httplib.go

/*
Copyright 2015 Gravitational, Inc.

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 httplib implements common utility functions for writing
// classic HTTP handlers
package httplib

import (
	"encoding/json"
	"io/ioutil"
	"net/http"
	"net/url"
	"regexp"
	"strconv"

	"github.com/gravitational/roundtrip"
	"github.com/gravitational/trace"
	"github.com/julienschmidt/httprouter"
)

// HandlerFunc specifies HTTP handler function that returns error
type HandlerFunc func(w http.ResponseWriter, r *http.Request, p httprouter.Params) (interface{}, error)

// StdHandlerFunc specifies HTTP handler function that returns error
type StdHandlerFunc func(w http.ResponseWriter, r *http.Request) (interface{}, error)

// MakeHandler returns a new httprouter.Handle func from a handler func
func MakeHandler(fn HandlerFunc) httprouter.Handle {
	return func(w http.ResponseWriter, r *http.Request, p httprouter.Params) {
		out, err := fn(w, r, p)
		if err != nil {
			trace.WriteError(w, err)
			return
		}
		if out != nil {
			roundtrip.ReplyJSON(w, http.StatusOK, out)
		}
	}
}

// MakeStdHandler returns a new http.Handle func from http.HandlerFunc
func MakeStdHandler(fn StdHandlerFunc) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		out, err := fn(w, r)
		if err != nil {
			trace.WriteError(w, err)
			return
		}
		if out != nil {
			roundtrip.ReplyJSON(w, http.StatusOK, out)
		}
	}
}

// ReadJSON reads HTTP json request and unmarshals it
// into passed interface{} obj
func ReadJSON(r *http.Request, val interface{}) error {
	data, err := ioutil.ReadAll(r.Body)
	if err != nil {
		return trace.Wrap(err)
	}
	if err := json.Unmarshal(data, &val); err != nil {
		return trace.BadParameter("request: %v", err.Error())
	}
	return nil
}

// ConvertResponse converts http error to internal error type
// based on HTTP response code and HTTP body contents
func ConvertResponse(re *roundtrip.Response, err error) (*roundtrip.Response, error) {
	if err != nil {
		if uerr, ok := err.(*url.Error); ok && uerr != nil && uerr.Err != nil {
			return nil, trace.Wrap(uerr.Err)
		}
		return nil, trace.Wrap(err)
	}
	return re, trace.ReadError(re.Code(), re.Bytes())
}

// InsecureSetDevmodeHeaders allows cross-origin requests, used in dev mode only
func InsecureSetDevmodeHeaders(w http.ResponseWriter) {
	w.Header().Set("Access-Control-Allow-Origin", "*")
	w.Header().Set("Access-Control-Allow-Methods", "POST, GET, PUT, DELETE, OPTIONS")
	w.Header().Set("Access-Control-Allow-Headers", "Accept, Origin, Content-type, Authorization")
	w.Header().Set("Access-Control-Allow-Credentials", "true")
	w.Header().Set("Access-Control-Max-Age", "1728000")
}

// ParseBool will parse boolean variable from url query
// returns value, ok, error
func ParseBool(q url.Values, name string) (bool, bool, error) {
	stringVal := q.Get(name)
	if stringVal == "" {
		return false, false, nil
	}

	val, err := strconv.ParseBool(stringVal)
	if err != nil {
		return false, false, trace.BadParameter(
			"'%v': expected 'true' or 'false', got %v", name, stringVal)
	}
	return val, true, nil
}

// RewritePair is a rewrite expression
type RewritePair struct {
	// Expr is matching expression
	Expr *regexp.Regexp
	// Replacement is replacement
	Replacement string
}

// Rewrite creates a rewrite pair, panics if in epxression
// is not a valid regular expressoin
func Rewrite(in, out string) RewritePair {
	return RewritePair{
		Expr:        regexp.MustCompile(in),
		Replacement: out,
	}
}

// RewritePaths creates a middleware that rewrites paths in incoming request
func RewritePaths(next http.Handler, rewrites ...RewritePair) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
		for _, rewrite := range rewrites {
			req.URL.Path = rewrite.Expr.ReplaceAllString(req.URL.Path, rewrite.Replacement)
		}
		next.ServeHTTP(w, req)
	})
}