From 3230f43a88729440ae7408b5b2914b186be95a84 Mon Sep 17 00:00:00 2001
From: Nick White <git@njw.name>
Date: Tue, 23 Nov 2021 15:59:06 +0000
Subject: rescribe: Improve pdf consumption by ensuring only jpg or png are
 saved to upload

---
 cmd/rescribe/main.go | 49 +++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 47 insertions(+), 2 deletions(-)

diff --git a/cmd/rescribe/main.go b/cmd/rescribe/main.go
index cd0b955..0724c88 100644
--- a/cmd/rescribe/main.go
+++ b/cmd/rescribe/main.go
@@ -15,6 +15,8 @@ import (
 	_ "embed"
 	"flag"
 	"fmt"
+	"image/jpeg"
+	"image/png"
 	"io"
 	"io/ioutil"
 	"log"
@@ -325,7 +327,8 @@ func extractPdfImgs(path string) (string, error) {
 			}
 
 			fn := fmt.Sprintf("%s-%04d.jpg", k, pgnum)
-			w, err := os.Create(filepath.Join(tempdir, fn))
+			path := filepath.Join(tempdir, fn)
+			w, err := os.Create(path)
 			defer w.Close()
 			if err != nil {
 				return tempdir, fmt.Errorf("Error creating file to extract PDF image: %v\n", err)
@@ -339,7 +342,10 @@ func extractPdfImgs(path string) (string, error) {
 			w.Close()
 			r.Close()
 
-			// TODO: check that what we've written is actually a JPEG
+			err = rmIfNotImage(path)
+			if err != nil {
+				return tempdir, fmt.Errorf("Error removing extracted image %s from PDF: %v\n", fn, err)
+			}
 		}
 	}
 	// TODO: check for places where there are multiple images per page, and only keep largest ones where that's the case
@@ -347,6 +353,45 @@ func extractPdfImgs(path string) (string, error) {
 	return tempdir, nil
 }
 
+// rmIfNotImage attempts to decode a given file as an image. If it is
+// decode-able as PNG, then rename file extension from .jpg to .png,
+// if it fails to be read as PNG or JPEG it will be deleted.
+func rmIfNotImage(f string) error {
+	r, err := os.Open(f)
+	defer r.Close()
+	if err != nil {
+		return fmt.Errorf("Failed to open image %s: %v\n", f, err)
+	}
+	_, err = png.Decode(r)
+	r.Close()
+	if err == nil {
+		b := strings.TrimSuffix(f, ".jpg")
+		fmt.Printf("%s is PNG; renaming\n", f)
+		err = os.Rename(f, b + ".png")
+		if err != nil {
+			return fmt.Errorf("Error renaming %s to %s: %v", f, b + ".png", err)
+		}
+		return nil
+	}
+
+	r, err = os.Open(f)
+	defer r.Close()
+	if err != nil {
+		return fmt.Errorf("Failed to open image %s: %v\n", f, err)
+	}
+	_, err = jpeg.Decode(r)
+	if err != nil {
+		r.Close()
+		fmt.Printf("%s is not PNG or JPEG; removing\n", f)
+		err = os.Remove(f)
+		if err != nil {
+			return fmt.Errorf("Failed to remove invalid image %s: %v", f, err)
+		}
+	}
+
+	return nil
+}
+
 func startProcess(logger log.Logger, tessCommand string, bookdir string, bookname string, trainingName string, systess bool, savedir string, tessdir string) error {
 	_, err := exec.Command(tessCommand, "--help").Output()
 	if err != nil {
-- 
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