Add zapio.Writer

This adds a new zapio package that provides a `Writer`. The writer
implements `io.WriteCloser` and `zapcore.WriteSyncer`.

It works by splitting the input on newlines, flushing to the logger as
new lines are encountered, and buffering input otherwise.

So for example, if write "foobar\n" is split across multiple Write calls
"foo" and "bar\n", instead of emitting two separate logs for "foo"
and "bar", the Writer will buffer the input until the newline is
encountered and write a single log for "foobar".

Resolves #929

zapio/writer.go

@@ -0,0 +1,108 @@
+// Copyright (c) 2021 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 zapio
+
+import (
+	"bytes"
+	"io"
+
+	"go.uber.org/zap"
+	"go.uber.org/zap/zapcore"
+)
+
+// Writer is an io.Writer that writes to the provided Zap logger, splitting log
+// messages on line boundaries.
+//
+// Writer must be closed when finished to flush buffered data to the logger.
+type Writer struct {
+	Log   *zap.Logger   // log to write to
+	Level zapcore.Level // log level to write at
+
+	buff bytes.Buffer
+}
+
+var (
+	_ zapcore.WriteSyncer = (*Writer)(nil)
+	_ io.Closer           = (*Writer)(nil)
+)
+
+// Write writes the provided bytes to the underlying logger at the configured
+// log level and returns the length of the bytes.
+func (w *Writer) Write(bs []byte) (n int, err error) {
+	// Skip all checks if the level isn't enabled.
+	if !w.Log.Core().Enabled(w.Level) {
+		return len(bs), nil
+	}
+
+	n = len(bs)
+	for len(bs) > 0 {
+		bs = w.writeLine(bs)
+	}
+
+	return n, nil
+}
+
+// writeLine writes a single line from the input, returning the remaining,
+// unconsumed bytes.
+func (w *Writer) writeLine(line []byte) (remaining []byte) {
+	idx := bytes.IndexByte(line, '\n')
+	if idx < 0 {
+		// If there are no newlines, buffer the entire string.
+		w.buff.Write(line)
+		return nil
+	}
+
+	// Split on the newline, buffer and flush the left.
+	line, remaining = line[:idx], line[idx+1:]
+	w.buff.Write(line)
+
+	// Log empty messages in the middle of the stream so that we don't lose
+	// information when the user writes "foo\n\nbar".
+	w.flush(true /* allowEmpty */)
+
+	return remaining
+}
+
+// Close closes the writer, flushing any buffered data in the process.
+func (w *Writer) Close() error {
+	return w.Sync()
+}
+
+// Sync flushes the buffered data from the writer, even if it doesn't end with
+// a newline.
+func (w *Writer) Sync() error {
+	// Don't allow empty messages on explicit Sync calls or on Close
+	// because we don't want an extraneous empty message at the end of the
+	// stream -- it's common for files to end with a newline.
+	w.flush(false /* allowEmpty */)
+	return nil
+}
+
+// flush flushes the buffered data to the logger, allowing empty messages only
+// if the bool is set.
+func (w *Writer) flush(allowEmpty bool) {
+	if allowEmpty || w.buff.Len() > 0 {
+		if ce := w.Log.Check(w.Level, w.buff.String()); ce != nil {
+			ce.Write()
+		}
+	}
+	w.buff.Reset()
+}

zapio/writer_test.go

@@ -0,0 +1,158 @@
+// Copyright (c) 2021 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 zapio
+
+import (
+	"io"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"go.uber.org/zap"
+	"go.uber.org/zap/zapcore"
+	"go.uber.org/zap/zaptest/observer"
+)
+
+func TestWriter(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		desc   string
+		level  zapcore.Level // defaults to info
+		writes []string
+		want   []zapcore.Entry
+	}{
+		{
+			desc: "simple",
+			writes: []string{
+				"foo\n",
+				"bar\n",
+				"baz\n",
+			},
+			want: []zapcore.Entry{
+				{Level: zap.InfoLevel, Message: "foo"},
+				{Level: zap.InfoLevel, Message: "bar"},
+				{Level: zap.InfoLevel, Message: "baz"},
+			},
+		},
+		{
+			desc:  "level too low",
+			level: zap.DebugLevel,
+			writes: []string{
+				"foo\n",
+				"bar\n",
+			},
+			want: []zapcore.Entry{},
+		},
+		{
+			desc:  "multiple newlines in a message",
+			level: zap.WarnLevel,
+			writes: []string{
+				"foo\nbar\n",
+				"baz\n",
+				"qux\nquux\n",
+			},
+			want: []zapcore.Entry{
+				{Level: zap.WarnLevel, Message: "foo"},
+				{Level: zap.WarnLevel, Message: "bar"},
+				{Level: zap.WarnLevel, Message: "baz"},
+				{Level: zap.WarnLevel, Message: "qux"},
+				{Level: zap.WarnLevel, Message: "quux"},
+			},
+		},
+		{
+			desc:  "message split across multiple writes",
+			level: zap.ErrorLevel,
+			writes: []string{
+				"foo",
+				"bar\nbaz",
+				"qux",
+			},
+			want: []zapcore.Entry{
+				{Level: zap.ErrorLevel, Message: "foobar"},
+				{Level: zap.ErrorLevel, Message: "bazqux"},
+			},
+		},
+		{
+			desc: "blank lines in the middle",
+			writes: []string{
+				"foo\n\nbar\nbaz",
+			},
+			want: []zapcore.Entry{
+				{Level: zap.InfoLevel, Message: "foo"},
+				{Level: zap.InfoLevel, Message: ""},
+				{Level: zap.InfoLevel, Message: "bar"},
+				{Level: zap.InfoLevel, Message: "baz"},
+			},
+		},
+		{
+			desc: "blank line at the end",
+			writes: []string{
+				"foo\nbar\nbaz\n",
+			},
+			want: []zapcore.Entry{
+				{Level: zap.InfoLevel, Message: "foo"},
+				{Level: zap.InfoLevel, Message: "bar"},
+				{Level: zap.InfoLevel, Message: "baz"},
+			},
+		},
+		{
+			desc: "multiple blank line at the end",
+			writes: []string{
+				"foo\nbar\nbaz\n\n",
+			},
+			want: []zapcore.Entry{
+				{Level: zap.InfoLevel, Message: "foo"},
+				{Level: zap.InfoLevel, Message: "bar"},
+				{Level: zap.InfoLevel, Message: "baz"},
+				{Level: zap.InfoLevel, Message: ""},
+			},
+		},
+	}
+
+	for _, tt := range tests {
+		tt := tt // for t.Parallel
+		t.Run(tt.desc, func(t *testing.T) {
+			t.Parallel()
+
+			core, observed := observer.New(zap.InfoLevel)
+
+			w := Writer{
+				Log:   zap.New(core),
+				Level: tt.level,
+			}
+
+			for _, s := range tt.writes {
+				_, err := io.WriteString(&w, s)
+				require.NoError(t, err, "Writer.Write failed.")
+			}
+
+			assert.NoError(t, w.Close(), "Writer.Close failed.")
+
+			// Turn []observer.LoggedEntry => []zapcore.Entry
+			got := make([]zapcore.Entry, observed.Len())
+			for i, ent := range observed.AllUntimed() {
+				got[i] = ent.Entry
+			}
+			assert.Equal(t, tt.want, got, "Logged entries do not match.")
+		})
+	}
+}