From 1e8004734f1f91bfb2f6b8ada9936956ee6c20bc Mon Sep 17 00:00:00 2001
From: Lucas CHOLLET <lucas.chollet@free.fr>
Date: Sat, 11 Nov 2023 18:26:44 -0500
Subject: [PATCH] LibPDF: Don't consider the End of Data code as normal ASCII85
 input

Data encoded with ASCII85 is terminated with the EOD code 0x7E3E. This
should not be considered as normal input but rather discarded.
---
 Userland/Libraries/LibPDF/Filter.cpp | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/Userland/Libraries/LibPDF/Filter.cpp b/Userland/Libraries/LibPDF/Filter.cpp
index 5d4377097b..700c753e1f 100644
--- a/Userland/Libraries/LibPDF/Filter.cpp
+++ b/Userland/Libraries/LibPDF/Filter.cpp
@@ -94,6 +94,8 @@ PDFErrorOr<ByteBuffer> Filter::decode_ascii_hex(ReadonlyBytes bytes)
 
 PDFErrorOr<ByteBuffer> Filter::decode_ascii85(ReadonlyBytes bytes)
 {
+    // 3.3.2 ASCII85Decode Filter
+
     ByteBuffer buffer;
     TRY(buffer.try_ensure_capacity(bytes.size()));
 
@@ -114,10 +116,21 @@ PDFErrorOr<ByteBuffer> Filter::decode_ascii85(ReadonlyBytes bytes)
 
         u32 number = 0;
 
-        auto const to_write = byte_index + 5 >= bytes.size() ? bytes.size() - byte_index : 5;
+        auto to_write = byte_index + 5 >= bytes.size() ? bytes.size() - byte_index : 5;
+
+        Optional<u32> end_of_data_index {};
 
         for (int i = 0; i < 5; i++) {
-            auto byte = byte_index >= bytes.size() ? 'u' : bytes[byte_index++];
+            // We check for the EOD sequence '~>', but as '~' can only appear in
+            // this sequence, there is no need to check for '>'.
+            if (!end_of_data_index.has_value() && bytes[byte_index] == '~') {
+                end_of_data_index = i;
+                to_write = i + 1;
+            }
+
+            bool const should_fake_end = byte_index >= bytes.size() || end_of_data_index.has_value();
+            auto const byte = should_fake_end ? 'u' : bytes[byte_index++];
+
             if (Reader::is_whitespace(byte)) {
                 i--;
                 continue;
@@ -127,6 +140,9 @@ PDFErrorOr<ByteBuffer> Filter::decode_ascii85(ReadonlyBytes bytes)
 
         for (size_t i = 0; i < to_write - 1; i++)
             buffer.append(reinterpret_cast<u8*>(&number)[3 - i]);
+
+        if (end_of_data_index.has_value())
+            break;
     }
 
     return buffer;