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wasi-http: don't send forbidden headers #136

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pchickey wants to merge 3 commits into from
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wasi-http: don't send forbidden headers #136

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c2fab21
header map translation: do not set FORBIDDEN_HEADERS
pchickey Jul 17, 2026
0b0692c
server: do not add a Content-Length header
pchickey Jul 17, 2026
35872be
lowercase search
pchickey Jul 20, 2026
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29 changes: 25 additions & 4 deletions src/http/fields.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -18,10 +18,31 @@ pub(crate) fn header_map_from_wasi(wasi_fields: Fields) -> Result<HeaderMap, Err
pub(crate) fn header_map_to_wasi(header_map: &HeaderMap) -> Result<Fields, Error> {
let wasi_fields = Fields::new();
for (key, value) in header_map {
// Unwrap because `HeaderMap` has already validated the headers.
wasi_fields
.append(key.as_str(), value.as_bytes())
.with_context(|| format!("wasi rejected header `{key}: {value:?}`"))?
let key = key.as_str().to_ascii_lowercase();
if FORBIDDEN_HEADERS
.iter()
.find(|k| k.as_str() == key)
.is_none()
{
wasi_fields
.append(key.as_str(), value.as_bytes())
.with_context(|| format!("wasi rejected header `{key}: {value:?}`"))?
}
}
Ok(wasi_fields)
}

// Optimization opportunity: use a trie here
const FORBIDDEN_HEADERS: [HeaderName; 11] = [
http::header::CONNECTION,
HeaderName::from_static("keep-alive"),
http::header::PROXY_AUTHENTICATE,
http::header::PROXY_AUTHORIZATION,
HeaderName::from_static("proxy-connection"),
http::header::TRANSFER_ENCODING,
http::header::UPGRADE,
http::header::HOST,
HeaderName::from_static("http2-settings"),
http::header::EXPECT,
http::header::CONTENT_LENGTH,
];
9 changes: 0 additions & 9 deletions src/http/server.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -19,7 +19,6 @@
//! [`http_server`]: crate::http_server

use super::{Body, Error, Response, error::ErrorCode, fields::header_map_to_wasi};
use http::header::CONTENT_LENGTH;
use wasip2::exports::http::incoming_handler::ResponseOutparam;
use wasip2::http::types::OutgoingResponse;

Expand All @@ -44,14 +43,6 @@ impl Responder {
// Consume the `response` and prepare to write the body.
let body = response.into_body().into();

// Automatically add a Content-Length header.
if let Some(len) = body.content_length() {
let mut buffer = itoa::Buffer::new();
wasi_headers
.append(CONTENT_LENGTH.as_str(), buffer.format(len).as_bytes())
.unwrap();
}

Comment on lines -47 to -54

@yoshuawuyts yoshuawuyts Jul 19, 2026

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I'm surprised this works? I'm looking at Jco's http.ts here, and this might cause problems for it? I'd feel a lot better if we had a test for this in wasi-testsuite to greenlight the behavior before we land it here.

let wasi_response = OutgoingResponse::new(wasi_headers);

// Unwrap because `StatusCode` has already validated the status.
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