Support specifying header order

Author: zyc9012

README.md

@@ -77,6 +77,11 @@ client = Wreq::Client.new(
   zstd: true,                  # enable zstd decompression
   emulation: "chrome_143",     # browser emulation (enabled by default)
   emulation_os: "windows",     # OS emulation: windows, macos (default), linux, android, ios
+  header_order: [              # wire order of headers (names only, case-sensitive)
+    "host",                    # listed headers appear first in the given order, remaining
+    "user-agent",              # emulation headers follow.
+    "accept",
+  ],
   headers: {                   # default headers for all requests
     "Accept" => "application/json"
   }

ext/wreq_rb/src/client.rs

@@ -10,7 +10,7 @@ use magnus::{
 };
 use tokio::runtime::Runtime;
 use tokio_util::sync::CancellationToken;
-use wreq::header::{HeaderMap, HeaderName, HeaderValue};
+use wreq::header::{HeaderMap, HeaderName, HeaderValue, OrigHeaderMap};
 use wreq_util::{Emulation as BrowserEmulation, EmulationOS, EmulationOption};
 
 use crate::error::{generic_error, to_magnus_error};
@@ -192,6 +192,12 @@ impl Client {
         let mut builder = wreq::Client::builder();
 
         if let Some(opts) = opts {
+            // Apply header_order BEFORE emulation so the user's ordering takes precedence
+            if let Some(ary) = hash_get_array(&opts, "header_order")? {
+                let orig = array_to_orig_header_map(ary)?;
+                builder = builder.orig_headers(orig);
+            }
+
             if let Some(val) = hash_get_value(&opts, "emulation")? {
                 let ruby = unsafe { Ruby::get_unchecked() };
                 if val.is_kind_of(ruby.class_false_class()) {
@@ -536,6 +542,27 @@ fn hash_get_hash(hash: &RHash, key: &str) -> Result<Option<RHash>, magnus::Error
     }
 }
 
+fn hash_get_array(hash: &RHash, key: &str) -> Result<Option<RArray>, magnus::Error> {
+    match hash_get_value(hash, key)? {
+        Some(v) => Ok(Some(RArray::try_convert(v)?)),
+        None => Ok(None),
+    }
+}
+
+fn array_to_orig_header_map(ary: RArray) -> Result<OrigHeaderMap, magnus::Error> {
+    let mut orig = OrigHeaderMap::with_capacity(ary.len());
+    for elem in ary.into_iter() {
+        let ruby = unsafe { Ruby::get_unchecked() };
+        let name_str: String = if elem.is_kind_of(ruby.class_symbol()) {
+            elem.funcall("to_s", ())?  
+        } else {
+            TryConvert::try_convert(elem)?
+        };
+        orig.insert(name_str);
+    }
+    Ok(orig)
+}
+
 fn hash_to_header_map(hash: &RHash) -> Result<HeaderMap, magnus::Error> {
     let mut hmap = HeaderMap::new();
     hash.foreach(|k: Value, v: Value| {

test/client_test.rb

@@ -47,4 +47,70 @@ def test_default_headers_with_mixed_types
     assert_nil body["headers"]["X-Nil"]
     assert_equal "ok", body["headers"]["X-Str"]
   end
+
+  def test_header_order
+    order = ["x-zzz", "x-aaa", "x-ccc"]
+    client = Wreq::Client.new(
+      emulation: false,
+      http1_only: true,
+      no_proxy: true,
+      header_order: order,
+      headers: { "x-aaa" => "1", "x-ccc" => "2", "x-zzz" => "3" }
+    )
+    received = capture_wire_headers { |url| client.get(url) }
+
+    positions = order.map { |h| received.index(h) }.compact
+    assert_equal order.size, positions.size,
+      "Not all target headers found in: #{received.inspect}"
+    assert_equal positions.sort, positions,
+      "Expected #{order.inspect} in order, got positions #{positions.inspect} in: #{received.inspect}"
+  end
+
+  def test_header_order_takes_precedence_over_emulation
+    # Chrome emulation normally puts "user-agent" before "accept". We reverse
+    # that relationship to prove the user's header_order wins.
+    order = ["host", "accept", "user-agent"]
+    client = Wreq::Client.new(
+      emulation: "chrome_145",
+      http1_only: true,
+      no_proxy: true,
+      header_order: order
+    )
+    received = capture_wire_headers { |url| client.get(url) }
+
+    positions = order.map { |h| received.index(h) }.compact
+    assert_equal order.size, positions.size,
+      "Not all target headers found in: #{received.inspect}"
+    assert_equal positions.sort, positions,
+      "Expected user's header_order #{order.inspect} to take precedence; " \
+      "got positions #{positions.inspect} in: #{received.inspect}"
+  end
+
+  private
+
+  # Spins up a local TCP server, yields the port formatted into a URL, captures
+  # the header names from the raw HTTP/1.1 request, then tears down the server.
+  def capture_wire_headers
+    require "socket"
+    server = TCPServer.new("127.0.0.1", 0)
+    port = server.addr[1]
+    received = []
+    t = Thread.new do
+      conn = server.accept
+      conn.gets # skip request line
+      loop do
+        line = conn.gets&.chomp
+        break if line.nil? || line.empty?
+        received << line.split(":", 2).first.downcase
+      end
+      conn.write "HTTP/1.1 200 OK\r\nContent-Length: 0\r\nConnection: close\r\n\r\n"
+      conn.close
+    rescue
+      conn&.close
+    end
+    yield format("http://127.0.0.1:#{port}/")
+    t.join(5)
+    server.close
+    received
+  end
 end