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std: use LinearFifo to implement io.PeekStream

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daurnimator 2019-11-11 03:07:57 +11:00 committed by Andrew Kelley
parent bdff2f43bd
commit 38ad7daebb
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2 changed files with 17 additions and 37 deletions
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46
lib/std/io.zig
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@ -196,7 +196,7 @@ test "io.BufferedInStream" {
/// Creates a stream which supports 'un-reading' data, so that it can be read again.
/// This makes look-ahead style parsing much easier.
pub fn PeekStream(comptime buffer_size: usize, comptime InStreamError: type) type {
pub fn PeekStream(comptime buffer_type: usize, comptime InStreamError: type) type {
return struct {
const Self = @This();
pub const Error = InStreamError;
@ -207,55 +207,35 @@ pub fn PeekStream(comptime buffer_size: usize, comptime InStreamError: type) typ
// Right now the look-ahead space is statically allocated, but a version with dynamic allocation
// is not too difficult to derive from this.
buffer: [buffer_size]u8,
index: usize,
at_end: bool,
const FifoType = std.fifo.LinearFifo(u8, .{ .Static = buffer_size });
fifo: FifoType,
pub fn init(base: *Stream) Self {
return Self{
return .{
.base = base,
.buffer = undefined,
.index = 0,
.at_end = false,
.fifo = FifoType.init(),
.stream = Stream{ .readFn = readFn },
};
}
pub fn putBackByte(self: *Self, byte: u8) void {
self.buffer[self.index] = byte;
self.index += 1;
pub fn putBackByte(self: *Self, byte: u8) !void {
try self.putBack(@ptrCast([*]const u8, &byte)[0..1]);
}
pub fn putBack(self: *Self, bytes: []const u8) void {
var pos = bytes.len;
while (pos != 0) {
pos -= 1;
self.putBackByte(bytes[pos]);
}
pub fn putBack(self: *Self, bytes: []const u8) !void {
try self.fifo.unget(bytes);
}
fn readFn(in_stream: *Stream, dest: []u8) Error!usize {
const self = @fieldParentPtr(Self, "stream", in_stream);
// copy over anything putBack()'d
var pos: usize = 0;
while (pos < dest.len and self.index != 0) {
dest[pos] = self.buffer[self.index - 1];
self.index -= 1;
pos += 1;
}
if (pos == dest.len or self.at_end) {
return pos;
}
var dest_index = self.fifo.read(dest);
if (dest_index == dest.len) return dest_index;
// ask the backing stream for more
const left = dest.len - pos;
const read = try self.base.read(dest[pos..]);
assert(read <= left);
self.at_end = (read < left);
return pos + read;
dest_index += try self.base.read(dest[dest_index..]);
return dest_index;
}
};
}

8
lib/std/io/test.zig
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@ -97,8 +97,8 @@ test "PeekStream" {
var dest: [4]u8 = undefined;
ps.putBackByte(9);
ps.putBackByte(10);
try ps.putBackByte(9);
try ps.putBackByte(10);
var read = try ps.stream.read(dest[0..4]);
expect(read == 4);
@ -114,8 +114,8 @@ test "PeekStream" {
expect(read == 2);
expect(mem.eql(u8, dest[0..2], bytes[6..8]));
ps.putBackByte(11);
ps.putBackByte(12);
try ps.putBackByte(11);
try ps.putBackByte(12);
read = try ps.stream.read(dest[0..4]);
expect(read == 2);