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This is an example of documentation generated by ZigDoc, an alternative to Zig's built-in Auto Doc feature. See also examples in other modes/formats. The project being documented here (as the example) is the Zig standard library. Public Type Function

Hashed

Doc Source

Public Type Function

std.Io.Writer.Hashed

pub fn Hashed(comptime Hasher: type) type

Provides a Writer implementation based on calling Hasher.update, sending all data also to an underlying Writer.

When using this, the underlying writer is best unbuffered because all writes are passed on directly to it.

This implementation makes suboptimal buffering decisions due to being generic. A better solution will involve creating a writer for each hash function, where the splat buffer can be tailored to the hash implementation details.

Contrast with Hashing which terminates the stream pipeline.

Fields

out: *Writer
hasher: Hasher
writer: Writer

Functions

pub fn init(out: *Writer, buffer: []u8) @This()
pub fn initHasher(out: *Writer, hasher: Hasher, buffer: []u8) @This()
fn drain(w: *Writer, data: []const []const u8, splat: usize) Error!usize

File

Io/Writer.zig:2519

pub fn Hashed(comptime Hasher: type) type {
    return struct {
        out: *Writer,
        hasher: Hasher,
        writer: Writer,

        pub fn init(out: *Writer, buffer: []u8) @This() {
            return .initHasher(out, .{}, buffer);
        }

        pub fn initHasher(out: *Writer, hasher: Hasher, buffer: []u8) @This() {
            return .{
                .out = out,
                .hasher = hasher,
                .writer = .{
                    .buffer = buffer,
                    .vtable = &.{ .drain = @This().drain },
                },
            };
        }

        fn drain(w: *Writer, data: []const []const u8, splat: usize) Error!usize {
            const this: *@This() = @alignCast(@fieldParentPtr("writer", w));
            const aux = w.buffered();
            const aux_n = try this.out.writeSplatHeader(aux, data, splat);
            if (aux_n < w.end) {
                this.hasher.update(w.buffer[0..aux_n]);
                const remaining = w.buffer[aux_n..w.end];
                @memmove(w.buffer[0..remaining.len], remaining);
                w.end = remaining.len;
                return 0;
            }
            this.hasher.update(aux);
            const n = aux_n - w.end;
            w.end = 0;
            var remaining: usize = n;
            for (data[0 .. data.len - 1]) |slice| {
                if (remaining <= slice.len) {
                    this.hasher.update(slice[0..remaining]);
                    return n;
                }
                remaining -= slice.len;
                this.hasher.update(slice);
            }
            const pattern = data[data.len - 1];
            assert(remaining <= splat * pattern.len);
            switch (pattern.len) {
                0 => {
                    assert(remaining == 0);
                },
                1 => {
                    var buffer: [64]u8 = undefined;
                    @memset(&buffer, pattern[0]);
                    while (remaining > 0) {
                        const update_len = @min(remaining, buffer.len);
                        this.hasher.update(buffer[0..update_len]);
                        remaining -= update_len;
                    }
                },
                else => {
                    while (remaining > 0) {
                        const update_len = @min(remaining, pattern.len);
                        this.hasher.update(pattern[0..update_len]);
                        remaining -= update_len;
                    }
                },
            }
            return n;
        }
    };
}