From 89c9282d346498e1b3ca9dfe26bf776311cd0ded Mon Sep 17 00:00:00 2001
From: Andrew Kelley <andrew@ziglang.org>
Date: Mon, 18 Aug 2025 17:22:56 -0700
Subject: [PATCH] std.http.Client: discard response body when reusing
 connection

When an error response was encountered, such as 404 not found, the body
wasn't discarded, leading to the string "404 not found" being
incorrectly interpreted as the next request's response.

closes #24732
---
 lib/std/http/Client.zig | 25 ++++++++++++++++++++++++-
 1 file changed, 24 insertions(+), 1 deletion(-)

diff --git a/lib/std/http/Client.zig b/lib/std/http/Client.zig
index 626036234c..b507128c9c 100644
--- a/lib/std/http/Client.zig
+++ b/lib/std/http/Client.zig
@@ -787,6 +787,13 @@ pub const Request = struct {
     /// Standard headers that have default, but overridable, behavior.
     headers: Headers,
 
+    /// Populated in `receiveHead`; used in `deinit` to determine whether to
+    /// discard the body to reuse the connection.
+    response_content_length: ?u64 = null,
+    /// Populated in `receiveHead`; used in `deinit` to determine whether to
+    /// discard the body to reuse the connection.
+    response_transfer_encoding: http.TransferEncoding = .none,
+
     /// These headers are kept including when following a redirect to a
     /// different domain.
     /// Externally-owned; must outlive the Request.
@@ -860,7 +867,15 @@ pub const Request = struct {
         if (r.connection) |connection| {
             connection.closing = connection.closing or switch (r.reader.state) {
                 .ready => false,
-                .received_head => r.method.requestHasBody(),
+                .received_head => c: {
+                    if (r.method.requestHasBody()) break :c true;
+                    if (!r.method.responseHasBody()) break :c false;
+                    const reader = r.reader.bodyReader(&.{}, r.response_transfer_encoding, r.response_content_length);
+                    _ = reader.discardRemaining() catch |err| switch (err) {
+                        error.ReadFailed => break :c true,
+                    };
+                    break :c r.reader.state != .ready;
+                },
                 else => true,
             };
             r.client.connection_pool.release(connection);
@@ -1102,6 +1117,8 @@ pub const Request = struct {
 
             if (head.status == .@"continue") {
                 if (r.handle_continue) continue;
+                r.response_transfer_encoding = head.transfer_encoding;
+                r.response_content_length = head.content_length;
                 return response; // we're not handling the 100-continue
             }
 
@@ -1113,6 +1130,8 @@ pub const Request = struct {
             if (r.method == .CONNECT and head.status.class() == .success) {
                 // This connection is no longer doing HTTP.
                 connection.closing = false;
+                r.response_transfer_encoding = head.transfer_encoding;
+                r.response_content_length = head.content_length;
                 return response;
             }
 
@@ -1126,6 +1145,8 @@ pub const Request = struct {
             if (r.method == .HEAD or head.status.class() == .informational or
                 head.status == .no_content or head.status == .not_modified)
             {
+                r.response_transfer_encoding = head.transfer_encoding;
+                r.response_content_length = head.content_length;
                 return response;
             }
 
@@ -1146,6 +1167,8 @@ pub const Request = struct {
             if (!r.accept_encoding[@intFromEnum(head.content_encoding)])
                 return error.HttpContentEncodingUnsupported;
 
+            r.response_transfer_encoding = head.transfer_encoding;
+            r.response_content_length = head.content_length;
             return response;
         }
     }