deepseek-harness/packages/web/web-fetch-http

description, kind

description	kind
The anonymous public HTTP(S) fetch backend for ctx.web: how deployments mount bounded, safe URL retrieval with same-origin redirects and text-only decoding.	package-reference

@deepseek-ai/dsh-web-fetch-http

English | 中文

Summary

With dsh-web-fetch-http, the harness can fetch public HTTP(S) pages through the web service (ctx.web) and get their status code plus bounded, decoded content without sending credentials. Choose it when a composition needs safe retrieval with URL validation, public-address resolution, connection pinning, same-origin redirects, byte and character caps, and an explicit product User-Agent. It returns non-2xx responses as results rather than errors, and rejects non-public destinations, binary data, and unsupported content types. The model-facing web_fetch tool lives in dsh-tool-web, which renders this provider's bodies.

Table of Contents

• Use this package
• Understand the implementation
• Further Exploration
• Model Experience
• Known Limitations and Deferred Work
• Dev Note

---

Use this package

Mount the provider in a composition that already loads the web service; it registers as the http fetch provider, so ctx.web.fetch() resolves it automatically when it is the only usable fetch backend — or pin it with fetchProvider: http.

When to choose it

Choose this backend when a deployment must fetch public pages with bounded output and safe transport: no credentials are sent, every resolved address must be public, each connection is pinned to the validated answer set, redirects cannot escape the origin, and every response is capped.

Minimal configuration

Load the web service and the provider; configurable limits have safe defaults and validate at plugin construction, so an invalid value fails loudly instead of building a provider with nonsensical caps. The URL security limit is fixed at 2,048 characters.

- name: '@deepseek-ai/dsh-web'
- name: '@deepseek-ai/dsh-web-fetch-http'

Field	Default	Meaning
maxResponseBytes	5,000,000	Maximum response body size in bytes
maxBodyChars	100,000	Maximum decoded body length in characters
timeoutMs	30,000	Fetch timeout — a resource backstop, not the model-facing tool budget
maxRedirects	5	Maximum same-origin redirect hops (0 follows none)
userAgent	deepseek-harness/…	User-Agent header sent on every request

The generated configuration catalog is the exhaustive source for every accepted field and its JSDoc.

What a fetch returns

A successful call yields a WebFetchResult: the final URL after allowed redirects, the HTTP status code, a decoded body classified as html or text, and a truncated flag. A non-2xx response is a result, not an error — the status code is part of the fetched resource state; WebError is reserved for failures to safely retrieve or represent the resource.

const page = await ctx.web.fetch({ url: 'https://example.com' })
// page.body.kind === 'html' | 'text'; page.statusCode === 200 | 404 | ...

Transport behavior

The provider keeps requests anonymous and bounded: it accepts only http: and https: URLs without embedded credentials and rejects URLs over 2,048 characters. It resolves each hostname once, rejects the complete result if any IPv4 or IPv6 address is not public unicast, and pins the connection to that validated set. IPv6 checks discover the active DNS64 prefix and reject translations to non-public IPv4. Each same-origin redirect repeats resolution and pinning; cross-origin redirects fail and require a fresh call. The provider also enforces byte, character, hop, and time caps, rejects unsupported content types, and sends an explicit product User-Agent.

Failures and recovery

Failures throw WebError with a machine-routable code: WEB_INVALID_URL, WEB_BLOCKED_URL, WEB_FETCH_TOO_LARGE, WEB_FETCH_TIMEOUT, WEB_REDIRECT_BLOCKED, WEB_UNSUPPORTED_CONTENT_TYPE, WEB_ABORTED, or WEB_PROVIDER_ERROR. Direct callers can route on the code; the model-facing web_fetch tool surfaces the failure text to the model under its own error wrapper.

---

Understand the implementation

Implementation internals — click to expand

This section explains the design decisions behind the provider; the observable behavior is fully covered in Use this package.

Design philosophy

The package is built on one separation and one layered timeout:

• Safe retrieval vs. presentation. This provider owns URL validation, public-address enforcement, connection pinning, HTTP transport, redirect policy, caps, charset decoding, and binary rejection; dsh-tool-web owns HTML→markdown and truncation formatting. A non-2xx response is data, not failure.
• Two timeout layers. The provider's timeoutMs is a resource backstop for direct ctx.web.fetch() callers; the model-facing tool-call budget belongs to dsh-tool-call-timeout-policy, which arms exec.signal. When the outer deadline fires first the provider reports WEB_ABORTED and the policy replaces it with TOOL_TIMEOUT; WEB_FETCH_TIMEOUT therefore identifies a direct service caller whose provider budget elapsed.

Source map

File	Role
src/index.ts	Plugin entry: config schema, limit validation, provider registration
src/provider.ts	The HttpFetchProvider: pinned transport, redirect following, capped reads, charset decoding
src/network.ts	Public-address resolution, DNS64 discovery, and connection pinning
src/policy.ts	URL validation, same-origin checks, content-type classification, charset parsing
src/invariant.ts	Invariant companion (no runtime invariant; limits are enforced in the provider)

Read path

A fetch validates the URL, resolves the hostname once, rejects the complete answer set when any address is not public, and pins the connection to the accepted addresses. It repeats that check for each same-origin redirect; a cross-origin redirect or non-public target fails before response bytes are accepted. The final response is classified by Content-Type, decoded from its declared charset, and read under the byte cap; the decoded text is then truncated to the character cap.

---

Further Exploration

Read these pages when the package-level contract is not enough. They move from the shared vocabulary to the service, the model-facing tools, and the design rationale.

• Web subsystem — the exhaustive fetch request/result vocabulary and error codes.
• Web package map — the six-package family and each role.
• dsh-web — the web service this provider registers into.
• dsh-tool-web — the model-facing web_fetch tool that renders this provider's bodies.
• Generated configuration catalog — every accepted config field and its source declaration.
• Web capability seam decision — why search and fetch share one provider-selection service.

---

Model Experience

Indirectly, through dsh-tool-web, which renders this provider's maxBodyChars-bounded decoded text or markdown-shaped HTML under its fetch-result wrapper while redirects, headers, and transport limits remain hidden.

KV Cache effect

No direct invalidation; the named consumer owns any request-prefix changes.

Known Limitations and Deferred Work

These limits define when the provider is unsafe or a poor fit. They are current package constraints.

• Only textual content decodes — html/xhtml and text/* plus JSON/XML families; a missing Content-Type or any binary type throws WEB_UNSUPPORTED_CONTENT_TYPE, and text-extractable PDF decoding is named deferred work.
• Charset comes only from the Content-Type header (UTF-8 default) — an HTML <meta charset> declaration is ignored, and a declared-but-unrecognized charset label throws rather than falling back.

Dev Note

Working context for maintainers — click to expand

None.