2 files changed, 17 insertions, 18 deletions

diff --git a/std/http/_io.ts b/std/http/_io.ts
index 631adafd0..6b3796c5b 100644
--- a/std/http/_io.ts
+++ b/std/http/_io.ts
@@ -113,11 +113,10 @@ export function chunkedBodyReader(h: Headers, r: BufReader): Deno.Reader {
   return { read };
 }
 
-const kProhibitedTrailerHeaders = [
-  "transfer-encoding",
-  "content-length",
-  "trailer",
-];
+function isProhibidedForTrailer(key: string): boolean {
+  const s = new Set(["transfer-encoding", "content-length", "trailer"]);
+  return s.has(key.toLowerCase());
+}
 
 /**
  * Read trailer headers from reader and append values to headers.
@@ -127,36 +126,36 @@ export async function readTrailers(
   headers: Headers,
   r: BufReader
 ): Promise<void> {
-  const keys = parseTrailer(headers.get("trailer"));
-  if (!keys) return;
+  const headerKeys = parseTrailer(headers.get("trailer"));
+  if (!headerKeys) return;
   const tp = new TextProtoReader(r);
   const result = await tp.readMIMEHeader();
   assert(result !== null, "trailer must be set");
   for (const [k, v] of result) {
-    if (!keys.has(k)) {
+    if (!headerKeys.has(k)) {
       throw new Error("Undeclared trailer field");
     }
-    keys.delete(k);
+    headerKeys.delete(k);
     headers.append(k, v);
   }
-  assert(keys.size === 0, "Missing trailers");
+  assert(Array.from(headerKeys).length === 0, "Missing trailers");
   headers.delete("trailer");
 }
 
-function parseTrailer(field: string | null): Set<string> | undefined {
+function parseTrailer(field: string | null): Headers | undefined {
   if (field == null) {
     return undefined;
   }
-  const keys = field.split(",").map((v) => v.trim());
+  const keys = field.split(",").map((v) => v.trim().toLowerCase());
   if (keys.length === 0) {
     throw new Error("Empty trailer");
   }
-  for (const invalid of kProhibitedTrailerHeaders) {
-    if (keys.includes(invalid)) {
+  for (const key of keys) {
+    if (isProhibidedForTrailer(key)) {
       throw new Error(`Prohibited field for trailer`);
     }
   }
-  return new Set(keys);
+  return new Headers(keys.map((key) => [key, ""]));
 }
 
 export async function writeChunkedBody(
@@ -199,7 +198,7 @@ export async function writeTrailers(
     .map((s) => s.trim().toLowerCase());
   for (const f of trailerHeaderFields) {
     assert(
-      !kProhibitedTrailerHeaders.includes(f),
+      !isProhibidedForTrailer(f),
       `"${f}" is prohibited for trailer header`
     );
   }
diff --git a/std/http/_io_test.ts b/std/http/_io_test.ts
index c22ebdf07..3e74e365d 100644
--- a/std/http/_io_test.ts
+++ b/std/http/_io_test.ts
@@ -82,7 +82,7 @@ test("chunkedBodyReader with trailers", async () => {
 
 test("readTrailers", async () => {
   const h = new Headers({
-    trailer: "deno,node",
+    trailer: "Deno, Node",
   });
   const trailer = ["deno: land", "node: js", "", ""].join("\r\n");
   await readTrailers(h, new BufReader(new Buffer(encode(trailer))));
@@ -112,7 +112,7 @@ test("readTrailer should throw if undeclared headers found in trailer", async ()
 });
 
 test("readTrailer should throw if trailer contains prohibited fields", async () => {
-  for (const f of ["content-length", "trailer", "transfer-encoding"]) {
+  for (const f of ["Content-Length", "Trailer", "Transfer-Encoding"]) {
     const h = new Headers({
       trailer: f,
     });