From 04584fb2da2a169fa39d6f84f86ce979f27fc65a Mon Sep 17 00:00:00 2001 From: claude Date: Thu, 6 Aug 2026 03:12:59 +0400 Subject: [PATCH] webfetch checks the status before it reads the body (V-581) A non-2xx reply was read in full first and only then rejected. Two costs followed. A 500 with a large error page pulled up to MaxBytes off the wire for nothing. An error page over the cap returned ErrTooLarge, which names the size and hides the status the server actually sent. The status is a typed error now. webfetch.StatusError carries the code and unwraps to ErrStatus, so errors.Is keeps working and errors.As reads the number. crawl.StatusError is the same shape on the other side of the seam, and cmd/mavend/crawls.go carries the code across. That removes the string grep in crawl.isServerError, which decided whether a failed robots.txt blocks a crawl by looking for " 50" in an error message it did not own. A reworded error would have turned a 503 robots.txt into permission to crawl. It reads the code now. Two comments corrected. webfetch.HostMatches said the crawler calls it and nothing outside the package does. rss.PlainText said the crawler's extractor goes through it and crawl/extract.go has its own pass. The rss poller parses the feed straight off the byte slice instead of copying a document that can run to a megabyte through a string. Co-Authored-By: Claude Opus 5 --- cmd/mavend/crawls.go | 7 +++++++ internal/crawl/crawl.go | 25 +++++++++++++++++-------- internal/crawl/politeness_test.go | 2 +- internal/rss/feed.go | 5 +++-- internal/rss/poller.go | 5 ++++- internal/webfetch/webfetch.go | 23 ++++++++++++++++++----- internal/webfetch/webfetch_test.go | 21 +++++++++++++++++++++ 7 files changed, 71 insertions(+), 17 deletions(-) diff --git a/cmd/mavend/crawls.go b/cmd/mavend/crawls.go index a2d8a7c..afc314f 100644 --- a/cmd/mavend/crawls.go +++ b/cmd/mavend/crawls.go @@ -173,6 +173,13 @@ func (a *crawlFetcher) Get(ctx context.Context, u string) (*crawl.Response, erro case errors.Is(err, webfetch.ErrBlocked), errors.Is(err, webfetch.ErrPrivate), errors.Is(err, webfetch.ErrScheme): return nil, fmt.Errorf("%w: %v", crawl.ErrFetchRefused, err) case errors.Is(err, webfetch.ErrStatus): + // Carry the code across the seam. The crawler needs to tell a 5xx + // from a 404 to decide what a failed robots.txt means, and it must + // not learn that by reading this sentence. + var se *webfetch.StatusError + if errors.As(err, &se) { + return nil, &crawl.StatusError{Code: se.Code} + } return nil, fmt.Errorf("%w: %v", crawl.ErrFetchStatus, err) } return nil, err diff --git a/internal/crawl/crawl.go b/internal/crawl/crawl.go index a01937f..b30e4c9 100644 --- a/internal/crawl/crawl.go +++ b/internal/crawl/crawl.go @@ -57,6 +57,16 @@ var ( ErrFetchStatus = errors.New("crawl: the server answered with an error status") ) +// StatusError is ErrFetchStatus with the code the server actually sent. The +// adapter builds it; isServerError reads Code rather than the message, so a +// reworded error can no longer turn a 503 robots.txt into permission to crawl. +type StatusError struct{ Code int } + +func (e *StatusError) Error() string { + return fmt.Sprintf("crawl: the server answered with status %d", e.Code) +} +func (e *StatusError) Unwrap() error { return ErrFetchStatus } + // Fetcher is the guarded HTTP door (internal/webfetch adapted by the daemon). An // interface so this package constructs no http.Client of its own and can be // tested without a network. @@ -233,16 +243,15 @@ func (c *Crawler) markFetched(host string) { c.mu.Unlock() } -// isServerError — a 5xx rather than any other non-2xx. The adapter formats the -// status into the message, which is the only place it survives. +// isServerError — a 5xx rather than any other non-2xx. A status the adapter +// could not recover reads as 0 and is not a server error, which keeps the +// standard's "404 means allow" as the default for an unknown. func isServerError(err error) bool { - s := err.Error() - for _, code := range []string{" 50", " 51", " 52", " 53"} { - if strings.Contains(s, code) { - return true - } + var se *StatusError + if !errors.As(err, &se) { + return false } - return false + return se.Code >= 500 && se.Code <= 599 } // Hash is the dedup key for a crawl result: the sha256 of the extracted text, diff --git a/internal/crawl/politeness_test.go b/internal/crawl/politeness_test.go index 3e19309..f2e0971 100644 --- a/internal/crawl/politeness_test.go +++ b/internal/crawl/politeness_test.go @@ -79,7 +79,7 @@ func TestPage_ABrokenRobotsServerIsNotPermissionToCrawl(t *testing.T) { // way to resolve an unknown. f := &timedFetcher{ pages: map[string]Response{"https://example.org/a": {Body: []byte("a")}}, - errs: map[string]error{"https://example.org/robots.txt": fmt.Errorf("%w: 503", ErrFetchStatus)}, + errs: map[string]error{"https://example.org/robots.txt": &StatusError{Code: 503}}, } c := New(f, Config{UserAgent: "Maven/1.0"}) if _, err := c.Page(context.Background(), "https://example.org/a"); !errors.Is(err, ErrFetchStatus) { diff --git a/internal/rss/feed.go b/internal/rss/feed.go index 06edfa3..d3b68e7 100644 --- a/internal/rss/feed.go +++ b/internal/rss/feed.go @@ -173,8 +173,9 @@ var ( ) // PlainText strips markup and decodes entities — feed summaries are HTML, and -// what reaches a note (and possibly the TTS) must be text. Exported because the -// crawler's extractor needs exactly this on a bigger input. +// what reaches a note (and possibly the TTS) must be text. Exported so a caller +// holding raw feed markup can reduce it the same way; crawl/extract.go does the +// bigger job on a whole document and does not go through here. func PlainText(s string) string { s = scriptRE.ReplaceAllString(s, " ") s = tagRE.ReplaceAllString(s, " ") diff --git a/internal/rss/poller.go b/internal/rss/poller.go index 24e3049..353619c 100644 --- a/internal/rss/poller.go +++ b/internal/rss/poller.go @@ -1,6 +1,7 @@ package rss import ( + "bytes" "context" "fmt" "log" @@ -164,7 +165,9 @@ func (p *Poller) PollFeed(ctx context.Context, f FeedConfig, now time.Time) (int if err != nil { return 0, err } - feed, err := Parse(strings.NewReader(string(body.Bytes))) + // bytes.NewReader and not strings.NewReader(string(…)): the latter copied a + // feed document that can run to a megabyte, for nothing. + feed, err := Parse(bytes.NewReader(body.Bytes)) if err != nil { return 0, err } diff --git a/internal/webfetch/webfetch.go b/internal/webfetch/webfetch.go index 5f58050..aea5284 100644 --- a/internal/webfetch/webfetch.go +++ b/internal/webfetch/webfetch.go @@ -61,6 +61,14 @@ var ( ErrStatus = errors.New("webfetch: non-2xx status") ) +// StatusError is a non-2xx reply, carrying the code. It unwraps to ErrStatus, +// so errors.Is keeps working, and it exists so a caller can tell a 404 from a +// 503 with errors.As instead of grepping the message for digits. +type StatusError struct{ Code int } + +func (e *StatusError) Error() string { return fmt.Sprintf("webfetch: non-2xx status: %d", e.Code) } +func (e *StatusError) Unwrap() error { return ErrStatus } + // Config are the limits. Every zero value means "the default above", so // Config{} is safe; the only field that changes behaviour by being empty is // AllowHosts (empty ⇒ any public host that is not denied). @@ -232,6 +240,13 @@ func (f *Fetcher) do(ctx context.Context, method, rawURL string, body []byte, hd } defer resp.Body.Close() + // Status first, body second. A server that answered 500 has no body worth + // reading, and reading it anyway cost up to MaxBytes off the wire and + // reported an oversized error page as ErrTooLarge, which names the wrong + // cause. The body is closed either way by the defer above. + if resp.StatusCode < 200 || resp.StatusCode > 299 { + return nil, &StatusError{Code: resp.StatusCode} + } respBody, err := io.ReadAll(io.LimitReader(resp.Body, f.cfg.MaxBytes+1)) if err != nil { return nil, err @@ -239,9 +254,6 @@ func (f *Fetcher) do(ctx context.Context, method, rawURL string, body []byte, hd if int64(len(respBody)) > f.cfg.MaxBytes { return nil, fmt.Errorf("%w (%d bytes)", ErrTooLarge, f.cfg.MaxBytes) } - if resp.StatusCode < 200 || resp.StatusCode > 299 { - return nil, fmt.Errorf("%w: %d", ErrStatus, resp.StatusCode) - } out := &Response{ URL: resp.Request.URL.String(), Status: resp.StatusCode, @@ -307,8 +319,9 @@ func (f *Fetcher) waitTurn(ctx context.Context, host string) error { } // HostMatches reports whether host equals one of pats or is a subdomain of one. -// Exported because the crawler applies the same rule to links it decides not to -// follow, before it ever builds a request. +// Exported so anything that wants to apply the same allow/deny rule to a link +// before building a request reads it from here rather than reimplementing it. +// Nothing outside this package calls it today. func HostMatches(host string, pats []string) bool { host = strings.ToLower(strings.TrimSuffix(host, ".")) for _, p := range pats { diff --git a/internal/webfetch/webfetch_test.go b/internal/webfetch/webfetch_test.go index fafdabb..3eb8d3a 100644 --- a/internal/webfetch/webfetch_test.go +++ b/internal/webfetch/webfetch_test.go @@ -1,6 +1,7 @@ package webfetch import ( + "bytes" "context" "errors" "io" @@ -212,6 +213,26 @@ func TestNon2xxIsAnError(t *testing.T) { } } +func TestNon2xxCarriesTheCodeAndBeatsTheSizeCap(t *testing.T) { + // A big error page used to be read in full and reported as ErrTooLarge, + // which names the size and hides the 503. The status is checked first now, + // and the code survives for a caller that has to tell 5xx from 404. + srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) { + w.WriteHeader(http.StatusServiceUnavailable) + w.Write(bytes.Repeat([]byte("x"), 5000)) + })) + defer srv.Close() + f := testFetcher(t, Config{MaxBytes: 100}) + _, err := f.Get(context.Background(), srv.URL) + if !errors.Is(err, ErrStatus) || errors.Is(err, ErrTooLarge) { + t.Fatalf("error = %v, want ErrStatus and not ErrTooLarge", err) + } + var se *StatusError + if !errors.As(err, &se) || se.Code != http.StatusServiceUnavailable { + t.Fatalf("error = %v, want a StatusError carrying 503", err) + } +} + func TestUserAgentIsSent(t *testing.T) { got := make(chan string, 1) srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {