From a3cf901b6d1246d3e00875a3e88c69bee068156d Mon Sep 17 00:00:00 2001
From: Paul Montag <paul.david.montag@gmail.com>
Date: Sat, 22 Dec 2018 18:54:08 -0600
Subject: Updated font id generation and image id (#222)

Generated font ID will now be the same across machines when generating
the same font file.
Generated image Id will now be the same across machines when generating
the same image file.
---
 def.go      | 24 +++++++++++++++++++++---
 fpdf.go     | 23 ++++++++++++++++-------
 template.go |  2 +-
 3 files changed, 38 insertions(+), 11 deletions(-)

diff --git a/def.go b/def.go
index 1187c8f..f19e86b 100644
--- a/def.go
+++ b/def.go
@@ -18,7 +18,10 @@ package gofpdf
 
 import (
 	"bytes"
+	"crypto/sha1"
 	"encoding/gob"
+	"encoding/json"
+	"fmt"
 	"io"
 	"time"
 )
@@ -164,7 +167,6 @@ func (p PointType) XY() (float64, float64) {
 type ImageInfoType struct {
 	data  []byte
 	smask []byte
-	i     int
 	n     int
 	w     float64
 	h     float64
@@ -176,11 +178,17 @@ type ImageInfoType struct {
 	trns  []int
 	scale float64 // document scaling factor
 	dpi   float64
+	i     string
+}
+
+func generateImageID(info *ImageInfoType) (string, error) {
+	b, err := info.GobEncode()
+	return fmt.Sprintf("%x", sha1.Sum(b)), err
 }
 
 // GobEncode encodes the receiving image to a byte slice.
 func (info *ImageInfoType) GobEncode() (buf []byte, err error) {
-	fields := []interface{}{info.data, info.smask, info.i, info.n, info.w, info.h, info.cs,
+	fields := []interface{}{info.data, info.smask, info.n, info.w, info.h, info.cs,
 		info.pal, info.bpc, info.f, info.dp, info.trns, info.scale, info.dpi}
 	w := new(bytes.Buffer)
 	encoder := gob.NewEncoder(w)
@@ -196,13 +204,15 @@ func (info *ImageInfoType) GobEncode() (buf []byte, err error) {
 // GobDecode decodes the specified byte buffer (generated by GobEncode) into
 // the receiving image.
 func (info *ImageInfoType) GobDecode(buf []byte) (err error) {
-	fields := []interface{}{&info.data, &info.smask, &info.i, &info.n, &info.w, &info.h,
+	fields := []interface{}{&info.data, &info.smask, &info.n, &info.w, &info.h,
 		&info.cs, &info.pal, &info.bpc, &info.f, &info.dp, &info.trns, &info.scale, &info.dpi}
 	r := bytes.NewBuffer(buf)
 	decoder := gob.NewDecoder(r)
 	for j := 0; j < len(fields) && err == nil; j++ {
 		err = decoder.Decode(fields[j])
 	}
+
+	info.i, err = generateImageID(info)
 	return
 }
 
@@ -686,6 +696,14 @@ type fontDefType struct {
 	i            string       // 1-based position in font list, set by font loader, not this program
 }
 
+// generateFontID generates a font Id from the font definition
+func generateFontID(fdt fontDefType) (string, error) {
+	// file can be different if generated in different instance
+	fdt.File = ""
+	b, err := json.Marshal(&fdt)
+	return fmt.Sprintf("%x", sha1.Sum(b)), err
+}
+
 type fontInfoType struct {
 	Data               []byte
 	File               string
diff --git a/fpdf.go b/fpdf.go
index 400c83f..bc047b1 100644
--- a/fpdf.go
+++ b/fpdf.go
@@ -23,7 +23,6 @@ package gofpdf
 
 import (
 	"bytes"
-	"crypto/sha1"
 	"encoding/binary"
 	"encoding/json"
 	"fmt"
@@ -1578,9 +1577,12 @@ func (f *Fpdf) AddFontFromBytes(familyStr, styleStr string, jsonFileBytes, zFile
 		return
 	}
 
-	// search existing encodings
-	info.i = fmt.Sprintf("%x", sha1.Sum(jsonFileBytes))
+	if info.i, err = generateFontID(info); err != nil {
+		f.err = err
+		return
+	}
 
+	// search existing encodings
 	if len(info.Diff) > 0 {
 		n := -1
 
@@ -2523,7 +2525,7 @@ func (f *Fpdf) imageOut(info *ImageInfoType, x, y, w, h float64, allowNegativeX,
 	}
 	// dbg("h %.2f", h)
 	// q 85.04 0 0 NaN 28.35 NaN cm /I2 Do Q
-	f.outf("q %.5f 0 0 %.5f %.5f %.5f cm /I%d Do Q", w*f.k, h*f.k, x*f.k, (f.h-(y+h))*f.k, info.i)
+	f.outf("q %.5f 0 0 %.5f %.5f %.5f cm /I%s Do Q", w*f.k, h*f.k, x*f.k, (f.h-(y+h))*f.k, info.i)
 	if link > 0 || len(linkStr) > 0 {
 		f.newLink(x, y, w, h, link, linkStr)
 	}
@@ -2660,7 +2662,10 @@ func (f *Fpdf) RegisterImageOptionsReader(imgName string, options ImageOptions,
 	if f.err != nil {
 		return
 	}
-	info.i = len(f.images) + 1
+
+	if info.i, f.err = generateImageID(info); f.err != nil {
+		return
+	}
 	f.images[imgName] = info
 
 	return
@@ -2952,8 +2957,12 @@ func (f *Fpdf) loadfont(r io.Reader) (def fontDefType) {
 	err = json.Unmarshal(buf.Bytes(), &def)
 	if err != nil {
 		f.err = err
+		return
+	}
+
+	if def.i, err = generateFontID(def); err != nil {
+		f.err = err
 	}
-	def.i = fmt.Sprintf("%x", sha1.Sum(buf.Bytes()))
 	// dump(def)
 	return
 }
@@ -3556,7 +3565,7 @@ func (f *Fpdf) putxobjectdict() {
 		}
 		for _, key = range keyList {
 			image = f.images[key]
-			f.outf("/I%d %d 0 R", image.i, image.n)
+			f.outf("/I%s %d 0 R", image.i, image.n)
 		}
 	}
 	{
diff --git a/template.go b/template.go
index e3e4fe5..31204c2 100644
--- a/template.go
+++ b/template.go
@@ -178,7 +178,7 @@ func (f *Fpdf) putTemplates() {
 				for _, key = range keyList {
 					// for _, ti := range tImages {
 					ti = tImages[key]
-					f.outf("/I%d %d 0 R", ti.i, ti.n)
+					f.outf("/I%s %d 0 R", ti.i, ti.n)
 				}
 			}
 			for _, tt := range tTemplates {
-- 
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