Branches the nghttp2_adapter interface from //net/http2.

PiperOrigin-RevId: 361667825
Change-Id: I94cab47ce471f23eb872a39173efbc9c159eb76b

http2/adapter/http2_protocol.h

diff --git a/http2/adapter/http2_protocol.h b/http2/adapter/http2_protocol.h
new file mode 100644
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+++ b/http2/adapter/http2_protocol.h
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+#ifndef QUICHE_HTTP2_ADAPTER_HTTP2_PROTOCOL_H_
+#define QUICHE_HTTP2_ADAPTER_HTTP2_PROTOCOL_H_
+
+#include <cstdint>
+#include <string>
+#include <utility>
+
+#include "base/integral_types.h"
+#include "absl/base/attributes.h"
+#include "absl/strings/string_view.h"
+
+namespace http2 {
+namespace adapter {
+
+// Represents an HTTP/2 stream ID, consistent with nghttp2.
+using Http2StreamId = int32_t;
+
+// Represents an HTTP/2 SETTINGS parameter as specified in RFC 7540 Section 6.5.
+using Http2SettingsId = uint16_t;
+
+// Represents the payload of an HTTP/2 PING frame.
+using Http2PingId = uint64_t;
+
+// Represents an HTTP/2 header field. A header field is a key-value pair with
+// lowercase keys (as specified in RFC 7540 Section 8.1.2).
+using Header = std::pair<std::string, std::string>;
+
+// Represents an HTTP/2 SETTINGS key-value parameter.
+struct Http2Setting {
+  Http2SettingsId id;
+  uint32_t value;
+};
+
+// The maximum possible stream ID.
+const Http2StreamId kMaxStreamId = 0x7FFFFFFF;
+
+// The stream ID that represents the connection (e.g., for connection-level flow
+// control updates).
+const Http2StreamId kConnectionStreamId = 0;
+
+// The default value for the size of the largest frame payload, according to RFC
+// 7540 Section 6.5.2 (SETTINGS_MAX_FRAME_SIZE).
+const int kDefaultFramePayloadSizeLimit = 16 * 1024;
+
+// The default value for the initial stream flow control window size, according
+// to RFC 7540 Section 6.9.2.
+const int kDefaultInitialStreamWindowSize = 64 * 1024 - 1;
+
+// The pseudo-header fields as specified in RFC 7540 Section 8.1.2.3 (request)
+// and Section 8.1.2.4 (response).
+ABSL_CONST_INIT extern const char kHttp2MethodPseudoHeader[];
+ABSL_CONST_INIT extern const char kHttp2SchemePseudoHeader[];
+ABSL_CONST_INIT extern const char kHttp2AuthorityPseudoHeader[];
+ABSL_CONST_INIT extern const char kHttp2PathPseudoHeader[];
+ABSL_CONST_INIT extern const char kHttp2StatusPseudoHeader[];
+
+// HTTP/2 error codes as specified in RFC 7540 Section 7.
+enum class Http2ErrorCode {
+  NO_ERROR = 0x0,
+  PROTOCOL_ERROR = 0x1,
+  INTERNAL_ERROR = 0x2,
+  FLOW_CONTROL_ERROR = 0x3,
+  SETTINGS_TIMEOUT = 0x4,
+  STREAM_CLOSED = 0x5,
+  FRAME_SIZE_ERROR = 0x6,
+  REFUSED_STREAM = 0x7,
+  CANCEL = 0x8,
+  COMPRESSION_ERROR = 0x9,
+  CONNECT_ERROR = 0xA,
+  ENHANCE_YOUR_CALM = 0xB,
+  INADEQUATE_SECURITY = 0xC,
+  HTTP_1_1_REQUIRED = 0xD,
+  MAX_ERROR_CODE = HTTP_1_1_REQUIRED,
+};
+
+// The SETTINGS parameters defined in RFC 7540 Section 6.5.2. Endpoints may send
+// SETTINGS parameters outside of these definitions as per RFC 7540 Section 5.5.
+// This is explicitly an enum instead of an enum class for ease of implicit
+// conversion to the underlying Http2SettingsId type and use with non-standard
+// extension SETTINGS parameters.
+enum Http2KnownSettingsId : Http2SettingsId {
+  HEADER_TABLE_SIZE = 0x1,
+  MIN_SETTING = HEADER_TABLE_SIZE,
+  ENABLE_PUSH = 0x2,
+  MAX_CONCURRENT_STREAMS = 0x3,
+  INITIAL_WINDOW_SIZE = 0x4,
+  MAX_FRAME_SIZE = 0x5,
+  MAX_HEADER_LIST_SIZE = 0x6,
+  MAX_SETTING = MAX_HEADER_LIST_SIZE
+};
+
+// Returns a human-readable string representation of the given SETTINGS |id| for
+// logging/debugging. Returns "SETTINGS_UNKNOWN" for IDs outside of the RFC 7540
+// Section 6.5.2 definitions.
+absl::string_view Http2SettingsIdToString(uint16_t id);
+
+// Returns a human-readable string representation of the given |error_code| for
+// logging/debugging. Returns "UNKNOWN_ERROR" for errors outside of RFC 7540
+// Section 7 definitions.
+absl::string_view Http2ErrorCodeToString(Http2ErrorCode error_code);
+
+}  // namespace adapter
+}  // namespace http2
+
+#endif  // QUICHE_HTTP2_ADAPTER_HTTP2_PROTOCOL_H_