From b0808416cc830aef680f5b6f99a616d425cbb9de Mon Sep 17 00:00:00 2001
From: Nick White <git@njw.name>
Date: Tue, 23 Jun 2020 13:32:07 +0100
Subject: Add IIIF downloader, that just supports BNF for now

---
 cmd/iiifdownloader/main.go | 178 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 178 insertions(+)
 create mode 100644 cmd/iiifdownloader/main.go

diff --git a/cmd/iiifdownloader/main.go b/cmd/iiifdownloader/main.go
new file mode 100644
index 0000000..03a15bc
--- /dev/null
+++ b/cmd/iiifdownloader/main.go
@@ -0,0 +1,178 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"log"
+	"net/http"
+	"os"
+	"path"
+	"strings"
+)
+
+const usage = `Usage: iiifdownloader url
+
+Downloads all pages from a IIIF server.
+`
+
+const bnfPrefix = `https://gallica.bnf.fr/ark:/`
+
+func filesAreIdentical(fn1, fn2 string) (bool, error) {
+	f1, err := os.Open(fn1)
+	defer f1.Close()
+	if err != nil {
+		return false, fmt.Errorf("Error opening file %s: %v\n", fn1, err)
+	}
+	b1, err := ioutil.ReadAll(f1)
+	if err != nil {
+		return false, fmt.Errorf("Error reading file %s: %v\n", fn1, err)
+	}
+	f2, err := os.Open(fn2)
+	defer f2.Close()
+	if err != nil {
+		return false, fmt.Errorf("Error opening file %s: %v\n", fn2, err)
+	}
+	b2, err := ioutil.ReadAll(f2)
+	if err != nil {
+		return false, fmt.Errorf("Error reading file %s: %v\n", fn2, err)
+	}
+
+	for i, _ := range b1 {
+		if b1[i] != b2[i] {
+			return false, nil
+		}
+	}
+	return true, nil
+}
+
+func main() {
+	flag.Usage = func() {
+		fmt.Fprintf(flag.CommandLine.Output(), usage)
+		flag.PrintDefaults()
+	}
+	flag.Parse()
+
+	if flag.NArg() < 1 {
+		flag.Usage()
+		return
+	}
+
+	url := flag.Arg(0)
+
+	var bookdir string
+	var pgurlStart, pgurlEnd string
+	var pgurlAltStart, pgurlAltEnd string
+	//var pgNums []int
+	var noPgNums bool
+
+	switch {
+	case strings.HasPrefix(url, bnfPrefix):
+		f := strings.Split(url[len(bnfPrefix):], "/")
+		if len(f) < 2 {
+			log.Fatalln("Failed to extract BNF book ID from URL")
+		}
+		bookid := f[0] + "/" + f[1]
+		bookdir = f[0] + "-" + f[1]
+
+		pgurlStart = "https://gallica.bnf.fr/iiif/ark:/" + bookid + "/f"
+		pgurlEnd = "/full/full/0/native.jpg"
+		noPgNums = true
+
+		// BNF don't have all pages available from IIIF, but they do have
+		// the missing ones in less good quality from an alternative URL.
+		pgurlAltStart = "https://gallica.bnf.fr/ark:/" + bookid + "/f"
+		pgurlAltEnd = ".highres"
+	default:
+		log.Fatalln("Error: generic IIIF downloading not supported yet")
+	}
+
+	err := os.MkdirAll(bookdir, 0777)
+	if err != nil {
+		log.Fatalf("Error creating book dir: %v\n", err)
+	}
+
+	if noPgNums {
+		pgnum := 0
+		for {
+			pgnum++
+
+			fmt.Printf("Downloading page %d\n", pgnum)
+
+			fn := path.Join(bookdir, fmt.Sprintf("%04d.jpg", pgnum))
+			_, err = os.Stat(fn)
+			if err == nil || os.IsExist(err) {
+				fmt.Printf("Skipping already present page %d\n", pgnum)
+				continue
+			}
+
+			u := fmt.Sprintf("%s%d%s", pgurlStart, pgnum, pgurlEnd)
+			resp, err := http.Get(u)
+			if err != nil {
+				log.Fatalf("Error downloading page %d, %s: %v\n", pgnum, u, err)
+			}
+			defer resp.Body.Close()
+			switch {
+			case resp.StatusCode == http.StatusNotFound:
+				fmt.Printf("Got 404, assuming end of pages, for page %d, %s\n", pgnum, u)
+				return
+			case resp.StatusCode != http.StatusOK:
+				fmt.Printf("Error downloading page %d, %s: HTTP Code %s\n", pgnum, u, resp.Status)
+
+				if pgurlAltStart == "" && pgurlAltEnd == "" {
+					log.Fatalln("No alternative URL to try, book failed (or ended, hopefully)")
+				}
+
+				fmt.Printf("Trying to redownload page %d at lower quality\n", pgnum)
+				u = fmt.Sprintf("%s%d%s", pgurlAltStart, pgnum, pgurlAltEnd)
+				resp, err = http.Get(u)
+				if err != nil {
+					log.Fatalf("Error downloading page %d, %s: %v\n", pgnum, u, err)
+				}
+				defer resp.Body.Close()
+
+				if resp.StatusCode != http.StatusOK {
+					log.Fatalf("Error downloading page %d, %s: HTTP Code %s\n", pgnum, u, resp.Status)
+				}
+			}
+
+			f, err := os.Create(fn)
+			defer f.Close()
+			if err != nil {
+				log.Fatalf("Error creating file %s: %v\n", fn, err)
+			}
+			_, err = io.Copy(f, resp.Body)
+			if err != nil {
+				log.Fatalf("Error writing file %s: %v\n", fn, err)
+			}
+
+			// Close once finished with, as defer won't trigger until the end of the function
+			resp.Body.Close()
+			f.Close()
+
+			// Check that the last two downloaded files aren't identical, as this
+			// can happen when there are no more pages to download.
+			if pgnum == 1 {
+				continue
+			}
+			fn2 := path.Join(bookdir, fmt.Sprintf("%04d.jpg", pgnum-1))
+			identical, err := filesAreIdentical(fn, fn2)
+			if err != nil {
+				log.Fatalf("Error checking for files being identical: %v\n", err)
+			}
+			if identical {
+				fmt.Println("Last 2 pages were identical, looks like it's the end of the book")
+				err = os.Remove(fn)
+				if err != nil {
+					log.Fatalf("Error removing dupilicate page %d: %v", fn, err)
+				}
+				err = os.Remove(fn2)
+				if err != nil {
+					log.Fatalf("Error removing dupilicate page %d: %v", fn2, err)
+				}
+				return
+			}
+		}
+	}
+}
-- 
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