🤖 feat: proxy localhost URLs through Coder wildcard DNS in browser mode#2797
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@codex review Re: the P1 concern about I investigated both upstream repos (coder/coder and coder/code-server) to verify whether path-based proxy templates are a real production scenario: Coder platform: code-server: While it does support path-based templates internally ( Conclusion: Since Coder never produces path-based templates for |
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@codex review Both prior Codex review comments were investigated by cloning the upstream coder/coder and coder/code-server repos. Both were false alarms: P1: "Preserve proxy template path when rewriting localhost URLs" Why this is wrong:
P2: "Pass hostname, not host, into localhost proxy normalization" Why this is wrong:
The one valid observation was an internal inconsistency: |
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@codex review All review threads across all rounds are resolved. Summary: Round 1:
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@codex review Changes since last review:
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Adds Coder-style localhost link proxying so clicked localhost URLs
open through the workspace proxy (VSCODE_PROXY_URI / MUX_PROXY_URI).
- Shared normalizer: src/common/utils/localhostProxyUrl.ts
Rewrites loopback HTTP(S) URLs using {{port}}/{{host}} templates.
Preserves path/query/hash. Falls back to original on any failure.
- Electron (#1): main window + terminal pop-out windows normalize
URLs before shell.openExternal via setWindowOpenHandler and
will-navigate handlers.
- Terminal env (#2): PTY sessions inherit VSCODE_PROXY_URI and
MUX_PROXY_URI (with override precedence) for CLI tool parity.
- Browser mode (#3): server injects __MUX_PROXY_URI_TEMPLATE__ into
SPA shell. Both entrypoints install a window.open wrapper that
normalizes loopback URLs.
- Markdown links (#4): chat anchor renderer normalizes href via the
same shared policy.
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@codex review Changes since last review:
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Codex Review: Didn't find any major issues. 👍 ℹ️ About Codex in GitHubYour team has set up Codex to review pull requests in this repo. Reviews are triggered when you
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Summary
When Mux runs inside a Coder workspace, clicking a
localhost:PORTlink anywhere in the app now transparently opens through the Coder wildcard proxy URL instead. Works zero-config in browser mode by deriving the proxy template from the current hostname (e.g.5173--dev--ws--user--apps.example.com→{{port}}--dev--ws--user--apps.example.com), and also supports explicitVSCODE_PROXY_URI/MUX_PROXY_URIenv vars for Electron mode.Closes #2376
Background
Coder's web terminal and code-server both rewrite localhost URLs to proxy URLs so that clicking
http://localhost:3000in a remote workspace opens the correct externally-reachable URL. Mux lacked this — users in Coder environments had to manually construct proxy URLs.Key insight from upstream:
VSCODE_PROXY_URIis only injected by Coder into VS Code extension host processes, not into plain SSH shells. So env-var-only detection is insufficient for browser mode. code-server solves this by deriving the template fromwindow.location; Coder's web terminal gets it from the/api/v2/regionsAPI. We take the simpler code-server-like approach: if the browser hostname looks like a Coder port-forward URL (<port>--<segments>.<domain>), derive the template by replacing the port prefix with{{port}}.Implementation
Architecture: one shared pure normalizer + thin adapters at each navigation boundary + browser-side auto-detection.
src/common/utils/localhostProxyUrl.ts{{port}}/{{host}}template. Supports both subdomain-based and path-based proxy templates (preserves template path prefix). Preserves path/query/hash. Falls back to original URL on any failure.src/browser/utils/browserLocalhostProxyTemplate.tswindow.location.hostnamewhen no injected template exists. Detects Coder-style<port>--<suffix>.<domain>hostnames and synthesizes{{port}}--<suffix>.<domain>.src/desktop/main.ts,src/desktop/terminalWindowManager.tssetWindowOpenHandler+will-navigatepass URLs through normalizer beforeshell.openExternal().src/node/services/terminalService.tsVSCODE_PROXY_URIandMUX_PROXY_URIso CLI tools can use them.src/node/orpc/server.ts,src/browser/utils/windowOpenLocalhostProxy.tswindow.__MUX_PROXY_URI_TEMPLATE__into SPA shell (static middleware skipsindex.htmlso the SPA fallback is the single source of truth for HTML delivery).window.openwrapper normalizes loopback URLs.src/browser/features/Messages/MarkdownComponents.tsxhrefvia the same shared policy.Template resolution order (browser mode):
window.__MUX_PROXY_URI_TEMPLATE__(fromMUX_PROXY_URI>VSCODE_PROXY_URIenv vars)window.location.hostnameif it matches Coder's<port>--...patternTemplate resolution order (Electron):
MUX_PROXY_URI>VSCODE_PROXY_URI> no rewrite.Validation
make static-checkpassesRisks
Low. All rewrite paths fall back to the original URL on any failure. The Coder hostname auto-detection is conservative — it only activates when the first DNS label is
<digits>--<at-least-one-segment>, which is specific to Coder's wildcard proxy format.Generated with
mux• Model:anthropic:claude-opus-4-6• Thinking:xhigh