/etc/scion/hosts and /etc/resolv.conf (#40)

* /etc/scion/hosts and /etc/resolv.conf --------- Co-authored-by: Tilmann Zäschke <tilmann.zaeschke@inf.ethz.ch>
scionproto-contrib · Apr 3, 2024 · 40a1418 · 40a1418
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diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -7,11 +7,12 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 ## [Unreleased]
 ### Added
 - Code coverage. [#11](https://github.com/tzaeschke/phtree-cpp/pull/11)
-- Global JUnit callback for initial setup. THis allows setting global properties before cantrally
+- Global JUnit callback for initial setup. THis allows setting global properties before centrally
   before running any tests.
   [#38](https://github.com/netsec-ethz/scion-java-client/pull/38)
-
-
+- Support for `/etc/scion/hosts` and for OS search domains (e.g. `/etc/resolv.conf`). 
+  [#40](https://github.com/netsec-ethz/scion-java-client/pull/40)
+
 ### Changed
 - BREAKING CHANGE: Changed maven artifactId to "client"
   [#9](https://github.com/netsec-ethz/scion-java-client/pull/9)

diff --git a/README.md b/README.md
@@ -24,7 +24,6 @@ The following artifact contains the complete SCION Java client:
 - `DatagramSocket` and `DatagramPacket`
 - `Selector` for `DatagramChannel`
 - Path creation with short-cuts, on-path and peering routes
-- `/etc/scion/hosts` and `/etc/hosts`, see https://github.com/netsec-ethz/scion-apps
 - Improve docs, demos and testing
 - EPIC, path authentication and other SCION features
 - TCP
@@ -80,10 +79,11 @@ Supported:
 - Path selection policies
 - Path expiry/refresh
 - Packet validation
-- DNS/TXT scion entry lookup
+- SCION address lookup via DNS/TXT entry or `/etc/scion/hosts` 
+  (see https://github.com/netsec-ethz/scion-apps)
 - Configurable:
   - daemon address
-  - bootstrapping via topo file, bootstrapper IP or DNS 
+  - bootstrapping via topo file, bootstrapper IP, DNS NAPTR entry or /etc/resolv.conf 
   - path expiry
 - Packet inspector for debugging
 - No "dispatcher"
@@ -171,31 +171,33 @@ For proper testing it is recommended to use one of the following:
 In order to find a path to a destination IP, a `DatagramChannel` or `DatagramSocket` must know the 
 ISD/AS numbers of the destination.
 
-
 If the destination host has a DNS TXT entry for SCION then this be used to determine the 
-destination ISD/AS.
-Alternatively, the ISD/AS can be specified explicitly.
-
-#### DNS lookup
-```
-$ dig TXT ethz.ch
-...
-ethz.ch.		610	IN	TXT	"scion=64-2:0:9,129.132.230.98"
-...
+destination ISD/AS. For example, if `dig TXT your-domain.org` returns something like
+`your-domain.org.		610	IN	TXT	"scion=64-2:0:9,129.x.x.x"`, then you can simply
+use something like:
+```java
+InetSocketAddress serverAddress = new InetSocketAddress("your-domain.org", 80);
+channel.connect(serverAddress);
 ```
 
+Alternatively, the ISD/AS can be specified explicitly in several ways.
+
+#### /etc/scion/hosts file
+
+Create a file `/etc/scion/hosts` to assign ISD/AS ans SCION IP to host names:
 ```
-InetSocketAddress serverAddress = new InetSocketAddress("ethz.ch", 80);
-channel.connect(serverAddress);
+# /etc/scion/hosts test file
+1-ff00:0:111,[42.0.0.11] test-server
+1-ff00:0:112,[42.0.0.12] test-server-1 test-server-2
+1-ff00:0:113,[::42] test-server-ipv6
 ```
 
-
-#### Explicit ISD/AS specification
+#### Specify ISD/AS in program
 
 We can use the ISD/AS directly to request a path:
 ```
 long isdAs = ScionUtil.parseIA("64-2:0:9");
-InetSocketAddress serverAddress = new InetSocketAddress("129.132.19.216", 80);
+InetSocketAddress serverAddress = new InetSocketAddress("129.x.x.x", 80);
 Path path = Scion.defaultService().getPaths(isdAs, serverAddress).get(0);
 channel.connect(path);
 ```
@@ -246,32 +248,44 @@ The following standard options are **not** supported:
 ## Configuration
 
 ### Bootstrapping / daemon
-In order to find paths and connect to the local AS, the application needs either a [local 
-installation of SCION](https://docs.scion.org/en/latest/dev/run.html) 
-or some other means to get bootstrap information.
+The SCION Java client can be used with a local daemon or in standalone mode (without daemon).
+The daemon is available if you have a [local installation of SCION](https://docs.scion.org/en/latest/dev/run.html).
+Standalone mode will directly connect to a topology server and control server, in a properly
+configured AS this should all happen automatically.
+
+There are also several methods that allow specifying a local topology file, a topology server 
+address or a different DNS server with a scion NAPTR record. These are only meant for debugging. 
 
 The method `Scion.defaultService()` (internally called by `DatagramChannel.open()`) will 
 attempt to get network information in the following order until it succeeds:
-- Check for local topology file (if file name is given)
-- Check for bootstrap server address (if address is given)
-- Check for DNS NAPTR record (if record entry name is given)
+- For debugging: Check for local topology file (if file name is given)
+- For debugging: Check for bootstrap server address (if address is given)
+- For debugging: Check for DNS NAPTR record (if record entry name is given)
 - Check for to daemon
+- Check search domain (as given in /etc/resolv.conf) for topology server
 
 The reason that the daemon is checked last is that it has a default setting (`localhost:30255`) 
 while the other options are skipped if no property or environment variable is defined. 
 
-| Option                              | Java property                    | Environment variable         | Default value   |
-|-------------------------------------|----------------------------------|------------------------------|-----------------|
-| Daemon port                         | `org.scion.daemon.port`          | `SCION_DAEMON`               | localhost:30255 | 
-| Bootstrap topology file path        | `org.scion.bootstrap.topoFile`   | `SCION_BOOTSTRAP_TOPO_FILE`  |                 | 
-| Bootstrap server host               | `org.scion.bootstrap.host`       | `SCION_BOOTSTRAP_HOST`       |                 |
-| Bootstrap DNS NAPTR entry host name | `org.scion.bootstrap.naptr.name` | `SCION_BOOTSTRAP_NAPTR_NAME` |                 | 
-
-### Other
-
-| Option                                                                                                               | Java property           | Environment variable | Default value |
-|----------------------------------------------------------------------------------------------------------------------|-------------------------|----------------------|---------------|
-| Path expiry margin. Before sending a packet a new path is requested if the path is about to expire within X seconds. | `org.scion.pathExpiryMargin` | `SCION_PATH_EXPIRY_MARGIN`  | 10           |
+| Option                              | Java property                    | Environment variable          | Default value   |
+|-------------------------------------|----------------------------------|-------------------------------|-----------------|
+| Daemon port                         | `org.scion.daemon.port`          | `SCION_DAEMON`                | localhost:30255 | 
+| Bootstrap topology file path        | `org.scion.bootstrap.topoFile`   | `SCION_BOOTSTRAP_TOPO_FILE`   |                 | 
+| Bootstrap server host               | `org.scion.bootstrap.host`       | `SCION_BOOTSTRAP_HOST`        |                 |
+| Bootstrap DNS NAPTR entry host name | `org.scion.bootstrap.naptr.name` | `SCION_BOOTSTRAP_NAPTR_NAME`  |                 | 
+| Bootstrap DNS NAPTR entry host name | `org.scion.test.useOsSearchDomains` | `SCION_USE_OS_SEARCH_DOMAINS` | true            | 
+
+### DNS
+The SCION Java client will check the OS default DNS server to resolve SCION addresses.
+In addition, addresses can be specified in a `/etc/scion/hosts` file. The location of the hosts file
+is configurable, see next section.  
+
+### Other Options
+
+| Option                                                                                                               | Java property           | Environment variable | Default value      |
+|----------------------------------------------------------------------------------------------------------------------|-------------------------|----------------------|--------------------|
+| Path expiry margin. Before sending a packet a new path is requested if the path is about to expire within X seconds. | `org.scion.pathExpiryMargin` | `SCION_PATH_EXPIRY_MARGIN`  | 10                 |
+| Location of `hosts` file. Multiple location can be specified separated by `;`.                                       | `org.scion.hostsFiles` | `SCION_HOSTS_FILES`  | `/etc/scion/hosts` |
 
 ## FAQ / trouble shooting
 

diff --git a/pom.xml b/pom.xml
@@ -32,7 +32,7 @@
         <scion.maven-plugin-plugin.version>3.8.2</scion.maven-plugin-plugin.version>
         <scion.maven-resources-plugin.version>3.3.1</scion.maven-resources-plugin.version>
         <scion.maven-source-plugin.version>3.2.1</scion.maven-source-plugin.version>
-        <scion.maven-surefire-plugin.version>3.0.0</scion.maven-surefire-plugin.version>
+        <scion.maven-surefire-plugin.version>3.1.2</scion.maven-surefire-plugin.version>
         <scion.nexus-staging-maven-plugin.version>1.6.13</scion.nexus-staging-maven-plugin.version>
     </properties>
 
@@ -101,7 +101,7 @@
 
         <dependency>
             <groupId>org.junit.jupiter</groupId>
-            <artifactId>junit-jupiter</artifactId>
+            <artifactId>junit-jupiter-engine</artifactId>
             <version>${scion.junit.version}</version>
             <scope>test</scope>
         </dependency>
@@ -281,7 +281,7 @@
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-surefire-plugin</artifactId>
-                <version>3.1.2</version>
+                <version>${scion.maven-surefire-plugin.version}</version>
             </plugin>
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>

diff --git a/src/main/java/org/scion/Constants.java b/src/main/java/org/scion/Constants.java
@@ -40,12 +40,35 @@ public final class Constants {
   /** Paths are refreshed when their expiry is less than X seconds away. */
   public static final String ENV_PATH_EXPIRY_MARGIN = "SCION_PATH_EXPIRY_MARGIN";
 
+  /**
+   * Semicolon separated list of full paths of SCION hosts files. On Linux the default is
+   * "/etc/scion/hosts".
+   */
+  public static final String PROPERTY_HOSTS_FILES = "org.scion.hostsFiles";
+
+  /**
+   * Semicolon separated list of full paths of SCION hosts files. On Linux the default is
+   * "/etc/scion/hosts".
+   */
+  public static final String ENV_HOSTS_FILES = "SCION_HOSTS_FILES";
+
   /** Time (in seconds) before expiration at which a paths is automatically renewed. */
   public static final int DEFAULT_PATH_EXPIRY_MARGIN = 10;
 
+  /**
+   * Disable usage of OS search domains for DNS lookup, e.g from /etc/resolv.conf. This needs to be
+   * disabled for JUnit testing.
+   */
+  public static final String PROPERTY_USE_OS_SEARCH_DOMAINS = "SCION_USE_OS_SEARCH_DOMAINS";
+
+  public static final String ENV_USE_OS_SEARCH_DOMAINS = "org.scion.test.useOsSearchDomains";
+  public static final boolean DEFAULT_USE_OS_SEARCH_DOMAINS = true;
+
   /**
    * Non-public property that allows specifying DNS TXT entries for debugging. Example with two
    * entries: server1.com="scion=1-ff00:0:110,127.0.0.1";server2.ch="scion=1-ff00:0:112,::1"
    */
   static final String DEBUG_PROPERTY_MOCK_DNS_TXT = "DEBUG_SCION_MOCK_DNS_TXT";
+
+  private Constants() {}
 }