luci-go: Basic support for event logging in Go.

common/eventlog/internal/logservice/logservice.go

Index: common/eventlog/internal/logservice/logservice.go
diff --git a/common/eventlog/internal/logservice/logservice.go b/common/eventlog/internal/logservice/logservice.go
new file mode 100644
index 0000000000000000000000000000000000000000..54e75691107852a89a72e73f64f61974cafb0838
--- /dev/null
+++ b/common/eventlog/internal/logservice/logservice.go
@@ -0,0 +1,73 @@
+// Copyright 2016 The LUCI Authors. All rights reserved.
+// Use of this source code is governed under the Apache License, Version 2.0
+// that can be found in the LICENSE file.
+
+// Package logservice provides a client which can be used to to collect and send batches of logs to the eventlog service.
+package logservice
+
+import (
+	"bytes"
+	"net/http"
+	"time"
+
+	"github.com/golang/protobuf/proto"
+
+	logpb "github.com/luci/luci-go/common/eventlog/proto"
+	"golang.org/x/net/context"
+)
+
+// Client sends event logs to the eventlog service.
+type Client struct {
+	HTTPClient *http.Client
+	serverAddr string
+	logSource  string
+}
+
+// NewClient constructs a new Client.
+// Users must call Close when the Client is no longer needed.
+func NewClient(serverAddr, logSourceName string) *Client {
+	return &Client{
+		serverAddr: serverAddr,
+		logSource:  logSourceName,
+	}
+}
+
+// TODO(mcgreevy): support bundling log requests.
+
+// LogSync synchronously logs events to the eventlog service.
+// The EventTime in each event must have been obtained from time.Now.
+func (c *Client) LogSync(ctx context.Context, events []*logpb.LogRequestLite_LogEventLite) error {
+	// TODO(mcgreevy): consider supporting custom clocks.
+	log := &logpb.LogRequestLite{
+		RequestTimeMs: proto.Int64(time.Now().UnixNano() / 1e6),
+		LogSourceName: &c.logSource,
+		LogEvent:      events,
+	}
+
+	buf, err := proto.Marshal(log)
+	if err != nil {
+		return err
+	}
+
+	req, err := http.NewRequest("POST", c.serverAddr, bytes.NewReader(buf))
+	if err != nil {
+		return err
+	}
+
+	req.Header.Set("Content-Type", "application/octet-stream")
+	req = req.WithContext(ctx)
+	resp, err := c.HTTPClient.Do(req)
+	if err != nil {
+		return err
+	}
+	resp.Body.Close()
+
+	return nil
+}
+
+// Close flushes any pending logs and releases any resources held by the client.
+// Close should be called when the client is no longer needed.
+func (c *Client) Close() error {
+	// We will need this later, but for now it's a no-op.
+	return nil
+}