Better error reporting in nacl helper.

chrome/nacl/nacl_helper_linux.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // A mini-zygote specifically for Native Client.
 
 #include "chrome/common/nacl_helper_linux.h"
 
 #include <errno.h>
 #include <link.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <sys/socket.h>
 #include <sys/types.h>
 
 #include <string>
 #include <vector>
 
 #include "base/at_exit.h"
 #include "base/command_line.h"
 #include "base/eintr_wrapper.h"
 #include "base/global_descriptors_posix.h"
+#include "base/json/string_escape.h"
 #include "base/logging.h"
 #include "base/message_loop.h"
 #include "base/posix/unix_domain_socket.h"
 #include "base/rand_util.h"
 #include "chrome/nacl/nacl_listener.h"
 #include "crypto/nss_util.h"
 #include "ipc/ipc_descriptors.h"
 #include "ipc/ipc_switches.h"
 
 namespace {
@@ skipping 183 matching lines @@
   while (true) {
     int badpid = -1;
     std::vector<int> fds;
     static const unsigned kMaxMessageLength = 2048;
     char buf[kMaxMessageLength];
     const ssize_t msglen = UnixDomainSocket::RecvMsg(kNaClZygoteDescriptor,
                                                      &buf, sizeof(buf), &fds);
     if (msglen == 0 || (msglen == -1 && errno == ECONNRESET)) {
       // EOF from the browser. Goodbye!
       _exit(0);
-    }
-    if (msglen == sizeof(kNaClForkRequest) - 1 &&
-        memcmp(buf, kNaClForkRequest, msglen) == 0) {
+    } else if (msglen < 0) {
+      LOG(ERROR) << "nacl_helper: receive from zygote failed, errno = "
+                 << errno;
+    } else if (msglen == sizeof(kNaClForkRequest) - 1 &&
+               memcmp(buf, kNaClForkRequest, msglen) == 0) {
       if (kNaClParentFDIndex + 1 == fds.size()) {
         HandleForkRequest(fds, prereserved_sandbox_size);
         continue;  // fork succeeded. Note: child does not return
       } else {
         LOG(ERROR) << "nacl_helper: unexpected number of fds, got "
                    << fds.size();
       }
     } else {
-      if (msglen != 0) {
-        LOG(ERROR) << "nacl_helper unrecognized request: %s";
-        _exit(-1);
-      }
+      LOG(ERROR) << "nacl_helper unrecognized request: "
+                 << base::GetDoubleQuotedJson(std::string(buf, buf + msglen));
+      _exit(-1);
     }
     // if fork fails, send PID=-1 to zygote
     if (!UnixDomainSocket::SendMsg(kNaClZygoteDescriptor, &badpid,
                                    sizeof(badpid), empty)) {
       LOG(ERROR) << "*** send() to zygote failed";
     }
   }
   CHECK(false);  // This routine must not return
 }