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+/*
+ * dnstap/dnstap_fstrm.h - Frame Streams protocol for dnstap
+ *
+ * Copyright (c) 2020, NLnet Labs. All rights reserved.
+ *
+ * This software is open source.
+ * 
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 
+ * Redistributions of source code must retain the above copyright notice,
+ * this list of conditions and the following disclaimer.
+ * 
+ * Redistributions in binary form must reproduce the above copyright notice,
+ * this list of conditions and the following disclaimer in the documentation
+ * and/or other materials provided with the distribution.
+ * 
+ * Neither the name of the NLNET LABS nor the names of its contributors may
+ * be used to endorse or promote products derived from this software without
+ * specific prior written permission.
+ * 
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
+ * TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+ * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+ * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+/**
+ * \file
+ *
+ * Definitions for the Frame Streams data transport protocol for
+ * dnstap message logs.
+ */
+
+#ifndef DNSTAP_FSTRM_H
+#define DNSTAP_FSTRM_H
+
+/* Frame Streams data transfer protocol encode for DNSTAP messages.
+ * The protocol looks to be specified in the libfstrm library.
+ *
+ * Quick writeup for DNSTAP usage, from reading fstrm/control.h eloquent
+ * comments and fstrm/control.c for some bytesize details (the content type
+ * length).
+ *
+ * The Frame Streams can be unidirectional or bi-directional.
+ * bi-directional streams use control frame types READY, ACCEPT and FINISH.
+ * uni-directional streams use control frame types START and STOP.
+ * unknown control frame types should be ignored by the receiver, they
+ * do not change the data frame encoding.
+ *
+ * bi-directional control frames implement a simple handshake protocol
+ * between sender and receiver.
+ *
+ * The uni-directional control frames have one start and one stop frame,
+ * before and after the data.  The start frame can have a content type.
+ * The start and stop frames are not optional.
+ *
+ * data frames are preceded by 4byte length, bigendian.
+ * zero length data frames are not possible, they are an escape that
+ * signals the presence of a control frame.
+ *
+ * a control frame consists of 0 value in 4byte bigendian, this is really
+ * the data frame length, with 0 the escape sequence that indicates one
+ * control frame follows.
+ * Then, 4byte bigendian, length of the control frame message.
+ * Then, the control frame payload (of that length). with in it:
+ *   4byte bigendian, control type (eg. START, STOP, READY, ACCEPT, FINISH).
+ *   perhaps nothing more (STOP, FINISH), but for other types maybe
+ *   control fields
+ *      4byte bigendian, the control-field-type, currently only content-type.
+ *      4byte bigendian, length of the string for this option.
+ *      .. bytes of that string.
+ *
+ * The START type can have only one field.  Field max len 256.
+ * control frame max frame length 512 (excludes the 0-escape and control
+ * frame length bytes).
+ *
+ * the bidirectional type of transmission is like this:
+ * client sends READY (with content type included),
+ * client waits for ACCEPT (with content type included),
+ * client sends START (with matched content type from ACCEPT)
+ * .. data frames
+ * client sends STOP.
+ * client waits for FINISH frame.
+ *
+ */
+
+/** max length of Frame Streams content type field string */
+#define FSTRM_CONTENT_TYPE_LENGTH_MAX 256
+/** control frame value to denote the control frame ACCEPT */
+#define FSTRM_CONTROL_FRAME_ACCEPT 0x01
+/** control frame value to denote the control frame START */
+#define FSTRM_CONTROL_FRAME_START 0x02
+/** control frame value to denote the control frame STOP */
+#define FSTRM_CONTROL_FRAME_STOP 0x03
+/** control frame value to denote the control frame READY */
+#define FSTRM_CONTROL_FRAME_READY 0x04
+/** control frame value to denote the control frame FINISH */
+#define FSTRM_CONTROL_FRAME_FINISH 0x05
+/** the constant that denotes the control field type that is the
+ * string for the content type of the stream. */
+#define FSTRM_CONTROL_FIELD_TYPE_CONTENT_TYPE 0x01
+/** the content type for DNSTAP frame streams */
+#define DNSTAP_CONTENT_TYPE             "protobuf:dnstap.Dnstap"
+
+/**
+ * This creates an FSTRM control frame of type START.
+ * @param contenttype: a zero delimited string with the content type.
+ * 	eg. use the constant DNSTAP_CONTENT_TYPE, which is defined as
+ * 	"protobuf:dnstap.Dnstap", for a dnstap frame stream.
+ * @param len: if a buffer is returned this is the length of that buffer.
+ * @return NULL on malloc failure.  Returns a malloced buffer with the
+ * protocol message.  The buffer starts with the 4 bytes of 0 that indicate
+ * a control frame.  The buffer should be sent without preceding it with
+ * the 'len' variable (like data frames are), but straight the content of the
+ * buffer, because the lengths are included in the buffer.  This is so that
+ * the zero control indicator can be included before the control frame length.
+ */
+void* fstrm_create_control_frame_start(char* contenttype, size_t* len);
+
+/**
+ * This creates an FSTRM control frame of type READY.
+ * @param contenttype: a zero delimited string with the content type.
+ * 	eg. use the constant DNSTAP_CONTENT_TYPE, which is defined as
+ * 	"protobuf:dnstap.Dnstap", for a dnstap frame stream.
+ * @param len: if a buffer is returned this is the length of that buffer.
+ * @return NULL on malloc failure.  Returns a malloced buffer with the
+ * protocol message.  The buffer starts with the 4 bytes of 0 that indicate
+ * a control frame.  The buffer should be sent without preceding it with
+ * the 'len' variable (like data frames are), but straight the content of the
+ * buffer, because the lengths are included in the buffer.  This is so that
+ * the zero control indicator can be included before the control frame length.
+ */
+void* fstrm_create_control_frame_ready(char* contenttype, size_t* len);
+
+/**
+ * This creates an FSTRM control frame of type STOP.
+ * @param len: if a buffer is returned this is the length of that buffer.
+ * @return NULL on malloc failure.  Returns a malloced buffer with the
+ * protocol message.  The buffer starts with the 4 bytes of 0 that indicate
+ * a control frame.  The buffer should be sent without preceding it with
+ * the 'len' variable (like data frames are), but straight the content of the
+ * buffer, because the lengths are included in the buffer.  This is so that
+ * the zero control indicator can be included before the control frame length.
+ */
+void* fstrm_create_control_frame_stop(size_t* len);
+
+/**
+ * This creates an FSTRM control frame of type ACCEPT.
+ * @param contenttype: a zero delimited string with the content type.
+ * 	for dnstap streams use DNSTAP_CONTENT_TYPE.
+ * @param len: if a buffer is returned this is the length of that buffer.
+ * @return NULL on malloc failure.  Returns a malloced buffer with the
+ * protocol message.  The buffer starts with the 4 bytes of 0 that indicate
+ * a control frame.  The buffer should be sent without preceding it with
+ * the 'len' variable (like data frames are), but straight the content of the
+ * buffer, because the lengths are included in the buffer.  This is so that
+ * the zero control indicator can be included before the control frame length.
+ */
+void* fstrm_create_control_frame_accept(char* contenttype, size_t* len);
+
+/**
+ * This creates an FSTRM control frame of type FINISH.
+ * @param len: if a buffer is returned this is the length of that buffer.
+ * @return NULL on malloc failure.  Returns a malloced buffer with the
+ * protocol message.  The buffer starts with the 4 bytes of 0 that indicate
+ * a control frame.  The buffer should be sent without preceding it with
+ * the 'len' variable (like data frames are), but straight the content of the
+ * buffer, because the lengths are included in the buffer.  This is so that
+ * the zero control indicator can be included before the control frame length.
+ */
+void* fstrm_create_control_frame_finish(size_t* len);
+
+/**
+ * Return string that describes a control packet.  For debug, logs.
+ * Like 'start content-type(protobuf:dnstap.Dnstap)' or 'stop'.
+ * @param pkt: the packet data, that is the data after the 4 zero start
+ * bytes and 4 length bytes.
+ * @param len: the length of the control packet data, in pkt.  This is the
+ * ntohl of the 4 bytes length preceding the data.
+ * @return zero delimited string, malloced.  Or NULL on malloc failure.
+ */
+char* fstrm_describe_control(void* pkt, size_t len);
+
+#endif /* DNSTAP_FSTRM_H */