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Merged
chetanyb merged 2 commits into from
Jan 4, 2026
Merged

Encoding fix #6

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03de38b
test: add test to reproduce panic: integer cast truncated bits
chetanyb Jan 2, 2026
e87ad07
fix: correct snappy literal length encoding
chetanyb Jan 2, 2026
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82 changes: 65 additions & 17 deletions snappy.zig
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Original file line number Diff line number Diff line change
Expand Up @@ -261,23 +261,32 @@ pub fn decode(allocator: Allocator, src: []const u8) ![]u8 {
// TODO: Split up encode and decode into separate files once I better understand modules.
fn emitLiteral(dst: []u8, lit: []const u8) usize {
var i: usize = 0;
const n = @as(usize, @intCast(lit.len - 1));
switch (n) {
0...59 => {
dst[0] = @as(u8, @intCast(n)) << 2 | tagLiteral;
i = 1;
},
60...255 => {
dst[0] = 60 << 2 | tagLiteral;
dst[1] = @as(u8, @intCast(n));
i = 2;
},
else => {
dst[0] = 61 << 2 | tagLiteral;
dst[1] = @as(u8, @truncate(n));
dst[2] = @as(u8, @truncate(n >> 8));
i = 3;
},
const n = @as(u32, @intCast(lit.len - 1));
if (n < 60) {
dst[0] = @as(u8, @intCast(n)) << 2 | tagLiteral;
i = 1;
} else if (n < (1 << 8)) {
dst[0] = 60 << 2 | tagLiteral;
dst[1] = @as(u8, @intCast(n));
i = 2;
} else if (n < (1 << 16)) {
dst[0] = 61 << 2 | tagLiteral;
dst[1] = @as(u8, @intCast(n & 0xff));
dst[2] = @as(u8, @intCast(n >> 8));
i = 3;
} else if (n < (1 << 24)) {
dst[0] = 62 << 2 | tagLiteral;
dst[1] = @as(u8, @intCast(n & 0xff));
dst[2] = @as(u8, @intCast((n >> 8) & 0xff));
dst[3] = @as(u8, @intCast(n >> 16));
i = 4;
} else {
dst[0] = 63 << 2 | tagLiteral;
dst[1] = @as(u8, @intCast(n & 0xff));
dst[2] = @as(u8, @intCast((n >> 8) & 0xff));
dst[3] = @as(u8, @intCast((n >> 16) & 0xff));
dst[4] = @as(u8, @intCast(n >> 24));
i = 5;
}
std.mem.copyForwards(u8, dst[i..], lit);

Expand Down Expand Up @@ -499,3 +508,42 @@ test "simple decode" {

try testing.expectEqualSlices(u8, decoded, "oh snap, snappy is cool!\n");
}

test "emit literal length > 255" {
var lit: [300]u8 = undefined;
for (&lit, 0..) |*b, i| {
b.* = @as(u8, @truncate(i * 31 + 7));
}

var dst: [320]u8 = undefined;
const written = emitLiteral(&dst, &lit);

const n: u32 = lit.len - 1;
try testing.expectEqual(@as(usize, 3 + lit.len), written);
try testing.expectEqual(@as(u8, 61 << 2 | tagLiteral), dst[0]);
try testing.expectEqual(@as(u8, @intCast(n & 0xff)), dst[1]);
try testing.expectEqual(@as(u8, @intCast(n >> 8)), dst[2]);
try testing.expectEqualSlices(u8, lit[0..], dst[3 .. 3 + lit.len]);
}

test "emit literal length > 65535" {
const allocator = testing.allocator;
const lit_len: usize = 70000;
var lit = try allocator.alloc(u8, lit_len);
defer allocator.free(lit);
for (lit, 0..) |*b, i| {
b.* = @as(u8, @truncate(i * 13 + 5));
}

const n: u32 = @as(u32, @intCast(lit.len - 1));
var dst = try allocator.alloc(u8, 4 + lit.len);
defer allocator.free(dst);
const written = emitLiteral(dst, lit);

try testing.expectEqual(@as(usize, 4 + lit.len), written);
try testing.expectEqual(@as(u8, 62 << 2 | tagLiteral), dst[0]);
try testing.expectEqual(@as(u8, @intCast(n & 0xff)), dst[1]);
try testing.expectEqual(@as(u8, @intCast((n >> 8) & 0xff)), dst[2]);
try testing.expectEqual(@as(u8, @intCast(n >> 16)), dst[3]);
try testing.expectEqualSlices(u8, lit[0..], dst[4 .. 4 + lit.len]);
}