fix: rewrite data-src/data-srcset for lazy-loaded images#4
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many sites (wired, conde nast, etc.) use data-src/data-srcset attributes for lazy loading. these bypassed the proxy because the HTMLRewriter only handled src/srcset. now we rewrite both variants on img and source elements. also makes SrcsetRewriter configurable for which attribute to target. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Pull request overview
This PR extends the HTML rewriting proxy so that lazy-loaded images using data-src / data-srcset are also rewritten to proxied URLs, preventing them from bypassing the proxy when they load later.
Changes:
- Make
SrcsetRewriteraccept a configurable attribute name (defaultsrcset). - Rewrite
data-srcforimg, sourceviaURLRewriter. - Rewrite
data-srcsetforimg, sourceviaSrcsetRewriter, and add an integration test targeting Wired’s markup.
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.
| File | Description |
|---|---|
src/rewriter.ts |
Adds rewriting support for data-src and data-srcset, and generalizes SrcsetRewriter to support non-srcset attribute names. |
src/rewriter.test.ts |
Adds an integration test intended to verify data-src rewriting on a real-world site (Wired). |
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| 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/")); |
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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).
| 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/")); |
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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/").
| 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/")); |
Summary
data-srcanddata-srcsetattributes for lazy loading images (Wired had 41 images using this pattern, all bypassing the proxy)data-srcrewriting onimg, sourceelements viaURLRewriterdata-srcsetrewriting onimg, sourceelements viaSrcsetRewriter(now accepts configurable attribute name)data-srcattributes get proxiedTest plan
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