Allow UrlRewriter to change protocol, i.e. https->http, and http->https

Fixes #13114

Closes #13115.

PiperOrigin-RevId: 360172767

Author: Denys Kurylenko

src/main/java/com/google/devtools/build/lib/bazel/repository/downloader/UrlRewriter.java

@@ -187,17 +187,24 @@ private ImmutableList<URL> applyRewriteRules(URL url) {
     }
 
     return rewrittenUrls.build().stream()
-        .map(
-            urlString -> {
-              try {
-                return new URL(url.getProtocol() + "://" + urlString);
-              } catch (MalformedURLException e) {
-                throw new IllegalStateException(e);
-              }
-            })
+        .map(urlString -> prefixWithProtocol(urlString, url.getProtocol()))
         .collect(toImmutableList());
   }
 
+  /** Prefixes url with protocol if not already prefixed by {@link #REWRITABLE_SCHEMES} */
+  private static URL prefixWithProtocol(String url, String protocol) {
+    try {
+      for (String schemaPrefix : REWRITABLE_SCHEMES) {
+        if (url.startsWith(schemaPrefix + "://")) {
+          return new URL(url);
+        }
+      }
+      return new URL(protocol + "://" + url);
+    } catch (MalformedURLException e) {
+      throw new IllegalStateException(e);
+    }
+  }
+
   @Nullable
   public String getAllBlockedMessage() {
     return config.getAllBlockedMessage();

src/test/java/com/google/devtools/build/lib/bazel/repository/downloader/UrlRewriterTest.java

@@ -212,4 +212,28 @@ public void multipleAllBlockedMessage() throws Exception {
       assertThat(e.getLocation()).isEqualTo(Location.fromFileLineColumn("/some/file", 3, 0));
     }
   }
+
+  @Test
+  public void rewritingUrlsAllowsProtocolRewrite() throws Exception {
+    String config =
+        ""
+            + "block *\n"
+            + "allow mycorp.com\n"
+            + "allow othercorp.com\n"
+            + "rewrite bad.com/foo/(.*) http://mycorp.com/$1\n"
+            + "rewrite bad.com/bar/(.*) https://othercorp.com/bar/$1\n";
+
+    UrlRewriter munger = new UrlRewriter(str -> {}, "/dev/null", new StringReader(config));
+
+    List<URL> amended =
+        munger.amend(
+            ImmutableList.of(
+                new URL("https://www.bad.com"),
+                new URL("https://bad.com/foo/bar"),
+                new URL("http://bad.com/bar/xyz")));
+
+    assertThat(amended)
+        .containsExactly(
+            new URL("http://mycorp.com/bar"), new URL("https://othercorp.com/bar/xyz"));
+  }
 }