perf: reduce memory allocation in some [n..m].method() use cases

[enghitalo]

Describe the feature

[(.+?)..(.+?)].trim_space()

-> \[(.+?)\.\.(.+?)\]\.(.+?)\(\)
-> \[(.+?)\.\.\]\.(.+?)\(\)
-> \[\.\.(.+?)\]\.(.+?)\(\)

In all string method case use substr_unsafe

[(.+?)..(.+?)].(.+?)()

vlib/crypto/bcrypt/bcrypt.v

// fn (mut h Hashed) decode_cost(sbytes []u8) !int {
	cost := sbytes[0..2].bytestr().int()

vlib/veb/veb.v and vlib/x/vweb/vweb.v

// fn handle_read[A, X](mut pv picoev.Picoev, mut params RequestParams, fd int) {
// line 422
		} else if n < bytes_to_read || params.idx[fd] + n < content_length.int() {
			// request is incomplete wait until the socket becomes ready to read again
			params.idx[fd] += n
			// TODO: change this to a memcpy function?
			req.data += buf[0..n].bytestr()
			params.incomplete_requests[fd] = req
			return
		} else {
			// request is complete: n = bytes_to_read
			params.idx[fd] += n
			req.data += buf[0..n].bytestr()
		}

vlib/io/buffered_reader.v

// pub fn (mut r BufferedReader) read(mut buf []u8) !int {
// pub fn (mut r BufferedReader) read_line(config BufferedReadLineConfig) !string {

Use Case

improve performance

Proposed Solution

No response

Other Information

No response

Acknowledgements

• I may be able to implement this feature request
• This feature might incur a breaking change

Version used

V 0.4.8 3326392

Environment details (OS name and version, etc.)

all

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[spytheman]

substr_unsafe is not safe to use in the general case.
It will produce a V string, that is a "slice" of the original, and it will not have the ending 0, that is needed for calling C APIs later.

[spytheman]

The result will also entangle the life times of the 2 strings, so it will conflict with -autofree too.