set content-length 0 in some cases (#3503)

2 files changed, 20 insertions, 2 deletions

diff --git a/src/http_client_async.zig b/src/http_client_async.zig
index a1962a8b9..2cb534ed2 100644
--- a/src/http_client_async.zig
+++ b/src/http_client_async.zig
@@ -1629,7 +1629,6 @@ pub fn buildRequest(this: *HTTPClient, body_len: usize) picohttp.Request {
     var override_accept_encoding = false;
     var override_accept_header = false;
     var override_host_header = false;
-
     var override_user_agent = false;
 
     for (header_names, 0..) |head, i| {
@@ -1710,7 +1709,7 @@ pub fn buildRequest(this: *HTTPClient, body_len: usize) picohttp.Request {
         header_count += 1;
     }
 
-    if (body_len > 0) {
+    if (body_len > 0 or this.method.hasRequestBody()) {
         request_headers_buf[header_count] = .{
             .name = content_length_header_name,
             .value = std.fmt.bufPrint(&this.request_content_len_buf, "{d}", .{body_len}) catch "0",
diff --git a/test/js/web/fetch/fetch.test.ts b/test/js/web/fetch/fetch.test.ts
index 4d529b231..6b87cc613 100644
--- a/test/js/web/fetch/fetch.test.ts
+++ b/test/js/web/fetch/fetch.test.ts
@@ -387,6 +387,25 @@ describe("fetch", () => {
       }).toThrow("fetch() request with GET/HEAD/OPTIONS method cannot have body.");
     }),
   );
+
+  it("content length is inferred", async () => {
+    startServer({
+      fetch(req) {
+        return new Response(req.headers.get("content-length"));
+      },
+      hostname: "localhost",
+    });
+
+    // POST with body
+    const url = `http://${server.hostname}:${server.port}`;
+    const response = await fetch(url, { method: "POST", body: "buntastic" });
+    expect(response.status).toBe(200);
+    expect(await response.text()).toBe("9");
+
+    const response2 = await fetch(url, { method: "POST", body: "" });
+    expect(response2.status).toBe(200);
+    expect(await response2.text()).toBe("0");
+  });
 });
 
 it("simultaneous HTTPS fetch", async () => {