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aggregator.go
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aggregator.go
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package plnt
import (
"bytes"
"context"
"encoding/json"
"fmt"
"io"
"io/ioutil"
"log"
"net/http"
"net/url"
"os"
"path"
"path/filepath"
"sort"
"strings"
"time"
"github.com/google/renameio"
"github.com/mmcdole/gofeed"
"golang.org/x/net/html"
"golang.org/x/net/html/atom"
"golang.org/x/sync/errgroup"
)
type Item struct {
gofeed.Item
FeedTitle string
FeedLink string
}
type Feed struct {
Title string
Link string
Items []Item
}
type FeedConfig struct {
ShortName string // used in the state directory name, e.g. “sur5r-blog”
Title string `toml:"title"` // human-readable, e.g. “sur5r’s Hardware Blog”
URL string `toml:"url"`
}
func (f *FeedConfig) cachePath() string {
// TODO: make cache dir overridable via config
cacheDir, err := os.UserCacheDir()
if err != nil {
cacheDir = "/var/cache"
}
return filepath.Join(cacheDir, "plnt", f.ShortName+".json")
}
type Aggregator struct {
Feeds []FeedConfig
ForceFromCache bool // force loading all files from cache for rapid development
}
func makeAbsolute(content, baseURL string) (string, error) {
nodes, err := html.ParseFragment(strings.NewReader(content), &html.Node{
Type: html.ElementNode,
Data: "body",
DataAtom: atom.Body,
})
if err != nil {
return "", err
}
var f func(*html.Node)
f = func(n *html.Node) {
if n.Type == html.ElementNode && n.Data == "img" {
for idx, a := range n.Attr {
if a.Key != "src" {
continue
}
if strings.Contains(a.Val, "://") {
continue // already absolute
}
// TODO(later): is there a more elegant way to join baseURL with a.Val in terms of path?
a.Val = strings.TrimSuffix(baseURL, "/") + a.Val
n.Attr[idx] = a
}
}
for c := n.FirstChild; c != nil; c = c.NextSibling {
f(c)
}
}
var out bytes.Buffer
for _, n := range nodes {
f(n)
if err := html.Render(&out, n); err != nil {
return "", err
}
}
return out.String(), nil
}
func from(r io.Reader, feed *FeedConfig) (*Feed, error) {
parser := gofeed.NewParser()
f, err := parser.Parse(r)
if err != nil {
return nil, err
}
u, err := url.Parse(feed.URL)
if err != nil {
return nil, err
}
u.Path = path.Dir(u.Path)
baseURL := u.String()
items := make([]Item, 0, len(f.Items))
for _, i := range f.Items {
if i.PublishedParsed == nil {
// fall back to the updated date, if any
i.Published = i.Updated
i.PublishedParsed = i.UpdatedParsed
if i.PublishedParsed == nil {
log.Printf("[%s] dropping post %q: neither published date nor updated date set", feed.ShortName, i.Title)
continue
}
}
var err error
i.Content, err = makeAbsolute(i.Content, baseURL)
if err != nil {
return nil, fmt.Errorf("makeAbsolute(%s): %v", feed.ShortName, err)
}
items = append(items, Item{
Item: *i,
FeedTitle: feed.Title,
FeedLink: f.Link,
})
}
return &Feed{
Title: f.Title,
Link: f.Link,
Items: items,
}, nil
}
func fromCache(feed *FeedConfig) (*Feed, error) {
b, err := ioutil.ReadFile(feed.cachePath())
if err != nil {
return nil, err
}
var f Feed
return &f, json.Unmarshal(b, &f)
}
func (a *Aggregator) fetchFeed(ctx context.Context, feed *FeedConfig) (*Feed, error) {
if a.ForceFromCache {
return fromCache(feed)
}
var modTime time.Time
if st, err := os.Stat(feed.cachePath()); err == nil {
modTime = st.ModTime()
}
log.Printf("[%s] fetching %s", feed.ShortName, feed.URL)
req, err := http.NewRequest("GET", feed.URL, nil)
if err != nil {
return nil, err
}
if !modTime.IsZero() {
req.Header.Set("If-Modified-Since", modTime.Format(http.TimeFormat))
}
req.Header.Set("User-Agent", "https://github.com/nnev/plnt")
req = req.WithContext(ctx)
resp, err := http.DefaultClient.Do(req)
if err != nil {
log.Printf("[%s] falling back to cache due to fetch error: %v", feed.ShortName, err)
return fromCache(feed)
}
defer resp.Body.Close()
if got, want := resp.StatusCode, http.StatusOK; got != want {
if resp.StatusCode == http.StatusNotModified {
return fromCache(feed)
}
log.Printf("[%s] falling back to cache due to fetch error: unexpected status code: got %v, want %v", feed.ShortName, got, want)
return fromCache(feed)
}
f, err := from(resp.Body, feed)
if err != nil {
log.Printf("[%s] falling back to cache due to fetch error: %v", feed.ShortName, err)
return fromCache(feed)
}
// Exhaust the reader to make HTTP connection pooling/keepalive work:
ioutil.ReadAll(resp.Body)
resp.Body.Close()
b, err := json.Marshal(f)
if err != nil {
return nil, err
}
fn := feed.cachePath()
if err := os.MkdirAll(filepath.Dir(fn), 0755); err != nil {
return nil, err
}
if err := renameio.WriteFile(fn, b, 0644); err != nil {
return nil, err
}
return f, nil
}
func (a *Aggregator) Fetch(ctx context.Context) ([]*Feed, []Item, error) {
eg, ctx := errgroup.WithContext(ctx)
feeds := make([]*Feed, len(a.Feeds))
for idx, f := range a.Feeds {
idx, f := idx, f // copy
eg.Go(func() error {
// TODO(later): limit concurrency?
parsed, err := a.fetchFeed(ctx, &f)
if err != nil {
return err
}
parsed.Title = f.Title // override
if parsed.Link == "" {
parsed.Link = f.URL // fallback
}
feeds[idx] = parsed
return nil
})
}
if err := eg.Wait(); err != nil {
return nil, nil, err
}
var items []Item
for _, f := range feeds {
items = append(items, f.Items...)
}
// Sort reverse chronologically by published date
sort.Slice(items, func(i, j int) bool {
return items[i].PublishedParsed.After(*items[j].PublishedParsed)
})
return feeds, items, nil
}