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c0f69548be
Add new `libssh2_session_callback_set2()` API that deprecates `libssh2_session_callback_set()`. The new implementation offers the same functionality, but accepts and returns a generic function pointer (of type `libssh2_cb_generic *`), as opposed to the old function that used data pointers (`void *`). The new solution thus avoids data to function (and vice versa) pointer conversions, which has undefined behaviour in standard C. About the name: It seems the `*2` suffix was used in the past for replacement functions for deprecated ones. Let's stick with that. `*_ex` was preferred for new functions that extend existing ones with new features. Closes #1285
140 lines
5.0 KiB
Groff
140 lines
5.0 KiB
Groff
.\" Copyright (C) The libssh2 project and its contributors.
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.\" SPDX-License-Identifier: BSD-3-Clause
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.TH libssh2_session_callback_set2 3 "13 Dec 2023" "libssh2 1.11.1" "libssh2"
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.SH NAME
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libssh2_session_callback_set2 - set a callback function
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.SH SYNOPSIS
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.nf
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#include <libssh2.h>
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libssh2_cb_generic *
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libssh2_session_callback_set2(LIBSSH2_SESSION *session, int cbtype,
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libssh2_cb_generic *callback);
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.fi
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.SH DESCRIPTION
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Sets a custom callback handler for a previously initialized session
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object. Callbacks are triggered by the receipt of special packets at the
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Transport layer. To disable a callback, set it to NULL.
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\fIsession\fP - Session instance as returned by
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.BR libssh2_session_init_ex(3)
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\fIcbtype\fP - Callback type. One of the types listed in Callback Types.
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\fIcallback\fP - Pointer to custom callback function. The prototype for
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this function must match the associated callback declaration macro.
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.SH CALLBACK TYPES
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.IP LIBSSH2_CALLBACK_IGNORE
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Called when a SSH_MSG_IGNORE message is received
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.IP LIBSSH2_CALLBACK_DEBUG
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Called when a SSH_MSG_DEBUG message is received
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.IP LIBSSH2_CALLBACK_DISCONNECT
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Called when a SSH_MSG_DISCONNECT message is received
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.IP LIBSSH2_CALLBACK_MACERROR
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Called when a mismatched MAC has been detected in the transport layer. If the
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function returns 0, the packet will be accepted nonetheless.
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.IP LIBSSH2_CALLBACK_X11
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Called when an X11 connection has been accepted
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.IP LIBSSH2_CALLBACK_SEND
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Called when libssh2 wants to send data on the connection. Can be set to a
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custom function to handle I/O your own way.
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The prototype of the callback:
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.nf
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ssize_t sendcb(libssh2_socket_t sockfd, const void *buffer,
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size_t length, int flags, void **abstract);
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.fi
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\fBsockfd\fP is the socket to write to, \fBbuffer\fP points to the data to
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send, \fBlength\fP is the size of the data, \fBflags\fP is the flags that
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would have been used to a \fIsend()\fP call and \fBabstract\fP is a pointer
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to the abstract pointer set in the \fIlibssh2_session_init_ex(3)\fP call.
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The callback returns the number of bytes sent, or \-1 for error. The special
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return code \fB-EAGAIN\fP can be returned to signal that the send was aborted
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to prevent getting blocked and it needs to be called again.
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.IP LIBSSH2_CALLBACK_RECV
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Called when libssh2 wants to read data from the connection. Can be set to a
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custom function to handle I/O your own way.
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The prototype of the callback:
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.nf
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ssize_t recvcb(libssh2_socket_t sockfd, void *buffer,
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size_t length, int flags, void **abstract);
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.fi
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\fBsockfd\fP is the socket to read from, \fBbuffer\fP where to store received
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data into, \fBlength\fP is the size of the buffer, \fBflags\fP is the flags
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that would have been used to a \fIrecv()\fP call and \fBabstract\fP is a pointer
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to the abstract pointer set in the \fIlibssh2_session_init_ex(3)\fP call.
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The callback returns the number of bytes read, or \-1 for error. The special
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return code \fB-EAGAIN\fP can be returned to signal that the read was aborted
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to prevent getting blocked and it needs to be called again.
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.IP LIBSSH2_CALLBACK_AUTHAGENT
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Called during authentication process to allow the client to connect to the
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ssh-agent and perform any setup, such as configuring the agent or adding keys.
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The prototype of the callback:
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.nf
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void authagent(LIBSSH2_SESSION* session, LIBSSH2_CHANNEL *channel,
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void **abstract);
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.fi
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.IP LIBSSH2_CALLBACK_AUTHAGENT_IDENTITIES
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Not called by libssh2. The client is responsible for calling this method when
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a SSH2_AGENTC_REQUEST_IDENTITIES message has been received.
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The prototype of the callback:
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.nf
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void identities(LIBSSH2_SESSION* session, void *buffer,
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const char *agent_path,
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void **abstract)
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.fi
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\fBbuffer\fP must be filled in by the callback. Different clients may implement
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this differently. For example, one client may pass in an unsigned char ** for
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this parameter, while another may pass in a pointer to a struct.
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Regardless of the type of buffer used, the client will need to send back a list
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of identities in the following format.
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uint32 buffer length
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uint32 number of entries
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entries
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Where each entry in the entries list is of the format:
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string data
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cstring comment
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\fBagent_path\fP The path to a running ssh-agent on the client machine, from
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which identities can be listed.
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.IP LIBSSH2_CALLBACK_AUTHAGENT_SIGN
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Not called by libssh2. The client is responsible for calling this method when
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a SSH2_AGENTC_SIGN_REQUEST message has been received.
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The prototype of the callback:
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.nf
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void sign(LIBSSH2_SESSION* session,
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unsigned char *blob, unsigned int blen,
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const unsigned char *data, unsigned int dlen,
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unsigned char **sig, unsigned int *sig_len,
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const char *agent_path,
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void **abstract);
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.fi
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When interfacing with an ssh-agent installed on the client system, this method
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can call libssh2_agent_sign(3) to perform signing.
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.SH RETURN VALUE
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Pointer to previous callback handler. Returns NULL if no prior callback
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handler was set or the callback type was unknown.
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.SH SEE ALSO
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.BR libssh2_session_init_ex(3)
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.BR libssh2_agent_sign(3)
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