Normalize remote web publication locators

readium/navigator/src/main/java/org/readium/r2/navigator/extensions/Publication.kt

@@ -10,10 +10,12 @@
 package org.readium.r2.navigator.extensions
 
 import kotlinx.coroutines.runBlocking
-import org.readium.r2.shared.InternalReadiumApi
+import org.readium.r2.shared.DelicateReadiumApi
 import org.readium.r2.shared.publication.Locator
 import org.readium.r2.shared.publication.Publication
+import org.readium.r2.shared.publication.UrlHref
 import org.readium.r2.shared.publication.services.positions
+import org.readium.r2.shared.util.AbsoluteUrl
 import org.readium.r2.shared.util.Url
 
 // These extensions will be removed in the next release, with `PositionsService`.
@@ -22,18 +24,29 @@ internal val Publication.positionsByResource: Map<Url, List<Locator>>
     get() = runBlocking { positions().groupBy { it.href } }
 
 /**
- * Historically, we used to have "absolute" HREFs starting with a `/` in the manifest for packaged
- * publications. We removed the root prefix, but we still need to support the locators created with
- * the old HREFs.
+ * Historically, we used to have "absolute" HREFs in the manifest:
+ *   - starting with a `/` for packaged publications.
+ *   - resolved to the `self` link for remote publications.
+ *
+ * We removed the normalization and now use relative HREFs everywhere, but we still need to support
+ * the locators created with the old absolute HREFs.
  */
-@InternalReadiumApi
+@DelicateReadiumApi
 public fun Publication.normalizeLocator(locator: Locator): Locator {
-    if (linkWithRel("self") != null) {
-        return locator
-    }
+    val self = (linkWithRel("self")?.href as? UrlHref)?.url as? AbsoluteUrl
 
-    return locator.copy(
-        href = Url(locator.href.toString().removePrefix("/"))
-            ?: return locator
-    )
+    return if (self == null) { // Packaged publication
+        locator.copy(
+            href = Url(locator.href.toString().removePrefix("/"))
+                ?: return locator
+        )
+    } else { // Remote publication
+        // Check that the locator HREF relative to `self` exists int he manifest.
+        val relativeHref = self.relativize(locator.href)
+        if (linkWithHref(relativeHref) != null) {
+            locator.copy(href = relativeHref)
+        } else {
+            locator
+        }
+    }
 }