Request Bodies and Java

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Request Bodies and Java

There's RFCs and there's the real world. Unfortunately, these two don't always play together. RFC 2616 defines HTTP methods and their rules and then there's an the implementation in Java's HttpURLConnection.

RFC 2616 states

The presence of a message-body in a request is signaled by the inclusion of a Content-Length or Transfer-Encoding header field in the request's message-headers. A message-body MUST NOT be included in a request if the specification of the request method (section 5.1.1) does not allow sending an entity-body in requests. A server SHOULD read and forward a message-body on any request; if the request method does not include defined semantics for an entity-body, then the message-body SHOULD be ignored when handling the request.

In plain english, this means that if you're sending a request body then servers should always forward it, even if they don't use it, unless the specification for that method type forbids bodies explicitly (Like the TRACE method). So when you're working with ElasticSearch or with a custom application that expects a request body in say, a GET or a DELETE request, you'd expect the body to make it to the server.

java.net.ProtocolException: HTTP method DELETE doesn't support output at sun.net.www.protocol.http.HttpURLConnection.getOutputStream(HttpURLConnection.java:1082)

Oops, because of a bug, you can't do this in java versions less than 1.7 for non-https connections.

The reason for this is the code around the getOutputStream method within the HttpURLConnection class:

if (method.equals("GET")) {
   method = "POST"; // Backward compatibility
}
if (!"POST".equals(method) && !"PUT".equals(method) &&
   "http".equals(url.getProtocol())) {
   throw new ProtocolException("HTTP method " + method +
                               " doesn't support output");
}

Why and when only POST and PUT were allowed to have output is beyond me (I don't want to try to read the file log without a blame tool to inspect those lines). But it is fixed in Java 8. But the fix has not been backported to java 6 or 7 unfortunately.

Perhaps the oddest thing is that the "work around" for needing to send a body with a DELETE request. The work around is to use HTTPS rather than HTTP. I've scanned the latest RFC, RFC 7230 Section 3.3, and haven't found any indication of why the http.equals(url.getProtocol()) line exists (But if you know, please comment and tell me where to read). Luckily, because Let's Encrypt exists, you can get a certificate to have a valid HTTPS connection without having to shell out hundreds of dollars for it. Regardless, it would still be nice if the fix was backported to Java 6 & 7.

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