Detect missing colon when parsing http headers with no value (#9871)

Motivation:

Technical speaking its valid to have http headers with no values so we should support it. That said we need to detect if these are "generated" because of an "invalid" fold.

Modifications:

- Detect if a colon is missing when parsing headers.
- Add unit test

Result:

Fixes https://github.com/netty/netty/issues/9866

codec-http/src/main/java/io/netty/handler/codec/http/HttpObjectDecoder.java

@@ -743,6 +743,11 @@ public abstract class HttpObjectDecoder extends ByteToMessageDecoder {
             }
         }
 
+        if (nameEnd == length) {
+            // There was no colon present at all.
+            throw new IllegalArgumentException("No colon found");
+        }
+
         for (colonEnd = nameEnd; colonEnd < length; colonEnd ++) {
             if (sb.charAtUnsafe(colonEnd) == ':') {
                 colonEnd ++;

codec-http/src/test/java/io/netty/handler/codec/http/HttpRequestDecoderTest.java

@@ -334,4 +334,20 @@ public class HttpRequestDecoderTest {
         assertTrue(request.decoderResult().cause() instanceof IllegalArgumentException);
         assertFalse(channel.finish());
     }
+
+    @Test
+    public void testHeaderWithNoValueAndMissingColon() {
+        EmbeddedChannel channel = new EmbeddedChannel(new HttpRequestDecoder());
+        String requestStr = "GET /some/path HTTP/1.1\r\n" +
+                "Content-Length: 0\r\n" +
+                "Host:\r\n" +
+                "netty.io\r\n\r\n";
+
+        assertTrue(channel.writeInbound(Unpooled.copiedBuffer(requestStr, CharsetUtil.US_ASCII)));
+        HttpRequest request = channel.readInbound();
+        System.err.println(request.headers().names().toString());
+        assertTrue(request.decoderResult().isFailure());
+        assertTrue(request.decoderResult().cause() instanceof IllegalArgumentException);
+        assertFalse(channel.finish());
+    }
 }