Add support for Android's logging subsystem.

This patch adds support for Android's logging subsystem in Tor. When
debugging Android applications it is useful to be able to collect
information about the application running on the platform via the
various system services that is available on the platform.

This patch allows you to add "Log notice android" to your torrc and have
Tor send everything above and including the notice severity to Android's
ring buffer which can be inspected using the 'adb logcat' program.

See: https://bugs.torproject.org/24362

7 files changed, 122 insertions, 5 deletions

diff --git a/changes/bug24362 b/changes/bug24362
new file mode 100644
index 0000000000..15e393cf3f
--- /dev/null
+++ b/changes/bug24362
@@ -0,0 +1,2 @@
+  o Minor features (logging, android):
+    - Added support for the Android logging subsystem. Closes ticket 24362.
diff --git a/configure.ac b/configure.ac
index 82e656d3c5..4316f4e09c 100644
--- a/configure.ac
+++ b/configure.ac
@@ -204,6 +204,20 @@ if test x$enable_event_tracing_debug = xyes; then
   AC_DEFINE([TOR_EVENT_TRACING_ENABLED], [1], [Compile the event tracing instrumentation])
 fi
 
+dnl Enable Android only features.
+AC_ARG_ENABLE(android,
+     AS_HELP_STRING(--enable-android, [build with Android features enabled]))
+AM_CONDITIONAL([USE_ANDROID], [test "x$enable_android" = "xyes"])
+
+if test "x$enable_android" = "xyes"; then
+  AC_DEFINE([USE_ANDROID], [1], [Compile with Android specific features enabled])
+
+  dnl Check if the Android log library is available.
+  AC_CHECK_HEADERS([android/log.h])
+  AC_SEARCH_LIBS(__android_log_write, [log])
+
+fi
+
 dnl check for the correct "ar" when cross-compiling.
 dnl   (AM_PROG_AR was new in automake 1.11.2, which we do not yet require,
 dnl    so kludge up a replacement for the case where it isn't there yet.)
diff --git a/doc/tor.1.txt b/doc/tor.1.txt
index 1814b8292a..b2218e33cc 100644
--- a/doc/tor.1.txt
+++ b/doc/tor.1.txt
@@ -727,6 +727,11 @@ GENERAL OPTIONS
     log entries are marked with "Tor-__tag__". Can not be changed while tor is
     running. (Default: none)
 
+[[AndroidIdentityTag]] **AndroidIdentityTag** __tag__::
+    When logging to Android's logging subsystem, adds a tag to the log identity
+    such that log entries are marked with "Tor-__tag__". Can not be changed while
+    tor is running. (Default: none)
+
 [[SafeLogging]] **SafeLogging** **0**|**1**|**relay**::
     Tor can scrub potentially sensitive strings from log messages (e.g.
     addresses) by replacing them with the string [scrubbed]. This way logs can
diff --git a/src/common/log.c b/src/common/log.c
index 80055fda04..ad3d1affd5 100644
--- a/src/common/log.c
+++ b/src/common/log.c
@@ -35,6 +35,9 @@
 #define LOG_PRIVATE
 #include "torlog.h"
 #include "container.h"
+#ifdef HAVE_ANDROID_LOG_H
+#include <android/log.h>
+#endif // HAVE_ANDROID_LOG_H.
 
 /** Given a severity, yields an index into log_severity_list_t.masks to use
  * for that severity. */
@@ -58,6 +61,8 @@ typedef struct logfile_t {
   int needs_close; /**< Boolean: true if the stream gets closed on shutdown. */
   int is_temporary; /**< Boolean: close after initializing logging subsystem.*/
   int is_syslog; /**< Boolean: send messages to syslog. */
+  int is_android; /**< Boolean: send messages to Android's log subsystem. */
+  char *android_tag; /**< Identity Tag used in Android's log subsystem. */
   log_callback callback; /**< If not NULL, send messages to this function. */
   log_severity_list_t *severities; /**< Which severity of messages should we
                                     * log for each log domain? */
@@ -103,6 +108,33 @@ should_log_function_name(log_domain_mask_t domain, int severity)
   }
 }
 
+#ifdef HAVE_ANDROID_LOG_H
+/** Helper function to convert Tor's log severity into the matching
+ * Android log priority.
+ */
+static int
+severity_to_android_log_priority(int severity)
+{
+  switch (severity) {
+    case LOG_DEBUG:
+      return ANDROID_LOG_VERBOSE;
+    case LOG_INFO:
+      return ANDROID_LOG_DEBUG;
+    case LOG_NOTICE:
+      return ANDROID_LOG_INFO;
+    case LOG_WARN:
+      return ANDROID_LOG_WARN;
+    case LOG_ERR:
+      return ANDROID_LOG_ERROR;
+    default:
+      // LCOV_EXCL_START
+      raw_assert(0);
+      return 0;
+      // LCOV_EXCL_STOP
+  }
+}
+#endif // HAVE_ANDROID_LOG_H.
+
 /** A mutex to guard changes to logfiles and logging. */
 static tor_mutex_t log_mutex;
 /** True iff we have initialized log_mutex */
@@ -411,7 +443,7 @@ logfile_wants_message(const logfile_t *lf, int severity,
   if (! (lf->severities->masks[SEVERITY_MASK_IDX(severity)] & domain)) {
     return 0;
   }
-  if (! (lf->fd >= 0 || lf->is_syslog || lf->callback)) {
+  if (! (lf->fd >= 0 || lf->is_syslog || lf->is_android || lf->callback)) {
     return 0;
   }
   if (lf->seems_dead) {
@@ -454,6 +486,11 @@ logfile_deliver(logfile_t *lf, const char *buf, size_t msg_len,
     syslog(severity, "%s", msg_after_prefix);
 #endif /* defined(MAXLINE) */
 #endif /* defined(HAVE_SYSLOG_H) */
+  } else if (lf->is_android) {
+#ifdef HAVE_ANDROID_LOG_H
+    int priority = severity_to_android_log_priority(severity);
+    __android_log_write(priority, lf->android_tag, msg_after_prefix);
+#endif // HAVE_ANDROID_LOG_H.
   } else if (lf->callback) {
     if (domain & LD_NOCB) {
       if (!*callbacks_deferred && pending_cb_messages) {
@@ -646,7 +683,7 @@ tor_log_update_sigsafe_err_fds(void)
      /* Don't try callback to the control port, or syslogs: We can't
       * do them from a signal handler. Don't try stdout: we always do stderr.
       */
-    if (lf->is_temporary || lf->is_syslog ||
+    if (lf->is_temporary || lf->is_syslog || lf->is_android ||
         lf->callback || lf->seems_dead || lf->fd < 0)
       continue;
     if (lf->severities->masks[SEVERITY_MASK_IDX(LOG_ERR)] &
@@ -683,7 +720,7 @@ tor_log_get_logfile_names(smartlist_t *out)
   LOCK_LOGS();
 
   for (lf = logfiles; lf; lf = lf->next) {
-    if (lf->is_temporary || lf->is_syslog || lf->callback)
+    if (lf->is_temporary || lf->is_syslog || lf->is_android || lf->callback)
       continue;
     if (lf->filename == NULL)
       continue;
@@ -732,6 +769,7 @@ log_free_(logfile_t *victim)
     return;
   tor_free(victim->severities);
   tor_free(victim->filename);
+  tor_free(victim->android_tag);
   tor_free(victim);
 }
 
@@ -1151,6 +1189,39 @@ add_syslog_log(const log_severity_list_t *severity,
 }
 #endif /* defined(HAVE_SYSLOG_H) */
 
+#ifdef HAVE_ANDROID_LOG_H
+/**
+ * Add a log handler to send messages to the Android platform log facility.
+ */
+int
+add_android_log(const log_severity_list_t *severity,
+                const char *android_tag)
+{
+  logfile_t *lf = NULL;
+
+  lf = tor_malloc_zero(sizeof(logfile_t));
+  lf->fd = -1;
+  lf->severities = tor_memdup(severity, sizeof(log_severity_list_t));
+  lf->filename = tor_strdup("<android>");
+  lf->is_android = 1;
+
+  if (android_tag == NULL)
+    lf->android_tag = tor_strdup("Tor");
+  else {
+    char buf[256];
+    tor_snprintf(buf, sizeof(buf), "Tor-%s", android_tag);
+    lf->android_tag = tor_strdup(buf);
+  }
+
+  LOCK_LOGS();
+  lf->next = logfiles;
+  logfiles = lf;
+  log_global_min_severity_ = get_min_log_level();
+  UNLOCK_LOGS();
+  return 0;
+}
+#endif // HAVE_ANDROID_LOG_H.
+
 /** If <b>level</b> is a valid log severity, return the corresponding
  * numeric value.  Otherwise, return -1. */
 int
@@ -1318,7 +1389,8 @@ parse_log_severity_config(const char **cfg_ptr,
     if (!strcasecmpstart(cfg, "file") ||
         !strcasecmpstart(cfg, "stderr") ||
         !strcasecmpstart(cfg, "stdout") ||
-        !strcasecmpstart(cfg, "syslog")) {
+        !strcasecmpstart(cfg, "syslog") ||
+        !strcasecmpstart(cfg, "android")) {
       goto done;
     }
     if (got_an_unqualified_range > 1)
diff --git a/src/common/torlog.h b/src/common/torlog.h
index 65bf41702a..b7d033adb9 100644
--- a/src/common/torlog.h
+++ b/src/common/torlog.h
@@ -146,7 +146,11 @@ int add_file_log(const log_severity_list_t *severity, const char *filename,
 #ifdef HAVE_SYSLOG_H
 int add_syslog_log(const log_severity_list_t *severity,
                    const char* syslog_identity_tag);
-#endif
+#endif // HAVE_SYSLOG_H.
+#ifdef HAVE_ANDROID_LOG_H
+int add_android_log(const log_severity_list_t *severity,
+                    const char *android_identity_tag);
+#endif // HAVE_ANDROID_LOG_H.
 int add_callback_log(const log_severity_list_t *severity, log_callback cb);
 void logs_set_domain_logging(int enabled);
 int get_min_log_level(void);
diff --git a/src/or/config.c b/src/or/config.c
index 676e7f605b..0f662a617d 100644
--- a/src/or/config.c
+++ b/src/or/config.c
@@ -403,6 +403,7 @@ static config_var_t option_vars_[] = {
   V(LogTimeGranularity,          MSEC_INTERVAL, "1 second"),
   V(TruncateLogFile,             BOOL,     "0"),
   V(SyslogIdentityTag,           STRING,   NULL),
+  V(AndroidIdentityTag,          STRING,   NULL),
   V(LongLivedPorts,              CSV,
         "21,22,706,1863,5050,5190,5222,5223,6523,6667,6697,8300"),
   VAR("MapAddress",              LINELIST, AddressMap,           NULL),
@@ -4692,6 +4693,12 @@ options_transition_allowed(const or_options_t *old,
     return -1;
   }
 
+  if (!opt_streq(old->AndroidIdentityTag, new_val->AndroidIdentityTag)) {
+    *msg = tor_strdup("While Tor is running, changing "
+                      "AndroidIdentityTag is not allowed.");
+    return -1;
+  }
+
   if ((old->HardwareAccel != new_val->HardwareAccel)
       || !opt_streq(old->AccelName, new_val->AccelName)
       || !opt_streq(old->AccelDir, new_val->AccelDir)) {
@@ -5743,6 +5750,18 @@ options_init_logs(const or_options_t *old_options, or_options_t *options,
 #endif /* defined(HAVE_SYSLOG_H) */
         goto cleanup;
       }
+
+      if (!strcasecmp(smartlist_get(elts, 0), "android")) {
+#ifdef HAVE_ANDROID_LOG_H
+        if (!validate_only) {
+          add_android_log(severity, options->AndroidIdentityTag);
+        }
+#else
+        log_warn(LD_CONFIG, "Android logging is not supported"
+                            " on this system. Sorry.");
+#endif // HAVE_ANDROID_LOG_H.
+        goto cleanup;
+      }
     }
 
     if (smartlist_len(elts) == 2 &&
diff --git a/src/or/or.h b/src/or/or.h
index b078022326..aff43f195b 100644
--- a/src/or/or.h
+++ b/src/or/or.h
@@ -3639,6 +3639,7 @@ typedef struct {
   int TruncateLogFile; /**< Boolean: Should we truncate the log file
                             before we start writing? */
   char *SyslogIdentityTag; /**< Identity tag to add for syslog logging. */
+  char *AndroidIdentityTag; /**< Identity tag to add for Android logging. */
 
   char *DebugLogFile; /**< Where to send verbose log messages. */
   char *DataDirectory_option; /**< Where to store long-term data, as