From 719763dfcb427af70a140767f4c76f055cb50d73 Mon Sep 17 00:00:00 2001
From: Peter Nelson <peter1138@openttd.org>
Date: Wed, 15 May 2024 22:16:50 +0100
Subject: [PATCH] Codechange: Store start and end position in RandomAccessFile.

This allows callers to do more bounds checking.
---
 src/random_access_file.cpp    | 16 +++++++++++++++-
 src/random_access_file_type.h |  5 +++++
 2 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/src/random_access_file.cpp b/src/random_access_file.cpp
index 29764521ed28e..e949ca865b5a9 100644
--- a/src/random_access_file.cpp
+++ b/src/random_access_file.cpp
@@ -24,13 +24,18 @@
  */
 RandomAccessFile::RandomAccessFile(const std::string &filename, Subdirectory subdir) : filename(filename)
 {
-	this->file_handle = FioFOpenFile(filename, "rb", subdir);
+	size_t file_size;
+	this->file_handle = FioFOpenFile(filename, "rb", subdir, &file_size);
 	if (this->file_handle == nullptr) UserError("Cannot open file '{}'", filename);
 
 	/* When files are in a tar-file, the begin of the file might not be at 0. */
 	long pos = ftell(this->file_handle);
 	if (pos < 0) UserError("Cannot read file '{}'", filename);
 
+	/* Make a note of start and end position for readers who check bounds. */
+	this->start_pos = pos;
+	this->end_pos = this->start_pos + file_size;
+
 	/* Store the filename without path and extension */
 	auto t = filename.rfind(PATHSEPCHAR);
 	std::string name_without_path = filename.substr(t != std::string::npos ? t + 1 : 0);
@@ -76,6 +81,15 @@ size_t RandomAccessFile::GetPos() const
 	return this->pos + (this->buffer - this->buffer_end);
 }
 
+/**
+ * Test if we have reached the end of the file.
+ * @return True iff the current position as at or after the end of the file.
+ */
+bool RandomAccessFile::AtEndOfFile() const
+{
+	return this->GetPos() >= this->GetEndPos();
+}
+
 /**
  * Seek in the current file.
  * @param pos New position.
diff --git a/src/random_access_file_type.h b/src/random_access_file_type.h
index 38b414824754d..600e89007fcf7 100644
--- a/src/random_access_file_type.h
+++ b/src/random_access_file_type.h
@@ -28,6 +28,8 @@ class RandomAccessFile {
 
 	FILE *file_handle;               ///< File handle of the open file.
 	size_t pos;                      ///< Position in the file of the end of the read buffer.
+	size_t start_pos; ///< Start position of file. May be non-zero if file is within a tar file.
+	size_t end_pos; ///< End position of file.
 
 	uint8_t *buffer;                    ///< Current position within the local buffer.
 	uint8_t *buffer_end;                ///< Last valid byte of buffer.
@@ -44,7 +46,10 @@ class RandomAccessFile {
 	const std::string &GetSimplifiedFilename() const;
 
 	size_t GetPos() const;
+	size_t GetStartPos() const { return this->start_pos; }
+	size_t GetEndPos() const { return this->end_pos; }
 	void SeekTo(size_t pos, int mode);
+	bool AtEndOfFile() const;
 
 	uint8_t ReadByte();
 	uint16_t ReadWord();