From 3da3d103216bf8966236621389e75943fdf08d24 Mon Sep 17 00:00:00 2001
From: Tor Andersson <tor.andersson@artifex.com>
Date: Wed, 4 Jul 2018 12:14:21 +0200
Subject: Add digital signature appearance synthesis.

The pdf_update_signature_appearance function must be called directly by
the signing code when it signs the document; as only the signing code has
all the text that needs to be written into the appearance.
---
 source/pdf/pdf-appearance.c | 86 +++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 84 insertions(+), 2 deletions(-)

(limited to 'source/pdf')

diff --git a/source/pdf/pdf-appearance.c b/source/pdf/pdf-appearance.c
index 0e2e2847..1bf0fd33 100644
--- a/source/pdf/pdf-appearance.c
+++ b/source/pdf/pdf-appearance.c
@@ -1202,9 +1202,91 @@ pdf_write_appearance(fz_context *ctx, pdf_annot *annot, fz_buffer *buf,
 	}
 }
 
-void pdf_update_signature_appearance(fz_context *ctx, pdf_annot *annot, const char *name, const char *text, const char *date)
+void pdf_update_signature_appearance(fz_context *ctx, pdf_annot *annot, const char *name, const char *dn, const char *date)
 {
-	fz_throw(ctx, FZ_ERROR_GENERIC, "writing digital signature appearance streams is not yet implemented");
+	pdf_obj *ap, *new_ap_n, *res_font;
+	char tmp[500];
+	fz_font *helv = NULL;
+	fz_font *zadb = NULL;
+	pdf_obj *res = NULL;
+	fz_buffer *buf;
+	fz_rect rect;
+	float w, h, size, name_w;
+
+	rect = pdf_to_rect(ctx, pdf_dict_get(ctx, annot->obj, PDF_NAME(Rect)));
+
+	fz_var(helv);
+	fz_var(zadb);
+	fz_var(res);
+
+	buf = fz_new_buffer(ctx, 1024);
+	fz_try(ctx)
+	{
+		helv = fz_new_base14_font(ctx, "Helvetica");
+		zadb = fz_new_base14_font(ctx, "ZapfDingbats");
+
+		res = pdf_new_dict(ctx, annot->page->doc, 1);
+		res_font = pdf_dict_put_dict(ctx, res, PDF_NAME(Font), 1);
+		pdf_dict_put_drop(ctx, res_font, PDF_NAME(Helv), pdf_add_simple_font(ctx, annot->page->doc, helv, 0));
+		pdf_dict_put_drop(ctx, res_font, PDF_NAME(ZaDb), pdf_add_simple_font(ctx, annot->page->doc, zadb, 0));
+
+		w = (rect.x1 - rect.x0) / 2;
+		h = (rect.y1 - rect.y0);
+
+		/* Use flower symbol from ZapfDingbats as sigil */
+		fz_append_printf(ctx, buf, "q 1 0.8 0.8 rg BT /ZaDb %g Tf %g %g Td (`) Tj ET Q\n",
+			h*1.1f,
+			rect.x0 + w - (h*0.4f),
+			rect.y0 + h*0.1f);
+
+		/* Name */
+		name_w = measure_simple_string(ctx, helv, name);
+		size = fz_min(fz_min((w - 4) / name_w, h), 24);
+		fz_append_string(ctx, buf, "BT\n");
+		fz_append_printf(ctx, buf, "/Helv %g Tf\n", size);
+		fz_append_printf(ctx, buf, "%g %g Td\n", rect.x0+2, rect.y1 - size*0.8f - (h-size)/2);
+		write_simple_string(ctx, buf, name, name + strlen(name));
+		fz_append_string(ctx, buf, " Tj\n");
+		fz_append_string(ctx, buf, "ET\n");
+
+		/* Information text */
+		size = fz_min(fz_min((w / 12), h / 6), 16);
+		fz_append_string(ctx, buf, "BT\n");
+		fz_append_printf(ctx, buf, "/Helv %g Tf\n", size);
+		fz_append_printf(ctx, buf, "%g TL\n", size);
+		fz_append_printf(ctx, buf, "%g %g Td\n", rect.x0+w+2, rect.y1);
+		fz_snprintf(tmp, sizeof tmp, "Digitally signed by %s", name);
+		write_simple_string_with_quadding(ctx, buf, helv, size, tmp, w-4, 0);
+		fz_snprintf(tmp, sizeof tmp, "DN: %s", dn);
+		write_simple_string_with_quadding(ctx, buf, helv, size, tmp, w-4, 0);
+		if (date)
+		{
+			fz_snprintf(tmp, sizeof tmp, "Date: %s", date);
+			write_simple_string_with_quadding(ctx, buf, helv, size, tmp, w-4, 0);
+		}
+		fz_append_string(ctx, buf, "ET\n");
+
+		/* Update the AP/N stream */
+		ap = pdf_dict_get(ctx, annot->obj, PDF_NAME(AP));
+		if (!ap)
+			ap = pdf_dict_put_dict(ctx, annot->obj, PDF_NAME(AP), 1);
+		new_ap_n = pdf_new_xobject(ctx, annot->page->doc, rect, fz_identity, res, buf);
+		pdf_dict_put(ctx, ap, PDF_NAME(N), new_ap_n);
+
+		pdf_drop_obj(ctx, annot->ap);
+		annot->ap = new_ap_n;
+		annot->has_new_ap = 1;
+	}
+	fz_always(ctx)
+	{
+		fz_drop_font(ctx, helv);
+		fz_drop_font(ctx, zadb);
+		pdf_drop_obj(ctx, res);
+	}
+	fz_catch(ctx)
+	{
+		fz_rethrow(ctx);
+	}
 }
 
 void pdf_update_appearance(fz_context *ctx, pdf_annot *annot)
-- 
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