dsh-safe-web-fetch

DeepSeek Harness ships with a web_fetch tool, but calling it directly in production means trusting raw DNS answers, accepting arbitrary redirect targets, and receiving unbounded response bodies with no guardrails. dsh-safe-web-fetch plugs into DSH's existing ctx.web service and inserts a verification layer before any socket is opened, so the normal tool and profile system keeps working without introducing a second search API.

For every request the provider resolves and inspects the hostname's DNS records—covering IPv4, IPv4-mapped IPv6, and special-purpose ranges—then pins the connection to the verified address through an isolated Undici dispatcher. Redirects are re-validated and must stay on the same origin; cross-origin hops are rejected outright. Response size in bytes and decoded characters, redirect count, concurrency, and total timeout are all capped with sensible defaults that can be tuned through DSH configuration. Only text-like media types (text, HTML, JSON, XML) are returned, and the plugin never adds cookies, authorization headers, browser state, or request bodies.

It is built for developers and architects deploying DSH in production fetch pipelines who want an application-level safety check layered on top of network controls. The plugin is explicitly not an egress firewall, content scanner, or zero-trust gateway; those responsibilities belong at the infrastructure layer. Think of it as a pre-connection gatekeeper that makes the default web_fetch behaviour predictable and bounded.