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std.compress.flate.Decompress: implement readVec and discard

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This commit is contained in:
Andrew Kelley
2025-07-29 23:28:41 -07:00
parent 81af4f3efc
commit afe9f3a9ec
1 changed files with 28 additions and 8 deletions
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36
lib/std/compress/flate/Decompress.zig
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@@ -56,11 +56,11 @@ pub const Error = Container.Error || error{
pub fn init(input: *Reader, container: Container, buffer: []u8) Decompress {
return .{
.reader = .{
// TODO populate discard so that when an amount is discarded that
// includes an entire frame, skip decoding that frame.
.vtable = &.{
.stream = stream,
.rebase = rebase,
.discard = discard,
.readVec = Reader.indirectReadVec,
},
.buffer = buffer,
.seek = 0,
@@ -81,12 +81,32 @@ pub fn init(input: *Reader, container: Container, buffer: []u8) Decompress {
fn rebase(r: *Reader, capacity: usize) Reader.RebaseError!void {
assert(capacity <= r.buffer.len - flate.history_len);
assert(r.end + capacity > r.buffer.len);
const buffered = r.buffer[0..r.end];
const discard = buffered.len - flate.history_len;
const keep = buffered[discard..];
const discard_n = r.end - flate.history_len;
const keep = r.buffer[discard_n..r.end];
@memmove(r.buffer[0..keep.len], keep);
r.end = keep.len;
r.seek -= discard;
r.seek -= discard_n;
}
/// This could be improved so that when an amount is discarded that includes an
/// entire frame, skip decoding that frame.
fn discard(r: *Reader, limit: std.Io.Limit) Reader.Error!usize {
r.rebase(flate.history_len) catch unreachable;
var writer: Writer = .{
.vtable = &.{
.drain = std.Io.Writer.Discarding.drain,
.sendFile = std.Io.Writer.Discarding.sendFile,
},
.buffer = r.buffer,
.end = r.end,
};
const n = r.stream(&writer, limit) catch |err| switch (err) {
error.WriteFailed => unreachable,
error.ReadFailed => return error.ReadFailed,
error.EndOfStream => return error.EndOfStream,
};
assert(n <= @intFromEnum(limit));
return n;
}
fn decodeLength(self: *Decompress, code: u8) !u16 {
@@ -268,8 +288,8 @@ fn readInner(d: *Decompress, w: *Writer, limit: std.Io.Limit) (Error || Reader.S
},
.stored_block => |remaining_len| {
const out = try w.writableSliceGreedyPreserve(flate.history_len, 1);
const limited_out = limit.min(.limited(remaining_len)).slice(out);
const n = try d.input.readVec(&.{limited_out});
var limited_out: [1][]u8 = .{limit.min(.limited(remaining_len)).slice(out)};
const n = try d.input.readVec(&limited_out);
if (remaining_len - n == 0) {
d.state = if (d.final_block) .protocol_footer else .block_header;
} else {