forked from cayleygraph/cayley
/
session.go
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/
session.go
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// Copyright 2014 The Cayley Authors. All rights reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// Package query defines the graph session interface general to all query languages.
package query
import (
"context"
"errors"
"io"
"github.com/cayleygraph/cayley/graph"
)
var ErrParseMore = errors.New("query: more input required")
type Result interface {
Result() interface{}
Err() error
}
func ErrorResult(err error) Result {
return errResult{err: err}
}
type errResult struct {
err error
}
func (errResult) Result() interface{} { return nil }
func (e errResult) Err() error { return e.err }
func TagMapResult(m map[string]graph.Value) Result {
return tagMap(m)
}
type tagMap map[string]graph.Value
func (m tagMap) Result() interface{} { return map[string]graph.Value(m) }
func (tagMap) Err() error { return nil }
type Session interface {
// Runs the query and returns individual results on the channel.
//
// Channel will be closed when function returns.
Execute(ctx context.Context, query string, out chan Result, limit int)
}
// TODO(dennwc): review HTTP interface (Collate is weird)
// TODO(dennwc): specify exact type to return from ShapeOf
// TODO(dennwc): add context to ShapeOf?
type HTTP interface {
Session
ShapeOf(string) (interface{}, error)
Collate(Result)
Results() (interface{}, error)
}
type REPLSession interface {
Session
FormatREPL(Result) string
}
// ResponseWriter is a subset of http.ResponseWriter
type ResponseWriter interface {
Write([]byte) (int, error)
WriteHeader(int)
}
// Language is a description of query language.
type Language struct {
Name string
Session func(graph.QuadStore) Session
REPL func(graph.QuadStore) REPLSession
HTTP func(graph.QuadStore) HTTP
// Custom HTTP handlers
HTTPQuery func(ctx context.Context, qs graph.QuadStore, w ResponseWriter, r io.Reader)
HTTPError func(w ResponseWriter, err error)
}
var languages = make(map[string]Language)
// RegisterLanguage register a new query language.
func RegisterLanguage(lang Language) {
languages[lang.Name] = lang
}
// NewSession creates a new session for specified query language.
// It returns nil if language was not registered.
func NewSession(qs graph.QuadStore, lang string) Session {
if l := languages[lang]; l.Session != nil {
return l.Session(qs)
}
return nil
}
// GetLanguage returns a query language description.
// It returns nil if language was not registered.
func GetLanguage(lang string) *Language {
l, ok := languages[lang]
if ok {
return &l
}
return nil
}
// Languages returns names of registered query languages.
func Languages() []string {
out := make([]string, 0, len(languages))
for name := range languages {
out = append(out, name)
}
return out
}