You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: scannerc.go
    path of file: ./repos/trickster/vendor/gopkg.in/yaml.v2
    
    the code of the file until where you have to start completion: package yaml

import (
	"bytes"
	"fmt"
)

// Introduction
// ************
//
// The following notes assume that you are familiar with the YAML specification
// (http://yaml.org/spec/1.2/spec.html).  We mostly follow it, although in
// some cases we are less restrictive that it requires.
//
// The process of transforming a YAML stream into a sequence of events is
// divided on two steps: Scanning and Parsing.
//
// The Scanner transforms the input stream into a sequence of tokens, while the
// parser transform the sequence of tokens produced by the Scanner into a
// sequence of parsing events.
//
// The Scanner is rather clever and complicated. The Parser, on the contrary,
// is a straightforward implementation of a recursive-descendant parser (or,
// LL(1) parser, as it is usually called).
//
// Actually there are two issues of Scanning that might be called "clever", the
// rest is quite straightforward.  The issues are "block collection start" and
// "simple keys".  Both issues are explained below
    
func yaml_parser_scan_tag_uri(parser *yaml_parser_t, directive bool, head []byte, start_mark yaml_mark_t, uri *[]byte) bool {
	//size_t length = head ? strlen((char *)head) : 0
	var s []byte
	hasTag := len(head) > 0

	// Copy the head if needed.
	//
	// Note that we don't copy the leading '!' character.
	if len(head) > 1 {
		s = append(s, head[1:]...)
	}

	// Scan the tag.
	if parser.unread < 1 && !yaml_parser_update_buffer(parser, 1) {
		return false
	}

	// The set of characters that may appear in URI is as follows:
	//
	//      '0'-'9', 'A'-'Z', 'a'-'z', '_', '-', ';', '/', '?', ':', '@', '&',
	//      '=', '+', '$', ',', '.', '!', '~', '*', '\'', '(', ')', '[', ']',
	//      '%'.
	// [Go] Convert this into more reasonable logic.
	for is_alpha(parser.buffer, parser.buffer_pos) || parser.buffer[parser.buffer_pos] == ';' ||
		parser.buffer[parser.buffer_pos] == '/' || parser.buffer[parser.buffer_pos] == '?' ||
		parser.buffer[parser.buffer_pos] == ':' || parser.buffer[parser.buffer_pos] == '@' ||
		parser.buffer[parser.buffer_pos] == '&' || parser.buffer[parser.buffer_pos] == '=' ||
		parser.buffer[parser.buffer_pos] == '+' || parser.buffer[parser.buffer_pos] == '$' ||
		parser.buffer[parser.buffer_pos] == ',' || parser.buffer[parser.buffer_pos] == '.' ||
		parser.buffer[parser.buffer_pos] == '!' || parser.buffer[parser.buffer_pos] == '~' ||
		parser.buffer[parser.buffer_pos] == '*' || parser.buffer[parser.buffer_pos] == '\'' ||
		parser.buffer[parser.buffer_pos] == '(' || parser.buffer[parser.buffer_pos] == ')' ||
		parser.buffer[parser.buffer_pos] == '[' || parser.buffer[parser.buffer_pos] == ']' ||
		parser.buffer[parser.buffer_pos] == '%' {
		// Check if it is a URI-escape sequence.
		if parser.buffer[parser.buffer_pos] == '%' {
			if !yaml_parser_scan_uri_escapes(parser, directive, start_mark, &s) {
				return false
			}
		} else {
			s = read(parser, s)
		}
		if parser.unread < 1 && !yaml_parser_update_buffer(parser, 1) {
			return false
		}
		hasTag = true
	}

	if !hasTag {
		yaml_parser_set_scanner_tag_error(parser, directive,
			start_mark, "did not find expected tag URI")
		return false
	}
	*uri = s
	return true
}