nghttpx: Add $ssl_session_reused log variable

The syntax for this variable is the same as nginx: if SSL/TLS session
was reused, "r" is produced.  Otherwise ".".

src/shrpx.cc

@@ -1348,6 +1348,8 @@ Logging:
               * $ssl_cipher: cipher used for SSL/TLS connection.
               * $ssl_protocol: protocol for SSL/TLS connection.
               * $ssl_session_id: session ID for SSL/TLS connection.
+              * $ssl_session_reused:  "r"   if  SSL/TLS   session  was
+                reused.  Otherwise, "."
 
               Default: )" << DEFAULT_ACCESSLOG_FORMAT << R"(
   --errorlog-file=<PATH>

src/shrpx_config.cc

@@ -389,6 +389,8 @@ std::vector<LogFragment> parse_log_format(const char *optarg) {
       type = SHRPX_LOGF_SSL_PROTOCOL;
     } else if (util::strieq_l("$ssl_session_id", var_start, varlen)) {
       type = SHRPX_LOGF_SSL_SESSION_ID;
+    } else if (util::strieq_l("$ssl_session_reused", var_start, varlen)) {
+      type = SHRPX_LOGF_SSL_SESSION_REUSED;
     } else {
       LOG(WARN) << "Unrecognized log format variable: "
                 << std::string(var_start, varlen);

src/shrpx_log.cc

@@ -294,6 +294,14 @@ void upstream_accesslog(const std::vector<LogFragment> &lfv,
           copy_hex_low(lgsp.tls_info->session_id,
                        lgsp.tls_info->session_id_length, avail, p);
       break;
+    case SHRPX_LOGF_SSL_SESSION_REUSED:
+      if (!lgsp.tls_info) {
+        std::tie(p, avail) = copy("-", avail, p);
+        break;
+      }
+      std::tie(p, avail) =
+          copy(lgsp.tls_info->session_reused ? "r" : ".", avail, p);
+      break;
     case SHRPX_LOGF_NONE:
       break;
     default:

src/shrpx_log.h

@@ -119,6 +119,7 @@ enum LogFragmentType {
   SHRPX_LOGF_SSL_CIPHER,
   SHRPX_LOGF_SSL_PROTOCOL,
   SHRPX_LOGF_SSL_SESSION_ID,
+  SHRPX_LOGF_SSL_SESSION_REUSED,
 };
 
 struct LogFragment {

src/ssl.cc

@@ -114,6 +114,7 @@ TLSSessionInfo *get_tls_session_info(TLSSessionInfo *tls_info, SSL *ssl) {
   tls_info->protocol = get_tls_protocol(ssl);
   tls_info->session_id = session->session_id;
   tls_info->session_id_length = session->session_id_length;
+  tls_info->session_reused = SSL_session_reused(ssl);
 
   return tls_info;
 }

src/ssl.h

@@ -53,6 +53,7 @@ struct TLSSessionInfo {
   const char *cipher;
   const char *protocol;
   const uint8_t *session_id;
+  bool session_reused;
   size_t session_id_length;
 };