Improve memory safety of Oar archive lookups

src/oar.zig

@@ -24,7 +24,7 @@ pub const Archive = struct {
     ///
     ///
     ///
-    const IndexCache = table.Hashed([]const u8, Entry.Header, table.string_context);
+    const IndexCache = table.Hashed([]const u8, u64, table.string_context);
 
     ///
     /// Finds an entry matching `entry_path` in `archive`.
@@ -34,40 +34,50 @@ pub const Archive = struct {
     pub fn find(archive: *Archive, entry_path: []const u8) FindError!Entry {
         return Entry{
             .header = find_header: {
-                if (archive.index_cache.lookup(entry_path)) |entry_header|
-                    break: find_header entry_header.*;
-
-                // Start from beginning of archive.
-                try archive.file_access.seek(0);
-
-                var entry_header = Entry.Header{
+                var header = Entry.Header{
                     .revision = 0,
                     .file_size = 0,
-                    .file_offset = 0
+                    .absolute_offset = 0
                 };
 
-                const read_buffer = std.mem.asBytes(&entry_header);
+                const header_size = @sizeOf(Entry.Header);
 
-                // Read first entry.
-                while ((try archive.file_access.read(read_buffer)) == @sizeOf(Entry.Header)) {
-                    if (std.mem.eql(u8, entry_path, entry_header.
-                        name_buffer[0 .. entry_header.name_length])) {
+                if (archive.index_cache.lookup(entry_path)) |cursor| {
+                    try archive.file_access.seek(cursor);
 
-                        // If caching fails... oh well...
-                        archive.index_cache.insert(entry_path, entry_header) catch {};
+                    if ((try archive.file_access.read(std.mem.asBytes(&header))) != header_size) {
+                        std.debug.assert(archive.index_cache.remove(entry_path) != null);
 
-                        break: find_header entry_header;
+                        return error.EntryNotFound;
                     }
 
-                    // Move over file data following the entry.
-                    var to_skip = entry_header.file_size;
+                    break: find_header header;
+                } else {
+                    const mem = std.mem;
 
-                    while (to_skip != 0) {
-                        const skipped = std.math.min(to_skip, std.math.maxInt(i64));
+                    // Start from beginning of archive.
+                    try archive.file_access.seek(0);
 
-                        try archive.file_access.skip(@intCast(i64, skipped));
+                    // Read first entry.
+                    while ((try archive.file_access.read(mem.asBytes(&header))) == header_size) {
+                        if (mem.eql(u8, entry_path, header.name_buffer[0 .. header.name_length])) {
+                            // If caching fails... oh well...
+                            archive.index_cache.insert(entry_path, header.absolute_offset) catch {};
 
-                        to_skip -= skipped;
+                            break: find_header header;
+                        }
+
+                        // Move over file data following the entry.
+                        var to_skip = header.file_size;
+
+                        while (to_skip != 0) {
+                            const math = std.math;
+                            const skipped = math.min(to_skip, math.maxInt(i64));
+
+                            try archive.file_access.skip(@intCast(i64, skipped));
+
+                            to_skip -= skipped;
+                        }
                     }
                 }
 
@@ -109,7 +119,7 @@ pub const Entry = struct {
         name_buffer: [255]u8 = std.mem.zeroes([255]u8),
         name_length: u8 = 0,
         file_size: u64,
-        file_offset: u64,
+        absolute_offset: u64,
         padding: [232]u8 = std.mem.zeroes([232]u8),
 
         comptime {

src/sys.zig

@@ -487,7 +487,7 @@ pub const FileSystem = union(enum) {
                                 if (archive_entry.cursor >= archive_entry.header.file_size)
                                     return error.FileInaccessible;
 
-                                try file_access.seek(archive_entry.header.file_offset);
+                                try file_access.seek(archive_entry.header.absolute_offset);
 
                                 return file_access.read(buffer[0 .. std.math.min(
                                     buffer.len, archive_entry.header.file_size)]);

src/table.zig

@@ -56,16 +56,18 @@ pub fn Hashed(comptime Key: type, comptime Value: type,
         }
 
         ///
-        /// Searches for `key` to delete it, returning the deleted value or `null` if no matching
-        /// key was found.
+        /// Searches for `key` and deletes it from `self.
         ///
-        pub fn remove(self: Self, key: Key) ?Value {
+        /// The removed value is returned or `null` if no key matching `key` was found.
+        ///
+        pub fn remove(self: *Self, key: Key) ?Value {
             var bucket = &(self.buckets[@mod(key_context.hash(key), self.buckets.len)]);
 
             if (bucket.maybe_entry) |*entry| if (key_context.equals(entry.key, key)) {
-                defer entry.value = null;
-
-                self.filled -= 1;
+                defer {
+                    bucket.maybe_entry = null;
+                    self.filled -= 1;
+                }
 
                 return entry.value;
             };
@@ -74,9 +76,10 @@ pub fn Hashed(comptime Key: type, comptime Value: type,
                 bucket = &(self.buckets[index]);
 
                 if (bucket.maybe_entry) |*entry| if (key_context.equals(entry.key, key)) {
-                    defer entry.value = null;
-
-                    self.filled -= 1;
+                    defer {
+                        bucket.maybe_entry = null;
+                        self.filled -= 1;
+                    }
 
                     return entry.value;
                 };
@@ -129,20 +132,21 @@ pub fn Hashed(comptime Key: type, comptime Value: type,
         }
 
         ///
-        /// Searches for a value indexed with `key` in `self`, returning it or `null` if no matching
-        /// entry was found.
+        /// Searches for a value indexed with `key` in `self`.
         ///
-        pub fn lookup(self: Self, key: Key) ?*Value {
+        /// The found value is returned or `null` if an key matching `key` failed to be found.
+        ///
+        pub fn lookup(self: Self, key: Key) ?Value {
             var bucket = &(self.buckets[@mod(key_context.hash(key), self.buckets.len)]);
 
-            if (bucket.maybe_entry) |*entry|
-                if (key_context.equals(entry.key, key)) return &entry.value;
+            if (bucket.maybe_entry) |entry|
+                if (key_context.equals(entry.key, key)) return entry.value;
 
             while (bucket.maybe_next_index) |index| {
                 bucket = &(self.buckets[index]);
 
-                if (bucket.maybe_entry) |*entry|
-                    if (key_context.equals(entry.key, key)) return &entry.value;
+                if (bucket.maybe_entry) |entry|
+                    if (key_context.equals(entry.key, key)) return entry.value;
             }
 
             return null;