Yield a Proxy for addresses without protocol

Addresses bazelbuild#14896

Closes bazelbuild#14897.

PiperOrigin-RevId: 431949154

Author: adamawolf

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

@@ -133,7 +133,7 @@ public static Proxy createProxy(@Nullable String proxyAddress) throws IOExceptio
 
     // Here there be dragons.
     Pattern urlPattern =
-        Pattern.compile("^(https?)://(([^:@]+?)(?::([^@]+?))?@)?([^:]+)(?::(\\d+))?/?$");
+        Pattern.compile("^(https?://)?(([^:@]+?)(?::([^@]+?))?@)?([^:]+)(?::(\\d+))?/?$");
     Matcher matcher = urlPattern.matcher(proxyAddress);
     if (!matcher.matches()) {
       throw new IOException("Proxy address " + proxyAddress + " is not a valid URL");
@@ -153,15 +153,19 @@ public static Proxy createProxy(@Nullable String proxyAddress) throws IOExceptio
     }
 
     boolean https;
-    switch (protocol) {
-      case "https":
-        https = true;
-        break;
-      case "http":
-        https = false;
-        break;
-      default:
-        throw new IOException("Invalid proxy protocol for " + cleanProxyAddress);
+    if (protocol == null) {
+      https = false;
+    } else {
+      switch (protocol) {
+        case "https://":
+          https = true;
+          break;
+        case "http://":
+          https = false;
+          break;
+        default:
+          throw new IOException("Invalid proxy protocol for " + cleanProxyAddress);
+      }
     }
 
     int port = https ? 443 : 80; // Default port numbers

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

@@ -204,18 +204,14 @@ public void testProxyExplicitPort() throws Exception {
 
   @Test
   public void testProxyNoProtocol() throws Exception {
-    IOException e =
-        assertThrows(IOException.class, () -> ProxyHelper.createProxy("my.example.com"));
-    assertThat(e).hasMessageThat().contains("Proxy address my.example.com is not a valid URL");
+    Proxy proxy = ProxyHelper.createProxy("my.example.com");
+    assertThat(proxy.toString()).endsWith(":80");
   }
 
   @Test
   public void testProxyNoProtocolWithPort() throws Exception {
-    IOException e =
-        assertThrows(IOException.class, () -> ProxyHelper.createProxy("my.example.com:12345"));
-    assertThat(e)
-        .hasMessageThat()
-        .contains("Proxy address my.example.com:12345 is not a valid URL");
+    Proxy proxy = ProxyHelper.createProxy("my.example.com:12345");
+    assertThat(proxy.toString()).endsWith(":12345");
   }
 
   @Test