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package funcs
import (
"fmt"
"strings"
)
// CallbackFunc is a function which can be executed by the mapreduce engine
type CallbackFunc func(text string) string
// Function embeddes the function name to the callback function
type Function struct {
// Name of the callback function
Name string
// The Go-callback function to call for this DTail function.
call CallbackFunc
}
// FunctionStack is a list of functions stacked each other
type FunctionStack []Function
// NewFunctionStack parses the input string, e.g. foo(bar("arg")) and returns
// a corresponding function stack. It returns an error for malformed inputs
// such as unbalanced parentheses (e.g. "foo(", "foo(bar)baz").
func NewFunctionStack(in string) (FunctionStack, string, error) {
var fs FunctionStack
aux := in
for strings.HasSuffix(aux, ")") {
index := strings.Index(aux, "(")
if index <= 0 {
return fs, "", fmt.Errorf("unable to parse function '%s' at '%s'", in, aux)
}
name := aux[0:index]
call, err := lookupCallback(name)
if err != nil {
return fs, "", err
}
fs = append(fs, Function{name, call})
// Strip the outer function name and its enclosing parens, leaving
// only the argument expression for the next iteration.
aux = aux[index+1 : len(aux)-1]
}
// Validate that no unbalanced parentheses remain in the argument string.
// Inputs like "foo(bar)baz" leave "bar)baz" after stripping, and inputs
// ending with "(" (no closing ")") are accepted as plain field literals
// without this check — both produce silently wrong behavior.
if err := validateParenBalance(aux, in); err != nil {
return fs, "", err
}
return fs, aux, nil
}
// lookupCallback maps a function name to its CallbackFunc implementation.
// It returns an error for unrecognised names so callers get a clear message.
func lookupCallback(name string) (CallbackFunc, error) {
switch name {
case "md5sum":
return Md5Sum, nil
case "maskdigits":
return MaskDigits, nil
default:
var zero CallbackFunc
return zero, fmt.Errorf("unknown function '%s'", name)
}
}
// validateParenBalance checks that the remaining argument string contains no
// unbalanced parentheses. A negative depth means a stray ')' was found; a
// non-zero depth after the loop means an unclosed '(' was found. The original
// full expression is included in the error message for context.
func validateParenBalance(aux, original string) error {
depth := 0
for _, r := range aux {
switch r {
case '(':
depth++
case ')':
depth--
}
if depth < 0 {
return fmt.Errorf("malformed function expression %q: unexpected ')' in argument", original)
}
}
if depth != 0 {
return fmt.Errorf("malformed function expression %q: unclosed '(' in argument", original)
}
return nil
}
// Call the function stack.
func (fs FunctionStack) Call(str string) string {
for i := len(fs) - 1; i >= 0; i-- {
//dlog.Common.Debug("Call", fs[i].Name, str)
str = fs[i].call(str)
//dlog.Common.Debug("Call.result", fs[i].Name, str)
}
return str
}
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