1 files changed, 50 insertions, 12 deletions

diff --git a/std/http/server.ts b/std/http/server.ts
index 0bd5d06b5..b8a41379f 100644
--- a/std/http/server.ts
+++ b/std/http/server.ts
@@ -12,14 +12,6 @@ import { deferred, Deferred, MuxAsyncIterator } from "../util/async.ts";
 
 const encoder = new TextEncoder();
 
-function bufWriter(w: Writer): BufWriter {
-  if (w instanceof BufWriter) {
-    return w;
-  } else {
-    return new BufWriter(w);
-  }
-}
-
 export function setContentLength(r: Response): void {
   if (!r.headers) {
     r.headers = new Headers();
@@ -30,16 +22,16 @@ export function setContentLength(r: Response): void {
       // typeof r.body === "string" handled in writeResponse.
       if (r.body instanceof Uint8Array) {
         const bodyLength = r.body.byteLength;
-        r.headers.append("Content-Length", bodyLength.toString());
+        r.headers.set("content-length", bodyLength.toString());
       } else {
-        r.headers.append("Transfer-Encoding", "chunked");
+        r.headers.set("transfer-encoding", "chunked");
       }
     }
   }
 }
 
 async function writeChunkedBody(w: Writer, r: Reader): Promise<void> {
-  const writer = bufWriter(w);
+  const writer = BufWriter.create(w);
 
   for await (const chunk of toAsyncIterator(r)) {
     if (chunk.byteLength <= 0) continue;
@@ -53,13 +45,54 @@ async function writeChunkedBody(w: Writer, r: Reader): Promise<void> {
   const endChunk = encoder.encode("0\r\n\r\n");
   await writer.write(endChunk);
 }
+const kProhibitedTrailerHeaders = [
+  "transfer-encoding",
+  "content-length",
+  "trailer"
+];
+
+/** write trailer headers to writer. it mostly should be called after writeResponse */
+export async function writeTrailers(
+  w: Writer,
+  headers: Headers,
+  trailers: Headers
+): Promise<void> {
+  const trailer = headers.get("trailer");
+  if (trailer === null) {
+    throw new Error('response headers must have "trailer" header field');
+  }
+  const transferEncoding = headers.get("transfer-encoding");
+  if (transferEncoding === null || !transferEncoding.match(/^chunked/)) {
+    throw new Error(
+      `trailer headers is only allowed for "transfer-encoding: chunked": got "${transferEncoding}"`
+    );
+  }
+  const writer = BufWriter.create(w);
+  const trailerHeaderFields = trailer
+    .split(",")
+    .map(s => s.trim().toLowerCase());
+  for (const f of trailerHeaderFields) {
+    assert(
+      !kProhibitedTrailerHeaders.includes(f),
+      `"${f}" is prohibited for trailer header`
+    );
+  }
+  for (const [key, value] of trailers) {
+    assert(
+      trailerHeaderFields.includes(key),
+      `Not trailer header field: ${key}`
+    );
+    await writer.write(encoder.encode(`${key}: ${value}\r\n`));
+  }
+  await writer.flush();
+}
 
 export async function writeResponse(w: Writer, r: Response): Promise<void> {
   const protoMajor = 1;
   const protoMinor = 1;
   const statusCode = r.status || 200;
   const statusText = STATUS_TEXT.get(statusCode);
-  const writer = bufWriter(w);
+  const writer = BufWriter.create(w);
   if (!statusText) {
     throw Error("bad status code");
   }
@@ -97,6 +130,10 @@ export async function writeResponse(w: Writer, r: Response): Promise<void> {
   } else {
     await writeChunkedBody(writer, r.body);
   }
+  if (r.trailers) {
+    const t = await r.trailers();
+    await writeTrailers(writer, headers, t);
+  }
   await writer.flush();
 }
 
@@ -572,4 +609,5 @@ export interface Response {
   status?: number;
   headers?: Headers;
   body?: Uint8Array | Reader | string;
+  trailers?: () => Promise<Headers> | Headers;
 }