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

@@ -28,6 +28,7 @@
 #include <optional>
 #include <span>
 #include <string>
+#include <string_view>
 #include <thread>
 #include <unordered_map>
 #include <vector>
@@ -714,3 +715,97 @@ void UnregisterHTTPHandler(const std::string &prefix, bool exactMatch)
         pathHandlers.erase(i);
     }
 }
+
+namespace http_bitcoin {
+
+std::optional<std::string> HTTPHeaders::FindFirst(const std::string_view key) const
+{
+    for (const auto& item : m_headers) {
+        if (CaseInsensitiveEqual(key, item.first)) {
+            return item.second;
+        }
+    }
+    return std::nullopt;
+}
+
+std::vector<std::string_view> HTTPHeaders::FindAll(const std::string_view key) const
+{
+    std::vector<std::string_view> ret;
+    for (const auto& item : m_headers) {
+        if (CaseInsensitiveEqual(key, item.first)) {
+            ret.push_back(item.second);
+        }
+    }
+    return ret;
+}
+
+void HTTPHeaders::Write(std::string&& key, std::string&& value)
+{
+    m_headers.emplace_back(std::move(key), std::move(value));
+}
+
+void HTTPHeaders::RemoveAll(std::string_view key)
+{
+    auto moved = std::ranges::remove_if(m_headers, [key] (auto& pair) {
+        return CaseInsensitiveEqual(key, pair.first);
+    });
+    m_headers.erase(moved.begin(), moved.end());
+}
+
+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
+    while (auto maybe_line = reader.ReadLine()) {
+        if (reader.Consumed() > MAX_HEADERS_SIZE) throw std::runtime_error("HTTP headers exceed size limit");
+
+        const std::string_view& line = *maybe_line;
+
+        // An empty line indicates end of the headers section https://www.rfc-editor.org/rfc/rfc2616#section-4
+        if (line.empty()) return true;
+
+        // "Field values containing CR, LF, or NUL characters are invalid and dangerous"
+        // https://httpwg.org/specs/rfc9110.html#rfc.section.5.5
+        // A sender MUST NOT generate a bare CR (a CR character not immediately followed by LF)
+        // within any protocol elements other than the content.
+        // A recipient of such a bare CR MUST consider that element to be invalid...
+        // https://httpwg.org/specs/rfc9112.html#rfc.section.2.2
+        if (line.find_first_of("\r\n\0", 0, 3) != std::string_view::npos) throw std::runtime_error("Header contains invalid character");
+
+        // 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_view::npos) throw std::runtime_error("HTTP header missing colon (:)");
+
+        // Whitespace is strictly not allowed in the field-name (key)
+        // https://www.rfc-editor.org/rfc/rfc9110.html#section-5.6.2
+        std::string_view key = line.substr(0, pos);
+        if (key.find_first_of(" \t\n\r\f\v") != std::string_view::npos) throw std::runtime_error("Invalid header field-name contains whitespace");
+        // Whitespace is optional in the value and can be trimmed
+        std::string value = util::TrimString(std::string_view(line).substr(pos + 1));
+
+        // Header keys are Field Names: https://httpwg.org/specs/rfc9110.html#fields.names
+        // which consist of "tokens": https://httpwg.org/specs/rfc9110.html#rfc.section.5.6.2
+        // that can not be empty.
+        if (key.empty()) throw std::runtime_error("Empty HTTP header name");
+
+        Write(std::string(key), std::move(value));
+    }
+
+    return false;
+}
+
+std::string HTTPHeaders::Stringify() const
+{
+    std::string out;
+    for (const auto& [key, value] : m_headers) {
+        out += key + ": " + value + "\r\n";
+    }
+
+    // Headers are terminated by an empty line
+    out += "\r\n";
+
+    return out;
+}
+} // namespace http_bitcoin