svnkit-dav checksums

CorruptingProxy.groovy

@Grab(group='org.eclipse.jetty', module='jetty-server', version='9.1.6.v20160112')
@Grab(group='org.eclipse.jetty', module='jetty-servlet', version='9.1.6.v20160112')
@Grab(group='org.eclipse.jetty', module='jetty-proxy', version='9.1.6.v20160112')
@Grab(group='com.google.guava', module='guava', version='29.0-jre')

import com.google.common.io.ByteStreams;
import org.eclipse.jetty.client.api.Request;
import org.eclipse.jetty.client.util.BytesContentProvider;
import org.eclipse.jetty.proxy.ProxyServlet;
import org.eclipse.jetty.server.Server;
import org.eclipse.jetty.servlet.ServletContextHandler;
import org.eclipse.jetty.servlet.ServletHolder;

import javax.servlet.ServletInputStream;
import javax.servlet.http.HttpServletRequest;
import java.io.IOException;

public class SvnProtocolProxy extends ProxyServlet.Transparent {

  @Override
  protected void customizeProxyRequest(Request proxyRequest, HttpServletRequest request) {
    if (isSvnPutRequest(request)) {
      try (ServletInputStream inputStream = request.getInputStream()) {
        byte[] original = ByteStreams.toByteArray(inputStream);
        byte[] corrupted = new byte[original.length];

        for (int i = 0; i < original.length; i++) {
          char c = (char) original[i];
          if (c == 'a') {
            corrupted[i] = 'z';
          } else {
            corrupted[i] = original[i];
          }
        }

        byte[][] chunks = new byte[][]{
            corrupted
        };

        proxyRequest.content(new BytesContentProvider(chunks));
      } catch (IOException ex) {
        ex.printStackTrace(System.err);
      }
    }
  }

  private boolean isSvnPutRequest(HttpServletRequest request) {
    return "PUT".equalsIgnoreCase(request.getMethod())
      && request.getHeader("X-SVN-Result-Fulltext-MD5") != null;
  }

}

Server server = new Server(8000);

ServletHolder proxyServlet = new ServletHolder(SvnProtocolProxy.class);
proxyServlet.setInitParameter("proxyTo", "http://localhost:8080/");
proxyServlet.setInitParameter("prefix", "/");

ServletContextHandler context = new ServletContextHandler();
context.addServlet(proxyServlet, "/*");

server.setHandler(context);
server.start();
server.join();

verify.sh

# first we have to create an svn repository via scm-manager
# in the following example we assume the repository scmadmin/hitchhiker was created
$ svn checkout http://localhost:8000/scm/repo/scmadmin/hitchhiker
$ cd hitchhiker
$ echo a > a.txt
$ svn add a.txt

# the corrupting proxy will replace the content of 'a' with 'z'
$ svn commit -m 'added a.txt'
Adding         a.txt
Transmitting file data .done
Committing transaction...
Committed revision 1.

# the local copy contains 'a' but the server has 'z'
$ svn commit -m 'update a.txt'
Sending        a.txt
Transmitting file data .svn: E200014: Commit failed (details follow):
svn: E200014: svn: E200014: Base checksum mismatch on '/a.txt':
   expected:  60b725f10c9c85c70d97880dfe8191b3
     actual:  a8a78d0ff555c931f045b6f448129846

$ cd ..
$ rm -rf hitchhiker
$ svn checkout http://localhost:8000/scm/repo/scmadmin/hitchhiker
A    hitchhiker/a.txt
Checked out revision 1.

$ cat hitchhiker/a.txt
z

# but the repository on the server side does not know about the corruption
$ svnadmin verify ${SCM_HOME}/repositories/idOfRepository/data 
* Verifying repository metadata ...
* Verified revision 0.
* Verified revision 1.