diff --git a/vendor/go.uber.org/zap/zapcore/core.go b/vendor/go.uber.org/zap/zapcore/core.go
new file mode 100644
index 0000000..a1ef8b0
--- /dev/null
+++ b/vendor/go.uber.org/zap/zapcore/core.go
@@ -0,0 +1,113 @@
+// Copyright (c) 2016 Uber Technologies, Inc.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+
+package zapcore
+
+// Core is a minimal, fast logger interface. It's designed for library authors
+// to wrap in a more user-friendly API.
+type Core interface {
+	LevelEnabler
+
+	// With adds structured context to the Core.
+	With([]Field) Core
+	// Check determines whether the supplied Entry should be logged (using the
+	// embedded LevelEnabler and possibly some extra logic). If the entry
+	// should be logged, the Core adds itself to the CheckedEntry and returns
+	// the result.
+	//
+	// Callers must use Check before calling Write.
+	Check(Entry, *CheckedEntry) *CheckedEntry
+	// Write serializes the Entry and any Fields supplied at the log site and
+	// writes them to their destination.
+	//
+	// If called, Write should always log the Entry and Fields; it should not
+	// replicate the logic of Check.
+	Write(Entry, []Field) error
+	// Sync flushes buffered logs (if any).
+	Sync() error
+}
+
+type nopCore struct{}
+
+// NewNopCore returns a no-op Core.
+func NewNopCore() Core                                        { return nopCore{} }
+func (nopCore) Enabled(Level) bool                            { return false }
+func (n nopCore) With([]Field) Core                           { return n }
+func (nopCore) Check(_ Entry, ce *CheckedEntry) *CheckedEntry { return ce }
+func (nopCore) Write(Entry, []Field) error                    { return nil }
+func (nopCore) Sync() error                                   { return nil }
+
+// NewCore creates a Core that writes logs to a WriteSyncer.
+func NewCore(enc Encoder, ws WriteSyncer, enab LevelEnabler) Core {
+	return &ioCore{
+		LevelEnabler: enab,
+		enc:          enc,
+		out:          ws,
+	}
+}
+
+type ioCore struct {
+	LevelEnabler
+	enc Encoder
+	out WriteSyncer
+}
+
+func (c *ioCore) With(fields []Field) Core {
+	clone := c.clone()
+	addFields(clone.enc, fields)
+	return clone
+}
+
+func (c *ioCore) Check(ent Entry, ce *CheckedEntry) *CheckedEntry {
+	if c.Enabled(ent.Level) {
+		return ce.AddCore(ent, c)
+	}
+	return ce
+}
+
+func (c *ioCore) Write(ent Entry, fields []Field) error {
+	buf, err := c.enc.EncodeEntry(ent, fields)
+	if err != nil {
+		return err
+	}
+	_, err = c.out.Write(buf.Bytes())
+	buf.Free()
+	if err != nil {
+		return err
+	}
+	if ent.Level > ErrorLevel {
+		// Since we may be crashing the program, sync the output. Ignore Sync
+		// errors, pending a clean solution to issue #370.
+		c.Sync()
+	}
+	return nil
+}
+
+func (c *ioCore) Sync() error {
+	return c.out.Sync()
+}
+
+func (c *ioCore) clone() *ioCore {
+	return &ioCore{
+		LevelEnabler: c.LevelEnabler,
+		enc:          c.enc.Clone(),
+		out:          c.out,
+	}
+}