Read docker location from PATH env variable on unix based systems

buildSrc/src/main/java/org/opensearch/gradle/docker/DockerSupportService.java

@@ -53,11 +53,13 @@
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.HashMap;
+import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
 import java.util.Optional;
 import java.util.stream.Collectors;
+import java.util.stream.Stream;
 
 /**
  * Build service for detecting available Docker installation and checking for compatibility with OpenSearch Docker image build
@@ -66,16 +68,24 @@
 public abstract class DockerSupportService implements BuildService<DockerSupportService.Parameters> {
 
     private static Logger LOGGER = Logging.getLogger(DockerSupportService.class);
+
+    private static String[] DEFAULT_PATH_UNIX = { "/usr/bin", "/usr/local/bin" };
+
+    // Get unix path from PATH env variable, with fallback to DEFAUL_PATH_UNIX
+    private static String[] PATH_UNIX = DockerSupportService.getUnixPath(System.getenv("PATH"), DEFAULT_PATH_UNIX);
+
     // Defines the possible locations of the Docker CLI. These will be searched in order.
-    private static String[] DOCKER_BINARIES_UNIX = { "/usr/bin/docker", "/usr/local/bin/docker" };
+    private static String[] DOCKER_BINARIES_UNIX = Arrays.stream(PATH_UNIX).map((String path) -> path + "/docker").toArray(String[]::new);
 
     private static String[] DOCKER_BINARIES_WINDOWS = {
         System.getenv("PROGRAMFILES") + "\\Docker\\Docker\\resources\\bin\\docker.exe",
         System.getenv("SystemRoot") + "\\System32\\docker.exe" /* Github Actions */ };
 
     private static String[] DOCKER_BINARIES = Os.isFamily(Os.FAMILY_WINDOWS) ? DOCKER_BINARIES_WINDOWS : DOCKER_BINARIES_UNIX;
 
-    private static String[] DOCKER_COMPOSE_BINARIES_UNIX = { "/usr/local/bin/docker-compose", "/usr/bin/docker-compose" };
+    private static String[] DOCKER_COMPOSE_BINARIES_UNIX = Arrays.stream(PATH_UNIX)
+        .map((String path) -> path + "/docker-compose")
+        .toArray(String[]::new);
 
     private static String[] DOCKER_COMPOSE_BINARIES_WINDOWS = {
         System.getenv("PROGRAMFILES") + "\\Docker\\Docker\\resources\\bin\\docker-compose.exe" };
@@ -289,6 +299,27 @@ static Map<String, String> parseOsRelease(final List<String> osReleaseLines) {
         return values;
     }
 
+    /**
+     * Visible for testing
+     *
+     * If the system is of Unix family it converts the PATH string to array, combines it with fallback
+     * path removing duplicates and returns it as array.
+     *
+     * @return an array containing PATH locations
+     */
+    static String[] getUnixPath(String pathEnvString, String[] fallbackPath) {
+        if (!Os.isFamily(Os.FAMILY_WINDOWS) && pathEnvString instanceof String) {
+            String[] resolvedUnixPath = pathEnvString.split(":");
+            Stream<String> filteredUnixPath = Arrays.stream(resolvedUnixPath).filter(path -> path.length() > 0);
+            return Stream.concat(filteredUnixPath, Arrays.stream(fallbackPath))
+                // LinkedHashSet removes duplicates and keeps the order
+                .collect(Collectors.toCollection(LinkedHashSet::new))
+                .toArray(String[]::new);
+        }
+
+        return fallbackPath;
+    }
+
     /**
      * Searches the entries in {@link #DOCKER_BINARIES} for the Docker CLI. This method does
      * not check whether the Docker installation appears usable, see {@link #getDockerAvailability()}

buildSrc/src/test/java/org/opensearch/gradle/docker/DockerSupportServiceTests.java

@@ -39,6 +39,7 @@
 import java.util.Map;
 
 import static org.opensearch.gradle.docker.DockerSupportService.deriveId;
+import static org.opensearch.gradle.docker.DockerSupportService.getUnixPath;
 import static org.opensearch.gradle.docker.DockerSupportService.parseOsRelease;
 import static org.hamcrest.CoreMatchers.equalTo;
 
@@ -123,4 +124,32 @@ public void testDeriveIdOnOracle() {
 
         assertThat("ol-6.10", equalTo(deriveId(osRelease)));
     }
+
+    public void testGetUnixPathDefault() {
+        final String[] fallbackPath = { "/usr/bin", "/usr/local/bin" };
+        final String path = null;
+
+        assertArrayEquals(fallbackPath, getUnixPath(path, fallbackPath));
+    }
+
+    public void testGetUnixPathEmptyString() {
+        final String[] fallbackPath = { "/usr/bin", "/usr/local/bin" };
+        final String path = "";
+
+        assertArrayEquals(fallbackPath, getUnixPath(path, fallbackPath));
+    }
+
+    /**
+     * Tests:
+     * 1. Duplicates are removed.
+     * 2. The order is preserved, prioritizing the order from path over the order from fallback.
+     */
+    public void testGetUnixPathWithDuplicatesAndEmptyEntries() {
+        final String[] fallbackPath = { "/usr/bin", "/usr/local/bin" };
+        final String path = "/home/User/bin:/usr/local/bin:/bin::/home/User/bin";
+
+        final String[] expected = { "/home/User/bin", "/usr/local/bin", "/bin", "/usr/bin" };
+
+        assertArrayEquals(expected, getUnixPath(path, fallbackPath));
+    }
 }