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fix: boundary short-string misclassified as long-string #32

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Merged
gballet merged 1 commit into from
Apr 24, 2026
Merged

fix: boundary short-string misclassified as long-string #32

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20 changes: 19 additions & 1 deletion src/deserialize.zig
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Original file line number Diff line number Diff line change
Expand Up @@ -47,7 +47,7 @@ fn sizeAndDataOffset(payload: []const u8) !struct { size: usize, offset: usize }
if (payload[0] < rlpByteListShortHeader) {
offset = 0;
size = 1;
} else if (payload[0] < rlpByteListLongHeader) {
} else if (payload[0] <= rlpByteListLongHeader) {
size = @as(usize, payload[0] - rlpByteListShortHeader);
offset = 1;
} else if (payload[0] < rlpListShortHeader) {
Expand Down Expand Up @@ -97,6 +97,7 @@ pub fn deserialize(comptime T: type, allocator: Allocator, serialized: []const u
return switch (info) {
.int => {
const r = try sizeAndDataOffset(serialized);
if (r.offset + r.size > serialized.len) return error.RlpPayloadTooShort;
try safeReadSliceIntBig(T, serialized[r.offset .. r.offset + r.size], out);
return r.offset + r.size;
},
Expand Down Expand Up @@ -130,6 +131,7 @@ pub fn deserialize(comptime T: type, allocator: Allocator, serialized: []const u
.pointer => |ptr| switch (ptr.size) {
.slice => if (ptr.child == u8) {
const r = try sizeAndDataOffset(serialized);
if (r.offset + r.size > serialized.len) return error.RlpPayloadTooShort;
out.* = serialized[r.offset .. r.offset + r.size];
return r.offset + r.size;
} else {
Expand Down Expand Up @@ -163,6 +165,7 @@ pub fn deserialize(comptime T: type, allocator: Allocator, serialized: []const u
},
.array => |ary| if (@sizeOf(ary.child) == 1) {
const r = try sizeAndDataOffset(serialized);
if (r.offset + r.size > serialized.len) return error.RlpPayloadTooShort;
// this is a fixed-size array, so the destination has already been allocated.
std.mem.copyForwards(u8, out.*[0..], serialized[r.offset .. r.offset + r.size]);
return r.offset + r.size;
Expand Down Expand Up @@ -404,3 +407,18 @@ test "deserialize a pointer to an integer" {
defer std.testing.allocator.destroy(out);
_ = try std.testing.expectEqual(out.*, 0x0102030405060708090a);
}

test "deserialize a 55-byte string (0xb7 prefix)" {
// 0xb7 == 0x80 + 55 is the short-string header for a 55-byte payload.
// we treated 0xb7 as the long-string sentinel (size_size=0),
// silently returning an empty string instead of the 55-byte payload.
const data = [_]u8{0xAB} ** 55;
var rlp_bytes: [56]u8 = undefined;
rlp_bytes[0] = 0xb7;
@memcpy(rlp_bytes[1..], &data);

var out: []const u8 = undefined;
const consumed = try deserialize([]const u8, std.testing.allocator, &rlp_bytes, &out);
try std.testing.expectEqual(56, consumed);
try std.testing.expectEqualSlices(u8, &data, out);
}
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