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package bolt_test
import (
"encoding/binary"
"fmt"
"io/ioutil"
"log"
"math/rand"
"net/http"
"net/http/httptest"
"os"
"github.com/boltdb/bolt"
)
// Set this to see how the counts are actually updated.
const verbose = false
// Counter updates a counter in Bolt for every URL path requested.
type counter struct {
db *bolt.DB
}
func (c counter) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
// Communicates the new count from a successful database
// transaction.
var result uint64
increment := func(tx *bolt.Tx) error {
b, err := tx.CreateBucketIfNotExists([]byte("hits"))
if err != nil {
return err
}
key := []byte(req.URL.String())
// Decode handles key not found for us.
count := decode(b.Get(key)) + 1
b.Put(key, encode(count))
// All good, communicate new count.
result = count
return nil
}
if err := c.db.Batch(increment); err != nil {
http.Error(rw, err.Error(), 500)
return
}
if verbose {
log.Printf("server: %s: %d", req.URL.String(), result)
}
rw.Header().Set("Content-Type", "application/octet-stream")
fmt.Fprintf(rw, "%d\n", result)
}
func client(id int, base string, paths []string) error {
// Process paths in random order.
rng := rand.New(rand.NewSource(int64(id)))
permutation := rng.Perm(len(paths))
for i := range paths {
path := paths[permutation[i]]
resp, err := http.Get(base + path)
if err != nil {
return err
}
defer resp.Body.Close()
buf, err := ioutil.ReadAll(resp.Body)
if err != nil {
return err
}
if verbose {
log.Printf("client: %s: %s", path, buf)
}
}
return nil
}
func ExampleDB_Batch() {
// Open the database.
db, _ := bolt.Open(tempfile(), 0666, nil)
defer os.Remove(db.Path())
defer db.Close()
// Start our web server
count := counter{db}
srv := httptest.NewServer(count)
defer srv.Close()
// Decrease the batch size to make things more interesting.
db.MaxBatchSize = 3
// Get every path multiple times concurrently.
const clients = 10
paths := []string{
"/foo",
"/bar",
"/baz",
"/quux",
"/thud",
"/xyzzy",
}
errors := make(chan error, clients)
for i := 0; i < clients; i++ {
go func(id int) {
errors <- client(id, srv.URL, paths)
}(i)
}
// Check all responses to make sure there's no error.
for i := 0; i < clients; i++ {
if err := <-errors; err != nil {
fmt.Printf("client error: %v", err)
return
}
}
// Check the final result
db.View(func(tx *bolt.Tx) error {
b := tx.Bucket([]byte("hits"))
c := b.Cursor()
for k, v := c.First(); k != nil; k, v = c.Next() {
fmt.Printf("hits to %s: %d\n", k, decode(v))
}
return nil
})
// Output:
// hits to /bar: 10
// hits to /baz: 10
// hits to /foo: 10
// hits to /quux: 10
// hits to /thud: 10
// hits to /xyzzy: 10
}
// encode marshals a counter.
func encode(n uint64) []byte {
buf := make([]byte, 8)
binary.BigEndian.PutUint64(buf, n)
return buf
}
// decode unmarshals a counter. Nil buffers are decoded as 0.
func decode(buf []byte) uint64 {
if buf == nil {
return 0
}
return binary.BigEndian.Uint64(buf)
}
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