terraform/config/interpolate.go

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package config
import (
"fmt"
"strconv"
"strings"
)
// Interpolation is something that can be contained in a "${}" in a
// configuration value.
//
// Interpolations might be simple variable references, or it might be
// function calls, or even nested function calls.
type Interpolation interface {
FullString() string
Interpolate(map[string]string) (string, error)
Variables() map[string]InterpolatedVariable
}
// An InterpolatedVariable is a variable reference within an interpolation.
//
// Implementations of this interface represents various sources where
// variables can come from: user variables, resources, etc.
type InterpolatedVariable interface {
FullKey() string
}
// VariableInterpolation implements Interpolation for simple variable
// interpolation. Ex: "${var.foo}" or "${aws_instance.foo.bar}"
type VariableInterpolation struct {
Variable InterpolatedVariable
key string
}
// A ResourceVariable is a variable that is referencing the field
// of a resource, such as "${aws_instance.foo.ami}"
type ResourceVariable struct {
Type string // Resource type, i.e. "aws_instance"
Name string // Resource name
Field string // Resource field
Multi bool // True if multi-variable: aws_instance.foo.*.id
Index int // Index for multi-variable: aws_instance.foo.1.id == 1
key string
}
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// A UserVariable is a variable that is referencing a user variable
// that is inputted from outside the configuration. This looks like
// "${var.foo}"
type UserVariable struct {
Name string
key string
}
// A UserMapVariable is a variable that is referencing a user
// variable that is a map. This looks like "${var.amis.us-east-1}"
type UserMapVariable struct {
Name string
Elem string
key string
}
// NewInterpolation takes some string and returns the valid
// Interpolation associated with it, or error if a valid
// interpolation could not be found or the interpolation itself
// is invalid.
func NewInterpolation(v string) (Interpolation, error) {
if idx := strings.Index(v, "."); idx >= 0 {
v, err := NewInterpolatedVariable(v)
if err != nil {
return nil, err
}
return &VariableInterpolation{
Variable: v,
key: v.FullKey(),
}, nil
}
return nil, fmt.Errorf(
"Interpolation '%s' is not a valid interpolation. " +
"Please check your syntax and try again.")
}
func NewInterpolatedVariable(v string) (InterpolatedVariable, error) {
if !strings.HasPrefix(v, "var.") {
return NewResourceVariable(v)
}
varKey := v[len("var."):]
if strings.Index(varKey, ".") == -1 {
return NewUserVariable(v)
} else {
return NewUserMapVariable(v)
}
}
func (i *VariableInterpolation) FullString() string {
return i.key
}
func (i *VariableInterpolation) Interpolate(
vs map[string]string) (string, error) {
return vs[i.key], nil
}
func (i *VariableInterpolation) Variables() map[string]InterpolatedVariable {
return map[string]InterpolatedVariable{i.key: i.Variable}
}
func NewResourceVariable(key string) (*ResourceVariable, error) {
parts := strings.SplitN(key, ".", 3)
field := parts[2]
multi := false
var index int
if idx := strings.Index(field, "."); idx != -1 {
indexStr := field[:idx]
multi = indexStr == "*"
index = -1
if !multi {
indexInt, err := strconv.ParseInt(indexStr, 0, 0)
if err == nil {
multi = true
index = int(indexInt)
}
}
if multi {
field = field[idx+1:]
}
}
return &ResourceVariable{
Type: parts[0],
Name: parts[1],
Field: field,
Multi: multi,
Index: index,
key: key,
}, nil
}
func (v *ResourceVariable) ResourceId() string {
return fmt.Sprintf("%s.%s", v.Type, v.Name)
}
func (v *ResourceVariable) FullKey() string {
return v.key
}
func NewUserVariable(key string) (*UserVariable, error) {
name := key[len("var."):]
return &UserVariable{
key: key,
Name: name,
}, nil
}
func (v *UserVariable) FullKey() string {
return v.key
}
func NewUserMapVariable(key string) (*UserMapVariable, error) {
name := key[len("var."):]
idx := strings.Index(name, ".")
if idx == -1 {
return nil, fmt.Errorf("not a user map variable: %s", key)
}
elem := name[idx+1:]
name = name[:idx]
return &UserMapVariable{
Name: name,
Elem: elem,
key: key,
}, nil
}
func (v *UserMapVariable) FullKey() string {
return v.key
}
func (v *UserMapVariable) GoString() string {
return fmt.Sprintf("%#v", *v)
}