Make sure meshlink_strerror() always returns a valid pointer to a string.

[meshlink] / src / meshlink.h

/*
    meshlink.h -- MeshLink API
    Copyright (C) 2014 Guus Sliepen <guus@meshlink.io>

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License along
    with this program; if not, write to the Free Software Foundation, Inc.,
    51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/

#ifndef MESHLINK_H
#define MESHLINK_H

#include <stdint.h>
#include <stdbool.h>
#include <stddef.h>
#include <unistd.h>

#ifdef __cplusplus
extern "C" {
#endif

/// The length in bytes of a signature made with meshlink_sign()
#define MESHLINK_SIGLEN  (64)

/// A handle for an instance of MeshLink.
typedef struct meshlink_handle meshlink_handle_t;

/// A handle for a MeshLink node.
typedef struct meshlink_node meshlink_node_t;

/// A handle for a MeshLink channel.
typedef struct meshlink_channel meshlink_channel_t;

/// Code of most recent error encountered.
typedef enum {
        MESHLINK_OK,     ///< Everything is fine
        MESHLINK_ENOMEM, ///< Out of memory
        MESHLINK_ENOENT, ///< Node is not known
} meshlink_errno_t;

/// A variable holding the last encountered error from MeshLink.
extern __thread meshlink_errno_t meshlink_errno;

#ifndef MESHLINK_INTERNAL_H

struct meshlink_handle {
};

struct meshlink_node {
        const char *name; ///< Textual name of this node.
        void *priv;       ///< Private pointer which the application can set at will.
};

struct meshlink_channel {
};

#endif // MESHLINK_INTERNAL_H

/// Get the text for the given MeshLink error code.
/** This function returns a pointer to the string containing the description of the given error code.
 *
 *  @param err      An error code returned by MeshLink.
 *
 *  @return         A pointer to a string containing the description of the error code.
 *                  This function will always return a valid pointer, even if an invalid error code has been passed.
 */
extern const char *meshlink_strerror(meshlink_errno_t err);

/// Open or create a MeshLink instance.
/** This function opens or creates a MeshLink instance.
 *  The state is stored in the configuration directory passed in the variable @a confbase @a.
 *  If the configuration directory does not exist yet, for example when it is the first time
 *  this instance is opened, the configuration directory will be automatically created and initialized.
 *  However, the parent directory should already exist, otherwise an error will be returned.
 *
 *  The name given should be a unique identifier for this instance.
 *
 *  This function returns a pointer to a struct meshlink_handle that will be allocated by MeshLink.
 *  When the application does no longer need to use this handle, it must call meshlink_close() to
 *  free its resources.
 *
 *  This function does not start any network I/O yet. The application should
 *  first set callbacks, and then call meshlink_start().
 *
 *  @param confbase The directory in which MeshLink will store its configuration files.
 *                  After the function returns, the application is free to overwrite or free @a confbase @a.
 *  @param name     The name which this instance of the application will use in the mesh.
 *                  After the function returns, the application is free to overwrite or free @a name @a.
 *
 *  @return         A pointer to a meshlink_handle_t which represents this instance of MeshLink, or NULL in case of an error.
 *                  The pointer is valid until meshlink_close() is called.
 */
extern meshlink_handle_t *meshlink_open(const char *confbase, const char *name);

/// Start MeshLink.
/** This function causes MeshLink to open network sockets, make outgoing connections, and
 *  create a new thread, which will handle all network I/O.
 *
 *  @param mesh     A handle which represents an instance of MeshLink.
 *
 *  @return         This function will return true if MeshLink has succesfully started its thread, false otherwise.
 */
extern bool meshlink_start(meshlink_handle_t *mesh);

/// Stop MeshLink.
/** This function causes MeshLink to disconnect from all other nodes,
 *  close all sockets, and shut down its own thread.
 *
 *  @param mesh     A handle which represents an instance of MeshLink.
 */
extern void meshlink_stop(meshlink_handle_t *mesh);

/// Close the MeshLink handle.
/** This function calls meshlink_stop() if necessary,
 *  and frees the struct meshlink_handle and all associacted memory allocated by MeshLink.
 *  Afterwards, the handle and any pointers to a struct meshlink_node or struct meshlink_channel are invalid.
 *
 *  @param mesh     A handle which represents an instance of MeshLink.
 */
extern void meshlink_close(meshlink_handle_t *mesh);

/// A callback for receiving data from the mesh.
/** @param mesh      A handle which represents an instance of MeshLink.
 *  @param source    A pointer to a meshlink_node_t describing the source of the data.
 *  @param data      A pointer to a buffer containing the data sent by the source.
 *                   The pointer is only valid during the lifetime of the callback.
 *                   The callback should mempcy() the data if it needs to be available outside the callback.
 *  @param len       The length of the received data.
 */
typedef void (*meshlink_receive_cb_t)(meshlink_handle_t *mesh, meshlink_node_t *source, const void *data, size_t len);

/// Set the receive callback.
/** This functions sets the callback that is called whenever another node sends data to the local node.
 *  The callback is run in MeshLink's own thread.
 *  It is therefore important that the callback uses apprioriate methods (queues, pipes, locking, etc.)
 *  to hand the data over to the application's thread.
 *  The callback should also not block itself and return as quickly as possible.
 *
 *  @param mesh      A handle which represents an instance of MeshLink.
 *  @param cb        A pointer to the function which will be called when another node sends data to the local node.
 *                   If a NULL pointer is given, the callback will be disabled.
 */
extern void meshlink_set_receive_cb(meshlink_handle_t *mesh, meshlink_receive_cb_t cb);

/// A callback reporting node status changes.
/** @param mesh       A handle which represents an instance of MeshLink.
 *  @param node       A pointer to a meshlink_node_t describing the node whose status changed.
 *  @param reachable  True if the node is reachable, false otherwise.
 */
typedef void (*meshlink_node_status_cb_t)(meshlink_handle_t *mesh, meshlink_node_t *node, bool reachable);

/// Set the node status callback.
/** This functions sets the callback that is called whenever another node's status changed.
 *  The callback is run in MeshLink's own thread.
 *  It is therefore important that the callback uses apprioriate methods (queues, pipes, locking, etc.)
 *  to hand the data over to the application's thread.
 *  The callback should also not block itself and return as quickly as possible.
 *
 *  @param mesh      A handle which represents an instance of MeshLink.
 *  @param cb        A pointer to the function which will be called when another node's status changes.
 *                   If a NULL pointer is given, the callback will be disabled.
 */
extern void meshlink_set_node_status_cb(meshlink_handle_t *mesh, meshlink_node_status_cb_t cb);

/// Severity of log messages generated by MeshLink.
typedef enum {
        MESHLINK_DEBUG,    ///< Internal debugging messages. Only useful during application development.
        MESHLINK_INFO,     ///< Informational messages.
        MESHLINK_WARNING,  ///< Warnings which might indicate problems, but which are not real errors.
        MESHLINK_ERROR,    ///< Errors which hamper correct functioning of MeshLink, without causing it to fail completely.
        MESHLINK_CRITICAL, ///< Critical errors which cause MeshLink to fail completely.
} meshlink_log_level_t;

/// A callback for receiving log messages generated by MeshLink.
/** @param mesh      A handle which represents an instance of MeshLink.
 *  @param level     An enum describing the severity level of the message.
 *  @param text      A pointer to a string containing the textual log message.
 *                   This pointer is only valid for the duration of the callback.
 *                   The application should strdup() the text if it has to be available outside the callback.
 */
typedef void (*meshlink_log_cb_t)(meshlink_handle_t *mesh, meshlink_log_level_t level, const char *text);

/// Set the log callback.
/** This functions sets the callback that is called whenever MeshLink has some information to log.
 *  The callback is run in MeshLink's own thread.
 *  It is important that the callback uses apprioriate methods (queues, pipes, locking, etc.)
 *  to hand the data over to the application's thread.
 *  The callback should also not block itself and return as quickly as possible.
 *
 *  @param mesh      A handle which represents an instance of MeshLink.
 *  @param level     An enum describing the minimum severity level. Debugging information with a lower level will not trigger the callback.
 *  @param cb        A pointer to the function which will be called when another node sends data to the local node.
 *                   If a NULL pointer is given, the callback will be disabled.
 */
extern void meshlink_set_log_cb(meshlink_handle_t *mesh, meshlink_log_level_t level, meshlink_log_cb_t cb);

/// Send data to another node.
/** This functions sends one packet of data to another node in the mesh.
 *  The packet is sent using UDP semantics, which means that
 *  the packet is sent as one unit and is received as one unit,
 *  and that there is no guarantee that the packet will arrive at the destination.
 *  The application should take care of getting an acknowledgement and retransmission if necessary.
 *
 *  @param mesh         A handle which represents an instance of MeshLink.
 *  @param destination  A pointer to a meshlink_node_t describing the destination for the data.
 *  @param data         A pointer to a buffer containing the data to be sent to the source.
 *                      After meshlink_send() returns, the application is free to overwrite or free this buffer.
 *  @param len          The length of the data.
 *  @return             This function will return true if MeshLink has queued the message for transmission, and false otherwise.
 *                      A return value of true does not guarantee that the message will actually arrive at the destination.
 */
extern bool meshlink_send(meshlink_handle_t *mesh, meshlink_node_t *destination, const void *data, unsigned int len);

/// Get a handle for a specific node.
/** This function returns a handle for the node with the given name.
 *
 *  @param mesh         A handle which represents an instance of MeshLink.
 *  @param name         The name of the node for which a handle is requested.
 *                      After this function returns, the application is free to overwrite or free @a name @a.
 *
 *  @return             A pointer to a meshlink_node_t which represents the requested node,
 *                      or NULL if the requested node does not exist.
 *                      The pointer is guaranteed to be valid until meshlink_close() is called.
 */
extern meshlink_node_t *meshlink_get_node(meshlink_handle_t *mesh, const char *name);

/// Get a list of all nodes.
/** This function returns a list with handles for all known nodes.
 *
 *  @param mesh         A handle which represents an instance of MeshLink.
 *  @param nodes        A pointer to an array of pointers to meshlink_node_t, which should be allocated by the application.
 *                      The pointers are valid until meshlink_close() is called.
 *  @param nmemb        The maximum number of pointers that can be stored in the nodes array.
 *
 *  @return             The number of known nodes, or -1 in case of an error.
 *                      The returned number of nodes can be larger than nmemb, in which case not all nodes were stored in the nodes array.
 */
extern ssize_t meshlink_get_all_nodes(meshlink_handle_t *mesh, meshlink_node_t **nodes, size_t nmemb);

/// Sign data using the local node's MeshLink key.
/** This function signs data using the local node's MeshLink key.
 *  The generated signature can be securely verified by other nodes.
 *
 *  @param mesh         A handle which represents an instance of MeshLink.
 *  @param data         A pointer to a buffer containing the data to be signed.
 *  @param len          The length of the data to be signed.
 *  @param signature    A pointer to a buffer where the signature will be stored.
 *                      The buffer must be allocated by the application, and should be at least MESHLINK_SIGLEN bytes big.
 *  @param siglen       The size of the signature buffer. Will be changed after the call to match the size of the signature itself.
 *
 *  @return             This function returns true if the signature was correctly generated, false otherwise.
 */
extern bool meshlink_sign(meshlink_handle_t *mesh, const void *data, size_t len, void *signature, size_t *siglen);

/// Verify the signature generated by another node of a piece of data.
/** This function verifies the signature that another node generated for a piece of data.
 *
 *  @param mesh         A handle which represents an instance of MeshLink.
 *  @param source       A pointer to a meshlink_node_t describing the source of the signature.
 *  @param data         A pointer to a buffer containing the data to be verified.
 *  @param len          The length of the data to be verified.
 *  @param signature    A pointer to a buffer where the signature will be stored.
 *  @param siglen       A pointer to a variable holding the size of the signature buffer.
 *                      The contents of the variable will be changed by meshlink_sign() to reflect the actual size of the signature.
 *
 *  @return             This function returns true if the signature is valid, false otherwise.
 */
extern bool meshlink_verify(meshlink_handle_t *mesh, meshlink_node_t *source, const void *data, size_t len, const void *signature, size_t siglen);

/// Add an Address for the local node.
/** This function adds an Address for the local node, which will be used for invitation URLs.
 *
 *  @param mesh         A handle which represents an instance of MeshLink.
 *  @param address      A string containing the address, which can be either in numeric format or a hostname.
 *
 *  @return             This function returns true if the address was added, false otherwise.
 */
extern bool meshlink_add_address(meshlink_handle_t *mesh, const char *address);

/// Invite another node into the mesh.
/** This function generates an invitation that can be used by another node to join the same mesh as the local node.
 *  The generated invitation is a string containing a URL.
 *  This URL should be passed by the application to the invitee in a way that no eavesdroppers can see the URL.
 *  The URL can only be used once, after the user has joined the mesh the URL is no longer valid.
 *
 *  @param mesh         A handle which represents an instance of MeshLink.
 *  @param name         The name that the invitee will use in the mesh.
 *                      After this function returns, the application is free to overwrite or free @a name @a.
 *
 *  @return             This function returns a string that contains the invitation URL, or NULL in case of an error.
 *                      The application should call free() after it has finished using the URL.
 */
extern char *meshlink_invite(meshlink_handle_t *mesh, const char *name);

/// Use an invitation to join a mesh.
/** This function allows the local node to join an existing mesh using an invitation URL generated by another node.
 *  An invitation can only be used if the local node has never connected to other nodes before.
 *  After a succesfully accepted invitation, the name of the local node may have changed.
 *
 *  @param mesh         A handle which represents an instance of MeshLink.
 *  @param invitation   A string containing the invitation URL.
 *                      After this function returns, the application is free to overwrite or free @a invitation @a.
 *
 *  @return             This function returns true if the local node joined the mesh it was invited to, false otherwise.
 */
extern bool meshlink_join(meshlink_handle_t *mesh, const char *invitation);

/// Export the local node's key and addresses.
/** This function generates a string that contains the local node's public key and one or more IP addresses.
 *  The application can pass it in some way to another node, which can then import it,
 *  granting the local node access to the other node's mesh.
 *
 *  @param mesh         A handle which represents an instance of MeshLink.
 *
 *  @return             This function returns a string that contains the exported key and addresses, or NULL in case of an error.
 *                      The application should call free() after it has finished using this string.
 */
extern char *meshlink_export(meshlink_handle_t *mesh);

/// Import another node's key and addresses.
/** This function accepts a string containing the exported public key and addresses of another node.
 *  By importing this data, the local node grants the other node access to its mesh.
 *
 *  @param mesh         A handle which represents an instance of MeshLink.
 *  @param data         A string containing the other node's exported key and addresses.
 *                      After this function returns, the application is free to overwrite or free @a data @a.
 *
 *  @return             This function returns true if the data was valid and the other node has been granted access to the mesh, false otherwise.
 */
extern bool meshlink_import(meshlink_handle_t *mesh, const char *data);

/// Blacklist a node from the mesh.
/** This function causes the local node to blacklist another node.
 *  The local node will drop any existing connections to that node,
 *  and will not send data to it nor accept any data received from it any more.
 *
 *  @param mesh         A handle which represents an instance of MeshLink.
 *  @param node         A pointer to a meshlink_node_t describing the node to be blacklisted.
 */
extern void meshlink_blacklist(meshlink_handle_t *mesh, meshlink_node_t *node);

/// A callback for accepting incoming channels.
/** This function is called whenever a remote node wants to open a channel to the local node.
 *  The application then has to decide whether to accept or reject this channel.
 *
 *  @param mesh         A handle which represents an instance of MeshLink.
 *  @param channel      A handle for the incoming channel.
 *                      If the application accepts the incoming channel by returning true,
 *                      then this handle is valid until meshlink_channel_close() is called on it.
 *                      If the application rejects the incoming channel by returning false,
 *                      then this handle is invalid after the callback returns
 *                      (the callback does not need to call meshlink_channel_close() itself in this case).
 *  @param node         The node from which this channel is being initiated.
 *                      The pointer is guaranteed to be valid until meshlink_close() is called.
 *  @param port         The port number the peer wishes to connect to.
 *  @param data         A pointer to a buffer containing data already received. (Not yet used.)
 *                      The pointer is only valid during the lifetime of the callback.
 *                      The callback should mempcy() the data if it needs to be available outside the callback.
 *  @param len          The length of the data. (Not yet used.)
 *
 *  @return             This function should return true if the application accepts the incoming channel, false otherwise.
 *                      If returning false, the channel is invalid and may not be used anymore.
 */
typedef bool (*meshlink_channel_accept_cb_t)(meshlink_handle_t *mesh, meshlink_channel_t *channel, meshlink_node_t *node, uint16_t port, const void *data, size_t len);

/// A callback for receiving data from a channel.
/** This function is called whenever a remote node wants to open a channel to the local node.
 *  The application then has to decide whether to accept or reject this channel.
 *
 *  @param mesh         A handle which represents an instance of MeshLink.
 *  @param channel      A handle for the channel.
 *  @param data         A pointer to a buffer containing data sent by the source.
 *                      The pointer is only valid during the lifetime of the callback.
 *                      The callback should mempcy() the data if it needs to be available outside the callback.
 *  @param len          The length of the data.
 */
typedef void (*meshlink_channel_receive_cb_t)(meshlink_handle_t *mesh, meshlink_channel_t *channel, const void *data, size_t len);

/// Set the accept callback.
/** This functions sets the callback that is called whenever another node sends data to the local node.
 *  The callback is run in MeshLink's own thread.
 *  It is therefore important that the callback uses apprioriate methods (queues, pipes, locking, etc.)
 *  to hand the data over to the application's thread.
 *  The callback should also not block itself and return as quickly as possible.
 *
 *  If no accept callback is set, incoming channels are rejected.
 *
 *  @param mesh      A handle which represents an instance of MeshLink.
 *  @param cb        A pointer to the function which will be called when another node sends data to the local node.
 *                   If a NULL pointer is given, the callback will be disabled.
 */
extern void meshlink_set_channel_accept_cb(meshlink_handle_t *mesh, meshlink_channel_accept_cb_t cb);

/// Set the receive callback.
/** This functions sets the callback that is called whenever another node sends data to the local node.
 *  The callback is run in MeshLink's own thread.
 *  It is therefore important that the callback uses apprioriate methods (queues, pipes, locking, etc.)
 *  to hand the data over to the application's thread.
 *  The callback should also not block itself and return as quickly as possible.
 *
 *  @param mesh      A handle which represents an instance of MeshLink.
 *  @param channel   A handle for the channel.
 *  @param cb        A pointer to the function which will be called when another node sends data to the local node.
 *                   If a NULL pointer is given, the callback will be disabled.
 */
extern void meshlink_set_channel_receive_cb(meshlink_handle_t *mesh, meshlink_channel_t *channel, meshlink_channel_receive_cb_t cb);

/// Open a reliable stream channel to another node.
/** This function is called whenever a remote node wants to open a channel to the local node.
 *  The application then has to decide whether to accept or reject this channel.
 *
 *  This function returns a pointer to a struct meshlink_channel that will be allocated by MeshLink.
 *  When the application does no longer need to use this channel, it must call meshlink_close()
 *  to free its resources.
 *
 *  @param mesh         A handle which represents an instance of MeshLink.
 *  @param node         The node to which this channel is being initiated.
 *  @param port         The port number the peer wishes to connect to.
 *  @param cb           A pointer to the function which will be called when the remote node sends data to the local node.
 *  @param data         A pointer to a buffer containing data to already queue for sending.
 *                      After meshlink_send() returns, the application is free to overwrite or free this buffer.
 *  @param len          The length of the data.
 *
 *  @return             A handle for the channel, or NULL in case of an error.
 *                      The handle is valid until meshlink_channel_close() is called.
 */
extern meshlink_channel_t *meshlink_channel_open(meshlink_handle_t *mesh, meshlink_node_t *node, uint16_t port, meshlink_channel_receive_cb_t cb, const void *data, size_t len);

/// Partially close a reliable stream channel.
/** This shuts down the read or write side of a channel, or both, without closing the handle.
 *  It can be used to inform the remote node that the local node has finished sending all data on the channel,
 *  but still allows waiting for incoming data from the remote node.
 *
 *  Shutting down the receive direction is also possible, and is equivalent to setting the receive callback to NULL.
 *
 *  @param mesh         A handle which represents an instance of MeshLink.
 *  @param channel      A handle for the channel.
 *  @param direction    Must be one of SHUT_RD, SHUT_WR or SHUT_RDWR.
 */
extern void meshlink_channel_shutdown(meshlink_handle_t *mesh, meshlink_channel_t *channel, int direction);

/// Close a reliable stream channel.
/** This informs the remote node that the local node has finished sending all data on the channel.
 *  It also causes the local node to stop accepting incoming data from the remote node.
 *  It will free the struct meshlink_channel and all associated resources.
 *  Afterwards, the channel handle is invalid and must not be used any more.
 *
 *  @param mesh         A handle which represents an instance of MeshLink.
 *  @param channel      A handle for the channel.
 */
extern void meshlink_channel_close(meshlink_handle_t *mesh, meshlink_channel_t *channel);

/// Transmit data on a channel
/** This queues data to send to the remote node.
 *
 *  @param mesh         A handle which represents an instance of MeshLink.
 *  @param channel      A handle for the channel.
 *  @param data         A pointer to a buffer containing data sent by the source.
 *                      After meshlink_send() returns, the application is free to overwrite or free this buffer.
 *  @param len          The length of the data.
 *
 *  @return             The amount of data that was queued, which can be less than len, or a negative value in case of an error.
 */
extern ssize_t meshlink_channel_send(meshlink_handle_t *mesh, meshlink_channel_t *channel, const void *data, size_t len);

#ifdef __cplusplus
}
#endif

#endif // MESHLINK_H