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vendor/cloud.google.com/go/examples/bigtable/usercounter/main.go

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+// Copyright 2015 Google Inc. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+/*
+User counter is a program that tracks how often a user has visited the index page.
+
+This program demonstrates usage of the Cloud Bigtable API for App Engine flexible environment and Go.
+Instructions for running this program are in the README.md.
+*/
+package main
+
+import (
+	"bytes"
+	"encoding/binary"
+	"html/template"
+	"log"
+	"net/http"
+
+	"cloud.google.com/go/bigtable"
+	"golang.org/x/net/context"
+	"google.golang.org/appengine"
+	aelog "google.golang.org/appengine/log"
+	"google.golang.org/appengine/user"
+)
+
+// User-provided constants.
+const (
+	project  = "PROJECT_ID"
+	instance = "INSTANCE"
+)
+
+var (
+	tableName  = "user-visit-counter"
+	familyName = "emails"
+
+	// Client is initialized by main.
+	client *bigtable.Client
+)
+
+func main() {
+	ctx := context.Background()
+
+	// Set up admin client, tables, and column families.
+	// NewAdminClient uses Application Default Credentials to authenticate.
+	adminClient, err := bigtable.NewAdminClient(ctx, project, instance)
+	if err != nil {
+		log.Fatalf("Unable to create a table admin client. %v", err)
+	}
+	tables, err := adminClient.Tables(ctx)
+	if err != nil {
+		log.Fatalf("Unable to fetch table list. %v", err)
+	}
+	if !sliceContains(tables, tableName) {
+		if err := adminClient.CreateTable(ctx, tableName); err != nil {
+			log.Fatalf("Unable to create table: %v. %v", tableName, err)
+		}
+	}
+	tblInfo, err := adminClient.TableInfo(ctx, tableName)
+	if err != nil {
+		log.Fatalf("Unable to read info for table: %v. %v", tableName, err)
+	}
+	if !sliceContains(tblInfo.Families, familyName) {
+		if err := adminClient.CreateColumnFamily(ctx, tableName, familyName); err != nil {
+			log.Fatalf("Unable to create column family: %v. %v", familyName, err)
+		}
+	}
+	adminClient.Close()
+
+	// Set up Bigtable data operations client.
+	// NewClient uses Application Default Credentials to authenticate.
+	client, err = bigtable.NewClient(ctx, project, instance)
+	if err != nil {
+		log.Fatalf("Unable to create data operations client. %v", err)
+	}
+
+	http.Handle("/", appHandler(mainHandler))
+	appengine.Main() // Never returns.
+}
+
+// mainHandler tracks how many times each user has visited this page.
+func mainHandler(w http.ResponseWriter, r *http.Request) *appError {
+	if r.URL.Path != "/" {
+		http.NotFound(w, r)
+		return nil
+	}
+
+	ctx := appengine.NewContext(r)
+	u := user.Current(ctx)
+	if u == nil {
+		login, err := user.LoginURL(ctx, r.URL.String())
+		if err != nil {
+			return &appError{err, "Error finding login URL", http.StatusInternalServerError}
+		}
+		http.Redirect(w, r, login, http.StatusFound)
+		return nil
+	}
+	logoutURL, err := user.LogoutURL(ctx, "/")
+	if err != nil {
+		return &appError{err, "Error finding logout URL", http.StatusInternalServerError}
+	}
+
+	// Increment visit count for user.
+	tbl := client.Open(tableName)
+	rmw := bigtable.NewReadModifyWrite()
+	rmw.Increment(familyName, u.Email, 1)
+	row, err := tbl.ApplyReadModifyWrite(ctx, u.Email, rmw)
+	if err != nil {
+		return &appError{err, "Error applying ReadModifyWrite to row: " + u.Email, http.StatusInternalServerError}
+	}
+	data := struct {
+		Username, Logout string
+		Visits           uint64
+	}{
+		Username: u.Email,
+		// Retrieve the most recently edited column.
+		Visits: binary.BigEndian.Uint64(row[familyName][0].Value),
+		Logout: logoutURL,
+	}
+
+	// Display hello page.
+	var buf bytes.Buffer
+	if err := tmpl.Execute(&buf, data); err != nil {
+		return &appError{err, "Error writing template", http.StatusInternalServerError}
+	}
+	buf.WriteTo(w)
+	return nil
+}
+
+var tmpl = template.Must(template.New("").Parse(`
+<html><body>
+
+<p>
+{{with .Username}} Hello {{.}}{{end}}
+{{with .Logout}}<a href="{{.}}">Sign out</a>{{end}}
+
+</p>
+
+<p>
+You have visited {{.Visits}}
+</p>
+
+</body></html>`))
+
+// sliceContains reports whether the provided string is present in the given slice of strings.
+func sliceContains(list []string, target string) bool {
+	for _, s := range list {
+		if s == target {
+			return true
+		}
+	}
+	return false
+}
+
+// More info about this method of error handling can be found at: http://blog.golang.org/error-handling-and-go
+type appHandler func(http.ResponseWriter, *http.Request) *appError
+
+type appError struct {
+	Error   error
+	Message string
+	Code    int
+}
+
+func (fn appHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	if e := fn(w, r); e != nil {
+		ctx := appengine.NewContext(r)
+		aelog.Errorf(ctx, "%v", e.Error)
+		http.Error(w, e.Message, e.Code)
+	}
+}