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// Package structtag provides parsing of the defacto struct tag style.
package structtag
import (
"errors"
"strconv"
)
var errInvalidTag = errors.New("invalid tag")
// Extract the quoted value for the given name returning it if it is found. The
// found boolean helps differentiate between the "empty and found" vs "empty
// and not found" nature of default empty strings.
func Extract(name, tag string) (found bool, value string, err error) {
for tag != "" {
// skip leading space
i := 0
for i < len(tag) && tag[i] == ' ' {
i++
}
tag = tag[i:]
if tag == "" {
break
}
// scan to colon.
// a space or a quote is a syntax error
i = 0
for i < len(tag) && tag[i] != ' ' && tag[i] != ':' && tag[i] != '"' {
i++
}
if i+1 >= len(tag) || tag[i] != ':' || tag[i+1] != '"' {
return false, "", errInvalidTag
}
foundName := string(tag[:i])
tag = tag[i+1:]
// scan quoted string to find value
i = 1
for i < len(tag) && tag[i] != '"' {
if tag[i] == '\\' {
i++
}
i++
}
if i >= len(tag) {
return false, "", errInvalidTag
}
qvalue := string(tag[:i+1])
tag = tag[i+1:]
if foundName == name {
value, err := strconv.Unquote(qvalue)
if err != nil {
return false, "", err
}
return true, value, nil
}
}
return false, "", nil
}
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