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linkstorage.go
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linkstorage.go
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package linkstorage
import (
"database/sql"
"fmt"
"log"
"net/url"
"strconv"
"strings"
"sync"
"time"
"github.com/jamesjarvis/web-graph/pkg/linkutils"
)
// Storage implements a PostgreSQL storage backend for colly
type Storage struct {
URI string
PageTable string
LinkTable string
db *sql.DB
linkLock *sync.RWMutex
pageLock *sync.RWMutex
}
// NewStorage is a wrapper for easily creating a storage object.
func NewStorage(
uri string,
pageTable string,
linkTable string,
) (*Storage, error) {
storage := &Storage{
URI: uri,
PageTable: pageTable,
LinkTable: linkTable,
}
err := storage.Init()
if err != nil {
return nil, err
}
return storage, nil
}
// KeepPingingOn periodically sends a ping to the db to keep the connection alive.
// You can kill this process by sending a boolean to the returned channel.
func (s *Storage) KeepPingingOn(d time.Duration) chan<- bool {
ticker := time.NewTicker(d)
killChan := make(chan bool)
go func() {
var err error
for {
select {
case <-killChan:
log.Println("Killing ping worker!")
ticker.Stop()
return
case <-ticker.C:
err = s.db.Ping()
if err != nil {
log.Printf("Error from ping: %v", err)
}
}
}
}()
return killChan
}
// Close closes connections.
func (s *Storage) Close() error {
return s.db.Close()
}
// Init initializes the PostgreSQL storage
func (s *Storage) Init() error {
var err error
if s.linkLock == nil {
s.linkLock = &sync.RWMutex{}
}
if s.pageLock == nil {
s.pageLock = &sync.RWMutex{}
}
if s.db, err = sql.Open("postgres", s.URI); err != nil {
return err
}
if err = s.db.Ping(); err != nil {
return err
}
query := fmt.Sprintf(`CREATE TABLE IF NOT EXISTS %s (
page_id text NOT NULL PRIMARY KEY UNIQUE,
host text NOT NULL,
path text NOT NULL,
url text NOT NULL
);`, s.PageTable)
if _, err = s.db.Exec(query); err != nil {
return err
}
query = fmt.Sprintf(`CREATE TABLE IF NOT EXISTS %s (
from_page_id text NOT NULL,
to_page_id text NOT NULL,
text text,
CONSTRAINT PK_Link PRIMARY KEY (from_page_id,to_page_id),
CONSTRAINT FK_from_page_id FOREIGN KEY (from_page_id) REFERENCES %s(page_id),
CONSTRAINT FK_to_page_id FOREIGN KEY (to_page_id) REFERENCES %s(page_id)
);`, s.LinkTable, s.PageTable, s.PageTable)
if _, err = s.db.Exec(query); err != nil {
return err
}
query = fmt.Sprintf(`CREATE INDEX IF NOT EXISTS idx_to_page_id
ON %s(to_page_id)`, s.LinkTable)
if _, err = s.db.Exec(query); err != nil {
return err
}
query = fmt.Sprintf(`CREATE INDEX IF NOT EXISTS idx_page_host
ON %s(host)`, s.PageTable)
if _, err = s.db.Exec(query); err != nil {
return err
}
return nil
}
// CheckPageExists checks that the page exists in the visited database
func (s *Storage) CheckPageExists(u *url.URL) (bool, error) {
var isVisited bool
query := fmt.Sprintf(`SELECT EXISTS(SELECT 1 FROM %s WHERE page_id = $1)`, s.PageTable)
s.pageLock.RLock()
err := s.db.QueryRow(query, linkutils.Hash(u)).Scan(&isVisited)
s.pageLock.RUnlock()
return isVisited, err
}
// GetPage retrieves info about the page hash if it exists.
func (s *Storage) GetPage(pageHash string) (*Page, error) {
query := fmt.Sprintf(`SELECT url FROM %s WHERE page_id = $1`, s.PageTable)
// Prepare query
stmt, err := s.db.Prepare(query)
if err != nil {
return nil, err
}
defer stmt.Close()
// Execute query
var urlString string
s.pageLock.RLock()
err = stmt.QueryRow(pageHash).Scan(&urlString)
s.pageLock.RUnlock()
if err == sql.ErrNoRows {
// Return nothing if nothing found
return nil, nil
}
if err != nil {
return nil, err
}
u, err := url.Parse(urlString)
if err != nil {
return nil, err
}
return &Page{
U: u,
}, nil
}
// GetPageHashesFromHost retrieves the page hashes of all pages with this host.
func (s *Storage) GetPageHashesFromHost(host string, limit int) ([]string, error) {
query := fmt.Sprintf(`SELECT page_id FROM %s WHERE host = $1 LIMIT $2`, s.PageTable)
// Prepare query
stmt, err := s.db.Prepare(query)
if err != nil {
return nil, err
}
defer stmt.Close()
// Execute query
var pageHashes []string
s.pageLock.RLock()
rows, err := stmt.Query(host, limit)
s.pageLock.RUnlock()
defer rows.Close()
for rows.Next() {
var pageID string
err = rows.Scan(&pageID)
if err != nil {
return nil, err
}
pageHashes = append(pageHashes, pageID)
}
// get any error encountered during iteration
err = rows.Err()
if err != nil {
return nil, err
}
return pageHashes, nil
}
// AddPage first checks that it does not exist, and then inserts the page
func (s *Storage) AddPage(page *Page) error {
visited, err := s.CheckPageExists(page.U)
if err != nil {
return err
}
if visited {
return nil
}
query := fmt.Sprintf(`INSERT INTO %s (page_id, host, path, url) VALUES($1, $2, $3, $4);`, s.PageTable)
// Prepare query
stmt, err := s.db.Prepare(query)
if err != nil {
return err
}
defer stmt.Close()
s.pageLock.Lock()
_, err = stmt.Exec(linkutils.Hash(page.U), page.U.Hostname(), page.U.EscapedPath(), page.U.String())
s.pageLock.Unlock()
return err
}
// CheckLinkExists checks that the link exists in the visited database
func (s *Storage) CheckLinkExists(fromU *url.URL, toU *url.URL) (bool, error) {
var isVisited bool
query := fmt.Sprintf(`SELECT EXISTS(SELECT 1 FROM %s WHERE from_page_id = $1 AND to_page_id = $2)`, s.LinkTable)
// s.linkLock.RLock()
err := s.db.QueryRow(query, linkutils.Hash(fromU), linkutils.Hash(toU)).Scan(&isVisited)
// s.linkLock.RUnlock()
return isVisited, err
}
// GetLinksFrom retrieves the links from this page hash.
func (s *Storage) GetLinksFrom(pageHash string, limit int) ([]string, error) {
query := fmt.Sprintf(`SELECT to_page_id FROM %s WHERE from_page_id = $1 LIMIT $2`, s.LinkTable)
// Prepare query
stmt, err := s.db.Prepare(query)
if err != nil {
return nil, err
}
defer stmt.Close()
// Execute query
var pageHashes []string
s.linkLock.RLock()
rows, err := stmt.Query(pageHash, limit)
s.linkLock.RUnlock()
defer rows.Close()
for rows.Next() {
var pageID string
err = rows.Scan(&pageID)
if err != nil {
return nil, err
}
pageHashes = append(pageHashes, pageID)
}
// get any error encountered during iteration
err = rows.Err()
if err != nil {
return nil, err
}
return pageHashes, nil
}
// GetLinksTo retrieves the links from this page hash.
func (s *Storage) GetLinksTo(pageHash string, limit int) ([]string, error) {
query := fmt.Sprintf(`SELECT from_page_id FROM %s WHERE to_page_id = $1 LIMIT $2`, s.LinkTable)
// Prepare query
stmt, err := s.db.Prepare(query)
if err != nil {
return nil, err
}
defer stmt.Close()
// Execute query
var pageHashes []string
s.linkLock.RLock()
rows, err := stmt.Query(pageHash, limit)
s.linkLock.RUnlock()
defer rows.Close()
for rows.Next() {
var pageID string
err = rows.Scan(&pageID)
if err != nil {
return nil, err
}
pageHashes = append(pageHashes, pageID)
}
// get any error encountered during iteration
err = rows.Err()
if err != nil {
return nil, err
}
return pageHashes, nil
}
// CountLinks retrieves an estimate of the number of links scraped.
func (s *Storage) CountLinks() (int, error) {
var count int
query := fmt.Sprintf(`SELECT reltuples::bigint AS estimate
FROM pg_class
WHERE relname='%s'`, s.LinkTable)
// Prepare query
stmt, err := s.db.Prepare(query)
if err != nil {
return count, err
}
defer stmt.Close()
// Execute query
err = stmt.QueryRow().Scan(&count)
if err != nil {
return count, err
}
return count, nil
}
// CountPages retrieves an estimate of the number of pages scraped.
func (s *Storage) CountPages() (int, error) {
var count int
query := fmt.Sprintf(`SELECT reltuples::bigint AS estimate
FROM pg_class
WHERE relname='%s'`, s.PageTable)
// Prepare query
stmt, err := s.db.Prepare(query)
if err != nil {
return count, err
}
defer stmt.Close()
// Execute query
err = stmt.QueryRow().Scan(&count)
if err != nil {
return count, err
}
return count, nil
}
// AddLink first checks that it does not exist, and then inserts the page
func (s *Storage) AddLink(link *Link) error {
s.linkLock.Lock()
defer s.linkLock.Unlock()
// First, check the link already exists
visited, err := s.CheckLinkExists(link.FromU, link.ToU)
if err != nil {
return err
}
if visited {
return nil
}
// Then try to add the pages
s.AddPage(&Page{U: link.FromU})
s.AddPage(&Page{U: link.ToU})
query := fmt.Sprintf(`INSERT INTO %s (from_page_id, to_page_id, text) VALUES($1, $2, $3);`, s.LinkTable)
_, err = s.db.Exec(query, linkutils.Hash(link.FromU), linkutils.Hash(link.ToU), link.LinkText)
return err
}
// BatchAddLinks takes a batch of links and inserts them, not giving a fuck whether or not they clash
func (s *Storage) BatchAddLinks(links []*Link) error {
// Hmmm, not sure what to do about this page bullshit, maybe I'll make a batch process for that too
// // Then try to add the pages
// s.AddPage(fromU)
// s.AddPage(toU)
valueStrings := make([]string, 0, len(links))
vals := []interface{}{}
for _, link := range links {
valueStrings = append(valueStrings, "(?, ?, ?)")
vals = append(vals, linkutils.Hash(link.FromU), linkutils.Hash(link.ToU), strings.ToValidUTF8(link.LinkText, ""))
}
sqlStr := fmt.Sprintf(
"INSERT INTO %s (from_page_id, to_page_id, text) VALUES %s ON CONFLICT DO NOTHING",
s.LinkTable,
strings.Join(valueStrings, ","),
)
//Replacing ? with $n for postgres
sqlStr = ReplaceSQL(sqlStr, "?")
//prepare the statement
stmt, err := s.db.Prepare(sqlStr)
if err != nil {
return err
}
defer stmt.Close()
//format all vals at once
_, err = stmt.Exec(vals...)
return err
}
// BatchAddPages takes a batch of pages and inserts them, not giving a fuck whether or not they clash
func (s *Storage) BatchAddPages(pages []*Page) error {
valueStrings := make([]string, 0, len(pages))
vals := []interface{}{}
for _, page := range pages {
valueStrings = append(valueStrings, "(?, ?, ?, ?)")
vals = append(vals, linkutils.Hash(page.U), page.U.Hostname(), page.U.EscapedPath(), page.U.String())
}
sqlStr := fmt.Sprintf(
"INSERT INTO %s (page_id, host, path, url) VALUES %s ON CONFLICT DO NOTHING ",
s.PageTable,
strings.Join(valueStrings, ","),
)
//Replacing ? with $n for postgres
sqlStr = ReplaceSQL(sqlStr, "?")
//prepare the statement
stmt, err := s.db.Prepare(sqlStr)
if err != nil {
return err
}
defer stmt.Close()
//format all vals at once
_, err = stmt.Exec(vals...)
return err
}
// ReplaceSQL replaces the instance occurrence of any string pattern with an increasing $n based sequence
func ReplaceSQL(old, searchPattern string) string {
tmpCount := strings.Count(old, searchPattern)
for m := 1; m <= tmpCount; m++ {
old = strings.Replace(old, searchPattern, "$"+strconv.Itoa(m), 1)
}
return old
}