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fetch.go
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fetch.go
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// Copyright 2016-2019 Google LLC. 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 fetch
import (
"encoding/json"
"errors"
"fmt"
"hash/crc64"
"io"
"io/ioutil"
"math"
"math/rand"
"net/http"
"net/url"
"os"
"path/filepath"
"strings"
"time"
"github.com/googlecodelabs/tools/claat/fetch/drive/auth"
"github.com/googlecodelabs/tools/claat/nodes"
"github.com/googlecodelabs/tools/claat/parser"
"github.com/googlecodelabs/tools/claat/types"
"github.com/googlecodelabs/tools/claat/util"
)
const (
// supported codelab source types must be registered parsers
// TODO: define these in claat/parser/..., e.g. in parser/gdoc
// alternate TODO: make this an iota-based enum?
SrcInvalid srcType = ""
SrcGoogleDoc srcType = "gdoc" // Google Docs doc
SrcMarkdown srcType = "md" // Markdown text
// driveAPI is a base URL for Drive API
driveAPI = "https://www.googleapis.com/drive/v3"
// Minimum image size in bytes for extension detection.
minImageSize = 11
)
// TODO: create an enum for use with "nometa" for readability's sake
// srcType is codelab source type
type srcType string
// resource is a codelab resource, loaded from local file
// or fetched from remote location.
type resource struct {
typ srcType // source type
body io.ReadCloser // resource body
mod time.Time // last update of content
}
// codelab wraps types.Codelab, while adding source type
// and modified timestamp fields.
type codelab struct {
*types.Codelab
Typ srcType // source type
Mod time.Time // last modified timestamp
Imgs map[string]string // Slurped local image paths
}
type MemoryFetcher struct {
passMetadata map[string]bool
}
func NewMemoryFetcher(pm map[string]bool) *MemoryFetcher {
return &MemoryFetcher{
passMetadata: pm,
}
}
func (m *MemoryFetcher) SlurpCodelab(rc io.ReadCloser) (*codelab, error) {
r := &resource{
body: rc,
typ: SrcMarkdown,
mod: time.Now(),
}
defer r.body.Close()
opts := *parser.NewOptions()
opts.PassMetadata = m.passMetadata
clab, err := parser.Parse(string(r.typ), r.body, opts)
if err != nil {
return nil, err
}
return &codelab{
Codelab: clab,
Typ: r.typ,
Mod: r.mod,
}, nil
}
type Fetcher struct {
authHelper *auth.Helper
authToken string
crcTable *crc64.Table
passMetadata map[string]bool
roundTripper http.RoundTripper
}
// NewFetcher creates an instance of Fetcher.
func NewFetcher(at string, pm map[string]bool, rt http.RoundTripper) (*Fetcher, error) {
return &Fetcher{
authHelper: nil,
authToken: at,
crcTable: crc64.MakeTable(crc64.ECMA),
passMetadata: pm,
roundTripper: rt,
}, nil
}
// SlurpCodelab retrieves and parses codelab source.
// It takes the source, plus an auth token and a set of extra metadata to pass along.
// It returns parsed codelab and its source type.
//
// The function will also fetch and parse fragments included
// with nodes.ImportNode.
func (f *Fetcher) SlurpCodelab(src string, output string) (*codelab, error) {
_, err := os.Stat(src)
// Only setup oauth if this source is not a local file.
if os.IsNotExist(err) {
if f.authHelper == nil {
f.authHelper, err = auth.NewHelper(f.authToken, auth.ProviderGoogle, f.roundTripper)
if err != nil {
return nil, err
}
}
}
res, err := f.fetch(src)
if err != nil {
return nil, err
}
defer res.body.Close()
opts := *parser.NewOptions()
opts.PassMetadata = f.passMetadata
clab, err := parser.Parse(string(res.typ), res.body, opts)
if err != nil {
return nil, err
}
images := make(map[string]string)
dir := codelabDir(output, &clab.Meta)
imgDir := filepath.Join(dir, util.ImgDirname)
if !isStdout(output) {
// download or copy codelab assets to disk, and rewrite image URLs
var nodes []nodes.Node
for _, step := range clab.Steps {
nodes = append(nodes, step.Content.Nodes...)
}
err := f.SlurpImages(src, imgDir, nodes, images)
if err != nil {
return nil, err
}
}
// fetch imports and parse them as fragments
var imports []*nodes.ImportNode
for _, st := range clab.Steps {
imports = append(imports, nodes.ImportNodes(st.Content.Nodes)...)
}
ch := make(chan error, len(imports))
defer close(ch)
for _, imp := range imports {
go func(n *nodes.ImportNode) {
frag, err := f.slurpFragment(n.URL)
if err != nil {
ch <- fmt.Errorf("%s: %v", n.URL, err)
return
}
if !isStdout(output) {
// download or copy codelab assets to disk, and rewrite image URLs
err = f.SlurpImages(gdocID(n.URL), imgDir, frag, images)
if err != nil {
return
}
}
n.Content.Nodes = frag
ch <- nil
}(imp)
}
for range imports {
if err := <-ch; err != nil {
return nil, err
}
}
v := &codelab{
Codelab: clab,
Typ: res.typ,
Mod: res.mod,
Imgs: images,
}
return v, nil
}
func (f *Fetcher) SlurpImages(src, dir string, n []nodes.Node, images map[string]string) error {
// make sure img dir exists
if err := os.MkdirAll(dir, 0755); err != nil {
return err
}
type res struct {
url, file string
err error
}
ch := make(chan *res, 100)
defer close(ch)
var count int
imageNodes := nodes.ImageNodes(n)
count += len(imageNodes)
for _, imageNode := range imageNodes {
go func(imageNode *nodes.ImageNode) {
url := imageNode.Src
file, err := f.slurpBytes(src, dir, url, imageNode.Bytes)
if err == nil {
imageNode.Src = filepath.Join(util.ImgDirname, file)
}
ch <- &res{url, file, err}
}(imageNode)
}
var errStr string
for i := 0; i < count; i++ {
r := <-ch
images[r.file] = r.url
if r.err != nil {
errStr += fmt.Sprintf("%s => %s: %v\n", r.url, r.file, r.err)
}
}
if len(errStr) > 0 {
return errors.New(errStr)
}
return nil
}
func (f *Fetcher) slurpBytes(codelabSrc, dir, imgURL string, imgBytes []byte) (string, error) {
// images can be data URLs, local in Markdown cases or remote.
// Only proceed a simple copy on local reference.
var b []byte
var ext string
var err error
if len(imgBytes) > 0 {
// Slurp bytes from image URL data.
b = imgBytes
if ext, err = imgExtFromBytes(b); err != nil {
return "", fmt.Errorf("Error reading image type: %v", err)
}
} else {
// Slurp bytes from local or remote URL.
u, err := url.Parse(imgURL)
if err != nil {
return "", err
}
// If the codelab source is being downloaded from the network, then we should interpret
// the image URL in the same way.
srcURL, err := url.Parse(codelabSrc)
if err == nil && srcURL.Host != "" {
u = srcURL.ResolveReference(u)
}
if u.Host == "" {
if imgURL, err = restrictPathToParent(imgURL, filepath.Dir(codelabSrc)); err != nil {
return "", err
}
if b, err = ioutil.ReadFile(imgURL); err != nil {
return "", err
}
ext = filepath.Ext(imgURL)
} else {
if b, err = f.slurpRemoteBytes(u.String(), 5); err != nil {
return "", fmt.Errorf("Error downloading image at %s: %v", u.String(), err)
}
if ext, err = imgExtFromBytes(b); err != nil {
return "", fmt.Errorf("Error reading image type at %s: %v", u.String(), err)
}
}
}
// Generate image file from slurped bytes.
crc := crc64.Checksum(b, f.crcTable)
file := fmt.Sprintf("%x%s", crc, ext)
dst := filepath.Join(dir, file)
return file, ioutil.WriteFile(dst, b, 0644)
}
func (f *Fetcher) slurpFragment(url string) ([]nodes.Node, error) {
res, err := f.fetch(url)
if err != nil {
return nil, err
}
defer res.body.Close()
opts := *parser.NewOptions()
opts.PassMetadata = f.passMetadata
return parser.ParseFragment(string(res.typ), res.body, opts)
}
// fetch retrieves codelab doc either from local disk
// or a remote location.
// The caller is responsible for closing returned stream.
func (f *Fetcher) fetch(name string) (*resource, error) {
fi, err := os.Stat(name)
if os.IsNotExist(err) {
return f.fetchRemote(name, false)
}
r, err := os.Open(name)
if err != nil {
return nil, err
}
return &resource{
body: r,
typ: SrcMarkdown,
mod: fi.ModTime(),
}, nil
}
// fetchRemote retrieves resource r from the network.
//
// If urlStr is not a URL, i.e. does not have the host part, it is considered to be
// a Google Doc ID and fetched accordingly. Otherwise, a simple GET request
// is used to retrieve the contents.
//
// The caller is responsible for closing returned stream.
// If nometa is true, resource.mod may have zero value.
func (f *Fetcher) fetchRemote(urlStr string, nometa bool) (*resource, error) {
u, err := url.Parse(urlStr)
if err != nil {
return nil, err
}
if u.Host == "" || u.Host == "docs.google.com" {
return f.fetchDriveFile(urlStr, nometa)
}
return f.fetchRemoteFile(urlStr)
}
// fetchRemoteFile retrieves codelab resource from url.
// It is a special case of fetchRemote function.
func (f *Fetcher) fetchRemoteFile(url string) (*resource, error) {
res, err := retryGet(f.authHelper.DriveClient(), url, 3)
if err != nil {
return nil, err
}
t, err := http.ParseTime(res.Header.Get("last-modified"))
if err != nil {
t = time.Now()
}
return &resource{
body: res.Body,
mod: t,
typ: SrcMarkdown,
}, nil
}
// fetchDriveFile uses Drive API to retrieve HTML representation of a Google Doc.
// See https://developers.google.com/drive/web/manage-downloads#downloading_google_documents
// for more details.
//
// If nometa is true, resource.mod will have zero value.
func (f *Fetcher) fetchDriveFile(id string, nometa bool) (*resource, error) {
id = gdocID(id)
exportURL := gdocExportURL(id)
if nometa {
res, err := retryGet(f.authHelper.DriveClient(), exportURL, 7)
if err != nil {
return nil, err
}
return &resource{body: res.Body, typ: SrcGoogleDoc}, nil
}
q := url.Values{
"fields": {"id,mimeType,modifiedTime"},
"supportsTeamDrives": {"true"},
}
u := fmt.Sprintf("%s/files/%s?%s", driveAPI, id, q.Encode())
res, err := retryGet(f.authHelper.DriveClient(), u, 7)
if err != nil {
return nil, err
}
defer res.Body.Close()
meta := &struct {
ID string `json:"id"`
MimeType string `json:"mimeType"`
Modified time.Time `json:"modifiedTime"`
}{}
if err := json.NewDecoder(res.Body).Decode(meta); err != nil {
return nil, err
}
if meta.MimeType != "application/vnd.google-apps.document" {
return nil, fmt.Errorf("%s: invalid mime type: %s", id, meta.MimeType)
}
if res, err = retryGet(f.authHelper.DriveClient(), exportURL, 7); err != nil {
return nil, err
}
return &resource{
body: res.Body,
mod: meta.Modified,
typ: SrcGoogleDoc,
}, nil
}
func (f *Fetcher) slurpRemoteBytes(url string, n int) ([]byte, error) {
res, err := retryGet(f.authHelper.DriveClient(), url, n)
if err != nil {
return nil, err
}
defer res.Body.Close()
return ioutil.ReadAll(res.Body)
}
// retryGet tries to GET specified url up to n times.
// Attempts are spaced out with exponential backoff.
// Default client will be used if not provided.
func retryGet(client *http.Client, url string, n int) (*http.Response, error) {
if client == nil {
client = http.DefaultClient
}
for i := 0; i <= n; i++ {
if i > 0 {
t := time.Duration((math.Pow(2, float64(i)) + rand.Float64()) * float64(time.Second))
time.Sleep(t)
}
res, err := client.Get(url)
// return early with a good response
// the rest is error handling
if err == nil && res.StatusCode == http.StatusOK {
return res, nil
}
// sometimes Drive API wouldn't even start a response,
// we get net/http: TLS handshake timeout instead:
// consider this a temporary failure and retry again
if err != nil {
continue
}
// otherwise, decode error response and check for "rate limit"
defer res.Body.Close()
var erres struct {
Error struct {
Errors []struct{ Reason string }
}
}
b, _ := ioutil.ReadAll(res.Body)
json.Unmarshal(b, &erres)
var rateLimit bool
for _, e := range erres.Error.Errors {
if e.Reason == "rateLimitExceeded" || e.Reason == "userRateLimitExceeded" {
rateLimit = true
break
}
}
// this is neither a rate limit error, nor a server error:
// retrying is useless
if !rateLimit && res.StatusCode < http.StatusInternalServerError {
return nil, fmt.Errorf("fetch %s: %s; %s", url, res.Status, b)
}
}
return nil, fmt.Errorf("%s: failed after %d retries", url, n)
}
func gdocID(url string) string {
const s = "/document/d/"
if i := strings.Index(url, s); i >= 0 {
url = url[i+len(s):]
}
if i := strings.IndexRune(url, '/'); i > 0 {
url = url[:i]
}
return url
}
func gdocExportURL(id string) string {
q := url.Values{
"mimeType": {"text/html"},
}
return fmt.Sprintf("%s/files/%s/export?%s", driveAPI, id, q.Encode())
}
// restrictPathToParent will ensure that assetPath is in parent.
// It will thus return an absolute path to the asset.
func restrictPathToParent(assetPath, parent string) (string, error) {
parent, err := filepath.Abs(parent)
if err != nil {
return "", err
}
if !filepath.IsAbs(assetPath) {
assetPath = filepath.Join(parent, assetPath)
}
if !strings.HasPrefix(assetPath, parent) {
return "", fmt.Errorf("%s isn't a subdirectory of %s", assetPath, parent)
}
return assetPath, nil
}
// isStdout reports whether filename is stdout.
func isStdout(filename string) bool {
const stdout = "-"
return filename == stdout
}
// codelabDir returns codelab root directory.
// The base argument is codelab parent directory.
func codelabDir(base string, m *types.Meta) string {
return filepath.Join(base, m.ID)
}
func imgExtFromBytes(b []byte) (string, error) {
if len(b) < minImageSize {
return "", fmt.Errorf("error parsing image - response \"%s\" is too small (< %d bytes)", b, minImageSize)
}
ext := ".png"
switch {
case string(b[6:10]) == "JFIF":
ext = ".jpeg"
case string(b[0:3]) == "GIF":
ext = ".gif"
}
return ext, nil
}