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const std = @import("../std.zig");
const io = std.io;
const testing = std.testing;
const mem = std.mem;
const assert = std.debug.assert;
/// This turns a byte buffer into an `io.Writer`, `io.Reader`, or `io.SeekableStream`.
/// If the supplied byte buffer is const, then `io.Writer` is not available.
pub fn FixedBufferStream(comptime Buffer: type) type {
return struct {
/// `Buffer` is either a `[]u8` or `[]const u8`.
buffer: Buffer,
pos: usize,
pub const ReadError = error{};
pub const WriteError = error{NoSpaceLeft};
pub const SeekError = error{};
pub const GetSeekPosError = error{};
pub const Reader = io.Reader(*Self, ReadError, read);
pub const Writer = io.Writer(*Self, WriteError, write);
pub const SeekableStream = io.SeekableStream(
*Self,
SeekError,
GetSeekPosError,
seekTo,
seekBy,
getPos,
getEndPos,
);
const Self = @This();
pub fn reader(self: *Self) Reader {
return .{ .context = self };
}
pub fn writer(self: *Self) Writer {
return .{ .context = self };
}
pub fn seekableStream(self: *Self) SeekableStream {
return .{ .context = self };
}
pub fn read(self: *Self, dest: []u8) ReadError!usize {
const size = @min(dest.len, self.buffer.len - self.pos);
const end = self.pos + size;
@memcpy(dest[0..size], self.buffer[self.pos..end]);
self.pos = end;
return size;
}
/// If the returned number of bytes written is less than requested, the
/// buffer is full. Returns `error.NoSpaceLeft` when no bytes would be written.
/// Note: `error.NoSpaceLeft` matches the corresponding error from
/// `std.fs.File.WriteError`.
pub fn write(self: *Self, bytes: []const u8) WriteError!usize {
if (bytes.len == 0) return 0;
if (self.pos >= self.buffer.len) return error.NoSpaceLeft;
const n = if (self.pos + bytes.len <= self.buffer.len)
bytes.len
else
self.buffer.len - self.pos;
@memcpy(self.buffer[self.pos..][0..n], bytes[0..n]);
self.pos += n;
if (n == 0) return error.NoSpaceLeft;
return n;
}
pub fn seekTo(self: *Self, pos: u64) SeekError!void {
self.pos = if (std.math.cast(usize, pos)) |x| @min(self.buffer.len, x) else self.buffer.len;
}
pub fn seekBy(self: *Self, amt: i64) SeekError!void {
if (amt < 0) {
const abs_amt = std.math.absCast(amt);
const abs_amt_usize = std.math.cast(usize, abs_amt) orelse std.math.maxInt(usize);
if (abs_amt_usize > self.pos) {
self.pos = 0;
} else {
self.pos -= abs_amt_usize;
}
} else {
const amt_usize = std.math.cast(usize, amt) orelse std.math.maxInt(usize);
const new_pos = std.math.add(usize, self.pos, amt_usize) catch std.math.maxInt(usize);
self.pos = @min(self.buffer.len, new_pos);
}
}
pub fn getEndPos(self: *Self) GetSeekPosError!u64 {
return self.buffer.len;
}
pub fn getPos(self: *Self) GetSeekPosError!u64 {
return self.pos;
}
pub fn getWritten(self: Self) Buffer {
return self.buffer[0..self.pos];
}
pub fn reset(self: *Self) void {
self.pos = 0;
}
};
}
pub fn fixedBufferStream(buffer: anytype) FixedBufferStream(Slice(@TypeOf(buffer))) {
return .{ .buffer = buffer, .pos = 0 };
}
fn Slice(comptime T: type) type {
switch (@typeInfo(T)) {
.Pointer => |ptr_info| {
var new_ptr_info = ptr_info;
switch (ptr_info.size) {
.Slice => {},
.One => switch (@typeInfo(ptr_info.child)) {
.Array => |info| new_ptr_info.child = info.child,
else => @compileError("invalid type given to fixedBufferStream"),
},
else => @compileError("invalid type given to fixedBufferStream"),
}
new_ptr_info.size = .Slice;
return @Type(.{ .Pointer = new_ptr_info });
},
else => @compileError("invalid type given to fixedBufferStream"),
}
}
test "FixedBufferStream output" {
var buf: [255]u8 = undefined;
var fbs = fixedBufferStream(&buf);
const stream = fbs.writer();
try stream.print("{s}{s}!", .{ "Hello", "World" });
try testing.expectEqualSlices(u8, "HelloWorld!", fbs.getWritten());
}
test "FixedBufferStream output at comptime" {
comptime {
var buf: [255]u8 = undefined;
var fbs = fixedBufferStream(&buf);
const stream = fbs.writer();
try stream.print("{s}{s}!", .{ "Hello", "World" });
try testing.expectEqualSlices(u8, "HelloWorld!", fbs.getWritten());
}
}
test "FixedBufferStream output 2" {
var buffer: [10]u8 = undefined;
var fbs = fixedBufferStream(&buffer);
try fbs.writer().writeAll("Hello");
try testing.expect(mem.eql(u8, fbs.getWritten(), "Hello"));
try fbs.writer().writeAll("world");
try testing.expect(mem.eql(u8, fbs.getWritten(), "Helloworld"));
try testing.expectError(error.NoSpaceLeft, fbs.writer().writeAll("!"));
try testing.expect(mem.eql(u8, fbs.getWritten(), "Helloworld"));
fbs.reset();
try testing.expect(fbs.getWritten().len == 0);
try testing.expectError(error.NoSpaceLeft, fbs.writer().writeAll("Hello world!"));
try testing.expect(mem.eql(u8, fbs.getWritten(), "Hello worl"));
try fbs.seekTo((try fbs.getEndPos()) + 1);
try testing.expectError(error.NoSpaceLeft, fbs.writer().writeAll("H"));
}
test "FixedBufferStream input" {
const bytes = [_]u8{ 1, 2, 3, 4, 5, 6, 7 };
var fbs = fixedBufferStream(&bytes);
var dest: [4]u8 = undefined;
var read = try fbs.reader().read(&dest);
try testing.expect(read == 4);
try testing.expect(mem.eql(u8, dest[0..4], bytes[0..4]));
read = try fbs.reader().read(&dest);
try testing.expect(read == 3);
try testing.expect(mem.eql(u8, dest[0..3], bytes[4..7]));
read = try fbs.reader().read(&dest);
try testing.expect(read == 0);
try fbs.seekTo((try fbs.getEndPos()) + 1);
read = try fbs.reader().read(&dest);
try testing.expect(read == 0);
}
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