chore: Release version 0.4.3

- Updated version to 0.4.3 in mix.exs
- Added comprehensive changelog for 0.4.3
- Updated README.md with new HTTP.Headers features
- Added documentation for set_default/3 and user_agent/0 methods
- Documented automatic User-Agent header functionality

Author: GSMLG-BOT

CHANGELOG.md

@@ -5,6 +5,24 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [0.4.3] - 2025-08-01
+
+### Added
+- Added `HTTP.Headers.set_default/3` method to set headers only if they don't already exist
+  - Uses case-insensitive header name matching
+  - Preserves existing headers when they already contain the specified name
+- Added automatic default `User-Agent` header to all HTTP requests
+  - Format: `Mozilla/5.0 (macOS; aarch64-apple-darwin24.3.0) OTP/27 BEAM/15.2.3 Elixir/1.18.3 http_fetch/0.4.3`
+  - Includes OS information, system architecture, OTP version, BEAM version, Elixir version, and library version
+  - Uses dynamic version detection via `Application.spec(:http_fetch, :vsn)`
+  - Preserves custom `User-Agent` headers when provided
+- Added `HTTP.Headers.user_agent/0` method to access the default User-Agent string
+
+### Changed
+- Enhanced User-Agent string to include system architecture information
+- Refactored User-Agent generation for consistency across the codebase
+- Updated default headers handling to use `set_default/3` for better extensibility
+
 ## [0.4.2] - 2025-08-01
 
 ### Added

README.md

@@ -133,6 +133,29 @@ binary_data = response.body
 :ok = HTTP.Response.write_to(response, "/tmp/large-file.zip")
 ```
 
+### HTTP.Headers
+Handle HTTP headers with utilities for parsing, normalizing, and manipulating headers.
+
+```elixir
+# Create headers
+headers = HTTP.Headers.new([{"Content-Type", "application/json"}])
+
+# Get header value
+type = HTTP.Headers.get(headers, "content-type")
+
+# Set header
+headers = HTTP.Headers.set(headers, "Authorization", "Bearer token")
+
+# Set header only if not already present
+headers = HTTP.Headers.set_default(headers, "User-Agent", "CustomAgent/1.0")
+
+# Access default user agent string
+default_ua = HTTP.Headers.user_agent()
+
+# Parse Content-Type
+{media_type, params} = HTTP.Headers.parse_content_type("application/json; charset=utf-8")
+```
+
 ### HTTP.Request
 Request configuration struct.
 

mix.exs

@@ -1,7 +1,7 @@
 defmodule HttpFetch.MixProject do
   use Mix.Project
 
-  @version "0.4.2"
+  @version "0.4.3"
   @source_url "https://github.com/gsmlg-dev/http_fetch"
 
   def project do