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check_password.go
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/
check_password.go
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// Copyright 2019 Google LLC
//
// 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
//
// https://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.
package passwordchecker
import (
"bufio"
"context"
"encoding/json"
"flag"
"log"
"net/http"
"time"
"cloud.google.com/go/storage"
"github.com/rs/cors"
"github.com/willf/bloom"
)
// RequestInput defines what the input looks like to the cloud function.
type RequestInput struct {
Cleartext string `json:"cleartext"`
}
type Response struct {
IsCommon bool `json:"is_common"`
}
var (
filter *bloom.BloomFilter
c = cors.AllowAll()
initializedChan = make(chan struct{})
bucket = flag.String("bucket", "password-check-fn-km-dictionary", "The cloud bucket that contains the password dictionary")
objectName = flag.String("object", "dictionary.txt", "Name of the dictionary object in the bucket")
)
func init() {
n := uint(1000000)
filter = bloom.NewWithEstimates(n, 0.00001)
go func() {
// Initialise the bloom filter.
ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
defer cancel()
if err := populateFilter(ctx); err != nil {
// Cannot function without the filter.
log.Fatalf("Attempted to populate filter, got error %q", err.Error())
}
close(initializedChan)
}()
}
// CheckPassword returns 200 if the password is okay, or 400
// if the password has been found in the dictionary.
func CheckPassword(w http.ResponseWriter, r *http.Request) {
// Only wait for 1 second for the system to initialize before failing fast.
ctx, cancel := context.WithTimeout(context.Background(), 1*time.Second)
defer cancel()
// Wait for the bloom filter to initialise before processing the request.
select {
case <-ctx.Done():
http.Error(w, ctx.Err().Error(), http.StatusServiceUnavailable)
return
case <-initializedChan:
}
// Add CORS headers.
c.HandlerFunc(w, r)
defer r.Body.Close()
dec := json.NewDecoder(r.Body)
input := new(RequestInput)
if err := dec.Decode(&input); err != nil {
http.Error(w, "Invalid input", http.StatusBadRequest)
return
}
if input.Cleartext == "" {
http.Error(w, "Empty cleartext", http.StatusBadRequest)
return
}
isCommon := filter.TestString(input.Cleartext)
enc := json.NewEncoder(w)
if err := enc.Encode(&Response{
IsCommon: isCommon,
}); err != nil {
http.Error(w, "Could not marshal response", http.StatusInternalServerError)
}
}
// PopulateFilter reads a dictionary from a cloud storage bucket
// and populates the bloom filter with the newline delimited words
// in that dictionary.
func populateFilter(ctx context.Context) (err error) {
client, err := storage.NewClient(ctx)
if err != nil {
return err
}
defer func() { err = client.Close() }()
rc, err := client.Bucket(*bucket).Object(*objectName).NewReader(ctx)
if err != nil {
return err
}
defer func() { err = rc.Close() }()
// Read each word (delimited by newlines) from the object.
scanner := bufio.NewScanner(rc)
n := 0
for scanner.Scan() {
filter.Add(scanner.Bytes())
n++
}
log.Printf("Added %d words to the filter", n)
return scanner.Err()
}