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preprocessor.go
40 lines (34 loc) · 914 Bytes
/
preprocessor.go
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package mktree
import (
"bytes"
"errors"
"fmt"
"io"
"io/ioutil"
"regexp"
"strings"
)
func preprocess(r io.Reader, vars map[string]string, allowUndefined bool) (io.Reader, error) {
input, err := ioutil.ReadAll(r)
if err != nil {
return nil, err
}
output := input
re := regexp.MustCompile(`%\([^)]*\)`)
matches := re.FindAll(input, -1)
for _, match := range matches {
m := string(match)
if m == "%()" {
return nil, errors.New("empty variable pattern '%()' is not allowed")
}
varname := m[2 : len(m)-1] // remove the surrounding %( and ).
varname = strings.TrimSpace(varname)
if value, ok := vars[varname]; !ok && !allowUndefined {
// Use quotes incase v contains leading or trailing whitespace.
return nil, fmt.Errorf("undefined variable: %q", varname)
} else {
output = bytes.ReplaceAll(output, []byte(m), []byte(value))
}
}
return bytes.NewReader(output), nil
}