okapi interface is a normal interface OKAPI-1199

doc/guide.md

@@ -3010,6 +3010,11 @@ expected that this interface will remain fairly stable over time.
 The internal module was introduced in Okapi version 1.9.0, and a fully
 detailed ModuleDescriptor in version 1.10.0.
 
+The internal module is always available, but only enabled by default
+for `supertenant`.
+Other tenants must enable the okapi module to use the Okapi API.
+Individual modules should add the `okapi` interface to the `"requires"` or `"optional"` property of their module descriptor.
+
 ### Deployment
 
 Deployment is specified by schemas

okapi-core/src/main/java/org/folio/okapi/managers/InternalModule.java

@@ -119,7 +119,6 @@ public static ModuleDescriptor moduleDescriptor(String okapiVersion) {
         + " }, {"
         + "   \"id\" : \"okapi\","
         + "   \"version\" : \"" + INTERFACE_VERSION + "\","
-        + "   \"interfaceType\" : \"internal\","
         + "   \"handlers\" : [ "
         // Deployment service
         + "   {"

okapi-core/src/test/java/org/folio/okapi/util/DepResolutionTest.java

@@ -19,6 +19,7 @@
 import org.folio.okapi.bean.TenantModuleDescriptor;
 import org.folio.okapi.bean.TenantModuleDescriptor.Action;
 import org.folio.okapi.common.OkapiLogger;
+import org.folio.okapi.managers.InternalModule;
 import org.folio.okapi.testing.UtilityClassTester;
 import org.junit.Assert;
 import org.junit.Before;
@@ -1475,4 +1476,33 @@ public void permissionCheckAlreadyMentioned() {
     assertThat(errors.get(mda), contains("Undefined permission 'inta.get' in permissionsRequired"));
   }
 
+  @Test
+  public void okapiInterface() {
+    InterfaceDescriptor intOkapi = new InterfaceDescriptor("okapi", "1.0");
+
+    ModuleDescriptor mdA = new ModuleDescriptor("modA-1.0.0");
+    mdA.setRequires(new InterfaceDescriptor[]{intOkapi});
+
+    List<TenantModuleDescriptor> tml1 = enableList(mdA);
+    OkapiError error = Assert.assertThrows(OkapiError.class,
+        () -> DepResolution.install(map(mdA), map(), tml1, false));
+    assertThat(error.getMessage(), is("interface okapi required by module modA-1.0.0 not found"));
+
+    ModuleDescriptor mdOkapi = InternalModule.moduleDescriptor("1.0");
+    List<TenantModuleDescriptor> tml2 = enableList(mdA);
+    DepResolution.install(map(mdA, mdOkapi), map(mdOkapi), tml2, false);
+    assertThat(tml2, contains(enable(mdA)));
+
+    ModuleDescriptor modOkapiB = new ModuleDescriptor("modB-1.0.0");
+    modOkapiB.setProvides(new InterfaceDescriptor[]{intOkapi});
+
+    List<TenantModuleDescriptor> tml3 = enableList(mdA);
+    error = Assert.assertThrows(OkapiError.class,
+      () -> DepResolution.install(map(mdA, modOkapiB, mdOkapi), map(), tml3, false));
+    assertThat(error.getMessage(), is("interface okapi required by module modA-1.0.0 is provided by multiple products: okapi, modB"));
+
+    List<TenantModuleDescriptor> tml4 = enableList(mdA, modOkapiB);
+    DepResolution.install(map(mdA, modOkapiB, mdOkapi), map(), tml4, false);
+    assertThat(tml4, contains(enable(modOkapiB), enable(mdA)));
+  }
 }