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fix: rewrite data-src/data-srcset for lazy-loaded images #4

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Merged
jergason merged 1 commit into from
Mar 23, 2026
Merged

fix: rewrite data-src/data-srcset for lazy-loaded images #4

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10 changes: 10 additions & 0 deletions src/rewriter.test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -107,4 +107,14 @@ describe("HTMLRewriter integration", () => {
expect(resp.headers.get("content-security-policy")).toBeNull();
expect(resp.headers.get("access-control-allow-origin")).toBe("*");
});

it("rewrites data-src attributes for lazy-loaded images", async () => {
const resp = await worker.fetch("/browse/https://www.wired.com");
if (resp.status !== 200) return;
const html = await resp.text();
const dataSrcMatches = html.match(/data-src="([^"]*)"/g) || [];
if (dataSrcMatches.length === 0) return; // skip if wired changed their pattern
const allProxied = dataSrcMatches.every((m) => m.includes("/browse/"));
Comment on lines +112 to +117
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Copilot AI Mar 23, 2026

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This test can pass without asserting the new behavior: it returns early when Wired is down/non-200, and also returns early when no data-src attributes are present. That makes CI green even if the rewrite regresses or Wired changes/blocks requests. Consider using Vitest's skip mechanism (so it shows as skipped) and/or make the test deterministic by transforming a small HTML fixture through buildRewriter() and asserting the rewritten data-src value(s).

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Comment on lines +115 to +117
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Copilot AI Mar 23, 2026

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The assertion m.includes("/browse/") is quite loose and can produce false positives if the original URL happens to contain /browse/ as part of its path/query. It would be more robust to capture the attribute value and assert it starts with the proxy prefix (e.g., data-src="/browse/), or parse out the value and check value.startsWith("/browse/").

Suggested change
const dataSrcMatches = html.match(/data-src="([^"]*)"/g) || [];
if (dataSrcMatches.length === 0) return; // skip if wired changed their pattern
const allProxied = dataSrcMatches.every((m) => m.includes("/browse/"));
const dataSrcMatches = [...html.matchAll(/data-src="([^"]*)"/g)];
if (dataSrcMatches.length === 0) return; // skip if wired changed their pattern
const allProxied = dataSrcMatches.every((m) => m[1].startsWith("/browse/"));

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expect(allProxied).toBe(true);
});
});
11 changes: 8 additions & 3 deletions src/rewriter.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -59,10 +59,13 @@ class URLRewriter implements HTMLRewriterElementContentHandlers {
}

class SrcsetRewriter implements HTMLRewriterElementContentHandlers {
constructor(private baseUrl: string) {}
constructor(
private baseUrl: string,
private attr: string = "srcset",
) {}

element(el: Element) {
const srcset = el.getAttribute("srcset");
const srcset = el.getAttribute(this.attr);
if (!srcset) return;
const rewritten = srcset
.split(",")
Expand All @@ -74,7 +77,7 @@ class SrcsetRewriter implements HTMLRewriterElementContentHandlers {
return parts.join(" ");
})
.join(", ");
el.setAttribute("srcset", rewritten);
el.setAttribute(this.attr, rewritten);
}
}

Expand Down Expand Up @@ -108,7 +111,9 @@ export function buildRewriter(targetUrl: string): HTMLRewriter {
.on("meta", new MetaCSPRemover())
.on("a, area", new URLRewriter(targetUrl, "href"))
.on("img", new URLRewriter(targetUrl, "src"))
.on("img, source", new URLRewriter(targetUrl, "data-src"))
.on("img, source", new SrcsetRewriter(targetUrl))
.on("img, source", new SrcsetRewriter(targetUrl, "data-srcset"))
.on("video", new URLRewriter(targetUrl, "src"))
.on("video", new URLRewriter(targetUrl, "poster"))
.on("audio", new URLRewriter(targetUrl, "src"))
Expand Down
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