no RVM support) and the config.yaml is at /opt/dyndnsd/config.yaml. Modify to your needs.
+### Startup
+
+There is a [Dockerfile](docs/Dockerfile) that can be used to build a Docker image for running dyndnsd.rb.
+
+The [Debian 6 init.d script](docs/debian-6-init-dyndnsd) assumes that dyndnsd.rb is installed into the system ruby (no RVM support) and the config.yaml is at /opt/dyndnsd/config.yaml. Modify to your needs.
+
 
 ### Monitoring
 
@@ -139,7 +235,7 @@ For monitoring dyndnsd.rb uses the [metriks](https://github.com/eric/metriks) fr
 
 ```yaml
 host: "0.0.0.0"
-port: "8245" # the DynDNS.com alternative HTTP port
+port: 8245 # the DynDNS.com alternative HTTP port
 db: "/opt/dyndnsd/db.json"
 domain: "dyn.example.org"
 # configure the Graphite backend to be used instead of proctitle
@@ -172,14 +268,16 @@ users:
     password: "ihavenohosts"
 ```
 
+
 ### Tracing (experimental)
 
-For tracing dyndnsd.rb is instrumented using the [OpenTracing](http://opentracing.io/) framework and will emit span tracing data for the most important operations happening during the request/response cycle. Using a middleware for Rack allows handling incoming OpenTracing span information properly.
+For tracing, dyndnsd.rb is instrumented using the [OpenTracing](http://opentracing.io/) framework and will emit span tracing data for the most important operations happening during the request/response cycle. Using a middleware for Rack allows handling incoming OpenTracing span information properly.
+
 Currently only one OpenTracing-compatible tracer implementation named [CNCF Jaeger](https://github.com/jaegertracing/jaeger) can be configured to use with dyndnsd.rb.
 
 ```yaml
 host: "0.0.0.0"
-port: "8245" # the DynDNS.com alternative HTTP port
+port: 8245 # the DynDNS.com alternative HTTP port
 db: "/opt/dyndnsd/db.json"
 domain: "dyn.example.org"
 # enable and configure tracing using the (currently only) tracer jaeger
@@ -210,6 +308,7 @@ users:
     password: "ihavenohosts"
 ```
 
+
 ## License
 
 dyndnsd.rb is licensed under the Apache License, Version 2.0. See LICENSE for more information.

Rakefile

@@ -1,8 +1,32 @@
+# frozen_string_literal: true
+
 require 'bundler/gem_tasks'
 require 'rspec/core/rake_task'
 require 'rubocop/rake_task'
+require 'bundler/audit/task'
 
 RSpec::Core::RakeTask.new(:spec)
 RuboCop::RakeTask.new
+Bundler::Audit::Task.new
 
-task default: [:rubocop, :spec]
+desc 'Run experimental solargraph type checker'
+task :solargraph do
+  sh 'solargraph typecheck'
+end
+
+namespace :solargraph do
+  desc 'Should be run by developer once to prepare initial solargraph usage (fill caches etc.)'
+  task :init do
+    sh 'solargraph download-core'
+  end
+end
+
+desc 'Run hadolint for Dockerfile linting'
+task :hadolint do
+  sh 'docker run --rm -i hadolint/hadolint:v1.18.0 hadolint --ignore DL3018 - < docker/Dockerfile'
+end
+
+task default: [:rubocop, :spec, 'bundle:audit', :solargraph]
+
+desc 'Run all tasks desired for CI'
+task ci: ['solargraph:init', :default, :hadolint]

bin/dyndnsd

@@ -1,4 +0,0 @@
-
-require 'dyndnsd'
-
-Dyndnsd::Daemon.run!

docker/Dockerfile

@@ -0,0 +1,15 @@
+FROM alpine:3.13.4
+
+EXPOSE 5353 8080
+
+ARG DYNDNSD_VERSION=3.3.3
+
+RUN apk --no-cache add openssl ca-certificates && \
+    apk --no-cache add ruby ruby-etc ruby-io-console ruby-json ruby-webrick && \
+    apk --no-cache add --virtual .build-deps linux-headers ruby-dev build-base tzdata && \
+    gem install --no-document dyndnsd -v ${DYNDNSD_VERSION} && \
+    # set timezone to Berlin
+    cp /usr/share/zoneinfo/Europe/Berlin /etc/localtime && \
+    apk del .build-deps
+
+ENTRYPOINT ["dyndnsd", "/etc/dyndnsd/config.yml"]

dyndnsd.gemspec

@@ -1,7 +1,6 @@
+# frozen_string_literal: true
 
-$LOAD_PATH.push File.expand_path('lib', __dir__)
-
-require 'dyndnsd/version'
+require_relative 'lib/dyndnsd/version'
 
 Gem::Specification.new do |s|
   s.name = 'dyndnsd'
@@ -9,28 +8,40 @@ Gem::Specification.new do |s|
   s.summary = 'dyndnsd.rb'
   s.description = 'A small, lightweight and extensible DynDNS server written with Ruby and Rack.'
   s.author = 'Christian Nicolai'
-  s.email = 'chrnicolai@gmail.com'
+
   s.homepage = 'https://github.com/cmur2/dyndnsd'
   s.license = 'Apache-2.0'
+  s.metadata = {
+    'bug_tracker_uri' => "#{s.homepage}/issues",
+    'changelog_uri' => "#{s.homepage}/blob/master/CHANGELOG.md",
+    'source_code_uri' => s.homepage
+  }
 
-  s.files = `git ls-files`.split($INPUT_RECORD_SEPARATOR)
-  s.test_files = s.files.grep(%r{^(test|spec|features)/})
+  s.files = `git ls-files -z`.split("\x0").select do |f|
+    f.match(%r{^(init.d|lib)/})
+  end
   s.require_paths = ['lib']
+  s.bindir = 'exe'
   s.executables = ['dyndnsd']
+  s.extra_rdoc_files = Dir['README.md', 'CHANGELOG.md', 'LICENSE']
 
-  s.required_ruby_version = '>= 2.3'
+  s.required_ruby_version = '>= 2.5'
 
-  s.add_runtime_dependency 'rack', '~> 2.0'
-  s.add_runtime_dependency 'json'
+  s.add_runtime_dependency 'async-dns', '~> 1.2.0'
+  s.add_runtime_dependency 'jaeger-client', '~> 1.1.0'
   s.add_runtime_dependency 'metriks'
-  s.add_runtime_dependency 'opentracing', '~> 0.4.0'
-  s.add_runtime_dependency 'rack-tracer', '~> 0.5.0'
-  s.add_runtime_dependency 'spanmanager', '~> 0.3.0'
-  s.add_runtime_dependency 'jaeger-client', '~> 0.4.0'
+  s.add_runtime_dependency 'opentracing', '~> 0.5.0'
+  s.add_runtime_dependency 'rack', '~> 2.0'
+  s.add_runtime_dependency 'rack-tracer', '~> 0.9.0'
+  s.add_runtime_dependency 'webrick', '>= 1.6.1'
 
   s.add_development_dependency 'bundler'
+  s.add_development_dependency 'bundler-audit', '~> 0.8.0'
+  s.add_development_dependency 'rack-test'
   s.add_development_dependency 'rake'
   s.add_development_dependency 'rspec'
-  s.add_development_dependency 'rack-test'
-  s.add_development_dependency 'rubocop', '~> 0.55.0'
+  s.add_development_dependency 'rubocop', '~> 1.12.0'
+  s.add_development_dependency 'rubocop-rake', '~> 0.5.1'
+  s.add_development_dependency 'rubocop-rspec', '~> 2.2.0'
+  s.add_development_dependency 'solargraph', '~> 0.40.0'
 end

exe/dyndnsd

@@ -0,0 +1,6 @@
+#!/usr/bin/env ruby
+# frozen_string_literal: true
+
+require 'dyndnsd'
+
+Dyndnsd::Daemon.run!

lib/dyndnsd.rb

@@ -1,5 +1,6 @@
-#!/usr/bin/env ruby
+# frozen_string_literal: true
 
+require 'date'
 require 'etc'
 require 'logger'
 require 'ipaddr'
@@ -10,10 +11,10 @@ require 'metriks'
 require 'metriks/reporter/graphite'
 require 'opentracing'
 require 'rack/tracer'
-require 'spanmanager'
 
 require 'dyndnsd/generator/bind'
 require 'dyndnsd/updater/command_with_bind_zone'
+require 'dyndnsd/updater/zone_transfer_server'
 require 'dyndnsd/responder/dyndns_style'
 require 'dyndnsd/responder/rest_style'
 require 'dyndnsd/database'
@@ -22,21 +23,32 @@ require 'dyndnsd/textfile_reporter'
 require 'dyndnsd/version'
 
 module Dyndnsd
+  # @return [Logger]
   def self.logger
     @logger
   end
 
+  # @param logger [Logger]
+  # @return [Logger]
   def self.logger=(logger)
     @logger = logger
   end
 
   class LogFormatter
+    # @param lvl [Object]
+    # @param _time [DateTime]
+    # @param _progname [String]
+    # @param msg [Object]
+    # @return [String]
     def call(lvl, _time, _progname, msg)
       format("[%s] %-5s %s\n", Time.now.strftime('%Y-%m-%d %H:%M:%S'), lvl, msg.to_s)
     end
   end
 
   class Daemon
+    # @param config [Hash{String => Object}]
+    # @param db [Dyndnsd::Database]
+    # @param updater [#update]
     def initialize(config, db, updater)
       @users = config['users']
       @domain = config['domain']
@@ -46,12 +58,15 @@ module Dyndnsd
       @db.load
       @db['serial'] ||= 1
       @db['hosts'] ||= {}
+      @updater.update(@db)
       if @db.changed?
         @db.save
-        @updater.update(@db)
       end
     end
 
+    # @param username [String]
+    # @param password [String]
+    # @return [Boolean]
     def authorized?(username, password)
       Helper.span('check_authorized') do |span|
         span.set_tag('dyndnsd.user', username)
@@ -65,6 +80,8 @@ module Dyndnsd
       end
     end
 
+    # @param env [Hash{String => String}]
+    # @return [Array{Integer,Hash{String => String},Array<String>}]
     def call(env)
       return [422, {'X-DynDNS-Response' => 'method_forbidden'}, []] if env['REQUEST_METHOD'] != 'GET'
       return [422, {'X-DynDNS-Response' => 'not_found'}, []] if env['PATH_INFO'] != '/nic/update'
@@ -72,6 +89,7 @@ module Dyndnsd
       handle_dyndns_request(env)
     end
 
+    # @return [void]
     def self.run!
       if ARGV.length != 1
         puts 'Usage: dyndnsd config_file'
@@ -96,8 +114,14 @@ module Dyndnsd
 
       # drop priviliges as soon as possible
       # NOTE: first change group than user
-      Process::Sys.setgid(Etc.getgrnam(config['group']).gid) if config['group']
-      Process::Sys.setuid(Etc.getpwnam(config['user']).uid) if config['user']
+      if config['group']
+        group = Etc.getgrnam(config['group'])
+        Process::Sys.setgid(group.gid) if group
+      end
+      if config['user']
+        user = Etc.getpwnam(config['user'])
+        Process::Sys.setuid(user.uid) if user
+      end
 
       setup_traps
 
@@ -110,6 +134,8 @@ module Dyndnsd
 
     private
 
+    # @param params [Hash{String => String}]
+    # @return [Array<String>]
     def extract_v4_and_v6_address(params)
       return [] if !(params['myip'])
       begin
@@ -121,6 +147,9 @@ module Dyndnsd
       end
     end
 
+    # @param env [Hash{String => String}]
+    # @param params [Hash{String => String}]
+    # @return [Array<String>]
     def extract_myips(env, params)
       # require presence of myip parameter as valid IPAddr (v4) and valid myip6
       return extract_v4_and_v6_address(params) if params.key?('myip6')
@@ -135,6 +164,9 @@ module Dyndnsd
       [env['REMOTE_ADDR']]
     end
 
+    # @param hostnames [String]
+    # @param myips [Array<String>]
+    # @return [Array<Symbol>]
     def process_changes(hostnames, myips)
       changes = []
       Helper.span('process_changes') do |span|
@@ -159,14 +191,17 @@ module Dyndnsd
       changes
     end
 
+    # @return [void]
     def update_db
       @db['serial'] += 1
       Dyndnsd.logger.info "Committing update ##{@db['serial']}"
-      @db.save
       @updater.update(@db)
+      @db.save
       Metriks.meter('updates.committed').mark
     end
 
+    # @param env [Hash{String => String}]
+    # @return [Array{Integer,Hash{String => String},Array<String>}]
     def handle_dyndns_request(env)
       params = Rack::Utils.parse_query(env['QUERY_STRING'])
 
@@ -205,28 +240,32 @@ module Dyndnsd
 
     # SETUP
 
+    # @param config [Hash{String => Object}]
+    # @return [void]
     private_class_method def self.setup_logger(config)
       if config['logfile']
         Dyndnsd.logger = Logger.new(config['logfile'])
       else
-        Dyndnsd.logger = Logger.new(STDOUT)
+        Dyndnsd.logger = Logger.new($stdout)
       end
 
       Dyndnsd.logger.progname = 'dyndnsd'
       Dyndnsd.logger.formatter = LogFormatter.new
+      Dyndnsd.logger.level = config['debug'] ? Logger::DEBUG : Logger::INFO
     end
 
+    # @return [void]
     private_class_method def self.setup_traps
       Signal.trap('INT') do
-        Dyndnsd.logger.info 'Quitting...'
         Rack::Handler::WEBrick.shutdown
       end
       Signal.trap('TERM') do
-        Dyndnsd.logger.info 'Quitting...'
         Rack::Handler::WEBrick.shutdown
       end
     end
 
+    # @param config [Hash{String => Object}]
+    # @return [void]
     private_class_method def self.setup_monitoring(config)
       # configure metriks
       if config['graphite']
@@ -254,6 +293,8 @@ module Dyndnsd
       end
     end
 
+    # @param config [Hash{String => Object}]
+    # @return [void]
     private_class_method def self.setup_tracing(config)
       # configure OpenTracing
       if config.dig('tracing', 'jaeger')
@@ -266,14 +307,19 @@ module Dyndnsd
           host: host, port: port, service_name: service_name, flush_interval: 1
         )
       end
-      # always use SpanManager
-      OpenTracing.global_tracer = SpanManager::Tracer.new(OpenTracing.global_tracer)
     end
 
+    # @param config [Hash{String => Object}]
+    # @return [void]
     private_class_method def self.setup_rack(config)
       # configure daemon
       db = Database.new(config['db'])
-      updater = Updater::CommandWithBindZone.new(config['domain'], config['updater']['params']) if config['updater']['name'] == 'command_with_bind_zone'
+      case config.dig('updater', 'name')
+      when 'command_with_bind_zone'
+        updater = Updater::CommandWithBindZone.new(config['domain'], config.dig('updater', 'params'))
+      when 'zone_transfer_server'
+        updater = Updater::ZoneTransferServer.new(config['domain'], config.dig('updater', 'params'))
+      end
       daemon = Daemon.new(config, db, updater)
 
       # configure rack

lib/dyndnsd/database.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 
 require 'forwardable'
 
@@ -7,19 +8,22 @@ module Dyndnsd
 
     def_delegators :@db, :[], :[]=, :each, :has_key?
 
+    # @param db_file [String]
     def initialize(db_file)
       @db_file = db_file
     end
 
+    # @return [void]
     def load
       if File.file?(@db_file)
-        @db = JSON.parse(File.open(@db_file, 'r', &:read))
+        @db = JSON.parse(File.read(@db_file, mode: 'r'))
       else
         @db = {}
       end
       @db_hash = @db.hash
     end
 
+    # @return [void]
     def save
       Helper.span('database_save') do |_span|
         File.open(@db_file, 'w') { |f| JSON.dump(@db, f) }
@@ -27,6 +31,7 @@ module Dyndnsd
       end
     end
 
+    # @return [Boolean]
     def changed?
       @db_hash != @db.hash
     end

lib/dyndnsd/generator/bind.rb

@@ -1,15 +1,20 @@
+# frozen_string_literal: true
 
 module Dyndnsd
   module Generator
     class Bind
-      def initialize(domain, config)
+      # @param domain [String]
+      # @param updater_params [Hash{String => Object}]
+      def initialize(domain, updater_params)
         @domain = domain
-        @ttl = config['ttl']
-        @dns = config['dns']
-        @email_addr = config['email_addr']
-        @additional_zone_content = config['additional_zone_content']
+        @ttl = updater_params['ttl']
+        @dns = updater_params['dns']
+        @email_addr = updater_params['email_addr']
+        @additional_zone_content = updater_params['additional_zone_content']
       end
 
+      # @param db [Dyndnsd::Database]
+      # @return [String]
       def generate(db)
         out = []
         out << "$TTL #{@ttl}"
@@ -22,7 +27,7 @@ module Dyndnsd
           ips.each do |ip|
             ip = IPAddr.new(ip).native
             type = ip.ipv6? ? 'AAAA' : 'A'
-            name = hostname.chomp('.' + @domain)
+            name = hostname.chomp(".#{@domain}")
             out << "#{name} IN #{type} #{ip}"
           end
         end

lib/dyndnsd/helper.rb

@@ -1,8 +1,12 @@
+# frozen_string_literal: true
 
 require 'ipaddr'
 
 module Dyndnsd
   class Helper
+    # @param hostname [String]
+    # @param domain [String]
+    # @return [Boolean]
     def self.fqdn_valid?(hostname, domain)
       return false if hostname.length < domain.length + 2
       return false if !hostname.end_with?(domain)
@@ -11,6 +15,8 @@ module Dyndnsd
       true
     end
 
+    # @param ip [String]
+    # @return [Boolean]
     def self.ip_valid?(ip)
       IPAddr.new(ip)
       true
@@ -18,23 +24,45 @@ module Dyndnsd
       false
     end
 
+    # @param username [String]
+    # @param password [String]
+    # @param users [Hash]
+    # @return [Boolean]
     def self.user_allowed?(username, password, users)
       (users.key? username) && (users[username]['password'] == password)
     end
 
+    # @param hostname [String]
+    # @param myips [Array]
+    # @param hosts [Hash]
+    # @return [Boolean]
     def self.changed?(hostname, myips, hosts)
       # myips order is always deterministic
       ((!hosts.include? hostname) || (hosts[hostname] != myips)) && !myips.empty?
     end
 
+    # @param operation [String]
+    # @param block [Proc]
+    # @return [void]
     def self.span(operation, &block)
-      span = OpenTracing.start_span(operation)
+      scope = OpenTracing.start_active_span(operation)
+      span = scope.span
       span.set_tag('component', 'dyndnsd')
       span.set_tag('span.kind', 'server')
       begin
         block.call(span)
+      rescue StandardError => e
+        span.set_tag('error', true)
+        span.log_kv(
+          event: 'error',
+          'error.kind': e.class.to_s,
+          'error.object': e,
+          message: e.message,
+          stack: e.backtrace&.join("\n") || ''
+        )
+        raise e
       ensure
-        span.finish
+        scope.close
       end
     end
   end

lib/dyndnsd/responder/dyndns_style.rb

@@ -1,11 +1,15 @@
+# frozen_string_literal: true
 
 module Dyndnsd
   module Responder
     class DynDNSStyle
+      # @param app [#call]
       def initialize(app)
         @app = app
       end
 
+      # @param env [Hash{String => String}]
+      # @return [Array{Integer,Hash{String => String},Array<String>}]
       def call(env)
         @app.call(env).tap do |status_code, headers, body|
           if headers.key?('X-DynDNS-Response')
@@ -18,26 +22,40 @@ module Dyndnsd
 
       private
 
+      # @param status_code [Integer]
+      # @param headers [Hash{String => String}]
+      # @param body [Array<String>]
+      # @return [Array{Integer,Hash{String => String},Array<String>}]
       def decorate_dyndnsd_response(status_code, headers, body)
-        if status_code == 200
+        case status_code
+        when 200
           [200, {'Content-Type' => 'text/plain'}, [get_success_body(body[0], body[1])]]
-        elsif status_code == 422
+        when 422
           error_response_map[headers['X-DynDNS-Response']]
         end
       end
 
+      # @param status_code [Integer]
+      # @param headers [Hash{String => String}]
+      # @param _body [Array<String>]
+      # @return [Array{Integer,Hash{String => String},Array<String>}]
       def decorate_other_response(status_code, headers, _body)
-        if status_code == 400
+        case status_code
+        when 400
           [status_code, headers, ['Bad Request']]
-        elsif status_code == 401
+        when 401
           [status_code, headers, ['badauth']]
         end
       end
 
+      # @param changes [Array<Symbol>]
+      # @param myips [Array<String>]
+      # @return [String]
       def get_success_body(changes, myips)
         changes.map { |change| "#{change} #{myips.join(' ')}" }.join("\n")
       end
 
+      # @return [Hash{String => Object}]
       def error_response_map
         {
           # general http errors

lib/dyndnsd/responder/rest_style.rb

@@ -1,11 +1,15 @@
+# frozen_string_literal: true
 
 module Dyndnsd
   module Responder
     class RestStyle
+      # @param app [#call]
       def initialize(app)
         @app = app
       end
 
+      # @param env [Hash{String => String}]
+      # @return [Array{Integer,Hash{String => String},Array<String>}]
       def call(env)
         @app.call(env).tap do |status_code, headers, body|
           if headers.key?('X-DynDNS-Response')
@@ -18,26 +22,40 @@ module Dyndnsd
 
       private
 
+      # @param status_code [Integer]
+      # @param headers [Hash{String => String}]
+      # @param body [Array<String>]
+      # @return [Array{Integer,Hash{String => String},Array<String>}]
       def decorate_dyndnsd_response(status_code, headers, body)
-        if status_code == 200
+        case status_code
+        when 200
           [200, {'Content-Type' => 'text/plain'}, [get_success_body(body[0], body[1])]]
-        elsif status_code == 422
+        when 422
           error_response_map[headers['X-DynDNS-Response']]
         end
       end
 
+      # @param status_code [Integer]
+      # @param headers [Hash{String => String}]
+      # @param _body [Array<String>]
+      # @return [Array{Integer,Hash{String => String},Array<String>}]
       def decorate_other_response(status_code, headers, _body)
-        if status_code == 400
+        case status_code
+        when 400
           [status_code, headers, ['Bad Request']]
-        elsif status_code == 401
+        when 401
           [status_code, headers, ['Unauthorized']]
         end
       end
 
+      # @param changes [Array<Symbol>]
+      # @param myips [Array<String>]
+      # @return [String]
       def get_success_body(changes, myips)
         changes.map { |change| change == :good ? "Changed to #{myips.join(' ')}" : "No change needed for #{myips.join(' ')}" }.join("\n")
       end
 
+      # @return [Hash{String => Object}]
       def error_response_map
         {
           # general http errors

lib/dyndnsd/textfile_reporter.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 
 # Adapted from https://github.com/eric/metriks-graphite/blob/master/lib/metriks/reporter/graphite.rb
 
@@ -5,8 +6,11 @@ require 'metriks'
 
 module Dyndnsd
   class TextfileReporter
+    # @return [String]
     attr_reader :file
 
+    # @param file [String]
+    # @param options [Hash{Symbol => Object}]
     def initialize(file, options = {})
       @file = file
 
@@ -14,35 +18,37 @@ module Dyndnsd
 
       @registry  = options[:registry] || Metriks::Registry.default
       @interval  = options[:interval] || 60
-      @on_error  = options[:on_error] || proc { |ex| }
+      @on_error  = options[:on_error] || proc { |ex| } # default: ignore errors
     end
 
+    # @return [void]
     def start
       @thread ||= Thread.new do
         loop do
           sleep @interval
 
           Thread.new do
-            begin
-              write
-            rescue StandardError => e
-              @on_error[e] rescue nil
-            end
+            write
+          rescue StandardError => e
+            @on_error[e] rescue nil
           end
         end
       end
     end
 
+    # @return [void]
     def stop
       @thread&.kill
       @thread = nil
     end
 
+    # @return [void]
     def restart
       stop
       start
     end
 
+    # @return [void]
     def write
       File.open(@file, 'w') do |f|
         @registry.each do |name, metric|
@@ -85,6 +91,12 @@ module Dyndnsd
       end
     end
 
+    # @param file [String]
+    # @param base_name [String]
+    # @param metric [Object]
+    # @param keys [Array<Symbol>]
+    # @param snapshot_keys [Array<Symbol>]
+    # @return [void]
     def write_metric(file, base_name, metric, keys, snapshot_keys = [])
       time = Time.now.to_i
 

lib/dyndnsd/updater/command_with_bind_zone.rb

@@ -1,26 +1,34 @@
+# frozen_string_literal: true
 
 module Dyndnsd
   module Updater
     class CommandWithBindZone
-      def initialize(domain, config)
-        @zone_file = config['zone_file']
-        @command = config['command']
-        @generator = Generator::Bind.new(domain, config)
+      # @param domain [String]
+      # @param updater_params [Hash{String => Object}]
+      def initialize(domain, updater_params)
+        @zone_file = updater_params['zone_file']
+        @command = updater_params['command']
+        @generator = Generator::Bind.new(domain, updater_params)
       end
 
-      def update(zone)
+      # @param db [Dyndnsd::Database]
+      # @return [void]
+      def update(db)
+        # do not regenerate zone file (assumed to be persistent) if DB did not change
+        return if !db.changed?
+
         Helper.span('updater_update') do |span|
-          span.set_tag('dyndnsd.updater.name', self.class.name.split('::').last)
+          span.set_tag('dyndnsd.updater.name', self.class.name&.split('::')&.last || 'None')
 
           # write zone file in bind syntax
-          File.open(@zone_file, 'w') { |f| f.write(@generator.generate(zone)) }
+          File.open(@zone_file, 'w') { |f| f.write(@generator.generate(db)) }
           # call user-defined command
           pid = fork do
             exec @command
           end
 
           # detach so children don't become zombies
-          Process.detach(pid)
+          Process.detach(pid) if pid
         end
       end
     end

lib/dyndnsd/updater/zone_transfer_server.rb

@@ -0,0 +1,158 @@
+# frozen_string_literal: true
+
+require 'resolv'
+require 'securerandom'
+
+require 'async/dns'
+
+module Dyndnsd
+  module Updater
+    class ZoneTransferServer
+      DEFAULT_SERVER_LISTENS = ['0.0.0.0@53'].freeze
+
+      # @param domain [String]
+      # @param updater_params [Hash{String => Object}]
+      def initialize(domain, updater_params)
+        @domain = domain
+
+        @server_listens = self.class.parse_endpoints(updater_params['server_listens'] || DEFAULT_SERVER_LISTENS)
+        @notify_targets = (updater_params['send_notifies'] || []).map { |e| self.class.parse_endpoints([e]) }
+
+        @zone_rr_ttl = updater_params['zone_ttl']
+        @zone_nameservers = updater_params['zone_nameservers'].map { |n| Resolv::DNS::Name.create(n) }
+        @zone_email_address = Resolv::DNS::Name.create(updater_params['zone_email_address'])
+        @zone_additional_ips = updater_params['zone_additional_ips'] || []
+
+        @server = ZoneTransferServerHelper.new(@server_listens, @domain)
+
+        # run Async::DNS server in background thread
+        Thread.new do
+          @server.run
+        end
+      end
+
+      # @param db [Dyndnsd::Database]
+      # @return [void]
+      def update(db)
+        Helper.span('updater_update') do |span|
+          span.set_tag('dyndnsd.updater.name', self.class.name&.split('::')&.last || 'None')
+
+          soa_rr = Resolv::DNS::Resource::IN::SOA.new(
+            @zone_nameservers[0], @zone_email_address,
+            db['serial'],
+            10_800,  # 3h
+            300,     # 5m
+            604_800, # 1w
+            3_600    # 1h
+          )
+
+          default_options = {ttl: @zone_rr_ttl}
+
+          # array containing all resource records for an AXFR request in the right order
+          rrs = []
+          # AXFR responses need to start with zone's SOA RR
+          rrs << [soa_rr, default_options]
+
+          # return RRs for all of the zone's nameservers
+          @zone_nameservers.each do |ns|
+            rrs << [Resolv::DNS::Resource::IN::NS.new(ns), default_options]
+          end
+
+          # return A/AAAA RRs for all additional IPv4s/IPv6s for the domain itself
+          @zone_additional_ips.each do |ip|
+            rrs << [create_addr_rr_for_ip(ip), default_options]
+          end
+
+          # return A/AAAA RRs for the dyndns hostnames
+          db['hosts'].each do |hostname, ips|
+            ips.each do |ip|
+              rrs << [create_addr_rr_for_ip(ip), default_options.merge({name: hostname})]
+            end
+          end
+
+          # AXFR responses need to end with zone's SOA RR again
+          rrs << [soa_rr, default_options]
+
+          # point Async::DNS server thread's variable to this new RR array
+          @server.axfr_rrs = rrs
+
+          # only send DNS NOTIFY if there really was a change
+          if db.changed?
+            send_dns_notify
+          end
+        end
+      end
+
+      # converts into suitable parameter form for Async::DNS::Resolver or Async::DNS::Server
+      #
+      # @param endpoint_list [Array<String>]
+      # @return [Array{Array{Object}}]
+      def self.parse_endpoints(endpoint_list)
+        endpoint_list.map { |addr_string| addr_string.split('@') }
+                     .map { |addr_parts| [addr_parts[0], addr_parts[1].to_i || 53] }
+                     .map { |addr| [:tcp, :udp].map { |type| [type] + addr } }
+                     .flatten(1)
+      end
+
+      private
+
+      # creates correct Resolv::DNS::Resource object for IP address type
+      #
+      # @param ip_string [String]
+      # @return [Resolv::DNS::Resource::IN::A,Resolv::DNS::Resource::IN::AAAA]
+      def create_addr_rr_for_ip(ip_string)
+        ip = IPAddr.new(ip_string).native
+
+        if ip.ipv6?
+          Resolv::DNS::Resource::IN::AAAA.new(ip.to_s)
+        else
+          Resolv::DNS::Resource::IN::A.new(ip.to_s)
+        end
+      end
+
+      # https://tools.ietf.org/html/rfc1996
+      #
+      # @return [void]
+      def send_dns_notify
+        Async::Reactor.run do
+          @notify_targets.each do |notify_target|
+            target = Async::DNS::Resolver.new(notify_target)
+
+            # assemble DNS NOTIFY message
+            request = Resolv::DNS::Message.new(SecureRandom.random_number(2**16))
+            request.opcode = Resolv::DNS::OpCode::Notify
+            request.add_question("#{@domain}.", Resolv::DNS::Resource::IN::SOA)
+
+            _response = target.dispatch_request(request)
+          end
+        end
+      end
+    end
+
+    class ZoneTransferServerHelper < Async::DNS::Server
+      attr_accessor :axfr_rrs
+
+      def initialize(endpoints, domain)
+        super(endpoints, logger: Dyndnsd.logger)
+        @domain = domain
+      end
+
+      # @param name [String]
+      # @param resource_class [Resolv::DNS::Resource]
+      # Since solargraph cannot parse this: param transaction [Async::DNS::Transaction]
+      # @return [void]
+      def process(name, resource_class, transaction)
+        if name != @domain || resource_class != Resolv::DNS::Resource::Generic::Type252_Class1
+          transaction.fail!(:NXDomain)
+          return
+        end
+
+        # https://tools.ietf.org/html/rfc5936
+        transaction.append_question!
+        @axfr_rrs.each do |rr|
+          transaction.add([rr[0]], rr[1])
+        end
+      end
+    end
+  end
+end

lib/dyndnsd/version.rb

@@ -1,4 +1,5 @@
+# frozen_string_literal: true
 
 module Dyndnsd
-  VERSION = '2.0.0.rc2'.freeze
+  VERSION = '3.3.3'
 end

spec/dyndnsd/daemon_spec.rb

@@ -1,10 +1,12 @@
-require 'spec_helper'
+# frozen_string_literal: true
+
+require_relative '../spec_helper'
 
 describe Dyndnsd::Daemon do
   include Rack::Test::Methods
 
   def app
-    Dyndnsd.logger = Logger.new(STDOUT)
+    Dyndnsd.logger = Logger.new($stdout)
     Dyndnsd.logger.level = Logger::UNKNOWN
 
     config = {

spec/spec_helper.rb

@@ -1,8 +1,10 @@
+# frozen_string_literal: true
 
 require 'rubygems'
 require 'bundler/setup'
 require 'rack/test'
 
 require 'dyndnsd'
-require 'support/dummy_database'
-require 'support/dummy_updater'
+
+require_relative 'support/dummy_database'
+require_relative 'support/dummy_updater'

spec/support/dummy_database.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 
 require 'forwardable'
 

spec/support/dummy_updater.rb

@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 
 module Dyndnsd
   module Updater