3 files changed, 16 insertions(+), 5 deletions(-)

M README.md
M src/bare.zig
M src/test.zig

@@ 41,11 41,11 @@ const x = Bar{
 var buf: [12]u8 = undefined;
 var fbs = io.fixedBufferStream(&buf);
 
-try Writer.init().write(x, fbs.outStream());
+try Writer.init().write(x, fbs.writer());
 try fbs.seekTo(0);
 var r = Reader.init(allocator);
 defer r.deinit();
-const y = try r.read(Bar, fbs.inStream());
+const y = try r.read(Bar, fbs.reader());
 warn("x: {}\ny: {}\n", .{ x, y });
 ```
 

@@ 185,11 185,14 @@ pub const Reader = struct {
         if (comptime !isValidHashMapKeyType(K))
             @compileError("unsupported hashmap key type " ++ @typeName(K));
 
-        var i = @intCast(u32, try self.readVarUint(reader));
+        var i = try self.readVarUint(reader);
         var map = T.init(&self.arena.allocator);
 
         if (i != 0) {
-            try map.ensureCapacity(i);
+            if (std.math.maxInt(T.Size) < i)
+                return ReadError.Overflow;
+
+            try map.ensureCapacity(@intCast(T.Size, i));
 
             while (i != 0) : (i -= 1) {
                 const key = try self.read(K, reader);


@@ 369,7 372,7 @@ fn isHashMap(comptime T: type) bool {
     // `HashMapKeyType` and `HashMapValueType` add further constraints.
     const has1 = @hasDecl(T, "iterator") or @hasDecl(T, "items");
     const has2 = @hasDecl(T, "putAssumeCapacity") and @hasDecl(T, "ensureCapacity");
-    return has1 and has2;
+    return has1 and has2 and @hasDecl(T, "Size");
 }
 
 fn HashMapKeyType(comptime T: type) type {

@@ 205,6 205,14 @@ test "read map[string]u8" {
     expectEqual(map.get("zomg") orelse unreachable, 4);
 }
 
+test "read map overflow" {
+    var r = Reader.init(testing.allocator);
+    defer r.deinit();
+    const T = std.StringHashMap(u8);
+    const map = r.read(T, io.fixedBufferStream("\xff\xff\xff\xff\xff\xff\xff\xff\xff\x00\x04zomg\x04\x03lol\x02").reader());
+    expectError(error.Overflow, map);
+}
+
 test "read map[u8]void" {
     try testCompileError(
         \\pub fn main() void {