http: Implement HTTPResponse class

HTTP Response message:
https://datatracker.ietf.org/doc/html/rfc1945#section-6

Status line (first line of response):
https://datatracker.ietf.org/doc/html/rfc1945#section-6.1

Status code definitions:
https://datatracker.ietf.org/doc/html/rfc1945#section-9

src/httpserver.cpp

@@ -846,4 +846,9 @@ std::string HTTPHeaders::Stringify() const
 
     return out;
 }
+
+std::string HTTPResponse::StringifyHeaders() const
+{
+    return strprintf("HTTP/%d.%d %d %s\r\n%s", m_version_major, m_version_minor, m_status, m_reason, m_headers.Stringify());
+}
 } // namespace http_bitcoin

src/httpserver.h

@@ -11,6 +11,7 @@
 #include <span>
 #include <string>
 
+#include <rpc/protocol.h>
 #include <util/strencodings.h>
 #include <util/string.h>
 
@@ -214,6 +215,20 @@ public:
 private:
     std::map<std::string, std::string, util::CaseInsensitiveComparator> m_map;
 };
+
+class HTTPResponse
+{
+public:
+    int m_version_major;
+    int m_version_minor;
+    HTTPStatusCode m_status;
+    std::string m_reason;
+    HTTPHeaders m_headers;
+    std::vector<std::byte> m_body;
+    bool m_keep_alive{false};
+
+    std::string StringifyHeaders() const;
+};
 } // namespace http_bitcoin
 
 #endif // BITCOIN_HTTPSERVER_H

src/rpc/protocol.h

@@ -20,6 +20,20 @@ enum HTTPStatusCode
     HTTP_SERVICE_UNAVAILABLE   = 503,
 };
 
+// Copied from libevent http.c success_phrases[] and client_error_phrases[]
+// TODO: Should HTTPStatusCode and HTTPReason be moved since they are not RPC protocols?
+const std::map<HTTPStatusCode, std::string> HTTPReason{
+    {HTTP_OK, "OK"},
+    {HTTP_NO_CONTENT, "No Content"},
+    {HTTP_BAD_REQUEST, "Bad Request"},
+    {HTTP_UNAUTHORIZED, "Unauthorized"},
+    {HTTP_FORBIDDEN, "Forbidden"},
+    {HTTP_NOT_FOUND, "Not Found"},
+    {HTTP_BAD_METHOD, "Method Not Allowed"},
+    {HTTP_INTERNAL_SERVER_ERROR, "Internal Server Error"},
+    {HTTP_SERVICE_UNAVAILABLE, "Service Unavailable"},
+};
+
 //! Bitcoin RPC error codes
 enum RPCErrorCode
 {

src/test/httpserver_tests.cpp

@@ -3,12 +3,14 @@
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
 #include <httpserver.h>
+#include <rpc/protocol.h>
 #include <test/util/setup_common.h>
 #include <util/strencodings.h>
 
 #include <boost/test/unit_test.hpp>
 
 using http_bitcoin::HTTPHeaders;
+using http_bitcoin::HTTPResponse;
 
 BOOST_FIXTURE_TEST_SUITE(httpserver_tests, BasicTestingSetup)
 
@@ -94,4 +96,30 @@ BOOST_AUTO_TEST_CASE(http_headers_tests)
         BOOST_CHECK(!headers.Find("Pizza"));
     }
 }
+
+BOOST_AUTO_TEST_CASE(http_response_tests)
+{
+    // Typical HTTP 1.1 response headers
+    HTTPHeaders headers{};
+    headers.Write("Content-Type", "application/json");
+    headers.Write("Date", "Tue, 15 Oct 2024 17:54:12 GMT");
+    headers.Write("Content-Length", "41");
+    // Response points to headers which already exist because some of them
+    // are set before we even know what the response will be.
+    HTTPResponse res;
+    res.m_version_major = 1;
+    res.m_version_minor = 1;
+    res.m_status = HTTP_OK;
+    res.m_reason = HTTPReason.find(res.m_status)->second;
+    res.m_body = StringToBuffer("{\"result\":865793,\"error\":null,\"id\":null\"}");
+    // Everything except the body, which might be raw bytes instead of a string
+    res.m_headers = std::move(headers);
+    BOOST_CHECK_EQUAL(
+        res.StringifyHeaders(),
+        "HTTP/1.1 200 OK\r\n"
+        "Content-Length: 41\r\n"
+        "Content-Type: application/json\r\n"
+        "Date: Tue, 15 Oct 2024 17:54:12 GMT\r\n"
+        "\r\n");
+}
 BOOST_AUTO_TEST_SUITE_END()