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unpaywall.go
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unpaywall.go
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//Package unpaywall provides utitlity functions for the unpaywall.org api
package unpaywall
import (
"encoding/json"
"errors"
"fmt"
"io/ioutil"
"math/rand"
"net/http"
"net/http/cookiejar"
"os"
"path/filepath"
"regexp"
"strconv"
"sync"
"time"
)
const (
unpaywallAPIURL = "https://api.unpaywall.org/v2/%s?email=%s"
workersCount = 5
)
//Unpaywall provides methods to request the unpaywall api
type Unpaywall struct {
email string
client *http.Client
}
//New returns a new unpaywall object to send requests to the API
func New(email string) (*Unpaywall, error) {
//regex from https://www.w3.org/TR/html5/forms.html#valid-e-mail-address
mailRegex := regexp.MustCompile("^[a-zA-Z0-9.!#$%&'*+/=?^_`{|}~-]+@[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?(?:\\.[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)*$")
if !mailRegex.MatchString(email) {
return nil, errors.New("invalid email address")
}
cookieJar, _ := cookiejar.New(nil)
client := &http.Client{
Jar: cookieJar,
}
u := &Unpaywall{
email,
client,
}
return u, nil
}
//SearchResult describes the returned data structure from unpaywall
type SearchResult struct {
StatusCode int
BestOaLocation struct {
Evidence string `json:"evidence"`
HostType string `json:"host_type"`
IsBest bool `json:"is_best"`
License string `json:"license"`
PmhID string `json:"pmh_id"`
Updated string `json:"updated"`
URL string `json:"url"`
URLForLandingPage string `json:"url_for_landing_page"`
URLForPdf string `json:"url_for_pdf"`
Version string `json:"version"`
} `json:"best_oa_location"`
DataStandard int `json:"data_standard"`
Doi string `json:"doi"`
DoiURL string `json:"doi_url"`
Genre string `json:"genre"`
IsOa bool `json:"is_oa"`
JournalIsInDoaj bool `json:"journal_is_in_doaj"`
JournalIsOa bool `json:"journal_is_oa"`
JournalIssns string `json:"journal_issns"`
JournalName string `json:"journal_name"`
OaLocations []struct {
Evidence string `json:"evidence"`
HostType string `json:"host_type"`
IsBest bool `json:"is_best"`
License string `json:"license"`
PmhID string `json:"pmh_id"`
Updated string `json:"updated"`
URL string `json:"url"`
URLForLandingPage string `json:"url_for_landing_page"`
URLForPdf string `json:"url_for_pdf"`
Version string `json:"version"`
} `json:"oa_locations"`
PublishedDate string `json:"published_date"`
Publisher string `json:"publisher"`
Title string `json:"title"`
Updated string `json:"updated"`
XReportedNoncompliantCopies []interface{} `json:"x_reported_noncompliant_copies"`
Year int `json:"year"`
ZAuthors []struct {
Family string `json:"family"`
Given string `json:"given"`
} `json:"z_authors"`
}
//RequestByDOI sends a new request to unpaywall with the given DOI
func (u *Unpaywall) RequestByDOI(doi string) (*SearchResult, error) {
searchResult := new(SearchResult)
if u == nil {
return searchResult, errors.New("check for errors while initializing Unpaywall")
}
requestURL := fmt.Sprintf(unpaywallAPIURL, doi, u.email)
res, err := u.client.Get(requestURL)
if err != nil {
return searchResult, err
}
defer res.Body.Close()
searchResult.StatusCode = res.StatusCode
if res.StatusCode != http.StatusOK {
return searchResult, fmt.Errorf("unsuccessful request %s", res.Status)
}
response := json.NewDecoder(res.Body)
if err != nil {
return searchResult, err
}
err = response.Decode(&searchResult)
return searchResult, err
}
//RequestByDOIs searches for the papers by DOI and returns all found results / errors
func (u *Unpaywall) RequestByDOIs(dois []string) (<-chan *SearchResult, <-chan error) {
var wg sync.WaitGroup
workerChan := make(chan string, len(dois))
resultChan := make(chan *SearchResult, int(len(dois)/2))
errorChan := make(chan error, int(len(dois)/2))
for i := 0; i < workersCount; i++ {
go func() {
for doi := range workerChan {
func(doi string) {
defer wg.Done()
res, err := u.RequestByDOI(doi)
if err == nil {
resultChan <- res
} else {
errorChan <- err
}
}(doi)
}
}()
}
wg.Add(len(dois))
for _, doi := range dois {
workerChan <- doi
}
close(workerChan)
go func() {
wg.Wait()
close(resultChan)
close(errorChan)
}()
return resultChan, errorChan
}
//DownloadByDOI searches for the paper by DOI and downloads it to the target path
//returns the filename / error
func (u *Unpaywall) DownloadByDOI(doi string, targetPath string) (string, error) {
res, err := u.RequestByDOI(doi)
if err != nil {
return "", err
}
if res.BestOaLocation.URLForPdf == "" {
return "", errors.New("could not find valid pdf")
}
pdfRes, err := u.client.Get(res.BestOaLocation.URLForPdf)
if err != nil {
return "", err
}
fileContent, err := ioutil.ReadAll(pdfRes.Body)
if err != nil {
return "", err
}
targetFilename := generateRandomFilename()
cleanFilenameRegex := regexp.MustCompile(`\W`)
if res.Title != "" {
targetFilename = cleanFilenameRegex.ReplaceAllString(res.Title, "_")
}
targetFilePath := fmt.Sprintf(filepath.Dir(targetPath)+"%s%s", string(os.PathSeparator), targetFilename+".pdf")
// Add random numbers to filename if file already exists
for fileExists(targetFilePath) {
targetFilePath = fmt.Sprintf(filepath.Dir(targetPath)+"%s%s", string(os.PathSeparator), targetFilename+generateRandomFilename()+".pdf")
}
err = ioutil.WriteFile(targetFilePath, fileContent, 777)
return targetFilePath, err
}
//DownloadByDOIs searches for the papers by DOI and downloads all found documents to the target path
//returns the filenames / errors
func (u *Unpaywall) DownloadByDOIs(dois []string, targetPath string) (<-chan string, <-chan error) {
var wg sync.WaitGroup
workerChan := make(chan string, len(dois))
resultChan := make(chan string, int(len(dois)/2))
errorChan := make(chan error, int(len(dois)/2))
for i := 0; i < workersCount; i++ {
go func() {
for doi := range workerChan {
func(doi string, targetPath string) {
defer wg.Done()
res, err := u.DownloadByDOI(doi, targetPath)
if res != "" {
resultChan <- res
}
if err != nil {
errorChan <- err
}
}(doi, targetPath)
}
}()
}
wg.Add(len(dois))
for _, doi := range dois {
workerChan <- doi
}
close(workerChan)
go func() {
wg.Wait()
close(resultChan)
close(errorChan)
}()
return resultChan, errorChan
}
func fileExists(filename string) bool {
_, err := os.Stat(filename)
return !os.IsNotExist(err)
}
func generateRandomFilename() string {
rand.Seed(time.Now().Unix())
return strconv.Itoa(rand.Intn(100000000) + 100000000)
}