[net/dns] Instrument DnsConfigService to measure performance and failures.

net/dns/dns_config_service_posix.cc

Index: net/dns/dns_config_service_posix.cc
diff --git a/net/dns/dns_config_service_posix.cc b/net/dns/dns_config_service_posix.cc
index 5daaf69aac7b1c1357d08ce7b099a83eac75c56f..4428c97abfda226eb3400bfd7f57390b1e91b092 100644
--- a/net/dns/dns_config_service_posix.cc
+++ b/net/dns/dns_config_service_posix.cc
@@ -11,6 +11,8 @@
 #include "base/file_path.h"
 #include "base/file_util.h"
 #include "base/memory/scoped_ptr.h"
+#include "base/metrics/histogram.h"
+#include "base/time.h"
 #include "net/base/ip_endpoint.h"
 #include "net/base/net_util.h"
 #include "net/dns/dns_hosts.h"
@@ -19,6 +21,7 @@
 
 namespace net {
 
+#if !defined(OS_ANDROID)
 namespace {
 
 #ifndef _PATH_RESCONF  // Normally defined in <resolv.h>
@@ -27,6 +30,24 @@ namespace {
 
 const FilePath::CharType* kFilePathHosts = FILE_PATH_LITERAL("/etc/hosts");
 
+enum ConfigParsePosixResult {
+  CONFIG_PARSE_POSIX_OK = 0,
+  CONFIG_PARSE_POSIX_RES_INIT_FAILED,
+  CONFIG_PARSE_POSIX_RES_INIT_UNSET,
+  CONFIG_PARSE_POSIX_BAD_ADDRESS,
+  CONFIG_PARSE_POSIX_BAD_EXT_STRUCT,
+  CONFIG_PARSE_POSIX_NULL_ADDRESS,
+  CONFIG_PARSE_POSIX_NO_NAMESERVERS,
+  CONFIG_PARSE_POSIX_MISSING_OPTIONS,
+  CONFIG_PARSE_POSIX_UNHANDLED_OPTIONS,
+  CONFIG_PARSE_POSIX_MAX  // Bounding values for enumeration.
+};
+
+static void RecordConfigParseResult(ConfigParsePosixResult result) {
+  UMA_HISTOGRAM_ENUMERATION("AsyncDNS.ConfigParsePosix",
+                            result, CONFIG_PARSE_POSIX_MAX);
+}
+
 // A SerialWorker that uses libresolv to initialize res_state and converts
 // it to DnsConfig.
 class ConfigReader : public SerialWorker {
@@ -36,21 +57,25 @@ class ConfigReader : public SerialWorker {
       : callback_(callback), success_(false) {}
 
   void DoWork() OVERRIDE {
+    base::TimeTicks start_time = base::TimeTicks::Now();
     success_ = false;
-#if defined(OS_ANDROID)
-    NOTIMPLEMENTED();
-#elif defined(OS_OPENBSD)
+#if defined(OS_OPENBSD)
     // Note: res_ninit in glibc always returns 0 and sets RES_INIT.
     // res_init behaves the same way.
     memset(&_res, 0, sizeof(_res));
-    if ((res_init() == 0) && (_res.options & RES_INIT))
+    if (res_init() == 0) {
       success_ = internal::ConvertResStateToDnsConfig(_res, &dns_config_);
+    } else {
+      RecordConfigParseResult(CONFIG_PARSE_POSIX_RES_INIT_FAILED);
+    }
 #else  // all other OS_POSIX
     struct __res_state res;
     memset(&res, 0, sizeof(res));
-    if ((res_ninit(&res) == 0) && (res.options & RES_INIT))
+    if (res_ninit(&res) == 0) {
       success_ = internal::ConvertResStateToDnsConfig(res, &dns_config_);
-
+    } else {
+      RecordConfigParseResult(CONFIG_PARSE_POSIX_RES_INIT_FAILED);
+    }
     // Prefer res_ndestroy where available.
 #if defined(OS_MACOSX) || defined(OS_FREEBSD)
     res_ndestroy(&res);
@@ -58,6 +83,9 @@ class ConfigReader : public SerialWorker {
     res_nclose(&res);
 #endif
 #endif
+    UMA_HISTOGRAM_BOOLEAN("AsyncDNS.ConfigParseResult", success_);

[mmenke, 2012/06/18 17:19:50]

Do these give us anything that AsyncDNS.ConfigParsePosix does not?

[szym, 2012/06/18 20:53:08]

They would share the name across platforms. Not sure if this benefit is worth an
extra histogram.

[mmenke, 2012/06/18 20:55:56]

They wouldn't, though, since the windows one is called
"AsyncDNS.ConfigParseWinResult" (Notice the Win).

[szym, 2012/06/18 20:59:55]

That was my mistake. Notice that initially both read "ConfigParseResult". I have
no strong feeling about it though, since the data can be retrieved from the
platform-specific histograms.

+    UMA_HISTOGRAM_TIMES("AsyncDNS.ConfigParseDuration",
+                        base::TimeTicks::Now() - start_time);
   }
 
   void OnWorkFinished() OVERRIDE {
@@ -91,7 +119,11 @@ class HostsReader : public SerialWorker {
   virtual ~HostsReader() {}
 
   virtual void DoWork() OVERRIDE {
+    base::TimeTicks start_time = base::TimeTicks::Now();
     success_ = ParseHostsFile(path_, &hosts_);
+    UMA_HISTOGRAM_BOOLEAN("AsyncDNS.HostParseResult", success_);
+    UMA_HISTOGRAM_TIMES("AsyncDNS.HostsParseDuration",
+                        base::TimeTicks::Now() - start_time);
   }
 
   virtual void OnWorkFinished() OVERRIDE {
@@ -150,11 +182,13 @@ void DnsConfigServicePosix::OnDNSChanged(unsigned detail) {
   }
 }
 
-#if !defined(OS_ANDROID)
 bool ConvertResStateToDnsConfig(const struct __res_state& res,
                                 DnsConfig* dns_config) {

[mmenke, 2012/06/18 17:19:50]

Optional:  I'd suggest making this return a ConfigParsePosixResult.  The
advantage of this is it guarantees every leaf logs a result, and it lets you do
all the histogram recording in one place.

Downside is you'd have to expose the enum in the header, or write a wrapper
function, though the former would let unit tests check the exact failure reason.

   CHECK(dns_config != NULL);
-  DCHECK(res.options & RES_INIT);
+  if (!(res.options & RES_INIT)) {
+    RecordConfigParseResult(CONFIG_PARSE_POSIX_RES_INIT_UNSET);
+    return false;
+  }
 
   dns_config->nameservers.clear();
 
@@ -168,6 +202,7 @@ bool ConvertResStateToDnsConfig(const struct __res_state& res,
     if (!ipe.FromSockAddr(
             reinterpret_cast<const struct sockaddr*>(&addresses[i]),
             sizeof addresses[i])) {
+      RecordConfigParseResult(CONFIG_PARSE_POSIX_BAD_ADDRESS);
       return false;
     }
     dns_config->nameservers.push_back(ipe);
@@ -191,10 +226,13 @@ bool ConvertResStateToDnsConfig(const struct __res_state& res,
       addr = reinterpret_cast<const struct sockaddr*>(res._u._ext.nsaddrs[i]);
       addr_len = sizeof *res._u._ext.nsaddrs[i];
     } else {
+      RecordConfigParseResult(CONFIG_PARSE_POSIX_BAD_EXT_STRUCT);
       return false;
     }
-    if (!ipe.FromSockAddr(addr, addr_len))
+    if (!ipe.FromSockAddr(addr, addr_len)) {
+      RecordConfigParseResult(CONFIG_PARSE_POSIX_BAD_ADDRESS);
       return false;
+    }
     dns_config->nameservers.push_back(ipe);
   }
 #else  // !(defined(OS_LINUX) || defined(OS_MACOSX) || defined(OS_FREEBSD))
@@ -204,6 +242,7 @@ bool ConvertResStateToDnsConfig(const struct __res_state& res,
     if (!ipe.FromSockAddr(
             reinterpret_cast<const struct sockaddr*>(&res.nsaddr_list[i]),
             sizeof res.nsaddr_list[i])) {
+      RecordConfigParseResult(CONFIG_PARSE_POSIX_BAD_ADDRESS);
       return false;
     }
     dns_config->nameservers.push_back(ipe);
@@ -223,15 +262,37 @@ bool ConvertResStateToDnsConfig(const struct __res_state& res,
 #endif
   dns_config->edns0 = res.options & RES_USE_EDNS0;
 
+  // The current implementation assumes these options are set. They normally
+  // cannot be overwritten by /etc/resolv.conf
+  unsigned kRequiredOptions = RES_RECURSE | RES_DEFNAMES | RES_DNSRCH;
+  if ((res.options & kRequiredOptions) != kRequiredOptions) {
+    RecordConfigParseResult(CONFIG_PARSE_POSIX_MISSING_OPTIONS);
+    return false;
+  }
+
+  unsigned kUnhandledOptions = RES_USEVC | RES_IGNTC | RES_USE_DNSSEC;
+  if (res.options & kUnhandledOptions) {
+    RecordConfigParseResult(CONFIG_PARSE_POSIX_UNHANDLED_OPTIONS);
+    return false;
+  }
+
+  if (dns_config->nameservers.empty()) {
+    RecordConfigParseResult(CONFIG_PARSE_POSIX_NO_NAMESERVERS);
+    return false;
+  }
+
   // If any name server is 0.0.0.0, assume the configuration is invalid.
   // TODO(szym): Measure how often this happens. http://crbug.com/125599
   const IPAddressNumber kEmptyAddress(kIPv4AddressSize);
-  for (unsigned i = 0; i < dns_config->nameservers.size(); ++i)
-    if (dns_config->nameservers[i].address() == kEmptyAddress)
+  for (unsigned i = 0; i < dns_config->nameservers.size(); ++i) {
+    if (dns_config->nameservers[i].address() == kEmptyAddress) {
+      RecordConfigParseResult(CONFIG_PARSE_POSIX_NULL_ADDRESS);
       return false;
+    }
+  }
+  RecordConfigParseResult(CONFIG_PARSE_POSIX_OK);
   return true;
 }
-#endif  // !defined(OS_ANDROID)
 
 }  // namespace internal
 
@@ -240,4 +301,18 @@ scoped_ptr<DnsConfigService> DnsConfigService::CreateSystemService() {
   return scoped_ptr<DnsConfigService>(new internal::DnsConfigServicePosix());
 }
 
+#else  // defined(OS_ANDROID)
+// Android NDK provides only a stub <resolv.h> header.
+class StubDnsConfigService : public DnsConfigService {
+ public:
+  StubDnsConfigService() {}
+  virtual ~StubDnsConfigService() {}
+  virtual void OnDNSChanged(unsigned detail) OVERRIDE {}
+};
+// static
+scoped_ptr<DnsConfigService> DnsConfigService::CreateSystemService() {
+  return scoped_ptr<DnsConfigService>(new StubDnsConfigService());
+}
+#endif
+
 }  // namespace net