//
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// Copyright 2020 Staysail Systems, Inc. <info@staysail.tech>
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//
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// This software is supplied under the terms of the MIT License, a
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// copy of which should be located in the distribution where this
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// file was obtained (LICENSE.txt). A copy of the license may also be
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// found online at https://opensource.org/licenses/MIT.
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//
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// This file is used to enable external TLS "engines", so
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// that third party TLS libraries can be plugged in
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#ifndef NNG_SUPPLEMENTAL_TLS_ENGINE_H
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#define NNG_SUPPLEMENTAL_TLS_ENGINE_H
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#include <nng/supplemental/tls/tls.h>
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// Locking theory statement for TLS engines. The engine is assumed
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// operate only from the context of threads called by the common
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// framework. That is to say, the callbacks made by the engine
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// should always be on a thread that has context from the framework
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// calling into the engine. This means that the lower level send
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// and receive functions can assume that they have lock ownership
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// inherited on the stack.
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// nng_tls_engine_conn represents the engine-specific private
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// state for a TLS connection. It is provided here for type
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// safety. Engine implementations should provide the structure
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// definition locally.
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typedef struct nng_tls_engine_conn nng_tls_engine_conn;
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// nng_tls_engine_config represents the engine-specific private
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// state for the TLS configuration. It is provided here for type
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// safety. Engine implementations should provide the structure
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// definition locally.
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typedef struct nng_tls_engine_config nng_tls_engine_config;
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typedef struct nng_tls_engine_conn_ops_s {
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// size is the size of the engine's per-connection state.
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// The framework will allocate this on behalf of the engine.
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// Typically this will be sizeof (struct nng_tls_engine_conn).
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size_t size;
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// init is used to initialize a connection object.
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// The passed in connection state will be aligned naturally,
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// and zeroed. On success this returns 0, else an NNG error code.
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int (*init)(nng_tls_engine_conn *, void *, nng_tls_engine_config *);
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// fini destroys a connection object. This will
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// be called only when no other external use of the connection
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// object exists, and only on fully initialed connection objects.
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void (*fini)(nng_tls_engine_conn *);
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// close closes the connection object, but should not
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// deallocate any memory. It may also issue a TLS close-notify.
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void (*close)(nng_tls_engine_conn *);
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// handshake attempts to complete the SSL handshake phase.
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// It returns zero on success, or an error if one occurred.
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// The value NNG_EAGAIN should be returned if underlying I/O
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// is required to be completed first. The framework will
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// ensure that the handshake completes before sending any data
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// down.
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int (*handshake)(nng_tls_engine_conn *);
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// recv attempts to read data (decrypted) from the connection.
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// It returns 0 on success, otherwise an error. The implementation
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// should return NNG_EAGAIN if I/O to the underlying stream is
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// required to complete the operation. On success, the count
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// is updated to reflect the number of bytes actually received.
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int (*recv)(nng_tls_engine_conn *, uint8_t *, size_t *);
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// send attempts to write data to the underlying connection.
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// It returns zero on success, otherwise an error. The implementation
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// should return NNG_EAGAIN if I/O to the underlying stream is
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// required to complete the operation. On success, the count
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// is updated to reflect the number of bytes actually sent.
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int (*send)(nng_tls_engine_conn *, const uint8_t *, size_t *);
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// verified returns true if the connection is fully
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// TLS verified, false otherwise.
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bool (*verified)(nng_tls_engine_conn *);
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} nng_tls_engine_conn_ops;
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typedef struct nng_tls_engine_config_ops_s {
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// size is the size of the engine's configuration object.
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// The framework will allocate this on behalf of the engine.
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// Typically this will be sizeof (struct nng_tls_engine_config).
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size_t size;
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// init prepares the configuration object object.
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// The mode indicates whether the object should be
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// initialized for use as a TLS server or client.
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// The config passed in will be aligned on a 64-bit boundary,
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// and will be initialized to zero. On success this returns
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// 0, else an NNG error code.
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int (*init)(nng_tls_engine_config *, nng_tls_mode);
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// fini is used to tear down the configuration object.
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// This will only be called on objects that have been properly
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// initialized with nte_config_init.
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void (*fini)(nng_tls_engine_config *);
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// server is used to set the server name. This can be used in SNI,
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// and will also be used on the client to validate the identity.
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// If this is not set, then no verification will be performed.
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int (*server)(nng_tls_engine_config *, const char *);
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// auth is used to configure the authentication mode. Values:
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// NNG_AUTH_MODE_NONE
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// No validation of the peer is performed. Public facing
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// servers often use this.
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// NNG_AUTH_MODE_OPTIONAL
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// The peer's identity is validated if a certificate is presented.
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// This is typically useful on servers.
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// NNG_AUTH_MODE_REQUIRED
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// The peer's certificate must be present and is verified.
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// This is standard for the client, and on servers it is used
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// when client (mutual) authentication is needed.
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int (*auth)(nng_tls_engine_config *, nng_tls_auth_mode);
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// ca_chain sets the configuration authorities that will be
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// used to validate peers. An optional CRL is supplied as well.
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// Both values are C strings (NUL terminated) containing
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// PEM data. There may be multiple PEM blocks. The
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// CRL may be NULL if not needed.
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int (*ca_chain)(nng_tls_engine_config *, const char *, const char *);
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// own_cert configures our identity -- the certificate containing
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// our public key, our private key (which might be encrypted), and
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// potentially a password used to decrypt the private key.
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// All of these are C strings. The cert may actually be a chain
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// which will be presented to our peer. This function may be
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// called multiple times to register different keys with different
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// parameters on a server. (For example, once for RSA parameters,
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// and again later with EC parameters.) The certificate and the
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// private key may be presented in the same file. The implementation
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// is responsible for parsing out the relevant data. If the password
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// is NULL, then the key file should be unencrypted. The supplied
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// password may be ignored if the key is not encrypted. Not all
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// engine implementations need support encryption of the key.
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int (*own_cert)(
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nng_tls_engine_config *, const char *, const char *, const char *);
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// version configures the minimum and maximum TLS versions. The
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// engine should default to supporting TLS1.0 through 1.2, and
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// optionally 1.3 if it can. The engine should restrict the
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// the requested range to what it can support -- if no version
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// within the range is supported (such as if NNG_TLS_1_3 is
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// specified for both min and max, and the engine lacks support
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// for v1.3, then NNG_ENOTSUP should be returned.
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int (*version)(
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nng_tls_engine_config *, nng_tls_version, nng_tls_version);
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} nng_tls_engine_config_ops;
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typedef enum nng_tls_engine_version_e {
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NNG_TLS_ENGINE_V0 = 0,
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NNG_TLS_ENGINE_V1 = 1,
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NNG_TLS_ENGINE_VERSION = NNG_TLS_ENGINE_V1,
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} nng_tls_engine_version;
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typedef struct nng_tls_engine_s {
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// _version is the engine version. This for now must
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// be NNG_TLS_ENGINE_VERSION. If the version does not match
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// then registration of the engine will fail.
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nng_tls_engine_version version;
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// config_ops is the operations for TLS configuration objects.
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nng_tls_engine_config_ops *config_ops;
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// conn_ops is the operations for TLS connections (stream-oriented).
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nng_tls_engine_conn_ops *conn_ops;
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// name contains the name of the engine, for example "wolfSSL".
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// It is acceptable to append a version number as well.
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const char *name;
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// description contains a human readable description. This can
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// supply information about the backing library, for example
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// "mbed TLS v2.7"
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const char *description;
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// fips_mode is true if the engine is in FIPS mode.
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// It is expected that this will be enabled either at compile
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// time, or via environment variables at engine initialization.
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// FIPS mode cannot be changed once the engine is registered.
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bool fips_mode;
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} nng_tls_engine;
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NNG_DECL int nng_tls_engine_register(const nng_tls_engine *);
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// nng_tls_engine_send is called by the engine to send data over the
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// underlying connection. It returns zero on success, NNG_EAGAIN if
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// the operation can't be completed yet (the transport is busy and cannot
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// accept more data yet), or some other error. On success the count is
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// updated with the number of bytes actually sent. The first argument
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// is the context structure passed in when starting the engine.
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NNG_DECL int nng_tls_engine_send(void *, const uint8_t *, size_t *);
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// nng_tls_engine_recv is called byu the engine to receive data over
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// the underlying connection. It returns zero on success, NNG_EAGAIN
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// if the operation can't be completed yet (there is no data available
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// for reading), or some other error. On success the count is updated
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// with the number of bytes actually received.
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NNG_DECL int nng_tls_engine_recv(void *, uint8_t *, size_t *);
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#endif // NNG_SUPPLEMENTAL_TLS_ENGINE_H
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