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Add path-based asset backend proxy routing #668

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fdf632f
asset proxy spec
ChristianPavilonis Apr 28, 2026
53cdf53
Add path-based asset backend proxy routing
ChristianPavilonis Apr 28, 2026
03569f7
fix clippy
ChristianPavilonis Apr 28, 2026
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120 changes: 68 additions & 52 deletions crates/trusted-server-adapter-fastly/src/main.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -16,8 +16,8 @@ use trusted_server_core::http_util::sanitize_forwarded_headers;
use trusted_server_core::integrations::IntegrationRegistry;
use trusted_server_core::platform::RuntimeServices;
use trusted_server_core::proxy::{
handle_first_party_click, handle_first_party_proxy, handle_first_party_proxy_rebuild,
handle_first_party_proxy_sign,
handle_asset_proxy_request, handle_first_party_click, handle_first_party_proxy,
handle_first_party_proxy_rebuild, handle_first_party_proxy_sign,
};
use trusted_server_core::publisher::{
handle_publisher_request, handle_tsjs_dynamic, stream_publisher_body, PublisherResponse,
Expand Down Expand Up @@ -150,6 +150,11 @@ async fn route_request(
let path = req.get_path().to_string();
let method = req.get_method().clone();

let matched_asset_route = match &method {
&Method::GET | &Method::HEAD => settings.asset_route_for_path(&path),
_ => None,
};
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@aram356 aram356 May 1, 2026

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♻️ refactor — match &method { &Method::GET | &Method::HEAD => ..., _ => None } is awkward; the &pat borrow dance only exists to avoid moving method before the outer match consumes it. Cleaner:

let matched_asset_route = matches!(method, Method::GET | Method::HEAD)
    .then(|| settings.asset_route_for_path(&path))
    .flatten();


// Match known routes and handle them
let result = match (method, path.as_str()) {
// Serve the tsjs library
Expand Down Expand Up @@ -202,62 +207,73 @@ async fn route_request(
}))
}),

// No known route matched, proxy to publisher origin as fallback
// No known route matched, proxy to an asset origin or publisher origin as fallback
_ => {
log::info!(
"No known route matched for path: {}, proxying to publisher origin",
path
);

match runtime_services_for_consent_route(settings, runtime_services) {
Ok(publisher_services) => {
match handle_publisher_request(
settings,
integration_registry,
&publisher_services,
req,
) {
Ok(PublisherResponse::Stream {
mut response,
body,
params,
}) => {
// Streaming path: finalize headers, then stream body to client.
finalize_response(settings, geo_info.as_ref(), &mut response);
let mut streaming_body = response.stream_to_client();
if let Err(e) = stream_publisher_body(
if let Some(asset_route) = matched_asset_route {
log::info!(
"No explicit route matched for path: {}, proxying via asset route prefix {} to {}",
path,
asset_route.prefix,
asset_route.origin_url
);
handle_asset_proxy_request(settings, runtime_services, req, &asset_route.origin_url)
.await
} else {
log::info!(
"No known route matched for path: {}, proxying to publisher origin",
path
);

match runtime_services_for_consent_route(settings, runtime_services) {
Ok(publisher_services) => {
match handle_publisher_request(
settings,
integration_registry,
&publisher_services,
req,
) {
Ok(PublisherResponse::Stream {
mut response,
body,
&mut streaming_body,
&params,
settings,
integration_registry,
) {
// Headers already committed. Log and abort — client
// sees a truncated response. Standard proxy behavior.
log::error!("Streaming processing failed: {e:?}");
drop(streaming_body);
} else if let Err(e) = streaming_body.finish() {
log::error!("Failed to finish streaming body: {e}");
params,
}) => {
// Streaming path: finalize headers, then stream body to client.
finalize_response(settings, geo_info.as_ref(), &mut response);
let mut streaming_body = response.stream_to_client();
if let Err(e) = stream_publisher_body(
body,
&mut streaming_body,
&params,
settings,
integration_registry,
) {
// Headers already committed. Log and abort — client
// sees a truncated response. Standard proxy behavior.
log::error!("Streaming processing failed: {e:?}");
drop(streaming_body);
} else if let Err(e) = streaming_body.finish() {
log::error!("Failed to finish streaming body: {e}");
}
// Response already sent via stream_to_client()
return None;
}
Ok(PublisherResponse::PassThrough { mut response, body }) => {
// Binary pass-through: reattach body and send via send_to_client().
// This preserves Content-Length and avoids chunked encoding overhead.
// Fastly streams the body from its internal buffer — no WASM
// memory buffering occurs.
response.set_body(body);
Ok(response)
}
Ok(PublisherResponse::Buffered(response)) => Ok(response),
Err(e) => {
log::error!("Failed to proxy to publisher origin: {:?}", e);
Err(e)
}
// Response already sent via stream_to_client()
return None;
}
Ok(PublisherResponse::PassThrough { mut response, body }) => {
// Binary pass-through: reattach body and send via send_to_client().
// This preserves Content-Length and avoids chunked encoding overhead.
// Fastly streams the body from its internal buffer — no WASM
// memory buffering occurs.
response.set_body(body);
Ok(response)
}
Ok(PublisherResponse::Buffered(response)) => Ok(response),
Err(e) => {
log::error!("Failed to proxy to publisher origin: {:?}", e);
Err(e)
}
}
Err(e) => Err(e),
}
Err(e) => Err(e),
}
}
};
Expand Down
91 changes: 90 additions & 1 deletion crates/trusted-server-adapter-fastly/src/route_tests.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -14,7 +14,7 @@ use trusted_server_core::platform::{
StoreName,
};
use trusted_server_core::request_signing::JWKS_CONFIG_STORE_NAME;
use trusted_server_core::settings::Settings;
use trusted_server_core::settings::{ProxyAssetRoute, Settings};

use super::route_request;

Expand Down Expand Up @@ -249,3 +249,92 @@ fn configured_missing_consent_store_only_breaks_consent_routes() {
"should scope consent store failures to the consent-dependent routes"
);
}

#[test]
fn asset_routes_bypass_publisher_consent_dependencies() {
let mut settings = create_test_settings();
settings.proxy.asset_routes = vec![ProxyAssetRoute {
prefix: "/.images/".to_string(),
origin_url: "https://assets.example.com".to_string(),
}];
let orchestrator = build_orchestrator(&settings).expect("should build auction orchestrator");
let integration_registry =
IntegrationRegistry::new(&settings).expect("should create integration registry");

let asset_req = Request::get("https://test.com/.images/logo.png?auto=webp");
let asset_services = test_runtime_services(&asset_req);
let asset_resp = futures::executor::block_on(route_request(
&settings,
&orchestrator,
&integration_registry,
&asset_services,
asset_req,
))
.expect("should return an error response for asset proxy requests");
assert_eq!(
asset_resp.get_status(),
StatusCode::BAD_GATEWAY,
"should bypass publisher consent dependencies and fail only on the missing upstream client"
);
}
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@aram356 aram356 May 1, 2026

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🔧 wrench — The spec (§9 / §"Failure Semantics") explicitly forbids silent fallback to publisher.origin_url when an asset origin fails. The current implementation does the right thing, but no test pins that behavior — a future refactor could regress it without anyone noticing.

asset_routes_bypass_publisher_consent_dependencies shows that asset routes don't run the consent path, but it doesn't prove the failure path stops at 502 instead of attempting publisher.origin_url. Please add a focused test that asserts:

  1. an asset-route request whose backend ensure() (or upstream send()) fails returns 502, and
  2. the publisher origin's send() is never invoked for that request (e.g., via a stub PlatformHttpClient that records call counts and asserts zero calls to the publisher origin).


#[test]
fn built_in_routes_take_precedence_over_asset_routes() {
let mut settings = create_test_settings();
settings.proxy.asset_routes = vec![ProxyAssetRoute {
prefix: "/.well-known/".to_string(),
origin_url: "https://assets.example.com".to_string(),
}];
let orchestrator = build_orchestrator(&settings).expect("should build auction orchestrator");
let integration_registry =
IntegrationRegistry::new(&settings).expect("should create integration registry");

let req = Request::get("https://test.com/.well-known/trusted-server.json");
let services = test_runtime_services(&req);
let resp = futures::executor::block_on(route_request(
&settings,
&orchestrator,
&integration_registry,
&services,
req,
))
.expect("should route discovery request");
assert_eq!(
resp.get_status(),
StatusCode::OK,
"should keep explicit built-in routes ahead of asset routes"
);
}

#[test]
fn integration_routes_take_precedence_over_asset_routes() {
let mut settings = create_test_settings();
settings.proxy.asset_routes = vec![ProxyAssetRoute {
prefix: "/prebid.js".to_string(),
origin_url: "https://assets.example.com".to_string(),
}];
let orchestrator = build_orchestrator(&settings).expect("should build auction orchestrator");
let integration_registry =
IntegrationRegistry::new(&settings).expect("should create integration registry");

let req = Request::get("https://test.com/prebid.js");
let services = test_runtime_services(&req);
let mut resp = futures::executor::block_on(route_request(
&settings,
&orchestrator,
&integration_registry,
&services,
req,
))
.expect("should route integration request");
assert_eq!(
resp.get_status(),
StatusCode::OK,
"should keep explicit integration routes ahead of asset routes"
);
assert_eq!(
resp.take_body_str(),
"// Script overridden by Trusted Server\n",
"should serve the integration response instead of proxying to the asset origin"
);
}
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🤔 thinking — The spec's "Recommended Tests" section calls out several invariants that aren't covered yet. All are a few lines given existing helpers (StubHttpClient, StaticResponseHttpClient):

  • HEAD passthrough (spec §12 / §"Method forwarding"): only GET is exercised in handle_asset_proxy_request_forwards_asset_headers_and_host.
  • Non-GET/HEAD bypass (spec §6): no test that POST /.images/foo skips asset matching and falls through to publisher.
  • Redirect pass-through (spec §11): no test that a 301/302 from upstream is returned to the client unchanged.
  • Query string ignored for matching (spec §"Matching algorithm"): not pinned in proxy_asset_route_for_path_* tests.

These keep the spec and tests in lockstep so behavior shifts surface as failing tests.

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