From 182639217f3ca359c1b5e10610231cb1bea77212 Mon Sep 17 00:00:00 2001
From: Nico Weber <thakis@chromium.org>
Date: Tue, 17 Oct 2023 08:07:59 -0400
Subject: [PATCH] LibPDF: Implement GoTo action for outline

Outline items can contain either a /Dest key or an /A key.

The /Dest key points to a "Destination" (various ways to reference a
page in the same document).

The /A key points to an "Action" which can have several types.
One type, the /GoTo type, just also points to a Destination.

Implement GoTo actions. This makes clicking "Contents" in the outline of
https://developer.apple.com/library/archive/documentation/mac/pdf/Text.pdf
work. (Almost all other items in this file's outline use /Dest.
"Contents" could too, but it uses /A /GoTo for some reason.)

(Other action types are things like opening a hyperlink, opening a
different file, playing a sound, submitting a form, etc. Actions
are also used for in-page links, not just in outlines. Many of
these action types we'll likely never want to implement.)
---
 Userland/Libraries/LibPDF/CommonNames.h |  2 ++
 Userland/Libraries/LibPDF/Document.cpp  | 16 ++++++++++++++++
 2 files changed, 18 insertions(+)

diff --git a/Userland/Libraries/LibPDF/CommonNames.h b/Userland/Libraries/LibPDF/CommonNames.h
index 7362983eb6..3c20a492af 100644
--- a/Userland/Libraries/LibPDF/CommonNames.h
+++ b/Userland/Libraries/LibPDF/CommonNames.h
@@ -9,6 +9,7 @@
 #include <AK/DeprecatedFlyString.h>
 
 #define ENUMERATE_COMMON_NAMES(X) \
+    X(A)                          \
     X(AIS)                        \
     X(Alternate)                  \
     X(ASCII85Decode)              \
@@ -134,6 +135,7 @@
     X(Root)                       \
     X(Rotate)                     \
     X(RunLengthDecode)            \
+    X(S)                          \
     X(SA)                         \
     X(SM)                         \
     X(SMask)                      \
diff --git a/Userland/Libraries/LibPDF/Document.cpp b/Userland/Libraries/LibPDF/Document.cpp
index 1c2402780a..fee1df2ab7 100644
--- a/Userland/Libraries/LibPDF/Document.cpp
+++ b/Userland/Libraries/LibPDF/Document.cpp
@@ -540,6 +540,22 @@ PDFErrorOr<NonnullRefPtr<OutlineItem>> Document::build_outline_item(NonnullRefPt
     if (outline_item_dict->contains(CommonNames::Dest)) {
         auto dest_obj = TRY(outline_item_dict->get_object(this, CommonNames::Dest));
         outline_item->dest = TRY(create_destination_from_object(dest_obj, page_number_by_index_ref));
+    } else if (outline_item_dict->contains(CommonNames::A)) {
+        // PDF 1.7 spec, "8.5 Actions"
+        auto action_dict = TRY(outline_item_dict->get_dict(this, CommonNames::A));
+        if (action_dict->contains(CommonNames::S)) {
+            // PDF 1.7 spec, "TABLE 8.48 Action types"
+            auto action_type = TRY(action_dict->get_name(this, CommonNames::S))->name();
+            if (action_type == "GoTo") {
+                // PDF 1.7 spec, "Go-To Actions"
+                if (action_dict->contains(CommonNames::D)) {
+                    auto dest_obj = TRY(action_dict->get_object(this, CommonNames::D));
+                    outline_item->dest = TRY(create_destination_from_object(dest_obj, page_number_by_index_ref));
+                }
+            } else {
+                dbgln("Unhandled action type {}", action_type);
+            }
+        }
     }
 
     if (outline_item_dict->contains(CommonNames::C)) {