mirror of
https://github.com/k3s-io/k3s.git
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122 lines
3.7 KiB
Go
122 lines
3.7 KiB
Go
/*
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Copyright 2018 The Kubernetes Authors.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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*/
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// Package expansion provides functions find and replace $(FOO) style variables in strings.
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package expansion
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import (
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"bytes"
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)
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const (
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operator = '$'
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referenceOpener = '('
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referenceCloser = ')'
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)
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// syntaxWrap returns the input string wrapped by the expansion syntax.
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func syntaxWrap(input string) string {
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return string(operator) + string(referenceOpener) + input + string(referenceCloser)
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}
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// MappingFuncFor returns a mapping function for use with Expand that
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// implements the expansion semantics defined in the expansion spec; it
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// returns the input string wrapped in the expansion syntax if no mapping
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// for the input is found.
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func MappingFuncFor(
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counts map[string]int,
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context ...map[string]string) func(string) string {
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return func(input string) string {
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for _, vars := range context {
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val, ok := vars[input]
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if ok {
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counts[input]++
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return val
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}
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}
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return syntaxWrap(input)
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}
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}
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// Expand replaces variable references in the input string according to
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// the expansion spec using the given mapping function to resolve the
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// values of variables.
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func Expand(input string, mapping func(string) string) string {
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var buf bytes.Buffer
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checkpoint := 0
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for cursor := 0; cursor < len(input); cursor++ {
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if input[cursor] == operator && cursor+1 < len(input) {
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// Copy the portion of the input string since the last
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// checkpoint into the buffer
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buf.WriteString(input[checkpoint:cursor])
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// Attempt to read the variable name as defined by the
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// syntax from the input string
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read, isVar, advance := tryReadVariableName(input[cursor+1:])
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if isVar {
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// We were able to read a variable name correctly;
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// apply the mapping to the variable name and copy the
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// bytes into the buffer
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buf.WriteString(mapping(read))
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} else {
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// Not a variable name; copy the read bytes into the buffer
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buf.WriteString(read)
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}
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// Advance the cursor in the input string to account for
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// bytes consumed to read the variable name expression
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cursor += advance
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// Advance the checkpoint in the input string
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checkpoint = cursor + 1
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}
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}
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// Return the buffer and any remaining unwritten bytes in the
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// input string.
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return buf.String() + input[checkpoint:]
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}
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// tryReadVariableName attempts to read a variable name from the input
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// string and returns the content read from the input, whether that content
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// represents a variable name to perform mapping on, and the number of bytes
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// consumed in the input string.
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//
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// The input string is assumed not to contain the initial operator.
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func tryReadVariableName(input string) (string, bool, int) {
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switch input[0] {
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case operator:
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// Escaped operator; return it.
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return input[0:1], false, 1
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case referenceOpener:
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// Scan to expression closer
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for i := 1; i < len(input); i++ {
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if input[i] == referenceCloser {
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return input[1:i], true, i + 1
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}
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}
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// Incomplete reference; return it.
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return string(operator) + string(referenceOpener), false, 1
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default:
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// Not the beginning of an expression, ie, an operator
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// that doesn't begin an expression. Return the operator
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// and the first rune in the string.
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return string(operator) + string(input[0]), false, 1
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}
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}
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