fix: resolve relative URLs against a pathless base on Android

Android's java.net.URI resolves a relative reference against a base with an
empty path by gluing it onto the host: `y18.svg` against
`https://news.ycombinator.com` became `https://news.ycombinator.comy18.svg`,
so Hacker News' compact link preview never loaded its icon (seen on an
SM-T220). The JDK follows RFC 3986 and treats the empty path as `/`, so
normalize the base to that before resolving. Rebuilt from the raw parts so an
encoded query is not encoded twice.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

commons/src/jvmAndroid/kotlin/com/vitorpamplona/amethyst/commons/util/HttpUrlResolution.jvmAndroid.kt

@@ -29,7 +29,7 @@ actual fun resolveHttpUrl(
     reference: String,
 ): String? =
     runCatching {
-        val baseUri = base?.let { runCatching { URI(it).toURL().toURI() }.getOrNull() }
+        val baseUri = base?.let { runCatching { URI(it).toURL().toURI().withRootPath() }.getOrNull() }
         val resolved = if (baseUri != null) baseUri.resolve(reference) else URI(reference)
         if (!resolved.scheme.equals("http", ignoreCase = true) &&
             !resolved.scheme.equals("https", ignoreCase = true)
@@ -39,3 +39,23 @@ actual fun resolveHttpUrl(
             resolved.toURL().toString()
         }
     }.getOrNull()
+
+/**
+ * `https://host` as `https://host/`. RFC 3986 resolves a relative reference against an empty base path
+ * as if the path were `/`, and the JDK does, but Android's `java.net.URI` does not: it glued
+ * `y18.svg` onto `https://news.ycombinator.com` as `https://news.ycombinator.comy18.svg`, so the
+ * page's icon (or a relative og:image) pointed at a host that does not exist.
+ */
+private fun URI.withRootPath(): URI =
+    if (isOpaque || !rawPath.isNullOrEmpty() || rawAuthority == null) {
+        this
+    } else {
+        // From the raw (still-encoded) parts: the multi-argument constructor would encode them again.
+        URI(
+            buildString {
+                append(scheme).append("://").append(rawAuthority).append('/')
+                rawQuery?.let { append('?').append(it) }
+                rawFragment?.let { append('#').append(it) }
+            },
+        )
+    }

commons/src/jvmTest/kotlin/com/vitorpamplona/amethyst/commons/util/HttpUrlResolutionTest.kt

@@ -0,0 +1,56 @@
+/*
+ * Copyright (c) 2025 Vitor Pamplona
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
+ * Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
+ * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+package com.vitorpamplona.amethyst.commons.util
+
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertNull
+
+/**
+ * A relative reference against a base with no path resolves as if the path were `/` (RFC 3986).
+ * Android's `java.net.URI` got this wrong — `y18.svg` against `https://news.ycombinator.com` became
+ * `https://news.ycombinator.comy18.svg` — so the base is normalized before resolving.
+ */
+class HttpUrlResolutionTest {
+    @Test
+    fun relativeReferenceAgainstAPathlessBase() {
+        assertEquals("https://news.ycombinator.com/y18.svg", resolveHttpUrl("https://news.ycombinator.com", "y18.svg"))
+        assertEquals("https://news.ycombinator.com/favicon.ico", resolveHttpUrl("https://news.ycombinator.com", "/favicon.ico"))
+    }
+
+    @Test
+    fun pathlessBaseKeepsItsQueryAndEncoding() {
+        assertEquals("https://a.example/icon.png", resolveHttpUrl("https://a.example?q=a%20b", "icon.png"))
+        // Encoded characters are carried over as they are, not encoded a second time.
+        assertEquals("https://a.example/icons/a%20b.png", resolveHttpUrl("https://a.example?q=a%20b", "icons/a%20b.png"))
+    }
+
+    @Test
+    fun basesWithAPathAreUnchanged() {
+        assertEquals("https://a.example/dir/icon.png", resolveHttpUrl("https://a.example/dir/page.html", "icon.png"))
+        assertEquals("https://cdn.example/x.png", resolveHttpUrl("https://a.example/dir/", "//cdn.example/x.png"))
+    }
+
+    @Test
+    fun nonHttpStaysRefused() {
+        assertNull(resolveHttpUrl("https://a.example", "file:///etc/passwd"))
+    }
+}