From 0bbf0461d9800ce5eba28cd32ef10492b2f80639 Mon Sep 17 00:00:00 2001
From: Luna Schwalbe <dev@luna.gl>
Date: Sun, 7 Dec 2025 04:28:01 +0100
Subject: [PATCH] std.http: reliably update reader state

Content length based reading would only set the reader state to `ready`
once it returned EOF, but wrapping readers (such as decompressors)
may stop reading from the underlying source without receiving EOF.
In such cases the http reader state would stay set to
`body_remaining_content_length`, even though the entire body had been
read.

Fixes #30060

Co-authored-by: Andrew Kelley <andre@ziglang.org>
---
 lib/std/http.zig      | 24 +++++++++++++-----------
 lib/std/http/test.zig | 22 ++++++++++++++++++++++
 2 files changed, 35 insertions(+), 11 deletions(-)

diff --git a/lib/std/http.zig b/lib/std/http.zig
index 291e22539b..300ae397ec 100644
--- a/lib/std/http.zig
+++ b/lib/std/http.zig
@@ -443,7 +443,7 @@ pub const Reader = struct {
             },
             .none => {
                 if (content_length) |len| {
-                    reader.state = .{ .body_remaining_content_length = len };
+                    reader.state = if (len == 0) .ready else .{ .body_remaining_content_length = len };
                     reader.interface = .{
                         .buffer = transfer_buffer,
                         .seek = 0,
@@ -509,27 +509,29 @@ pub const Reader = struct {
         limit: std.Io.Limit,
     ) std.Io.Reader.StreamError!usize {
         const reader: *Reader = @alignCast(@fieldParentPtr("interface", io_r));
+        if (reader.state == .ready) return error.EndOfStream;
         const remaining_content_length = &reader.state.body_remaining_content_length;
         const remaining = remaining_content_length.*;
-        if (remaining == 0) {
-            reader.state = .ready;
-            return error.EndOfStream;
-        }
         const n = try reader.in.stream(w, limit.min(.limited64(remaining)));
-        remaining_content_length.* = remaining - n;
+        if (n == remaining) {
+            reader.state = .ready;
+        } else {
+            remaining_content_length.* = remaining - n;
+        }
         return n;
     }
 
     fn contentLengthDiscard(io_r: *std.Io.Reader, limit: std.Io.Limit) std.Io.Reader.Error!usize {
         const reader: *Reader = @alignCast(@fieldParentPtr("interface", io_r));
+        if (reader.state == .ready) return error.EndOfStream;
         const remaining_content_length = &reader.state.body_remaining_content_length;
         const remaining = remaining_content_length.*;
-        if (remaining == 0) {
-            reader.state = .ready;
-            return error.EndOfStream;
-        }
         const n = try reader.in.discard(limit.min(.limited64(remaining)));
-        remaining_content_length.* = remaining - n;
+        if (n == remaining) {
+            reader.state = .ready;
+        } else {
+            remaining_content_length.* = remaining - n;
+        }
         return n;
     }
 
diff --git a/lib/std/http/test.zig b/lib/std/http/test.zig
index b061f4b2ac..42fd9f8fc9 100644
--- a/lib/std/http/test.zig
+++ b/lib/std/http/test.zig
@@ -11,6 +11,28 @@ const expectEqual = std.testing.expectEqual;
 const expectEqualStrings = std.testing.expectEqualStrings;
 const expectError = std.testing.expectError;
 
+test "content length reader state update" {
+    var in = Io.Reader.fixed("HTTP/1.1 200 OK\r\nContent-Length: 6\r\n\r\nHello!\r\nHTTP/1.1 200 OK\r\n\r\n");
+    var reader: http.Reader = .{
+        .in = &in,
+        .interface = undefined,
+        .state = .ready,
+        .max_head_len = 1024,
+    };
+
+    _ = try reader.receiveHead();
+    var body: [6]u8 = undefined;
+    _ = try reader.bodyReader(&.{}, .none, body.len).readSliceAll(&body);
+    try expectEqual(.ready, reader.state);
+    _ = try reader.receiveHead();
+
+    in.seek = 0;
+    _ = try reader.receiveHead();
+    try reader.bodyReader(&.{}, .none, body.len).discardAll(body.len);
+    try expectEqual(.ready, reader.state);
+    _ = try reader.receiveHead();
+}
+
 test "trailers" {
     if (builtin.cpu.arch.isPowerPC64() and builtin.mode != .Debug) return error.SkipZigTest; // https://github.com/llvm/llvm-project/issues/171879
     if (builtin.os.tag == .openbsd) return error.SkipZigTest; // https://codeberg.org/ziglang/zig/issues/30806