js: fix strings module (#11353)

vlib/strings/builder.c.v

@@ -0,0 +1,163 @@
+// Copyright (c) 2019-2021 Alexander Medvednikov. All rights reserved.
+// Use of this source code is governed by an MIT license
+// that can be found in the LICENSE file.
+module strings
+
+// strings.Builder is used to efficiently append many strings to a large
+// dynamically growing buffer, then use the resulting large string. Using
+// a string builder is much better for performance/memory usage than doing
+// constantly string concatenation.
+pub type Builder = []byte
+
+// new_builder returns a new string builder, with an initial capacity of `initial_size`
+pub fn new_builder(initial_size int) Builder {
+	return Builder([]byte{cap: initial_size})
+}
+
+// write_ptr writes `len` bytes provided byteptr to the accumulated buffer
+[unsafe]
+pub fn (mut b Builder) write_ptr(ptr &byte, len int) {
+	if len == 0 {
+		return
+	}
+	unsafe { b.push_many(ptr, len) }
+}
+
+// write_rune appends a single rune to the accumulated buffer
+[manualfree]
+pub fn (mut b Builder) write_rune(r rune) {
+	mut buffer := [5]byte{}
+	res := unsafe { utf32_to_str_no_malloc(u32(r), &buffer[0]) }
+	if res.len == 0 {
+		return
+	}
+	unsafe { b.push_many(res.str, res.len) }
+}
+
+// write_runes appends all the given runes to the accumulated buffer
+pub fn (mut b Builder) write_runes(runes []rune) {
+	mut buffer := [5]byte{}
+	for r in runes {
+		res := unsafe { utf32_to_str_no_malloc(u32(r), &buffer[0]) }
+		if res.len == 0 {
+			continue
+		}
+		unsafe { b.push_many(res.str, res.len) }
+	}
+}
+
+// write_b appends a single `data` byte to the accumulated buffer
+pub fn (mut b Builder) write_b(data byte) {
+	b << data
+}
+
+// write implements the Writer interface
+pub fn (mut b Builder) write(data []byte) ?int {
+	if data.len == 0 {
+		return 0
+	}
+	b << data
+	return data.len
+}
+
+[inline]
+pub fn (b &Builder) byte_at(n int) byte {
+	return unsafe { (&[]byte(b))[n] }
+}
+
+// write appends the string `s` to the buffer
+[inline]
+pub fn (mut b Builder) write_string(s string) {
+	if s.len == 0 {
+		return
+	}
+	unsafe { b.push_many(s.str, s.len) }
+	// for c in s {
+	// b.buf << c
+	// }
+	// b.buf << []byte(s)  // TODO
+}
+
+// go_back discards the last `n` bytes from the buffer
+pub fn (mut b Builder) go_back(n int) {
+	b.trim(b.len - n)
+}
+
+// cut_last cuts the last `n` bytes from the buffer and returns them
+pub fn (mut b Builder) cut_last(n int) string {
+	cut_pos := b.len - n
+	x := unsafe { (&[]byte(b))[cut_pos..] }
+	res := x.bytestr()
+	b.trim(cut_pos)
+	return res
+}
+
+// cut_to cuts the string after `pos` and returns it.
+// if `pos` is superior to builder length, returns an empty string
+// and cancel further operations
+pub fn (mut b Builder) cut_to(pos int) string {
+	if pos > b.len {
+		return ''
+	}
+	return b.cut_last(b.len - pos)
+}
+
+// go_back_to resets the buffer to the given position `pos`
+// NB: pos should be < than the existing buffer length.
+pub fn (mut b Builder) go_back_to(pos int) {
+	b.trim(pos)
+}
+
+// writeln appends the string `s`, and then a newline character.
+[inline]
+pub fn (mut b Builder) writeln(s string) {
+	// for c in s {
+	// b.buf << c
+	// }
+	if s.len > 0 {
+		unsafe { b.push_many(s.str, s.len) }
+	}
+	// b.buf << []byte(s)  // TODO
+	b << byte(`\n`)
+}
+
+// last_n(5) returns 'world'
+// buf == 'hello world'
+pub fn (b &Builder) last_n(n int) string {
+	if n > b.len {
+		return ''
+	}
+	x := unsafe { (&[]byte(b))[b.len - n..] }
+	return x.bytestr()
+}
+
+// after(6) returns 'world'
+// buf == 'hello world'
+pub fn (b &Builder) after(n int) string {
+	if n >= b.len {
+		return ''
+	}
+	x := unsafe { (&[]byte(b))[n..] }
+	return x.bytestr()
+}
+
+// str returns a copy of all of the accumulated buffer content.
+// NB: after a call to b.str(), the builder b should not be
+// used again, you need to call b.free() first, or just leave
+// it to be freed by -autofree when it goes out of scope.
+// The returned string *owns* its own separate copy of the
+// accumulated data that was in the string builder, before the
+// .str() call.
+pub fn (mut b Builder) str() string {
+	b << byte(0)
+	bcopy := unsafe { &byte(memdup(b.data, b.len)) }
+	s := unsafe { bcopy.vstring_with_len(b.len - 1) }
+	b.trim(0)
+	return s
+}
+
+// free is for manually freeing the contents of the buffer
+[unsafe]
+pub fn (mut b Builder) free() {
+	unsafe { free(b.data) }
+}