package ingestion
import (
"context"
"fmt"
"html"
"io"
"net/http"
"regexp"
"strings"
"time"
)
// Match in either attribute order,
// and the twitter:image variant.
var metaImageRe = regexp.MustCompile(
`(?is)]*(?:property|name)\s*=\s*["'](?:og:image(?::secure_url|:url)?|twitter:image(?::src)?)["'][^>]*content\s*=\s*["']([^"']+)["']` +
`|]*content\s*=\s*["']([^"']+)["'][^>]*(?:property|name)\s*=\s*["'](?:og:image(?::secure_url|:url)?|twitter:image(?::src)?)["']`)
var ogClient = &http.Client{Timeout: 8 * time.Second}
// FetchOGImage fetches the article URL and returns the first og:image or
// twitter:image found in the . Returns "" on any failure — callers
// should treat this as best-effort.
func FetchOGImage(articleURL string) string {
if articleURL == "" {
return ""
}
ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
defer cancel()
req, err := http.NewRequestWithContext(ctx, "GET", articleURL, nil)
if err != nil {
return ""
}
req.Header.Set("User-Agent", userAgent)
req.Header.Set("Accept", "text/html,application/xhtml+xml")
resp, err := ogClient.Do(req)
if err != nil {
return ""
}
defer resp.Body.Close()
if resp.StatusCode != http.StatusOK {
return ""
}
// og:image lives in ; cap read at 512KB to avoid pulling whole articles.
body, err := io.ReadAll(io.LimitReader(resp.Body, 512*1024))
if err != nil {
return ""
}
m := metaImageRe.FindSubmatch(body)
if len(m) == 0 {
return ""
}
// One of the two capture groups will be non-empty depending on attr order.
for i := 1; i < len(m); i++ {
if len(m[i]) > 0 {
return resolveURL(articleURL, html.UnescapeString(string(m[i])))
}
}
return ""
}
// resolveURL turns a possibly-relative image URL into an absolute one using
// the article URL as the base. Returns the raw input on parse failure.
func resolveURL(base, ref string) string {
ref = strings.TrimSpace(ref)
if ref == "" {
return ""
}
if strings.HasPrefix(ref, "http://") || strings.HasPrefix(ref, "https://") {
return ref
}
if strings.HasPrefix(ref, "//") {
if i := strings.Index(base, "://"); i > 0 {
return base[:i+1] + ref
}
return "https:" + ref
}
// relative path — naive join: scheme://host + ref
i := strings.Index(base, "://")
if i < 0 {
return ref
}
rest := base[i+3:]
slash := strings.Index(rest, "/")
if slash < 0 {
return fmt.Sprintf("%s%s", base, ref)
}
host := base[:i+3+slash]
if strings.HasPrefix(ref, "/") {
return host + ref
}
return host + "/" + ref
}