Make header_map_to_wasi bubble up its error.

The client can bubble this into a `wstd::http::Error`. The server
currently just does `.expect`, but at least now, if we want it to
do something different, it's more clear what the options are.

Author: sunfishcode

src/http/error.rs

@@ -1,3 +1,4 @@
+use crate::http::fields::ToWasiHeaderError;
 use std::fmt;
 
 /// The `http` result type.
@@ -78,9 +79,12 @@ impl From<WasiHttpErrorCode> for Error {
     }
 }
 
-impl From<WasiHttpHeaderError> for Error {
-    fn from(e: WasiHttpHeaderError) -> Error {
-        ErrorVariant::WasiHeader(e).into()
+impl From<ToWasiHeaderError> for Error {
+    fn from(error: ToWasiHeaderError) -> Error {
+        Error {
+            variant: ErrorVariant::WasiHeader(error.error),
+            context: vec![error.context],
+        }
     }
 }
 

src/http/fields.rs

@@ -1,9 +1,9 @@
 pub use http::header::{HeaderMap, HeaderName, HeaderValue};
 
-use super::{Error, Result};
-use wasi::http::types::Fields;
+use super::Error;
+use wasi::http::types::{Fields, HeaderError as WasiHttpHeaderError};
 
-pub(crate) fn header_map_from_wasi(wasi_fields: Fields) -> Result<HeaderMap> {
+pub(crate) fn header_map_from_wasi(wasi_fields: Fields) -> Result<HeaderMap, Error> {
     let mut output = HeaderMap::new();
     for (key, value) in wasi_fields.entries() {
         let key = HeaderName::from_bytes(key.as_bytes())
@@ -15,13 +15,22 @@ pub(crate) fn header_map_from_wasi(wasi_fields: Fields) -> Result<HeaderMap> {
     Ok(output)
 }
 
-pub(crate) fn header_map_to_wasi(header_map: &HeaderMap) -> Fields {
+pub(crate) fn header_map_to_wasi(header_map: &HeaderMap) -> Result<Fields, ToWasiHeaderError> {
     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())
-            .unwrap_or_else(|err| panic!("header named {key}: {err:?}"));
+            .map_err(|error| ToWasiHeaderError {
+                error,
+                context: format!("header {key}: {value:?}"),
+            })?;
     }
-    wasi_fields
+    Ok(wasi_fields)
+}
+
+#[derive(Debug)]
+pub(crate) struct ToWasiHeaderError {
+    pub(crate) error: WasiHttpHeaderError,
+    pub(crate) context: String,
 }

src/http/request.rs

@@ -13,7 +13,7 @@ use wasi::http::types::IncomingRequest;
 pub use http::Request;
 
 pub(crate) fn try_into_outgoing<T>(request: Request<T>) -> Result<(OutgoingRequest, T), Error> {
-    let wasi_req = OutgoingRequest::new(header_map_to_wasi(request.headers()));
+    let wasi_req = OutgoingRequest::new(header_map_to_wasi(request.headers())?);
 
     let (parts, body) = request.into_parts();
 

src/http/server.rs

@@ -61,7 +61,7 @@ impl Responder {
     /// # }
     /// ```
     pub fn start_response(self, response: Response<BodyForthcoming>) -> OutgoingBody {
-        let wasi_headers = header_map_to_wasi(response.headers());
+        let wasi_headers = header_map_to_wasi(response.headers()).expect("header error");
         let wasi_response = OutgoingResponse::new(wasi_headers);
         let wasi_status = response.status().as_u16();
 
@@ -100,7 +100,7 @@ impl Responder {
         let headers = response.headers();
         let status = response.status().as_u16();
 
-        let wasi_headers = header_map_to_wasi(headers);
+        let wasi_headers = header_map_to_wasi(headers).expect("header error");
 
         // Consume the `response` and prepare to write the body.
         let mut body = response.into_body();
@@ -173,7 +173,8 @@ impl Finished {
         // If there was an I/O error, panic and don't call `OutgoingBody::finish`.
         let _ = result.expect("I/O error while writing the body");
 
-        let wasi_trailers = trailers.map(|trailers| header_map_to_wasi(&trailers));
+        let wasi_trailers =
+            trailers.map(|trailers| header_map_to_wasi(&trailers).expect("header error"));
 
         wasi::http::types::OutgoingBody::finish(body, wasi_trailers)
             .expect("body length did not match Content-Length header value");