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deflate: Better Huffman.construct errors and error handling

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This brings construct error handling in line with puff.c
This commit is contained in:
Ryan Liptak 2021-10-01 22:01:31 -07:00
parent c4cd592f0e
commit 933fd5110d
1 changed files with 33 additions and 6 deletions
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39
lib/std/compress/deflate.zig
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@ -45,7 +45,9 @@ const Huffman = struct {
min_code_len: u16,
fn construct(self: *Huffman, code_length: []const u16) !void {
const ConstructError = error{ Oversubscribed, IncompleteSet };
fn construct(self: *Huffman, code_length: []const u16) ConstructError!void {
for (self.count) |*val| {
val.* = 0;
}
@ -70,7 +72,7 @@ const Huffman = struct {
// Make sure the number of codes with this length isn't too high.
left -= @as(isize, @bitCast(i16, val));
if (left < 0)
return error.InvalidTree;
return error.Oversubscribed;
}
// Compute the offset of the first symbol represented by a code of a
@ -125,6 +127,9 @@ const Huffman = struct {
self.last_code = codes[PREFIX_LUT_BITS + 1];
self.last_index = offset[PREFIX_LUT_BITS + 1] - self.count[PREFIX_LUT_BITS + 1];
if (left > 0)
return error.IncompleteSet;
}
};
@ -322,7 +327,13 @@ pub fn InflateStream(comptime ReaderType: type) type {
try lencode.construct(len_lengths[0..]);
const dist_lengths = [_]u16{5} ** MAXDCODES;
try distcode.construct(dist_lengths[0..]);
distcode.construct(dist_lengths[0..]) catch |err| switch (err) {
// This error is expected because we only compute distance codes
// 0-29, which is fine since "distance codes 30-31 will never actually
// occur in the compressed data" (from section 3.2.6 of RFC1951).
error.IncompleteSet => {},
else => return err,
};
}
self.hlen = &lencode;
@ -357,7 +368,7 @@ pub fn InflateStream(comptime ReaderType: type) type {
lengths[val] = @intCast(u16, try self.readBits(3));
}
try lencode.construct(lengths[0..]);
lencode.construct(lengths[0..]) catch return error.InvalidTree;
}
// Read the length/literal and distance code length tables.
@ -406,8 +417,24 @@ pub fn InflateStream(comptime ReaderType: type) type {
if (lengths[256] == 0)
return error.MissingEOBCode;
try self.huffman_tables[0].construct(lengths[0..nlen]);
try self.huffman_tables[1].construct(lengths[nlen .. nlen + ndist]);
self.huffman_tables[0].construct(lengths[0..nlen]) catch |err| switch (err) {
error.Oversubscribed => return error.InvalidTree,
error.IncompleteSet => {
// incomplete code ok only for single length 1 code
if (nlen != self.huffman_tables[0].count[0] + self.huffman_tables[0].count[1]) {
return error.InvalidTree;
}
},
};
self.huffman_tables[1].construct(lengths[nlen .. nlen + ndist]) catch |err| switch (err) {
error.Oversubscribed => return error.InvalidTree,
error.IncompleteSet => {
// incomplete code ok only for single length 1 code
if (ndist != self.huffman_tables[1].count[0] + self.huffman_tables[1].count[1]) {
return error.InvalidTree;
}
},
};
self.hlen = &self.huffman_tables[0];
self.hdist = &self.huffman_tables[1];