From 64eb5fb23f64f209e3d813e017097044a111151f Mon Sep 17 00:00:00 2001
From: ale <ale@incal.net>
Date: Sun, 20 Jan 2019 08:15:22 +0000
Subject: [PATCH] Refactor Handlers in terms of a Publisher interface
Introduce an interface to decouple the Enqueue functionality from the
Crawler implementation.
---
cmd/crawl/crawl.go | 8 ++++----
cmd/links/links.go | 4 ++--
crawler.go | 28 +++++++++++++++++-----------
crawler_test.go | 4 ++--
4 files changed, 25 insertions(+), 19 deletions(-)
diff --git a/cmd/crawl/crawl.go b/cmd/crawl/crawl.go
index 2ebba98..54bb505 100644
--- a/cmd/crawl/crawl.go
+++ b/cmd/crawl/crawl.go
@@ -82,7 +82,7 @@ func (f *excludesFileFlag) Set(s string) error {
return nil
}
-func extractLinks(c *crawl.Crawler, u string, depth int, resp *http.Response, _ error) error {
+func extractLinks(p crawl.Publisher, u string, depth int, resp *http.Response, _ error) error {
links, err := analysis.GetLinks(resp)
if err != nil {
// This is not a fatal error, just a bad web page.
@@ -90,7 +90,7 @@ func extractLinks(c *crawl.Crawler, u string, depth int, resp *http.Response, _
}
for _, link := range links {
- if err := c.Enqueue(link, depth+1); err != nil {
+ if err := p.Enqueue(link, depth+1); err != nil {
return err
}
}
@@ -127,7 +127,7 @@ func (h *warcSaveHandler) writeWARCRecord(typ, uri string, data []byte) error {
return w.Close()
}
-func (h *warcSaveHandler) Handle(c *crawl.Crawler, u string, depth int, resp *http.Response, _ error) error {
+func (h *warcSaveHandler) Handle(p crawl.Publisher, u string, depth int, resp *http.Response, _ error) error {
// Read the response body (so we can save it to the WARC
// output) and replace it with a buffer.
data, derr := ioutil.ReadAll(resp.Body)
@@ -157,7 +157,7 @@ func (h *warcSaveHandler) Handle(c *crawl.Crawler, u string, depth int, resp *ht
h.numWritten++
- return extractLinks(c, u, depth, resp, nil)
+ return extractLinks(p, u, depth, resp, nil)
}
func newWarcSaveHandler(w *warc.Writer) (crawl.Handler, error) {
diff --git a/cmd/links/links.go b/cmd/links/links.go
index bf91f3f..2263414 100644
--- a/cmd/links/links.go
+++ b/cmd/links/links.go
@@ -20,7 +20,7 @@ var (
validSchemes = flag.String("schemes", "http,https", "comma-separated list of allowed protocols")
)
-func extractLinks(c *crawl.Crawler, u string, depth int, resp *http.Response, _ error) error {
+func extractLinks(p crawl.Publisher, u string, depth int, resp *http.Response, _ error) error {
links, err := analysis.GetLinks(resp)
if err != nil {
// Not a fatal error, just a bad web page.
@@ -28,7 +28,7 @@ func extractLinks(c *crawl.Crawler, u string, depth int, resp *http.Response, _
}
for _, link := range links {
- if err := c.Enqueue(link, depth+1); err != nil {
+ if err := p.Enqueue(link, depth+1); err != nil {
return err
}
}
diff --git a/crawler.go b/crawler.go
index e7bbf3c..b48646e 100644
--- a/crawler.go
+++ b/crawler.go
@@ -112,21 +112,27 @@ func (f FetcherFunc) Fetch(u string) (*http.Response, error) {
// unless the handler returns the special error ErrRetryRequest.
type Handler interface {
// Handle the response from a URL.
- Handle(*Crawler, string, int, *http.Response, error) error
+ Handle(Publisher, string, int, *http.Response, error) error
}
// HandlerFunc wraps a function into the Handler interface.
-type HandlerFunc func(*Crawler, string, int, *http.Response, error) error
+type HandlerFunc func(Publisher, string, int, *http.Response, error) error
// Handle the response from a URL.
-func (f HandlerFunc) Handle(db *Crawler, u string, depth int, resp *http.Response, err error) error {
- return f(db, u, depth, resp, err)
+func (f HandlerFunc) Handle(p Publisher, u string, depth int, resp *http.Response, err error) error {
+ return f(p, u, depth, resp, err)
}
// ErrRetryRequest is returned by a Handler when the request should be
// retried after some time.
var ErrRetryRequest = errors.New("retry_request")
+// Publisher is an interface to something with an Enqueue() method to
+// add new potential URLs to crawl.
+type Publisher interface {
+ Enqueue(Outlink, int) error
+}
+
// The Crawler object contains the crawler state.
type Crawler struct {
db *gobDB
@@ -341,8 +347,8 @@ func (c *Crawler) Close() {
// and adds them to the queue for crawling. It will call the wrapped
// handler on all requests regardless.
func FollowRedirects(wrap Handler) Handler {
- return HandlerFunc(func(c *Crawler, u string, depth int, resp *http.Response, err error) error {
- if herr := wrap.Handle(c, u, depth, resp, err); herr != nil {
+ return HandlerFunc(func(p Publisher, u string, depth int, resp *http.Response, err error) error {
+ if herr := wrap.Handle(p, u, depth, resp, err); herr != nil {
return herr
}
@@ -356,7 +362,7 @@ func FollowRedirects(wrap Handler) Handler {
if uerr != nil {
log.Printf("error parsing Location header: %v", uerr)
} else {
- return c.Enqueue(Outlink{URL: locationURL, Tag: TagPrimary}, depth+1)
+ return p.Enqueue(Outlink{URL: locationURL, Tag: TagPrimary}, depth+1)
}
}
return nil
@@ -367,14 +373,14 @@ func FollowRedirects(wrap Handler) Handler {
// "successful" HTTP status code (anything < 400). When using this
// wrapper, subsequent Handle calls will always have err set to nil.
func FilterErrors(wrap Handler) Handler {
- return HandlerFunc(func(c *Crawler, u string, depth int, resp *http.Response, err error) error {
+ return HandlerFunc(func(p Publisher, u string, depth int, resp *http.Response, err error) error {
if err != nil {
return nil
}
if resp.StatusCode >= 400 {
return nil
}
- return wrap.Handle(c, u, depth, resp, nil)
+ return wrap.Handle(p, u, depth, resp, nil)
})
}
@@ -382,11 +388,11 @@ func FilterErrors(wrap Handler) Handler {
// temporary errors (all transport-level errors are considered
// temporary, as well as any HTTP status code >= 500).
func HandleRetries(wrap Handler) Handler {
- return HandlerFunc(func(c *Crawler, u string, depth int, resp *http.Response, err error) error {
+ return HandlerFunc(func(p Publisher, u string, depth int, resp *http.Response, err error) error {
if err != nil || resp.StatusCode == http.StatusTooManyRequests || resp.StatusCode >= 500 {
return ErrRetryRequest
}
- return wrap.Handle(c, u, depth, resp, nil)
+ return wrap.Handle(p, u, depth, resp, nil)
})
}
diff --git a/crawler_test.go b/crawler_test.go
index 7b5c92c..0ad469b 100644
--- a/crawler_test.go
+++ b/crawler_test.go
@@ -33,11 +33,11 @@ func TestCrawler(t *testing.T) {
)
var crawledPages int
- h := HandlerFunc(func(c *Crawler, u string, depth int, resp *http.Response, err error) error {
+ h := HandlerFunc(func(p Publisher, u string, depth int, resp *http.Response, err error) error {
crawledPages++
next := fmt.Sprintf(srv.URL+"/page/%d", crawledPages)
log.Printf("%s -> %s", u, next)
- c.Enqueue(Outlink{
+ p.Enqueue(Outlink{
URL: mustParseURL(next),
Tag: TagPrimary,
}, depth+1)
--
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