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Serve linked source maps from loopback server (#660)
With cloudflare/workerd#710, `workerd` supports breakpoint debugging! Support for this in Miniflare just worked, assuming you were using a plain JavaScript worker, or you had inline source maps. `workerd` doesn't know where workers are located on disk, it just knows files' locations relative to each other. This means it's unable to resolve locations of corresponding linked `.map` files in `sourceMappingURL` comments. Miniflare _does_ have this information though. This change detects linked source maps and rewrites `sourceMappingURL` comments to `http` URLs pointing to Miniflare's loopback server. This then looks for the source map relative to the known on-disk source location. Source maps' `sourceRoot` attributes are updated to ensure correct locations are displayed in DevTools. **This enables breakpoint debugging for compiled TypeScript with linked source maps!** 🎉 Closes DEVX-872
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,105 @@ | ||
| import crypto from "crypto"; | ||
| import fs from "fs/promises"; | ||
| import path from "path"; | ||
| import { fileURLToPath, pathToFileURL } from "url"; | ||
| import type { RawSourceMap } from "source-map"; | ||
| import { Response } from "../../http"; | ||
| import { Log } from "../../shared"; | ||
|
|
||
| function maybeParseURL(url: string): URL | undefined { | ||
| if (path.isAbsolute(url)) return; | ||
| try { | ||
| return new URL(url); | ||
| } catch {} | ||
| } | ||
|
|
||
| export class SourceMapRegistry { | ||
| static PATHNAME_PREFIX = "/core/source-map/"; | ||
|
|
||
| constructor( | ||
| private readonly log: Log, | ||
| private readonly loopbackPort: number | ||
| ) {} | ||
|
|
||
| readonly #map = new Map<string /* id */, string /* sourceMapPath */>(); | ||
|
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||
| register(script: string, scriptPath: string): string /* newScript */ { | ||
| // Try to find the last source mapping URL in the file, if none could be | ||
| // found, return the script as is | ||
| const mappingURLIndex = script.lastIndexOf("//# sourceMappingURL="); | ||
| if (mappingURLIndex === -1) return script; | ||
|
|
||
| // `pathToFileURL()` will resolve `scriptPath` relative to the current | ||
| // working directory if needed | ||
| const scriptURL = pathToFileURL(scriptPath); | ||
|
|
||
| const sourceSegment = script.substring(0, mappingURLIndex); | ||
| const mappingURLSegment = script | ||
| .substring(mappingURLIndex) | ||
| .replace(/^\/\/# sourceMappingURL=(.+)/, (substring, mappingURL) => { | ||
| // If the mapping URL is already a URL (e.g. `data:`), return it as is | ||
| if (maybeParseURL(mappingURL) !== undefined) return substring; | ||
|
|
||
| // Otherwise, resolve it relative to the script, and register it | ||
| const resolvedMappingURL = new URL(mappingURL, scriptURL); | ||
| const resolvedMappingPath = fileURLToPath(resolvedMappingURL); | ||
|
|
||
| // We intentionally register source maps in a map to prevent arbitrary | ||
| // file access via the loopback server. | ||
| const id = crypto.randomUUID(); | ||
| this.#map.set(id, resolvedMappingPath); | ||
| mappingURL = `http://localhost:${this.loopbackPort}${SourceMapRegistry.PATHNAME_PREFIX}${id}`; | ||
|
|
||
| this.log.verbose( | ||
| `Registered source map ${JSON.stringify( | ||
| resolvedMappingPath | ||
| )} at ${mappingURL}` | ||
| ); | ||
|
|
||
| return `//# sourceMappingURL=${mappingURL}`; | ||
| }); | ||
|
|
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| return sourceSegment + mappingURLSegment; | ||
| } | ||
|
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||
| async get(url: URL): Promise<Response | undefined> { | ||
| // Try to get source map from registry | ||
| const id = url.pathname.substring(SourceMapRegistry.PATHNAME_PREFIX.length); | ||
| const sourceMapPath = this.#map.get(id); | ||
| if (sourceMapPath === undefined) return; | ||
|
|
||
| // Try to load and parse source map from disk | ||
| let contents: string; | ||
| try { | ||
| contents = await fs.readFile(sourceMapPath, "utf8"); | ||
| } catch (e) { | ||
| this.log.warn( | ||
| `Error reading source map ${JSON.stringify(sourceMapPath)}: ${e}` | ||
| ); | ||
| return; | ||
| } | ||
| let map: RawSourceMap; | ||
| try { | ||
| map = JSON.parse(contents); | ||
| } catch (e) { | ||
| this.log.warn( | ||
| `Error parsing source map ${JSON.stringify(sourceMapPath)}: ${e}` | ||
| ); | ||
| return; | ||
| } | ||
|
|
||
| // Modify the `sourceRoot` so source files get the correct paths. Note, | ||
| // `sourceMapPath` will always be an absolute path. | ||
| const sourceMapDir = path.dirname(sourceMapPath); | ||
| map.sourceRoot = | ||
| map.sourceRoot === undefined | ||
| ? sourceMapDir | ||
| : path.resolve(sourceMapDir, map.sourceRoot); | ||
|
|
||
| return Response.json(map, { | ||
| // This source map will be served from the loopback server to DevTools, | ||
| // which will likely be on a different origin. | ||
| headers: { "Access-Control-Allow-Origin": "*" }, | ||
| }); | ||
| } | ||
| } |
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