open-consul/agent/consul/prepared_query/template.go

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package prepared_query
import (
"fmt"
"reflect"
"regexp"
"strings"
"github.com/hashicorp/consul/agent/structs"
"github.com/hashicorp/hil"
"github.com/hashicorp/hil/ast"
"github.com/mitchellh/copystructure"
)
// IsTemplate returns true if the given query is a template.
func IsTemplate(query *structs.PreparedQuery) bool {
return query.Template.Type != ""
}
// CompiledTemplate is an opaque object that can be used later to render a
// prepared query template.
type CompiledTemplate struct {
// query keeps a copy of the original query for rendering.
query *structs.PreparedQuery
// trees contains a map with paths to string fields in a structure to
// parsed syntax trees, suitable for later evaluation.
trees map[string]ast.Node
// re is the compiled regexp, if they supplied one (this can be nil).
re *regexp.Regexp
// removeEmptyTags will cause the service tags to be stripped of any
// empty strings after interpolation.
removeEmptyTags bool
}
// Compile validates a prepared query template and returns an opaque compiled
// object that can be used later to render the template.
func Compile(query *structs.PreparedQuery) (*CompiledTemplate, error) {
// Make sure it's a type we understand.
if query.Template.Type != structs.QueryTemplateTypeNamePrefixMatch {
return nil, fmt.Errorf("Bad Template.Type '%s'", query.Template.Type)
}
// Start compile.
ct := &CompiledTemplate{
trees: make(map[string]ast.Node),
removeEmptyTags: query.Template.RemoveEmptyTags,
}
// Make a copy of the query to use as the basis for rendering later.
dup, err := copystructure.Copy(query)
if err != nil {
return nil, err
}
var ok bool
ct.query, ok = dup.(*structs.PreparedQuery)
if !ok {
return nil, fmt.Errorf("Failed to copy query")
}
// Walk over all the string fields in the Service sub-structure and
// parse them as HIL.
parse := func(path string, v reflect.Value) error {
tree, err := hil.Parse(v.String())
if err != nil {
return fmt.Errorf("Bad format '%s' in Service%s: %s", v.String(), path, err)
}
ct.trees[path] = tree
return nil
}
if err := walk(&ct.query.Service, parse); err != nil {
return nil, err
}
// If they supplied a regexp then compile it.
if ct.query.Template.Regexp != "" {
var err error
ct.re, err = regexp.Compile(ct.query.Template.Regexp)
if err != nil {
return nil, fmt.Errorf("Bad Regexp: %s", err)
}
}
// Finally do a test render with the supplied name prefix. This will
// help catch errors before run time, and this is the most minimal
// prefix it will be expected to run with. The results might not make
// sense and create a valid service to lookup, but it should render
// without any errors.
if _, err = ct.Render(ct.query.Name, structs.QuerySource{}); err != nil {
return nil, err
}
return ct, nil
}
// Render takes a compiled template and renders it for the given name. For
// example, if the user looks up foobar.query.consul via DNS then we will call
// this function with "foobar" on the compiled template.
func (ct *CompiledTemplate) Render(name string, source structs.QuerySource) (*structs.PreparedQuery, error) {
// Make it "safe" to render a default structure.
if ct == nil {
return nil, fmt.Errorf("Cannot render an uncompiled template")
}
// Start with a fresh, detached copy of the original so we don't disturb
// the prototype.
dup, err := copystructure.Copy(ct.query)
if err != nil {
return nil, err
}
query, ok := dup.(*structs.PreparedQuery)
if !ok {
return nil, fmt.Errorf("Failed to copy query")
}
var matches []string
if ct.re != nil {
matches = ct.re.FindStringSubmatch(name)
}
// Create a safe match function that can't fail at run time. It will
// return an empty string for any invalid input.
match := ast.Function{
ArgTypes: []ast.Type{ast.TypeInt},
ReturnType: ast.TypeString,
Variadic: false,
Callback: func(inputs []interface{}) (interface{}, error) {
i, ok := inputs[0].(int)
if ok && i >= 0 && i < len(matches) {
return matches[i], nil
}
return "", nil
},
}
// Build up the HIL evaluation context.
config := &hil.EvalConfig{
GlobalScope: &ast.BasicScope{
VarMap: map[string]ast.Variable{
"name.full": ast.Variable{
Type: ast.TypeString,
Value: name,
},
"name.prefix": ast.Variable{
Type: ast.TypeString,
Value: query.Name,
},
"name.suffix": ast.Variable{
Type: ast.TypeString,
Value: strings.TrimPrefix(name, query.Name),
},
"agent.segment": ast.Variable{
Type: ast.TypeString,
Value: source.Segment,
},
},
FuncMap: map[string]ast.Function{
"match": match,
},
},
}
// Run through the Service sub-structure and evaluate all the strings
// as HIL.
eval := func(path string, v reflect.Value) error {
tree, ok := ct.trees[path]
if !ok {
return nil
}
res, err := hil.Eval(tree, config)
if err != nil {
return fmt.Errorf("Bad evaluation for '%s' in Service%s: %s", v.String(), path, err)
}
if res.Type != hil.TypeString {
return fmt.Errorf("Expected Service%s field to be a string, got %s", path, res.Type)
}
v.SetString(res.Value.(string))
return nil
}
if err := walk(&query.Service, eval); err != nil {
return nil, err
}
if ct.removeEmptyTags {
tags := make([]string, 0, len(query.Service.Tags))
for _, tag := range query.Service.Tags {
if tag != "" {
tags = append(tags, tag)
}
}
query.Service.Tags = tags
}
return query, nil
}