http: Implement HTTPHeaders class

see:
https://www.rfc-editor.org/rfc/rfc2616#section-4.2
https://www.rfc-editor.org/rfc/rfc7231#section-5
https://www.rfc-editor.org/rfc/rfc7231#section-7
https://httpwg.org/specs/rfc9111.html#header.field.definitions

src/httpserver.cpp

@@ -781,3 +781,69 @@ void UnregisterHTTPHandler(const std::string &prefix, bool exactMatch)
         pathHandlers.erase(i);
     }
 }
+
+
+namespace http_bitcoin {
+std::optional<std::string> HTTPHeaders::Find(const std::string key) const
+{
+    const auto it = m_map.find(key);
+    if (it == m_map.end()) return std::nullopt;
+    return it->second;
+}
+
+void HTTPHeaders::Write(const std::string key, const std::string value)
+{
+    // If present, append value to list
+    const auto existing_value = Find(key);
+    if (existing_value) {
+        m_map[key] = existing_value.value() + ", " + value;
+    } else {
+        m_map[key] = value;
+    }
+}
+
+void HTTPHeaders::Remove(const std::string key)
+{
+    m_map.erase(key);
+}
+
+bool HTTPHeaders::Read(util::LineReader& reader)
+{
+    // Headers https://httpwg.org/specs/rfc9110.html#rfc.section.6.3
+    // A sequence of Field Lines https://httpwg.org/specs/rfc9110.html#rfc.section.5.2
+    do {
+        auto maybe_line = reader.ReadLine();
+        if (!maybe_line) return false;
+        const std::string& line = *maybe_line;
+
+        // An empty line indicates end of the headers section https://www.rfc-editor.org/rfc/rfc2616#section-4
+        if (line.length() == 0) break;
+
+        // Header line must have at least one ":"
+        // keys are not allowed to have delimiters like ":" but values are
+        // https://httpwg.org/specs/rfc9110.html#rfc.section.5.6.2
+        const size_t pos{line.find(':')};
+        if (pos == std::string::npos) throw std::runtime_error("HTTP header missing colon (:)");
+
+        // Whitespace is optional
+        std::string key = util::TrimString(line.substr(0, pos));
+        std::string value = util::TrimString(line.substr(pos + 1));
+        Write(key, value);
+    } while (true);
+
+    return true;
+}
+
+std::string HTTPHeaders::Stringify() const
+{
+    std::string out;
+    for (auto it = m_map.begin(); it != m_map.end(); ++it) {
+        out += it->first + ": " + it->second + "\r\n";
+    }
+
+    // Headers are terminated by an empty line
+    out += "\r\n";
+
+    return out;
+}
+} // namespace http_bitcoin

src/httpserver.h

@@ -6,10 +6,14 @@
 #define BITCOIN_HTTPSERVER_H
 
 #include <functional>
+#include <map>
 #include <optional>
 #include <span>
 #include <string>
 
+#include <util/strencodings.h>
+#include <util/string.h>
+
 namespace util {
 class SignalInterrupt;
 } // namespace util
@@ -197,4 +201,19 @@ private:
     struct event* ev;
 };
 
+namespace http_bitcoin {
+class HTTPHeaders
+{
+public:
+    std::optional<std::string> Find(const std::string key) const;
+    void Write(const std::string key, const std::string value);
+    void Remove(const std::string key);
+    bool Read(util::LineReader& reader);
+    std::string Stringify() const;
+
+private:
+    std::map<std::string, std::string, util::CaseInsensitiveComparator> m_map;
+};
+} // namespace http_bitcoin
+
 #endif // BITCOIN_HTTPSERVER_H

src/test/httpserver_tests.cpp

@@ -4,9 +4,12 @@
 
 #include <httpserver.h>
 #include <test/util/setup_common.h>
+#include <util/strencodings.h>
 
 #include <boost/test/unit_test.hpp>
 
+using http_bitcoin::HTTPHeaders;
+
 BOOST_FIXTURE_TEST_SUITE(httpserver_tests, BasicTestingSetup)
 
 BOOST_AUTO_TEST_CASE(test_query_parameters)
@@ -40,4 +43,55 @@ BOOST_AUTO_TEST_CASE(test_query_parameters)
     uri = "/rest/endpoint/someresource.json&p1=v1&p2=v2%";
     BOOST_CHECK_EXCEPTION(GetQueryParameterFromUri(uri.c_str(), "p1"), std::runtime_error, HasReason("URI parsing failed, it likely contained RFC 3986 invalid characters"));
 }
+
+BOOST_AUTO_TEST_CASE(http_headers_tests)
+{
+    {
+        // Writing response headers
+        HTTPHeaders headers{};
+        BOOST_CHECK(!headers.Find("Cache-Control"));
+        headers.Write("Cache-Control", "no-cache");
+        // Check case-insensitive key matching
+        BOOST_CHECK_EQUAL(headers.Find("Cache-Control").value(), "no-cache");
+        BOOST_CHECK_EQUAL(headers.Find("cache-control").value(), "no-cache");
+        // Additional values are comma-separated and appended
+        headers.Write("Cache-Control", "no-store");
+        BOOST_CHECK_EQUAL(headers.Find("Cache-Control").value(), "no-cache, no-store");
+        // Add a few more
+        headers.Write("Pie", "apple");
+        headers.Write("Sandwich", "ham");
+        headers.Write("Coffee", "black");
+        BOOST_CHECK_EQUAL(headers.Find("Pie").value(), "apple");
+        // Remove
+        headers.Remove("Pie");
+        BOOST_CHECK(!headers.Find("Pie"));
+        // Combine for transmission
+        // std::map sorts alphabetically by key, no order is specified for HTTP
+        BOOST_CHECK_EQUAL(
+            headers.Stringify(),
+            "Cache-Control: no-cache, no-store\r\n"
+            "Coffee: black\r\n"
+            "Sandwich: ham\r\n\r\n");
+    }
+    {
+        // Reading request headers captured from bitcoin-cli
+        std::vector<std::byte> buffer{TryParseHex<std::byte>(
+            "486f73743a203132372e302e302e310d0a436f6e6e656374696f6e3a20636c6f73"
+            "650d0a436f6e74656e742d547970653a206170706c69636174696f6e2f6a736f6e"
+            "0d0a417574686f72697a6174696f6e3a204261736963205831396a623239726157"
+            "5666587a6f7a597a4a6b4e5441784e44466c4d474a69596d56684d5449354f4467"
+            "334e7a49354d544d334e54526d4e54686b4e6a63324f574d775a5459785a6a677a"
+            "4e5467794e7a4577595459314f47526b596a566d5a4751330d0a436f6e74656e74"
+            "2d4c656e6774683a2034360d0a0d0a").value()};
+        util::LineReader reader(buffer, /*max_read=*/1028);
+        HTTPHeaders headers{};
+        headers.Read(reader);
+        BOOST_CHECK_EQUAL(headers.Find("Host").value(), "127.0.0.1");
+        BOOST_CHECK_EQUAL(headers.Find("Connection").value(), "close");
+        BOOST_CHECK_EQUAL(headers.Find("Content-Type").value(), "application/json");
+        BOOST_CHECK_EQUAL(headers.Find("Authorization").value(), "Basic X19jb29raWVfXzozYzJkNTAxNDFlMGJiYmVhMTI5ODg3NzI5MTM3NTRmNThkNjc2OWMwZTYxZjgzNTgyNzEwYTY1OGRkYjVmZGQ3");
+        BOOST_CHECK_EQUAL(headers.Find("Content-Length").value(), "46");
+        BOOST_CHECK(!headers.Find("Pizza"));
+    }
+}
 BOOST_AUTO_TEST_SUITE_END()