std.compress.flate.Decompress: allow users to swap out Writer

Author: andrewrk

lib/std/compress/flate/Decompress.zig

@@ -58,7 +58,7 @@ pub fn init(input: *Reader, container: Container, buffer: []u8) Decompress {
         .reader = .{
             .vtable = &.{
                 .stream = stream,
-                .rebase = rebase,
+                .rebase = rebaseFallible,
                 .discard = discard,
                 .readVec = readVec,
             },
@@ -78,12 +78,19 @@ pub fn init(input: *Reader, container: Container, buffer: []u8) Decompress {
     };
 }
 
-fn rebase(r: *Reader, capacity: usize) Reader.RebaseError!void {
+fn rebaseFallible(r: *Reader, capacity: usize) Reader.RebaseError!void {
+    const d: *Decompress = @alignCast(@fieldParentPtr("reader", r));
+    rebase(d, capacity);
+}
+
+fn rebase(d: *Decompress, capacity: usize) void {
+    const r = &d.reader;
     assert(capacity <= r.buffer.len - flate.history_len);
     assert(r.end + capacity > r.buffer.len);
     const discard_n = r.end - flate.history_len;
     const keep = r.buffer[discard_n..r.end];
     @memmove(r.buffer[0..keep.len], keep);
+    assert(keep.len != 0);
     r.end = keep.len;
     r.seek -= discard_n;
 }
@@ -101,6 +108,7 @@ fn discard(r: *Reader, limit: std.Io.Limit) Reader.Error!usize {
         .end = r.end,
     };
     defer {
+        assert(writer.end != 0);
         r.end = writer.end;
         r.seek = r.end;
     }
@@ -115,14 +123,20 @@ fn discard(r: *Reader, limit: std.Io.Limit) Reader.Error!usize {
 
 fn readVec(r: *Reader, data: [][]u8) Reader.Error!usize {
     _ = data;
-    assert(r.seek == r.end);
-    r.rebase(flate.history_len) catch unreachable;
+    const d: *Decompress = @alignCast(@fieldParentPtr("reader", r));
+    return streamIndirect(d);
+}
+
+fn streamIndirect(d: *Decompress) Reader.Error!usize {
+    const r = &d.reader;
+    if (r.end + flate.history_len > r.buffer.len) rebase(d, flate.history_len);
     var writer: Writer = .{
         .buffer = r.buffer,
         .end = r.end,
         .vtable = &.{ .drain = Writer.fixedDrain },
     };
-    r.end += r.vtable.stream(r, &writer, .limited(writer.buffer.len - writer.end)) catch |err| switch (err) {
+    defer r.end = writer.end;
+    _ = streamFallible(d, &writer, .limited(writer.buffer.len - writer.end)) catch |err| switch (err) {
         error.WriteFailed => unreachable,
         else => |e| return e,
     };
@@ -188,7 +202,12 @@ fn decodeSymbol(self: *Decompress, decoder: anytype) !Symbol {
 
 pub fn stream(r: *Reader, w: *Writer, limit: std.Io.Limit) Reader.StreamError!usize {
     const d: *Decompress = @alignCast(@fieldParentPtr("reader", r));
-    return readInner(d, w, limit) catch |err| switch (err) {
+    if (w.end >= r.end) return streamFallible(d, w, limit);
+    return streamIndirect(d);
+}
+
+fn streamFallible(d: *Decompress, w: *Writer, limit: std.Io.Limit) Reader.StreamError!usize {
+    return streamInner(d, w, limit) catch |err| switch (err) {
         error.EndOfStream => {
             if (d.state == .end) {
                 return error.EndOfStream;
@@ -207,7 +226,7 @@ pub fn stream(r: *Reader, w: *Writer, limit: std.Io.Limit) Reader.StreamError!us
     };
 }
 
-fn readInner(d: *Decompress, w: *Writer, limit: std.Io.Limit) (Error || Reader.StreamError)!usize {
+fn streamInner(d: *Decompress, w: *Writer, limit: std.Io.Limit) (Error || Reader.StreamError)!usize {
     var remaining = @intFromEnum(limit);
     const in = d.input;
     sw: switch (d.state) {