[jwrosewell]

Summary

• Let a middleware run on a media type other than HTML.
• Row 19 of the stack listed in the pluggable modules issue (Pluggable, competition-neutral modules with a technical permission model #777), on feature/18-inmobi. James Rogers (Jamesr51d) approved this change at 149280a on the fork's pull request A middleware may run on a media type other than HTML jwrosewell/trusted-server#14, closed when the review moved here.

Changes

Area	Change
crates/trusted-server-core/src	5 files, 1152 lines added, 49 removed
docs/guide	2 files, 75 lines added, 2 removed
crates/cmp/inmobi	1 file, 8 lines added, 4 removed
CHANGELOG.md	1 file, 1 line added, 0 removed

Closes

Closes #1277

Spec

Spec: middleware-media-types

Test plan

CI on this pull request at 18d9ff9 passed all 32 checks.

• cargo test-fastly && cargo test-axum
• cargo clippy-fastly && cargo clippy-axum
• cargo fmt --all -- --check
• JS tests: cd crates/trusted-server-js/lib && npx vitest run
• JS format: cd crates/trusted-server-js/lib && npm run format
• Docs format: cd docs && npm run format
• WASM build: cargo build --package trusted-server-adapter-fastly --release --target wasm32-wasip1
• Manual testing via fastly compute serve
• Other: the full workflow set of this repository, run on this pull request at 18d9ff9

Checklist

• Changes follow AGENTS.md conventions
• No unwrap() in production code (clippy denies unwrap_used in CI)
• Uses log macros as AGENTS.md asks (not println!)
• New code has tests
• No secrets or credentials committed

---

Stacks on the InMobi Choice consent prompt (#1359).

What this pull request does

[[fetch]]
media_type = "text/plain"
path = "/ads.txt"
middleware = ["example.sellers"]

An entry may cover any media type core streams as text: text/html, another text/ type other than text/x-component, application/javascript or application/json, written as a bare type/subtype in lower case. A response takes the entry for the type and subtype of its content type, without the parameters, so text/plain; charset=utf-8 takes the entry for text/plain. An image, a length prefixed stream or a response that declares a charset other than UTF-8 passes through untouched and no entry can cover it.

pub trait Middleware: Send + Sync {
    fn middleware_id(&self) -> &'static str;
    fn handles_media_type(&self, media_type: &str) -> bool {
        media_type == HTML_MEDIA_TYPE
    }
    fn phases(&self) -> &[MiddlewarePhase];
    fn create(&self, context: &MiddlewareContext<'_>) -> MiddlewareAction;
}

• A middleware says what it works on. HTML alone unless it says otherwise, so every module in the stack keeps its behavior with no change to its code. An entry naming a middleware under a media type it does not handle is refused when the registry is built, naming the entry and the middleware.
• A chain carries its media type. On one other than HTML its plan refuses an action that decides about HTML, being head markup or an element or text handler, by the middleware's name. A stream processor is the one thing that applies to any body.
• Core runs the stream processors on the body after it has moved the origin's addresses in it, the fetch entry's and then the serve entry's. None can be stored, because the template cache refuses anything that is not HTML.

Configuration	Refused with
An entry for image/png, image/svg+xml, text/x-component, */*, TEXT/HTML, a type with parameters, an empty subtype or whitespace	"is not a media type a middleware runs on", and the types to write
An entry naming a middleware under a media type it does not handle	The entry, the media type and the middleware's name
A middleware's head markup or handler on a body that is not HTML	The middleware's name and the media type, when the chain is planned

Why

Every middleware in the stack changes HTML, and [[fetch]] and [[serve]] refused any other media type. A publisher's ads.txt, robots.txt beside it, a script or a stylesheet are text that passes through the same path, and a module that has something to add to one of them had no place to do it.

How it was verified

Not exercised: no module of the stack changes a body that is not HTML yet. The fixture middleware in core's tests is the one that does, through the publisher's own path.

References #1277.