SERVER-18717 compose electionId in OID format from term

2 files changed, 16 insertions, 0 deletions

diff --git a/src/mongo/bson/oid.cpp b/src/mongo/bson/oid.cpp
index a78bcbde682..a8ef6bb56ef 100644
--- a/src/mongo/bson/oid.cpp
+++ b/src/mongo/bson/oid.cpp
@@ -138,6 +138,12 @@ void OID::init() {
     setIncrement(Increment::next());
 }
 
+void OID::init(int64_t term) {
+    // each set* method handles endianness
+    setTimestamp(time(0));
+    _view().write<BigEndian<int64_t>>(term, kInstanceUniqueOffset);
+}
+
 void OID::init(const std::string& s) {
     verify(s.size() == 24);
     const char* p = s.c_str();
diff --git a/src/mongo/bson/oid.h b/src/mongo/bson/oid.h
index 476e15d1048..ed7086159c6 100644
--- a/src/mongo/bson/oid.h
+++ b/src/mongo/bson/oid.h
@@ -93,6 +93,13 @@ public:
         std::memcpy(_data, arr, sizeof(arr));
     }
 
+    static_assert(sizeof(int64_t) == kInstanceUniqueSize + kIncrementSize,
+                  "size of term must be size of instance unique + increment");
+    /** init with a 8 byte term id. used for ElectionID */
+    explicit OID(int64_t term) {
+        init(term);
+    }
+
     /** initialize to 'null' */
     void clear() {
         std::memset(_data, 0, kOIDSize);
@@ -137,6 +144,9 @@ public:
     /** Set to the min/max OID that could be generated at given timestamp. */
     void init(Date_t date, bool max = false);
 
+    /** Sets the contents to contain the time followed by an big endian 8 byte term id */
+    void init(int64_t term);
+
     time_t asTimeT() const;
     Date_t asDateT() const {
         return Date_t::fromMillisSinceEpoch(asTimeT() * 1000LL);