feat(std/http/server): Respond with 400 on request parse failure (#4551)

1 files changed, 28 insertions, 7 deletions

diff --git a/std/http/io.ts b/std/http/io.ts
index 2875be44f..e12c9fb6e 100644
--- a/std/http/io.ts
+++ b/std/http/io.ts
@@ -342,17 +342,38 @@ export function parseHTTPVersion(vers: string): [number, number] {
 
 export async function readRequest(
   conn: Deno.Conn,
-  bufr: BufReader
+  // The reader and writer buffers may be constructed externally so they can be
+  // shared by requests on the same connection -- see `Server`.
+  reader?: BufReader,
+  writer?: BufWriter
 ): Promise<ServerRequest | Deno.EOF> {
-  const tp = new TextProtoReader(bufr);
-  const firstLine = await tp.readLine(); // e.g. GET /index.html HTTP/1.0
-  if (firstLine === Deno.EOF) return Deno.EOF;
-  const headers = await tp.readMIMEHeader();
-  if (headers === Deno.EOF) throw new Deno.errors.UnexpectedEof();
+  reader = reader ?? new BufReader(conn);
+  writer = writer ?? new BufWriter(conn);
+  const tp = new TextProtoReader(reader);
+  let firstLine: string | Deno.EOF;
+  let headers: Headers | Deno.EOF;
+  try {
+    firstLine = await tp.readLine(); // e.g. GET /index.html HTTP/1.0
+    if (firstLine == Deno.EOF) {
+      return Deno.EOF;
+    }
+    headers = await tp.readMIMEHeader();
+    if (headers == Deno.EOF) {
+      throw new Deno.errors.UnexpectedEof();
+    }
+  } catch (error) {
+    // An error was thrown while parsing request headers.
+    await writeResponse(writer, {
+      status: 400,
+      body: encoder.encode(`${error.message}\r\n\r\n`),
+    });
+    throw error;
+  }
 
   const req = new ServerRequest();
   req.conn = conn;
-  req.r = bufr;
+  req.r = reader;
+  req.w = writer;
   [req.method, req.url, req.proto] = firstLine.split(" ", 3);
   [req.protoMinor, req.protoMajor] = parseHTTPVersion(req.proto);
   req.headers = headers;