Support --add-host with defaults for linux

Add a new `--add-host` multi flag to the `kl network start` command
which allows configuring additional hosts on the proxy container.

In addition to this, on linux, the `host.docker.internal:172.17.0.1`
host is added to be consistent with macos.

Author: julienvincent

README.md

@@ -95,7 +95,7 @@ Now you can start the docker network and proxy containers:
 kl network start
 ```
 
-> [!NOTE]  
+> [!NOTE]
 > On linux the host DNS network container's port defaults to binding to `5343`. If you would like to change this you can start the networking components with a different port by running `kl network start --host-dns-port=<custom-port>`. You will then also need to update your `/etc/systemd/resolved.conf` file to match.
 
 ---
@@ -208,18 +208,16 @@ Below are some common ways of addressing services running in different contexts:
   + `http://example:8080`
   + `http://<container-ip>:8080`
 + A process running on the host and bound to port `8080` could be addressed as
-  + On macos - `http://host.docker.internal:8080`
+  + On macos and linux* - `http://host.docker.internal:8080`
   + On linux - `http://172.17.0.1:8080`
 
-Because of this host address discrepancy between linux and macos it is highly recommended for **linux based users** to add the following to their `/etc/hosts` file:
-
-```bash
-172.17.0.1 host.docker.internal
-```
-
-**DO NOT** do this if you are on macos.
-
-This is an acceptable compromise to allow for a stable way of addressing the host in module configs that are intended to be consumed by developers on different operating systems.
+> [!NOTE]
+> 
+> On **linux\*** docker does not configure the `host.docker.internal` domain which is typically only available on macos when using something like Docker Desktop.
+>
+> To allow for a consistent way of addressing the host that works across all operating systems kl manually adds the `host.docker.internal:172.17.0.1` host to to the proxy container.
+>
+> If you don't want this behaviour you can disable it by running `kl network start --add-host "host.docker.internal:"` (note the empty ip after the ':').
 
 ## Routes
 

src/k16/kl/commands/network.clj

@@ -31,16 +31,38 @@
 
     module))
 
-(defn- start-network! [{:keys [host-dns host-dns-port]}]
+(def ^:private os
+  (-> (System/getProperty "os.name") .toLowerCase))
+
+(def ^:private default-hosts
+  (cond
+    (str/includes? os "linux") ["host.docker.internal:172.17.0.1"]
+    :else []))
+
+(defn- start-network! [{:keys [host-dns host-dns-port add-host]}]
   (let [workdir (api.fs/from-config-dir ".kl/network")
+
+        extra-hosts (->> (concat default-hosts add-host)
+                         (reduce (fn [acc host]
+                                   (let [[host ip] (str/split host #":")]
+                                     (assoc acc host ip)))
+                                 {})
+                         (filter (fn [[_ ip]]
+                                   (and ip (not= "" ip))))
+                         (map (fn [[host ip]] (str host ":" ip))))
+
         module (cond-> (write-network-module)
                  (not host-dns)
                  (assoc-in [:containers :dnsmasq-external :enabled]
                            false)
 
                  host-dns-port
                  (assoc-in [:containers :dnsmasq-external :ports]
-                           [(str host-dns-port ":53/udp") (str host-dns-port ":53/tcp")]))]
+                           [(str host-dns-port ":53/udp") (str host-dns-port ":53/tcp")])
+
+                 (seq extra-hosts)
+                 (assoc-in [:containers :proxy :extra_hosts]
+                           extra-hosts))]
 
     (api.proxy/write-proxy-config! {:module-name "kl"
                                     :module module})
@@ -61,11 +83,10 @@
     (api.fs/rm-dir! workdir)))
 
 (def ^:private default-port
-  (let [os (-> (System/getProperty "os.name") .toLowerCase)]
-    (cond
-      (str/includes? os "mac") "53"
-      (str/includes? os "linux") "5343"
-      :else "5343")))
+  (cond
+    (str/includes? os "mac") "53"
+    (str/includes? os "linux") "5343"
+    :else "5343"))
 
 (def cmd
   {:command "network"
@@ -79,6 +100,9 @@
                           :type :with-flag}
                          {:option "host-dns-port"
                           :default default-port
+                          :type :string}
+                         {:option "add-host"
+                          :multiple true
                           :type :string}]
 
                   :runs start-network!}