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std.io.BufferedReader: implement readVecLimit

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This commit is contained in:
Andrew Kelley 2025-05-05 13:42:32 -07:00
parent b78e375a2d
commit 42cc1bd76e
1 changed files with 51 additions and 43 deletions
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94
lib/std/io/BufferedReader.zig
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@ -51,7 +51,7 @@ pub fn reader(br: *BufferedReader) Reader {
/// Equivalent semantics to `std.io.Reader.VTable.readVec`.
pub fn readVec(br: *BufferedReader, data: []const []u8) Reader.Error!usize {
return passthruReadVec(br, data);
return readVecLimit(br, data, .unlimited);
}
/// Equivalent semantics to `std.io.Reader.VTable.read`.
@ -106,10 +106,55 @@ pub fn readRemaining(br: *BufferedReader, bw: *BufferedWriter) Reader.RwRemainin
/// Equivalent to `readVec` but reads at most `limit` bytes.
pub fn readVecLimit(br: *BufferedReader, data: []const []u8, limit: Reader.Limit) Reader.Error!usize {
_ = br;
_ = data;
_ = limit;
@panic("TODO");
assert(@intFromEnum(Reader.Limit.unlimited) == std.math.maxInt(usize));
var remaining = @intFromEnum(limit);
for (data, 0..) |buf, i| {
const buffered = br.buffer[br.seek..br.end];
const copy_len = @min(buffered.len, buf.len, remaining);
@memcpy(buf[0..copy_len], buffered[0..copy_len]);
br.seek += copy_len;
remaining -= copy_len;
if (remaining == 0) break;
if (buf.len - copy_len == 0) continue;
br.seek = 0;
br.end = 0;
var vecs: [8][]u8 = undefined; // Arbitrarily chosen value.
const available_remaining_buf = buf[copy_len..];
vecs[0] = available_remaining_buf[0..@min(available_remaining_buf.len, remaining)];
const vec_start_remaining = remaining;
remaining -= vecs[0].len;
var vecs_i: usize = 1;
var data_i: usize = i + 1;
while (true) {
if (vecs.len - vecs_i == 0) {
const n = try br.unbuffered_reader.readVec(&vecs);
return @intFromEnum(limit) - vec_start_remaining + n;
}
if (remaining == 0 or data.len - data_i == 0) {
vecs[vecs_i] = br.buffer;
vecs_i += 1;
const n = try br.unbuffered_reader.readVec(vecs[0..vecs_i]);
const cutoff = vec_start_remaining - remaining;
if (n > cutoff) {
br.end = n - cutoff;
return @intFromEnum(limit) - remaining;
} else {
return @intFromEnum(limit) - vec_start_remaining + n;
}
}
if (data[data_i].len == 0) {
data_i += 1;
continue;
}
const data_elem = data[data_i];
vecs[vecs_i] = data_elem[0..@min(data_elem.len, remaining)];
remaining -= vecs[vecs_i].len;
vecs_i += 1;
data_i += 1;
}
}
return @intFromEnum(limit) - remaining;
}
fn passthruRead(context: ?*anyopaque, bw: *BufferedWriter, limit: Reader.Limit) Reader.RwError!usize {
@ -144,44 +189,7 @@ fn passthruDiscard(context: ?*anyopaque, limit: Reader.Limit) Reader.Error!usize
fn passthruReadVec(context: ?*anyopaque, data: []const []u8) Reader.Error!usize {
const br: *BufferedReader = @alignCast(@ptrCast(context));
var total: usize = 0;
for (data, 0..) |buf, i| {
const buffered = br.buffer[br.seek..br.end];
const copy_len = @min(buffered.len, buf.len);
@memcpy(buf[0..copy_len], buffered[0..copy_len]);
total += copy_len;
br.seek += copy_len;
if (copy_len < buf.len) {
br.seek = 0;
br.end = 0;
var vecs: [8][]u8 = undefined; // Arbitrarily chosen value.
vecs[0] = buf[copy_len..];
const vecs_len: usize = @min(vecs.len, data.len - i);
var vec_data_len: usize = vecs[0].len;
for (vecs[1..vecs_len], data[i + 1 ..][0 .. vecs_len - 1]) |*v, d| {
vec_data_len += d.len;
v.* = d;
}
if (vecs_len < vecs.len) {
vecs[vecs_len] = br.buffer;
const n = try br.unbuffered_reader.readVec(vecs[0 .. vecs_len + 1]);
total += @min(n, vec_data_len);
br.end = n -| vec_data_len;
return total;
}
if (vecs[vecs.len - 1].len >= br.buffer.len) {
total += try br.unbuffered_reader.readVec(&vecs);
return total;
}
vec_data_len -= vecs[vecs.len - 1].len;
vecs[vecs.len - 1] = br.buffer;
const n = try br.unbuffered_reader.readVec(&vecs);
total += @min(n, vec_data_len);
br.end = n -| vec_data_len;
return total;
}
}
return total;
return readVecLimit(br, data, .unlimited);
}
pub fn seekBy(br: *BufferedReader, seek_by: i64) !void {