1 files changed, 237 insertions, 0 deletions
diff --git a/util.go b/util.go
new file mode 100644
index 0000000..93bf0a6
--- /dev/null
+++ b/util.go
@@ -0,0 +1,237 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"net"
+	"net/http"
+	"os"
+	"regexp"
+)
+
+var privateIPBlocks []*net.IPNet
+
+// isPrivateIP checks to if the provided IP address is a loopback, link-local
+// or unique-local address
+//
+// credit: https://stackoverflow.com/a/50825191
+func isPrivateIP(ip net.IP) bool {
+	if privateIPBlocks == nil {
+		for _, cidr := range []string{
+			"127.0.0.0/8",    // IPv4 loopback
+			"10.0.0.0/8",     // RFC1918
+			"172.16.0.0/12",  // RFC1918
+			"192.168.0.0/16", // RFC1918
+			"169.254.0.0/16", // RFC3927 link-local
+			"::1/128",        // IPv6 loopback
+			"fe80::/10",      // IPv6 link-local
+			"fc00::/7",       // IPv6 unique local addr
+		} {
+			_, block, err := net.ParseCIDR(cidr)
+			if err != nil {
+				panic(fmt.Errorf("parse error on %q: %v", cidr, err))
+			}
+			privateIPBlocks = append(privateIPBlocks, block)
+		}
+	}
+	if ip.IsLoopback() || ip.IsLinkLocalUnicast() || ip.IsLinkLocalMulticast() {
+		return true
+	}
+	for _, block := range privateIPBlocks {
+		if block.Contains(ip) {
+			return true
+		}
+	}
+	return false
+}
+
+// getDOIFromBytes returns the DOI parsed from the provided []byte slice
+func getDOIFromBytes(b []byte) []byte {
+	re := regexp.MustCompile(`(10[.][0-9]{4,}[^\s"/<>]*/[^\s"'<>,\{\};:\[\]\?&]+)`)
+	return re.Find(b)
+}
+
+// makeRequest makes a request to a remote resource using the provided
+// *http.Client and returns its *http.Response
+func makeRequest(client *http.Client, u string) (*http.Response, error) {
+	req, err := http.NewRequest("GET", u, nil)
+
+	// sciencedirect and company block atypical user agents
+	req.Header.Add("User-Agent", "Mozilla/5.0 (Windows NT 10.0; rv:78.0) Gecko/20100101 Firefox/78.0")
+
+	resp, err := client.Do(req)
+	if err != nil {
+		return nil, err
+	}
+	if resp.StatusCode != http.StatusOK {
+		return nil, fmt.Errorf("%q: status code not OK", u)
+	}
+	return resp, nil
+}
+
+// getDOIFromPage returns the parsed DOI from the body of the *http.Response
+// provided
+func getDOIFromPage(resp *http.Response) []byte {
+	defer resp.Body.Close()
+	scanner := bufio.NewScanner(resp.Body)
+	for scanner.Scan() {
+		doi := getDOIFromBytes(scanner.Bytes())
+		if doi != nil {
+			return doi
+		}
+		if err := scanner.Err(); err != nil {
+			return nil
+		}
+	}
+	return nil
+}
+
+// renameFile is an alternative to os.Rename which supports moving files
+// between devices where os.Rename would return an error (cross-device link)
+func renameFile(src string, dst string) (err error) {
+	if src == dst {
+		return nil
+	}
+	err = copyFile(src, dst)
+	if err != nil {
+		return fmt.Errorf("failed to copy source file %s to %s: %s", src, dst, err)
+	}
+	err = os.RemoveAll(src)
+	if err != nil {
+		return fmt.Errorf("failed to cleanup source file %s: %s", src, err)
+	}
+	return nil
+}
+
+// copyFile copies a file located at src to dst, used by renameFile()
+//
+// credit: https://gist.github.com/r0l1/92462b38df26839a3ca324697c8cba04
+func copyFile(src, dst string) (err error) {
+	in, err := os.Open(src)
+	if err != nil {
+		return
+	}
+	defer in.Close()
+
+	out, err := os.Create(dst)
+	if err != nil {
+		return
+	}
+	defer func() {
+		if e := out.Close(); e != nil {
+			err = e
+		}
+	}()
+
+	_, err = io.Copy(out, in)
+	if err != nil {
+		return
+	}
+
+	err = out.Sync()
+	if err != nil {
+		return
+	}
+
+	si, err := os.Stat(src)
+	if err != nil {
+		return
+	}
+	err = os.Chmod(dst, si.Mode())
+	if err != nil {
+		return
+	}
+
+	return
+}
+
+// getMetaFromDOI saves doi.org API data to TempFile and returns its path
+func getMetaFromDOI(client *http.Client, doi []byte) (string, error) {
+	u := "https://doi.org/" + string(doi)
+	req, err := http.NewRequest("GET", u, nil)
+
+	req.Header.Add("Accept", "application/vnd.crossref.unixref+xml;q=1,application/rdf+xml;q=0.5")
+	resp, err := client.Do(req)
+	if err != nil {
+		return "", err
+	}
+
+	if resp.StatusCode != http.StatusOK {
+		return "", fmt.Errorf("%q: status code not OK, DOI invalid?", u)
+	}
+	if resp.Header.Get("Content-Type") != "application/vnd.crossref.unixref+xml" {
+		return "", fmt.Errorf("%q: content-type not application/vnd.crossref.unixref+xml", u)
+	}
+	if err != nil {
+		return "", err
+	}
+
+	// create a temporary file to store XML stream
+	tmpXML, err := ioutil.TempFile("", "tmp-*.meta.xml")
+	if err != nil {
+		return "", err
+	}
+
+	// incrementally save XML data to the temporary file; saves memory using
+	// the filesystem instead of passing around buffers
+	if err := saveRespBody(resp, tmpXML.Name()); err != nil {
+		return "", err
+	}
+	if err := tmpXML.Close(); err != nil {
+		return "", err
+	}
+	return tmpXML.Name(), nil
+}
+
+// getPaper saves makes an outbound request to a remote resource and saves the
+// response body to a temporary file, returning its path, provided the response
+// has the content-type application/pdf
+func getPaper(client *http.Client, u string) (string, error) {
+	req, err := http.NewRequest("GET", u, nil)
+
+	// sci-hub gives us the paper directly (no iframe) if we're on mobile
+	req.Header.Add("User-Agent", "Mozilla/5.0 (iPhone; CPU iPhone OS 13_7 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/13.1.2 Mobile/15E148 Safari/604.1")
+
+	resp, err := client.Do(req)
+	if err != nil {
+		return "", err
+	}
+
+	if resp.StatusCode != http.StatusOK {
+		return "", fmt.Errorf("%q: status code not OK", u)
+	}
+	if resp.Header.Get("Content-Type") != "application/pdf" {
+		return "", fmt.Errorf("%q: content-type not application/pdf", u)
+	}
+	tmpPDF, err := ioutil.TempFile("", "tmp-*.pdf")
+	if err != nil {
+		return "", err
+	}
+
+	// write resp.Body (paper data) to tmpPDF
+	if err := saveRespBody(resp, tmpPDF.Name()); err != nil {
+		return "", err
+	}
+	if err := tmpPDF.Close(); err != nil {
+		return "", err
+	}
+	return tmpPDF.Name(), nil
+}
+
+// saveRespBody writes the provided http.Response to path
+func saveRespBody(resp *http.Response, path string) error {
+	out, err := os.Create(path)
+	if err != nil {
+		return err
+	}
+	defer out.Close()
+
+	r := http.MaxBytesReader(nil, resp.Body, MAX_SIZE)
+	_, err = io.Copy(out, r)
+	if err != nil {
+		return err
+	}
+	return nil
+}