android_ingest/go/recent/recent.go

// Package recent tracks the last 20 incoming JSON request.
package recent

import (
	"bytes"
	"encoding/json"
	"sync"
	"time"
)

const (
	// maxRecent is the largest number of recent requests that will be displayed.
	maxRecent = 20
)

// Request is a record of a single POST request.
type Request struct {
	TS     string
	JSON   string
	Reason string
}

// Recent tracks the last MAX_RECENT Requests.
type Recent struct {
	// mutex guards access to recent.
	mutex sync.Mutex

	// recentGood is just the last MAX_RECENT requests.
	recentGood []*Request

	// recentBad is just the last MAX_RECENT requests.
	recentBad []*Request
}

// New returns a new Recent instance.
func New() *Recent {
	return &Recent{
		recentGood: []*Request{},
		recentBad:  []*Request{},
	}
}

func (r *Recent) add(recent []*Request, b []byte, msg string) []*Request {
	// Store locally.
	r.mutex.Lock()
	defer r.mutex.Unlock()

	recent = append([]*Request{{
		TS:     time.Now().UTC().String(),
		JSON:   string(b),
		Reason: msg,
	}}, recent...)

	// Keep track of the last N events.
	if len(recent) > maxRecent {
		recent = recent[:maxRecent]
	}
	return recent
}

// AddBad the JSON body that was POST'd to the server.
func (r *Recent) AddBad(b []byte, msg string) {
	// Try to pretty print the JSON is possible, otherwise just use the raw bytes.
	buf := bytes.NewReader(b)
	var i interface{}
	if err := json.NewDecoder(buf).Decode(&i); err != nil {
		r.recentBad = r.add(r.recentBad, b, msg)
		return
	}
	pretty, err := json.MarshalIndent(i, "", "  ")
	if err != nil {
		r.recentBad = r.add(r.recentBad, b, msg)
		return
	}
	r.recentBad = r.add(r.recentBad, pretty, msg)
}

// AddGood the JSON body that was POST'd to the server.
func (r *Recent) AddGood(b []byte) {
	r.recentGood = r.add(r.recentGood, b, "")
}

// List returns the last MAX_RECENT Good and Bad Requests, with the most recent
// Requests first.
func (r *Recent) List() ([]*Request, []*Request) {
	r.mutex.Lock()
	defer r.mutex.Unlock()
	good := make([]*Request, len(r.recentGood), len(r.recentGood))
	for i, req := range r.recentGood {
		good[i] = req
	}
	bad := make([]*Request, len(r.recentBad), len(r.recentBad))
	for i, req := range r.recentBad {
		bad[i] = req
	}
	return good, bad
}