encode.c

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/*
 *   This library is free software; you can redistribute it and/or
 *   modify it under the terms of the GNU Lesser General Public
 *   License as published by the Free Software Foundation; either
 *   version 2.1 of the License, or (at your option) any later version.
 *
 *   This library 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
 *   Lesser General Public License for more details.
 *
 *   You should have received a copy of the GNU Lesser General Public
 *   License along with this library; if not, write to the Free Software
 *   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
 */
 
/**
 * $Id: 6773ee45f06dea4f8815b3e8ada08d7712519463 $
 *
 * @file protocols/radius/encode.c
 * @brief Functions to encode RADIUS attributes
 *
 * @copyright 2000-2003,2006-2015 The FreeRADIUS server project
 */
#include "protocols/radius/radius.h"
RCSID("$Id: 6773ee45f06dea4f8815b3e8ada08d7712519463 $")
 
#include <freeradius-devel/util/dbuff.h>
#include <freeradius-devel/util/md5.h>
#include <freeradius-devel/util/struct.h>
#include <freeradius-devel/io/test_point.h>
#include <freeradius-devel/protocol/radius/freeradius.internal.h>
#include "attrs.h"
 
#define TAG_VALID(x)            ((x) > 0 && (x) < 0x20)
 
static const bool allow_tunnel_passwords[FR_RADIUS_CODE_MAX] = {
        [ 0 ] = true,           /* only for testing */
        [ FR_RADIUS_CODE_ACCESS_ACCEPT ] = true,
        [ FR_RADIUS_CODE_COA_REQUEST ] = true,
};
 
 
static ssize_t encode_value(fr_dbuff_t *dbuff,
                            fr_da_stack_t *da_stack, unsigned int depth,
                            fr_dcursor_t *cursor, void *encode_ctx);
 
static ssize_t encode_child(fr_dbuff_t *dbuff,
                            fr_da_stack_t *da_stack, unsigned int depth,
                            fr_dcursor_t *cursor, void *encode_ctx);
 
/** "encrypt" a password RADIUS style
 *
 * Input and output buffers can be identical if in-place encryption is needed.
 */
static ssize_t encode_password(fr_dbuff_t *dbuff, fr_dbuff_marker_t *input, size_t inlen, fr_radius_encode_ctx_t *packet_ctx)
{
        fr_md5_ctx_t    *md5_ctx, *md5_ctx_old;
        uint8_t digest[RADIUS_AUTH_VECTOR_LENGTH];
        uint8_t passwd[RADIUS_MAX_PASS_LENGTH] = {0};
        size_t          i, n;
        size_t          len;
 
        /*
         *      If the length is zero, round it up.
         */
        len = inlen;
 
        if (len > RADIUS_MAX_PASS_LENGTH) len = RADIUS_MAX_PASS_LENGTH;
 
        (void) fr_dbuff_out_memcpy(passwd, input, len);
        if (len < sizeof(passwd)) memset(passwd + len, 0, sizeof(passwd) - len);
 
        if (len == 0) len = AUTH_PASS_LEN;
        else if ((len & 0x0f) != 0) {
                len += 0x0f;
                len &= ~0x0f;
        }
 
        md5_ctx = fr_md5_ctx_alloc_from_list();
        md5_ctx_old = fr_md5_ctx_alloc_from_list();
 
        fr_md5_update(md5_ctx, (uint8_t const *) packet_ctx->common->secret, packet_ctx->common->secret_length);
        fr_md5_ctx_copy(md5_ctx_old, md5_ctx);
 
        /*
         *      Do first pass.
         */
        fr_md5_update(md5_ctx, packet_ctx->request_authenticator, AUTH_PASS_LEN);
 
        for (n = 0; n < len; n += AUTH_PASS_LEN) {
                if (n > 0) {
                        fr_md5_ctx_copy(md5_ctx, md5_ctx_old);
                        fr_md5_update(md5_ctx, passwd + n - AUTH_PASS_LEN, AUTH_PASS_LEN);
                }
 
                fr_md5_final(digest, md5_ctx);
                for (i = 0; i < AUTH_PASS_LEN; i++) passwd[i + n] ^= digest[i];
        }
 
        fr_md5_ctx_free_from_list(&md5_ctx);
        fr_md5_ctx_free_from_list(&md5_ctx_old);
 
        return fr_dbuff_in_memcpy(dbuff, passwd, len);
}
 
 
static ssize_t encode_tunnel_password(fr_dbuff_t *dbuff, fr_dbuff_marker_t *in, size_t inlen, fr_radius_encode_ctx_t *packet_ctx)
{
        fr_md5_ctx_t    *md5_ctx, *md5_ctx_old;
        uint8_t         digest[RADIUS_AUTH_VECTOR_LENGTH];
        uint8_t         tpasswd[RADIUS_MAX_STRING_LENGTH];
        size_t          i, n;
        uint32_t        r;
        size_t          output_len, encrypted_len, padding;
        ssize_t         slen;
        fr_dbuff_t      work_dbuff = FR_DBUFF_MAX(dbuff, RADIUS_MAX_STRING_LENGTH);
 
        /*
         *      Limit the maximum size of the input password.  2 bytes
         *      are taken up by the salt, and one by the encoded
         *      "length" field.
         */
        if (inlen > (RADIUS_MAX_STRING_LENGTH - 3)) {
        fail:
                fr_strerror_const("Input password is too large for tunnel password encoding");
                return -(inlen + 3);
        }
 
        /*
         *      Length of the encrypted data is the clear-text
         *      password length plus one byte which encodes the length
         *      of the password.  We round up to the nearest encoding
         *      block, and bound it by the size of the output buffer,
         *      while accounting for 2 bytes of salt.
         *
         *      And also ensuring that we don't truncate the input
         *      password.
         */
        encrypted_len = ROUND_UP(inlen + 1, 16);
        if (encrypted_len > (RADIUS_MAX_STRING_LENGTH - 2)) encrypted_len = (RADIUS_MAX_STRING_LENGTH - 2);
 
        /*
         *      Get the number of padding bytes in the last block.
         */
        padding = encrypted_len - (inlen + 1);
 
        output_len = encrypted_len + 2; /* account for the salt */
 
        /*
         *      We will have up to 253 octets of data in the output
         *      buffer, some of which are padding.
         *
         *      If we over-run the output buffer, see if we can drop
         *      some of the padding bytes.  If not, we return an error
         *      instead of truncating the password.
         *
         *      Otherwise we lower the amount of data we copy into the
         *      output buffer, because the last bit is just padding,
         *      and can be safely discarded.
         */
        slen = fr_dbuff_set(&work_dbuff, output_len);
        if (slen < 0) {
                if (((size_t) -slen) > padding) goto fail;
 
                output_len += slen;
        }
        fr_dbuff_set_to_start(&work_dbuff);
 
        /*
         *      Copy the password over, and fill the remainder with random data.
         */
        (void) fr_dbuff_out_memcpy(tpasswd + 3, in, inlen);
 
        for (i = 3 + inlen; i < sizeof(tpasswd); i++) {
                tpasswd[i] = fr_fast_rand(&packet_ctx->rand_ctx);
        }
 
        /*
         *      Generate salt.  The RFCs say:
         *
         *      The high bit of salt[0] must be set, each salt in a
         *      packet should be unique, and they should be random
         *
         *      So, we set the high bit, add in a counter, and then
         *      add in some PRNG data.  should be OK..
         */
        r = fr_fast_rand(&packet_ctx->rand_ctx);
        tpasswd[0] = (0x80 | (((packet_ctx->salt_offset++) & 0x07) << 4) | ((r >> 8) & 0x0f));
        tpasswd[1] = r & 0xff;
        tpasswd[2] = inlen;     /* length of the password string */
 
        md5_ctx = fr_md5_ctx_alloc_from_list();
        md5_ctx_old = fr_md5_ctx_alloc_from_list();
 
        fr_md5_update(md5_ctx, (uint8_t const *) packet_ctx->common->secret, packet_ctx->common->secret_length);
        fr_md5_ctx_copy(md5_ctx_old, md5_ctx);
 
        fr_md5_update(md5_ctx, packet_ctx->request_authenticator, RADIUS_AUTH_VECTOR_LENGTH);
        fr_md5_update(md5_ctx, &tpasswd[0], 2);
 
        /*
         *      Do various hashing, and XOR the length+password with
         *      the output of the hash blocks.
         */
        for (n = 0; n < encrypted_len; n += AUTH_PASS_LEN) {
                size_t block_len;
 
                if (n > 0) {
                        fr_md5_ctx_copy(md5_ctx, md5_ctx_old);
                        fr_md5_update(md5_ctx, tpasswd + 2 + n - AUTH_PASS_LEN, AUTH_PASS_LEN);
                }
                fr_md5_final(digest, md5_ctx);
 
                block_len = encrypted_len - n;
                if (block_len > AUTH_PASS_LEN) block_len = AUTH_PASS_LEN;
 
#ifdef __COVERITY__
                /*
                 *      Coverity is not doing the calculations correctly - it doesn't see
                 *      that setting block_len = encrypted_len - n puts a safe boundary
                 *      on block_len so the access to tpasswd won't overflow.
                 */
                if ((block_len + 2 + n) > RADIUS_MAX_STRING_LENGTH) {
                        block_len = RADIUS_MAX_STRING_LENGTH - n - 3;
                }
#endif
                for (i = 0; i < block_len; i++) tpasswd[i + 2 + n] ^= digest[i];
        }
 
        fr_md5_ctx_free_from_list(&md5_ctx);
        fr_md5_ctx_free_from_list(&md5_ctx_old);
 
        FR_DBUFF_IN_MEMCPY_RETURN(&work_dbuff, tpasswd, output_len);
 
        return fr_dbuff_set(dbuff, &work_dbuff);
}
 
/*
 *      Encode the contents of an attribute of type TLV.
 */
static ssize_t encode_tlv(fr_dbuff_t *dbuff,
                          fr_da_stack_t *da_stack, unsigned int depth,
                          fr_dcursor_t *cursor, void *encode_ctx)
{
        ssize_t         slen;
        fr_pair_t const *vp = fr_dcursor_current(cursor);
        fr_dict_attr_t const    *da = da_stack->da[depth];
        fr_dbuff_t              work_dbuff = FR_DBUFF_MAX(dbuff, RADIUS_MAX_STRING_LENGTH);
 
        for (;;) {
                FR_PROTO_STACK_PRINT(da_stack, depth);
 
                /*
                 *      This attribute carries sub-TLVs.  The sub-TLVs
                 *      can only carry a total of 253 bytes of data.
                 */
 
                /*
                 *      Determine the nested type and call the appropriate encoder
                 */
                if (!da_stack->da[depth + 1]) {
                        fr_dcursor_t child_cursor;
 
                        if (vp->da != da_stack->da[depth]) {
                                fr_strerror_printf("%s: Can't encode empty TLV", __FUNCTION__);
                                return 0;
                        }
 
                        fr_pair_dcursor_child_iter_init(&child_cursor, &vp->vp_group, cursor);
                        vp = fr_dcursor_current(&child_cursor);
                        if (!vp) goto next;
 
                        fr_proto_da_stack_build(da_stack, vp->da);
 
                        /*
                         *      Call ourselves recursively to encode children.
                         */
                        slen = encode_tlv(&work_dbuff, da_stack, depth, &child_cursor, encode_ctx);
                        if (slen < 0) return slen;
 
                next:
                        vp = fr_dcursor_next(cursor);
                        fr_proto_da_stack_build(da_stack, vp ? vp->da : NULL);
 
                } else {
                        slen = encode_child(&work_dbuff, da_stack, depth + 1, cursor, encode_ctx);
                        if (slen < 0) return slen;
                }
 
                /*
                 *      If nothing updated the attribute, stop
                 */
                if (!fr_dcursor_current(cursor) || (vp == fr_dcursor_current(cursor))) break;
 
                /*
                 *      We can encode multiple sub TLVs, if after
                 *      rebuilding the TLV Stack, the attribute
                 *      at this depth is the same.
                 */
                if ((da != da_stack->da[depth]) || (da_stack->depth < da->depth)) break;
                vp = fr_dcursor_current(cursor);
        }
 
        return fr_dbuff_set(dbuff, &work_dbuff);
}
 
static ssize_t encode_pairs(fr_dbuff_t *dbuff, fr_pair_list_t const *vps, void *encode_ctx)
{
        ssize_t                 slen;
        fr_pair_t const *vp;
        fr_dcursor_t            cursor;
 
        /*
         *      Note that we skip tags inside of tags!
         */
        fr_pair_dcursor_iter_init(&cursor, vps, fr_proto_next_encodable, dict_radius);
        while ((vp = fr_dcursor_current(&cursor))) {
                PAIR_VERIFY(vp);
 
                /*
                 *      Encode an individual VP
                 */
                slen = fr_radius_encode_pair(dbuff, &cursor, encode_ctx);
                if (slen < 0) return slen;
        }
 
        return fr_dbuff_used(dbuff);
}
 
 
/** Encodes the data portion of an attribute
 *
 * @return
 *      > 0, Length of the data portion.
 *      = 0, we could not encode anything, skip this attribute (and don't encode the header)
 *        unless it's one of a list of exceptions.
 *      < 0, How many additional bytes we'd need as a negative integer.
 *      PAIR_ENCODE_FATAL_ERROR - Abort encoding the packet.
 */
static ssize_t encode_value(fr_dbuff_t *dbuff,
                            fr_da_stack_t *da_stack, unsigned int depth,
                            fr_dcursor_t *cursor, void *encode_ctx)
{
        ssize_t                         slen;
        size_t                          len;
        fr_pair_t const                 *vp = fr_dcursor_current(cursor);
        fr_dict_attr_t const            *da = da_stack->da[depth];
        fr_radius_encode_ctx_t          *packet_ctx = encode_ctx;
        fr_dbuff_t                      work_dbuff = FR_DBUFF(dbuff);
        fr_dbuff_t                      value_dbuff;
        fr_dbuff_marker_t               value_start, src, dest;
        bool                            encrypted = false;
 
        PAIR_VERIFY(vp);
        FR_PROTO_STACK_PRINT(da_stack, depth);
 
        /*
         *      TLVs are just another type of value.
         */
        if (da->type == FR_TYPE_TLV) return encode_tlv(dbuff, da_stack, depth, cursor, encode_ctx);
 
        if (da->type == FR_TYPE_GROUP) return fr_pair_ref_to_network(dbuff, da_stack, depth, cursor);
 
        /*
         *      Catch errors early on.
         */
        if (fr_radius_flag_encrypted(vp->da) && !packet_ctx) {
                fr_strerror_const("Asked to encrypt attribute, but no packet context provided");
                return PAIR_ENCODE_FATAL_ERROR;
        }
 
        /*
         *      This has special requirements.
         */
        if ((vp->vp_type == FR_TYPE_STRUCT) || (da->type == FR_TYPE_STRUCT)) {
                slen = fr_struct_to_network(&work_dbuff, da_stack, depth, cursor, encode_ctx, encode_value, encode_child);
                if (slen <= 0) return slen;
 
                vp = fr_dcursor_current(cursor);
                fr_proto_da_stack_build(da_stack, vp ? vp->da : NULL);
                return fr_dbuff_set(dbuff, &work_dbuff);
        }
 
        /*
         *      If it's not a TLV, it should be a value type RFC
         *      attribute make sure that it is.
         */
        if (da_stack->da[depth + 1] != NULL) {
                fr_strerror_printf("%s: Encoding value but not at top of stack", __FUNCTION__);
                return PAIR_ENCODE_FATAL_ERROR;
        }
 
        if (vp->da != da) {
                fr_strerror_printf("%s: Top of stack does not match vp->da", __FUNCTION__);
                return PAIR_ENCODE_FATAL_ERROR;
        }
 
        if (fr_type_is_structural(da->type)) {
                fr_strerror_printf("%s: Called with structural type %s", __FUNCTION__,
                                   fr_type_to_str(da_stack->da[depth]->type));
                return PAIR_ENCODE_FATAL_ERROR;
        }
 
        /*
         *      Write tag byte
         *
         *      The Tag field is one octet in length and is intended to provide a
         *      means of grouping attributes in the same packet which refer to the
         *      same tunnel.  If the value of the Tag field is greater than 0x00
         *      and less than or equal to 0x1F, it SHOULD be interpreted as
         *      indicating which tunnel (of several alternatives) this attribute
         *      pertains.  If the Tag field is greater than 0x1F, it SHOULD be
         *      interpreted as the first byte of the following String field.
         *
         *      If the first byte of the string value looks like a
         *      tag, then we always encode a tag byte, even one that
         *      is zero.
         */
        if ((vp->vp_type == FR_TYPE_STRING) && fr_radius_flag_has_tag(vp->da)) {
                if (packet_ctx->tag) {
                        FR_DBUFF_IN_RETURN(&work_dbuff, (uint8_t)packet_ctx->tag);
                } else if (TAG_VALID(vp->vp_strvalue[0])) {
                        FR_DBUFF_IN_RETURN(&work_dbuff, (uint8_t)0x00);
                }
        }
 
        /*
         * Starting here is a value that may require encryption.
         */
        value_dbuff = FR_DBUFF(&work_dbuff);
        fr_dbuff_marker(&value_start, &value_dbuff);
        fr_dbuff_marker(&src, &value_dbuff);
        fr_dbuff_marker(&dest, &value_dbuff);
 
        switch (vp->vp_type) {
                /*
                 *      IPv4 addresses are normal, but IPv6 addresses are special to RADIUS.
                 */
        case FR_TYPE_COMBO_IP_ADDR:
                if (vp->vp_ip.af == AF_INET) goto encode;
                FALL_THROUGH;
 
        /*
         *      Common encoder might add scope byte, which we don't want.
         */
        case FR_TYPE_IPV6_ADDR:
                FR_DBUFF_IN_MEMCPY_RETURN(&value_dbuff, vp->vp_ipv6addr, sizeof(vp->vp_ipv6addr));
                break;
 
        case FR_TYPE_COMBO_IP_PREFIX:
                if (vp->vp_ip.af == AF_INET) goto ipv4_prefix;
                FALL_THROUGH;
 
        /*
         *      Common encoder doesn't add reserved byte
         */
        case FR_TYPE_IPV6_PREFIX:
                len = fr_bytes_from_bits(vp->vp_ip.prefix);
                FR_DBUFF_IN_BYTES_RETURN(&value_dbuff, 0x00, vp->vp_ip.prefix);
                /* Only copy the minimum number of address bytes required */
                FR_DBUFF_IN_MEMCPY_RETURN(&value_dbuff, (uint8_t const *)vp->vp_ipv6addr, len);
                break;
 
        /*
         *      Common encoder doesn't add reserved byte
         */
        case FR_TYPE_IPV4_PREFIX:
        ipv4_prefix:
                FR_DBUFF_IN_BYTES_RETURN(&value_dbuff, 0x00, vp->vp_ip.prefix);
                FR_DBUFF_IN_MEMCPY_RETURN(&value_dbuff, (uint8_t const *)&vp->vp_ipv4addr, sizeof(vp->vp_ipv4addr));
                break;
 
        /*
         *      Special handling for "abinary".  Otherwise, fall
         *      through to using the common encoder.
         */
        case FR_TYPE_STRING:
                if (fr_radius_flag_abinary(da)) {
                        slen = fr_radius_encode_abinary(vp, &value_dbuff);
                        if (slen < 0) return slen;
                        break;
                }
                FALL_THROUGH;
 
        case FR_TYPE_OCTETS:
 
        /*
         *      Simple data types use the common encoder.
         */
        default:
        encode:
                slen = fr_value_box_to_network(&value_dbuff, &vp->data);
                if (slen < 0) return slen;
                break;
        }
 
        /*
         *      No data: don't encode the value.  The type and length should still
         *      be written.
         */
        if (fr_dbuff_used(&value_dbuff) == 0) {
        return_0:
                vp = fr_dcursor_next(cursor);
                fr_proto_da_stack_build(da_stack, vp ? vp->da : NULL);
                return 0;
        }
 
        /*
         *      Encrypt the various password styles
         *
         *      Attributes with encrypted values MUST be less than
         *      128 bytes long.
         */
        switch (fr_radius_flag_encrypted(da)) {
        case RADIUS_FLAG_ENCRYPT_USER_PASSWORD:
                /*
                 *      Encode the password in place
                 */
                slen = encode_password(&work_dbuff, &value_start, fr_dbuff_used(&value_dbuff), packet_ctx);
                if (slen < 0) return slen;
                encrypted = true;
                break;
 
        case RADIUS_FLAG_ENCRYPT_TUNNEL_PASSWORD:
        {
                bool has_tag = fr_radius_flag_has_tag(vp->da);
 
                fr_assert(packet_ctx->code < FR_RADIUS_CODE_MAX);
                if (!allow_tunnel_passwords[packet_ctx->code]) {
                        fr_strerror_printf("Attributes with 'encrypt=Tunnel-Password' set cannot go into %s.",
                                           fr_radius_packet_name[packet_ctx->code]);
                        goto return_0;
                }
 
                /*
                 *      Always encode the tag even if it's zero.
                 *
                 *      The Tunnel-Password uses 2 salt fields which
                 *      MAY have any value.  As a result, we always
                 *      encode a tag.  If we would omit the tag, then
                 *      perhaps one of the salt fields could be
                 *      mistaken for the tag.
                 */
                if (has_tag) fr_dbuff_advance(&work_dbuff, 1);
 
                slen = encode_tunnel_password(&work_dbuff, &value_start, fr_dbuff_used(&value_dbuff), packet_ctx);
                if (slen < 0) {
                        fr_strerror_printf("%s too long", vp->da->name);
                        return slen - has_tag;
                }
 
                /*
                 *      Do this after so we don't mess up the input
                 *      value.
                 */
                if (has_tag) {
                        fr_dbuff_set_to_start(&value_start);
                        fr_dbuff_in(&value_start, (uint8_t) 0x00);
                }
                encrypted = true;
        }
                break;
 
        /*
         *      The code above ensures that this attribute
         *      always fits.
         */
        case RADIUS_FLAG_ENCRYPT_ASCEND_SECRET:
                /*
                 *      @todo radius decoding also uses fr_radius_ascend_secret() (Vernam cipher
                 *      is its own inverse). As part of converting decode, make sure the caller
                 *      there can pass a marker so we can use it here, too.
                 */
                slen = fr_radius_ascend_secret(&work_dbuff, fr_dbuff_current(&value_start), fr_dbuff_used(&value_dbuff),
                                               packet_ctx->common->secret, packet_ctx->request_authenticator);
                if (slen < 0) return slen;
                encrypted = true;
                break;
 
        case RADIUS_FLAG_ENCRYPT_NONE:
                break;
 
        case RADIUS_FLAG_ENCRYPT_INVALID:
                fr_strerror_const("Invalid encryption type");
                return PAIR_ENCODE_FATAL_ERROR;
        }
 
        if (!encrypted) {
                fr_dbuff_set(&work_dbuff, &value_dbuff);
                fr_dbuff_set(&value_start, fr_dbuff_start(&value_dbuff));
        }
 
        /*
         *      High byte of 32bit integers gets set to the tag
         *      value.
         *
         *      The Tag field is one octet in length and is intended to provide a
         *      means of grouping attributes in the same packet which refer to the
         *      same tunnel.  Valid values for this field are 0x01 through 0x1F,
         *      inclusive.  If the Tag field is unused, it MUST be zero (0x00).
         */
        if ((vp->vp_type == FR_TYPE_UINT32) && fr_radius_flag_has_tag(vp->da)) {
                uint8_t msb = 0;
                /*
                 *      Only 24bit integers are allowed here
                 */
                fr_dbuff_set(&src,  &value_start);
                (void) fr_dbuff_out(&msb, &src);
                if (msb != 0) {
                        fr_strerror_const("Integer overflow for tagged uint32 attribute");
                        goto return_0;
                }
                fr_dbuff_set(&dest, &value_start);
                fr_dbuff_in(&dest, packet_ctx->tag);
        }
 
        FR_PROTO_HEX_DUMP(fr_dbuff_start(&work_dbuff), fr_dbuff_used(&work_dbuff), "value %s",
                          fr_type_to_str(vp->vp_type));
 
        /*
         *      Rebuilds the TLV stack for encoding the next attribute
         */
        vp = fr_dcursor_next(cursor);
        fr_proto_da_stack_build(da_stack, vp ? vp->da : NULL);
 
        return fr_dbuff_set(dbuff, &work_dbuff);
}
 
/** Breaks down large data into pieces, each with a header
 *
 * @param[out] data             we're fragmenting.
 * @param[in] data_len          the amount of data in the dbuff that makes up the value we're
 *                              splitting.
 * @param[in,out] hdr           marker that points at said header
 * @param[in] hdr_len           length of the headers that will be added
 * @param[in] flag_offset       offset within header of a flag byte whose MSB is set for all
 *                              but the last piece.
 * @param[in] vsa_offset        if non-zero, the offset of a length field in a (sub?)-header
 *                              of size 3 that also needs to be adjusted to include the number
 *                              of bytes of data in the piece
 * @return
 *      - <0 the number of bytes we would have needed to create
 *        space for another attribute header in the buffer.
 *      - 0 data was not modified.
 *      - >0 the number additional bytes we used inserting extra
 *        headers.
 */
static ssize_t attr_fragment(fr_dbuff_t *data, size_t data_len, fr_dbuff_marker_t *hdr, size_t hdr_len,
                             int flag_offset, int vsa_offset)
{
        unsigned int            num_fragments, i = 0;
        size_t                  max_frag_data = UINT8_MAX - hdr_len;
        fr_dbuff_t              frag_data = FR_DBUFF_ABS(hdr);
        fr_dbuff_marker_t       frag_hdr, frag_hdr_p;
 
        if (unlikely(!data_len)) return 0;      /* Shouldn't have been called */
 
        num_fragments = ROUND_UP_DIV(data_len, max_frag_data);
        if (num_fragments == 1) return 0;       /* Nothing to do */
 
        fr_dbuff_marker(&frag_hdr, &frag_data);
        fr_dbuff_marker(&frag_hdr_p, &frag_data);
 
        fr_dbuff_advance(&frag_data, hdr_len);
 
        FR_PROTO_HEX_DUMP(fr_dbuff_current(hdr), hdr_len + data_len, "attr_fragment in");
        for (;;) {
                bool    last = (i + 1) == num_fragments;
                uint8_t frag_len;
 
                /*
                 *      How long is this fragment?
                 */
                if (last) {
                        frag_len = (data_len - (max_frag_data * (num_fragments - 1)));
                } else {
                        frag_len = max_frag_data;
                }
 
                /*
                 *      Update the "outer" header to reflect the actual
                 *      length of the fragment
                 */
                fr_dbuff_set(&frag_hdr_p, &frag_hdr);
                fr_dbuff_advance(&frag_hdr_p, 1);
                fr_dbuff_in(&frag_hdr_p, (uint8_t)(hdr_len + frag_len));
 
                /*
                 *      Update the "inner" header.  The length here is
                 *      the inner VSA header length (3) + the fragment
                 *      length.
                 */
                if (vsa_offset) {
                        fr_dbuff_set(&frag_hdr_p, fr_dbuff_current(&frag_hdr) + vsa_offset);
                        fr_dbuff_in(&frag_hdr_p, (uint8_t)(3 + frag_len));
                }
 
                /*
                 *      Just over-ride the flag field.  Nothing else
                 *      uses it.
                 */
                if (flag_offset) {
                        fr_dbuff_set(&frag_hdr_p, fr_dbuff_current(&frag_hdr) + flag_offset);
                        fr_dbuff_in(&frag_hdr_p, (uint8_t)(!last << 7));
                }
 
                FR_PROTO_HEX_DUMP(fr_dbuff_current(hdr), frag_len + hdr_len,
                                  "attr_fragment fragment %u/%u", i + 1, num_fragments);
 
                fr_dbuff_advance(&frag_data, frag_len); /* Go to the start of the next fragment */
                if (last) break;
 
                /*
                 *      There's still trailing data after this
                 *      fragment.  Move the trailing data to *past*
                 *      the next header.  And after there's room, copy
                 *      the header over.
                 *
                 *      This process leaves the next header in place,
                 *      ready for the next iteration of the loop.
                 *
                 *      Yes, moving things multiple times is less than
                 *      efficient.  Oh well.  it's ~1K memmoved()
                 *      maybe 4 times.  We are nowhere near the CPU /
                 *      electrical requirements of Bitcoin.
                 */
                i++;
 
                fr_dbuff_set(&frag_hdr, &frag_data);            /* Remember where the header should be */
                fr_dbuff_advance(&frag_data, hdr_len);          /* Advance past the header */
 
                /*
                 *      Shift remaining data by hdr_len.
                 */
                FR_DBUFF_IN_MEMCPY_RETURN(&FR_DBUFF(&frag_data), &frag_hdr, data_len - (i * max_frag_data));
                fr_dbuff_in_memcpy(&FR_DBUFF(&frag_hdr), hdr, hdr_len); /* Copy the old header over */
        }
 
        return fr_dbuff_set(data, &frag_data);
}
 
/** Encode an "extended" attribute
 *
 */
static ssize_t encode_extended(fr_dbuff_t *dbuff,
                                   fr_da_stack_t *da_stack, NDEBUG_UNUSED unsigned int depth,
                                   fr_dcursor_t *cursor, void *encode_ctx)
{
        ssize_t                 slen;
        uint8_t                 hlen;
        size_t                  vendor_hdr;
        bool                    extra;
        int                     my_depth;
        fr_dict_attr_t const    *da;
        fr_dbuff_marker_t       hdr, length_field;
        fr_pair_t const         *vp = fr_dcursor_current(cursor);
        fr_dbuff_t              work_dbuff;
 
        PAIR_VERIFY(vp);
        FR_PROTO_STACK_PRINT(da_stack, depth);
 
        extra = fr_radius_flag_long_extended(da_stack->da[0]);
 
        /*
         *      The data used here can be more than 255 bytes, but only for the
         *      "long" extended type.
         */
        if (extra) {
                work_dbuff = FR_DBUFF_BIND_CURRENT(dbuff);
        } else {
                work_dbuff = FR_DBUFF_MAX_BIND_CURRENT(dbuff, UINT8_MAX);
        }
        fr_dbuff_marker(&hdr, &work_dbuff);
 
        /*
         *      Encode the header for "short" or "long" attributes
         */
        hlen = 3 + extra;
        FR_DBUFF_IN_BYTES_RETURN(&work_dbuff, (uint8_t)da_stack->da[0]->attr);
        fr_dbuff_marker(&length_field, &work_dbuff);
        FR_DBUFF_IN_BYTES_RETURN(&work_dbuff, hlen); /* this gets overwritten later*/
 
        /*
         *      Encode which extended attribute it is.
         */
        FR_DBUFF_IN_BYTES_RETURN(&work_dbuff, (uint8_t)da_stack->da[1]->attr);
 
        if (extra) FR_DBUFF_IN_BYTES_RETURN(&work_dbuff, 0x00); /* flags start off at zero */
 
        FR_PROTO_STACK_PRINT(da_stack, depth);
 
        /*
         *      Handle VSA as "VENDOR + attr"
         */
        if (da_stack->da[1]->type == FR_TYPE_VSA) {
                fr_assert(da_stack->da[2]);
                fr_assert(da_stack->da[2]->type == FR_TYPE_VENDOR);
 
                FR_DBUFF_IN_RETURN(&work_dbuff, (uint32_t) da_stack->da[2]->attr);
 
                fr_assert(da_stack->da[3]);
 
                FR_DBUFF_IN_BYTES_RETURN(&work_dbuff, (uint8_t)da_stack->da[3]->attr);
 
                hlen += 5;
                vendor_hdr = 5;
 
                FR_PROTO_STACK_PRINT(da_stack, depth);
                FR_PROTO_HEX_DUMP(fr_dbuff_current(&hdr), hlen, "header extended vendor specific");
 
                my_depth = 3;
        } else {
                vendor_hdr = 0;
                FR_PROTO_HEX_DUMP(fr_dbuff_current(&hdr), hlen, "header extended");
 
                my_depth = 1;
        }
 
        /*
         *      We're at the point where we need to encode something.
         */
        da = da_stack->da[my_depth];
        fr_assert(vp->da == da);
 
        if (da->type != FR_TYPE_STRUCT) {
                slen = encode_value(&work_dbuff, da_stack, my_depth, cursor, encode_ctx);
 
        } else {
                slen = fr_struct_to_network(&work_dbuff, da_stack, my_depth, cursor, encode_ctx, encode_value, encode_child);
        }
        if (slen <= 0) return slen;
 
        /*
         *      There may be more than 255 octets of data encoded in
         *      the attribute.  If so, move the data up in the packet,
         *      and copy the existing header over.  Set the "M" flag ONLY
         *      after copying the rest of the data.
         *
         *      Note that we add "vendor_hdr" to the length of the
         *      encoded data.  That 5 octet field is logically part of
         *      the data, and not part of the header.
         */
        if (slen > (UINT8_MAX - hlen)) {
                slen = attr_fragment(&work_dbuff, (size_t)vendor_hdr + slen, &hdr, 4, 3, 0);
                if (slen <= 0) return slen;
 
                return fr_dbuff_set(dbuff, &work_dbuff);
        }
 
        fr_dbuff_in_bytes(&length_field, (uint8_t) fr_dbuff_used(&work_dbuff));
        FR_PROTO_HEX_DUMP(fr_dbuff_current(&hdr), hlen, "header extended");
 
        return fr_dbuff_set(dbuff, &work_dbuff);
}
 
/*
 *      The encode_extended() function expects to see the TLV or
 *      STRUCT inside of the extended attribute, in which case it
 *      creates the attribute header and calls encode_value() for the
 *      leaf type, or child TLV / struct.
 *
 *      If we see VSA or VENDOR, then we recurse past that to a child
 *      which is either a leaf, or a TLV, or a STRUCT.
 */
static ssize_t encode_extended_nested(fr_dbuff_t *dbuff,
                                      fr_da_stack_t *da_stack, unsigned int depth,
                                      fr_dcursor_t *cursor, void *encode_ctx)
{
        ssize_t                 slen;
        fr_pair_t               *parent, *vp;
        fr_dcursor_t            child_cursor;
        fr_dbuff_t              work_dbuff = FR_DBUFF(dbuff);
 
        parent = fr_dcursor_current(cursor);
        fr_assert(fr_type_is_structural(parent->vp_type));
 
        (void) fr_pair_dcursor_child_iter_init(&child_cursor, &parent->vp_group, cursor);
 
        FR_PROTO_STACK_PRINT(da_stack, depth);
 
        while ((vp = fr_dcursor_current(&child_cursor)) != NULL) {
                if ((vp->vp_type == FR_TYPE_VSA) || (vp->vp_type == FR_TYPE_VENDOR)) {
                        slen = encode_extended_nested(&work_dbuff, da_stack, depth + 1, &child_cursor, encode_ctx);
 
                } else {
                        fr_proto_da_stack_build(da_stack, vp->da);
                        slen = encode_extended(&work_dbuff, da_stack, depth, &child_cursor, encode_ctx);
                        if (slen < 0) return slen;
                }
 
                if (slen < 0) return slen;
        }
 
        vp = fr_dcursor_next(cursor);
 
        fr_proto_da_stack_build(da_stack, vp ? vp->da : NULL);
 
        return fr_dbuff_set(dbuff, &work_dbuff);
}
 
 
/** Encode an RFC format attribute, with the "concat" flag set
 *
 * If there isn't enough freespace in the packet, the data is
 * truncated to fit.
 *
 * The attribute is split on 253 byte boundaries, with a header
 * prepended to each chunk.
 */
static ssize_t encode_concat(fr_dbuff_t *dbuff,
                             fr_da_stack_t *da_stack, unsigned int depth,
                             fr_dcursor_t *cursor, UNUSED void *encode_ctx)
{
        uint8_t const           *p;
        size_t                  data_len;
        fr_pair_t const         *vp = fr_dcursor_current(cursor);
        fr_dbuff_t              work_dbuff = FR_DBUFF(dbuff);
        fr_dbuff_marker_t       hdr;
 
        FR_PROTO_STACK_PRINT(da_stack, depth);
 
        p = vp->vp_octets;
        data_len = vp->vp_length;
        fr_dbuff_marker(&hdr, &work_dbuff);
 
        while (data_len > 0) {
                size_t frag_len = (data_len > RADIUS_MAX_STRING_LENGTH) ? RADIUS_MAX_STRING_LENGTH : data_len;
 
                fr_dbuff_set(&hdr, &work_dbuff);
                FR_DBUFF_IN_BYTES_RETURN(&work_dbuff, (uint8_t) da_stack->da[depth]->attr, 0x00);
 
                FR_DBUFF_IN_MEMCPY_RETURN(&work_dbuff, p, frag_len);
 
                fr_dbuff_advance(&hdr, 1);
                fr_dbuff_in(&hdr, (uint8_t) (2 + frag_len));
 
                FR_PROTO_HEX_DUMP(fr_dbuff_current(&hdr) - 1, 2 + frag_len, "encode_concat fragment");
 
                p += frag_len;
                data_len -= frag_len;
        }
 
        vp = fr_dcursor_next(cursor);
 
        /*
         *      @fixme: attributes with 'concat' MUST of type
         *      'octets', and therefore CANNOT have any TLV data in them.
         */
        fr_proto_da_stack_build(da_stack, vp ? vp->da : NULL);
 
        return fr_dbuff_set(dbuff, &work_dbuff);
}
 
/** Encode an RFC format attribute.
 *
 * This could be a standard attribute, or a TLV data type.
 * If it's a standard attribute, then vp->da->attr == attribute.
 * Otherwise, attribute may be something else.
 */
static ssize_t encode_child(fr_dbuff_t *dbuff,
                                 fr_da_stack_t *da_stack, unsigned int depth,
                                 fr_dcursor_t *cursor, void *encode_ctx)
{
        ssize_t                 slen;
        uint8_t                 hlen;
        fr_dbuff_marker_t       hdr;
        fr_dbuff_t              work_dbuff = FR_DBUFF_MAX(dbuff, UINT8_MAX);
 
        FR_PROTO_STACK_PRINT(da_stack, depth);
 
        fr_assert(da_stack->da[depth] != NULL);
 
        fr_dbuff_marker(&hdr, &work_dbuff);
 
        hlen = 2;
        FR_DBUFF_IN_BYTES_RETURN(&work_dbuff, (uint8_t)da_stack->da[depth]->attr, hlen);
 
        slen = encode_value(&work_dbuff, da_stack, depth, cursor, encode_ctx);
        if (slen <= 0) return slen;
 
        fr_dbuff_advance(&hdr, 1);
        fr_dbuff_in_bytes(&hdr, (uint8_t)(hlen + slen));
 
        FR_PROTO_HEX_DUMP(fr_dbuff_start(&work_dbuff), 2, "header rfc");
 
        return fr_dbuff_set(dbuff, &work_dbuff);
}
 
 
/** Encode one full Vendor-Specific + Vendor-ID + Vendor-Attr + Vendor-Length + ...
 */
static ssize_t encode_vendor_attr(fr_dbuff_t *dbuff,
                                  fr_da_stack_t *da_stack, unsigned int depth,
                                  fr_dcursor_t *cursor, void *encode_ctx)
{
        ssize_t                 slen;
        size_t                  hdr_len;
        fr_dbuff_marker_t       hdr, length_field, vsa_length_field;
        fr_dict_attr_t const    *da, *dv;
        fr_dbuff_t              work_dbuff;
 
        FR_PROTO_STACK_PRINT(da_stack, depth);
 
        dv = da_stack->da[depth++];
 
        if (dv->type != FR_TYPE_VENDOR) {
                fr_strerror_const("Expected Vendor");
                return PAIR_ENCODE_FATAL_ERROR;
        }
 
        /*
         *      Now we encode one vendor attribute.
         */
        da = da_stack->da[depth];
        fr_assert(da != NULL);
 
        /*
         *      Most VSAs get limited to the one attribute.  Only refs
         *      (e.g. DHCPv4, DHCpv6) can get fragmented.
         */
        if (da->type != FR_TYPE_GROUP) {
                work_dbuff = FR_DBUFF_MAX(dbuff, UINT8_MAX);
        } else {
                work_dbuff = FR_DBUFF(dbuff);
        }
 
        fr_dbuff_marker(&hdr, &work_dbuff);
 
        /*
         *      Build the Vendor-Specific header
         */
        FR_DBUFF_IN_BYTES_RETURN(&work_dbuff, FR_VENDOR_SPECIFIC);
 
        fr_dbuff_marker(&length_field, &work_dbuff);
        FR_DBUFF_IN_BYTES_RETURN(&work_dbuff, 0);
 
        FR_DBUFF_IN_RETURN(&work_dbuff, (uint32_t)dv->attr);    /* Copy in the 32bit vendor ID */
 
 
        hdr_len = dv->flags.type_size + dv->flags.length;
 
        /*
         *      Vendors use different widths for their
         *      attribute number fields.
         */
        switch (dv->flags.type_size) {
        default:
                fr_strerror_printf("%s: Internal sanity check failed, type %u", __FUNCTION__, (unsigned) dv->flags.type_size);
                return PAIR_ENCODE_FATAL_ERROR;
 
        case 4:
                fr_dbuff_in(&work_dbuff, (uint32_t)da->attr);
                break;
 
        case 2:
                fr_dbuff_in(&work_dbuff, (uint16_t)da->attr);
                break;
 
        case 1:
                fr_dbuff_in(&work_dbuff, (uint8_t)da->attr);
                break;
        }
 
        /*
         *      The length fields will get over-written later.
         */
        switch (dv->flags.length) {
        default:
                fr_strerror_printf("%s: Internal sanity check failed, length %u", __FUNCTION__, (unsigned) dv->flags.length);
                return PAIR_ENCODE_FATAL_ERROR;
 
        case 0:
                break;
 
        case 2:
                fr_dbuff_in_bytes(&work_dbuff, 0);
                FALL_THROUGH;
 
        case 1:
                /*
                 *      Length fields are set to zero, because they
                 *      will get over-ridden later.
                 */
                fr_dbuff_marker(&vsa_length_field, &work_dbuff);
                fr_dbuff_in_bytes(&work_dbuff, 0);
                break;
        }
 
        slen = encode_value(&work_dbuff, da_stack, depth, cursor, encode_ctx);
        if (slen <= 0) return slen;
 
        /*
         *      There may be more than 253 octets of data encoded in
         *      the attribute.  If so, move the data up in the packet,
         *      and copy the existing header over.  Set the "C" flag
         *      ONLY after copying the rest of the data.
         *
         *      Note that we do NOT check 'slen' here, as it's only
         *      the size of the sub-sub attribute, and doesn't include
         *      the RADIUS attribute header, or Vendor-ID.
         */
        if (fr_dbuff_used(&work_dbuff) > UINT8_MAX) {
                size_t length_offset = 0;
 
                if (dv->flags.length) length_offset = 6 + hdr_len - 1;
 
                slen = attr_fragment(&work_dbuff, (size_t)slen, &hdr, 6 + hdr_len, 0, length_offset);
                if (slen <= 0) return slen;
        } else {
                if (dv->flags.length) {
                        fr_dbuff_in(&vsa_length_field, (uint8_t)(hdr_len + slen));
                }
 
                fr_dbuff_in(&length_field, (uint8_t) fr_dbuff_used(&work_dbuff));
        }
 
        FR_PROTO_HEX_DUMP(fr_dbuff_current(&hdr), 6 + hdr_len, "header vsa");
 
        return fr_dbuff_set(dbuff, &work_dbuff);
}
 
/** Encode a WiMAX attribute
 *
 */
static ssize_t encode_wimax(fr_dbuff_t *dbuff,
                                fr_da_stack_t *da_stack, unsigned int depth,
                                fr_dcursor_t *cursor, void *encode_ctx)
{
        ssize_t                 slen;
        fr_dbuff_t              work_dbuff = FR_DBUFF(dbuff);
        fr_dbuff_marker_t       hdr, length_field, vsa_length_field;
        fr_dict_attr_t const    *dv;
        fr_pair_t const         *vp = fr_dcursor_current(cursor);
 
        fr_dbuff_marker(&hdr, &work_dbuff);
 
        PAIR_VERIFY(vp);
        FR_PROTO_STACK_PRINT(da_stack, depth);
 
        dv = da_stack->da[depth++];
 
        if (dv->type != FR_TYPE_VENDOR) {
                fr_strerror_const("Expected Vendor");
                return PAIR_ENCODE_FATAL_ERROR;
        }
 
        FR_PROTO_STACK_PRINT(da_stack, depth);
 
        /*
         *      Build the Vendor-Specific header
         */
        FR_DBUFF_IN_BYTES_RETURN(&work_dbuff, FR_VENDOR_SPECIFIC);
        fr_dbuff_marker(&length_field, &work_dbuff);
        FR_DBUFF_IN_BYTES_RETURN(&work_dbuff, 0x09);
 
        FR_DBUFF_IN_RETURN(&work_dbuff, (uint32_t) dv->attr);
 
        /*
         *      Encode the first attribute
         */
        FR_DBUFF_IN_BYTES_RETURN(&work_dbuff, (uint8_t)da_stack->da[depth]->attr);
 
        fr_dbuff_marker(&vsa_length_field, &work_dbuff);
        FR_DBUFF_IN_BYTES_RETURN(&work_dbuff, 0x03, 0x00); /* length + continuation, both may be overwritten later */
 
        /*
         *      We don't bound the size of work_dbuff; it can use more than UINT8_MAX bytes
         *      because of the "continuation" byte.
         */
        slen = encode_value(&work_dbuff, da_stack, depth, cursor, encode_ctx);
        if (slen <= 0) return slen;
 
        /*
         *      There may be more than 253 octets of data encoded in
         *      the attribute.  If so, move the data up in the packet,
         *      and copy the existing header over.  Set the "C" flag
         *      ONLY after copying the rest of the data.
         *
         *      Note that we do NOT check 'slen' here, as it's only
         *      the size of the sub-sub attribute, and doesn't include
         *      the RADIUS attribute header, or Vendor-ID.
         */
        if (fr_dbuff_used(&work_dbuff) > UINT8_MAX) {
                slen = attr_fragment(&work_dbuff, (size_t)slen, &hdr, 9, 8, 7);
                if (slen <= 0) return slen;
 
                return fr_dbuff_set(dbuff, &work_dbuff);
        }
 
        fr_dbuff_in_bytes(&vsa_length_field, (uint8_t) (fr_dbuff_used(&work_dbuff) - 6));
        fr_dbuff_in_bytes(&length_field, (uint8_t) fr_dbuff_used(&work_dbuff));
 
        FR_PROTO_HEX_DUMP(fr_dbuff_current(&hdr), 9, "header wimax");
 
        return fr_dbuff_set(dbuff, &work_dbuff);
}
 
static ssize_t encode_vendor(fr_dbuff_t *dbuff,
                                 fr_da_stack_t *da_stack, unsigned int depth,
                                 fr_dcursor_t *cursor, void *encode_ctx)
{
        fr_dict_attr_t const    *da = da_stack->da[depth];
        ssize_t                 slen;
        fr_pair_t               *vp;
        fr_dict_vendor_t const  *dv;
        fr_dcursor_t            child_cursor;
        fr_dbuff_t              work_dbuff;
 
        FR_PROTO_STACK_PRINT(da_stack, depth);
 
        if (da->type != FR_TYPE_VENDOR) {
                fr_strerror_printf("%s: Expected type \"vendor\" got \"%s\"", __FUNCTION__,
                                   fr_type_to_str(da->type));
                return PAIR_ENCODE_FATAL_ERROR;
        }
 
        dv = fr_dict_vendor_by_da(da_stack->da[depth]);
 
        /*
         *      Flat hierarchy, encode one attribute at a time.
         *
         *      Note that there's no attempt to encode multiple VSAs
         *      into one attribute.  We can add that back as a flag,
         *      once all of the nested attribute conversion has been
         *      done.
         */
        if (da_stack->da[depth + 1]) {
                if (dv && dv->continuation) {
                        return encode_wimax(dbuff, da_stack, depth, cursor, encode_ctx);
                }
 
                return encode_vendor_attr(dbuff, da_stack, depth, cursor, encode_ctx);
        }
 
        /*
         *      Loop over the children of this attribute of type Vendor.
         */
        vp = fr_dcursor_current(cursor);
        fr_assert(vp->da == da);
        work_dbuff = FR_DBUFF(dbuff);
 
        fr_pair_dcursor_child_iter_init(&child_cursor, &vp->vp_group, cursor);
        while ((vp = fr_dcursor_current(&child_cursor)) != NULL) {
                fr_proto_da_stack_build(da_stack, vp->da);
 
                if (dv && dv->continuation) {
                        slen = encode_wimax(&work_dbuff, da_stack, depth, &child_cursor, encode_ctx);
                } else {
                        slen = encode_vendor_attr(&work_dbuff, da_stack, depth, &child_cursor, encode_ctx);
                }
                if (slen < 0) return slen;
        }
 
        vp = fr_dcursor_next(cursor);
        fr_proto_da_stack_build(da_stack, vp ? vp->da : NULL);
 
        return fr_dbuff_set(dbuff, &work_dbuff);
}
 
/** Encode a Vendor-Specific attribute
 *
 */
static ssize_t encode_vsa(fr_dbuff_t *dbuff,
                              fr_da_stack_t *da_stack, unsigned int depth,
                              fr_dcursor_t *cursor, void *encode_ctx)
{
        ssize_t                 slen;
        fr_pair_t               *vp;
        fr_dcursor_t            child_cursor;
        fr_dict_attr_t const    *da = da_stack->da[depth];
        fr_dbuff_t              work_dbuff;
 
        FR_PROTO_STACK_PRINT(da_stack, depth);
 
        if (da->type != FR_TYPE_VSA) {
                fr_strerror_printf("%s: Expected type \"vsa\" got \"%s\"", __FUNCTION__,
                                   fr_type_to_str(da->type));
                return PAIR_ENCODE_FATAL_ERROR;
        }
 
        /*
         *      Loop over the contents of Vendor-Specific, each of
         *      which MUST be of type FR_TYPE_VENDOR.
         */
        if (da_stack->da[depth + 1]) {
                return encode_vendor(dbuff, da_stack, depth + 1, cursor, encode_ctx);
        }
 
        work_dbuff = FR_DBUFF(dbuff);
 
        vp = fr_dcursor_current(cursor);
        if (vp->da != da_stack->da[depth]) {
                fr_strerror_printf("%s: Can't encode empty Vendor-Specific", __FUNCTION__);
                return 0;
        }
 
        /*
         *      Loop over the children of this Vendor-Specific
         *      attribute.
         */
        fr_pair_dcursor_child_iter_init(&child_cursor, &vp->vp_group, cursor);
        while ((vp = fr_dcursor_current(&child_cursor)) != NULL) {
                fr_proto_da_stack_build(da_stack, vp->da);
 
                fr_assert(da_stack->da[depth + 1]->type == FR_TYPE_VENDOR);
 
                slen = encode_vendor(&work_dbuff, da_stack, depth + 1, &child_cursor, encode_ctx);
                if (slen < 0) return slen;
        }
 
        /*
         *      Fix up the da stack, and return the data we've encoded.
         */
        vp = fr_dcursor_next(cursor);
        fr_proto_da_stack_build(da_stack, vp ? vp->da : NULL);
 
        FR_PROTO_HEX_DUMP(fr_dbuff_start(&work_dbuff), 6, "header vsa");
 
        return fr_dbuff_set(dbuff, &work_dbuff);
}
 
/** Encode NAS-Filter-Rule
 *
 *  Concatenating the string attributes together, separated by a 0x00 byte,
 */
static ssize_t encode_nas_filter_rule(fr_dbuff_t *dbuff,
                                      fr_da_stack_t *da_stack, NDEBUG_UNUSED unsigned int depth,
                                      fr_dcursor_t *cursor, UNUSED void *encode_ctx)
{
        fr_dbuff_t              work_dbuff = FR_DBUFF(dbuff);
        fr_dbuff_marker_t       hdr, frag_hdr;
        fr_pair_t               *vp = fr_dcursor_current(cursor);
        size_t                  attr_len = 2;
 
        FR_PROTO_STACK_PRINT(da_stack, depth);
 
        fr_assert(vp);
        fr_assert(vp->da);
 
        fr_dbuff_marker(&hdr, &work_dbuff);
        fr_dbuff_marker(&frag_hdr, &work_dbuff);
        fr_dbuff_advance(&hdr, 1);
        FR_DBUFF_IN_BYTES_RETURN(&work_dbuff, (uint8_t)vp->da->attr, 0x00);
 
        fr_assert(vp->da == attr_nas_filter_rule);
 
        while (true) {
                size_t data_len = vp->vp_length;
                size_t frag_len;
                char const *p = vp->vp_strvalue;
 
                /*
                 *      Keep encoding this attribute until it's done.
                 */
                while (data_len > 0) {
                        frag_len = data_len;
 
                        /*
                         *      This fragment doesn't overflow the
                         *      attribute.  Copy it over, update the
                         *      length, but leave the marker at the
                         *      current header.
                         */
                        if ((attr_len + frag_len) <= UINT8_MAX) {
                                FR_DBUFF_IN_MEMCPY_RETURN(&work_dbuff, p, frag_len);
                                attr_len += frag_len;
 
                                fr_dbuff_set(&frag_hdr, &hdr);
                                fr_dbuff_in(&frag_hdr, (uint8_t) attr_len); /* there's no fr_dbuff_in_no_advance() */
                                break;
                        }
 
                        /*
                         *      This fragment overflows the attribute.
                         *      Copy the fragment in, and create a new
                         *      attribute header.
                         */
                        frag_len = UINT8_MAX - attr_len;
                        FR_DBUFF_IN_MEMCPY_RETURN(&work_dbuff, p, frag_len);
                        fr_dbuff_in(&hdr, (uint8_t) UINT8_MAX);
 
                        fr_dbuff_marker(&hdr, &work_dbuff);
                        fr_dbuff_advance(&hdr, 1);
                        FR_DBUFF_IN_BYTES_RETURN(&work_dbuff, (uint8_t)vp->da->attr, 0x02);
                        attr_len = 2;
 
                        p += frag_len;
                        data_len -= frag_len;
                }
 
                /*
                 *      If we have nothing more to do here, then stop.
                 */
                vp = fr_dcursor_next(cursor);
                if (!vp || (vp->da != attr_nas_filter_rule)) {
                        break;
                }
 
                /*
                 *      We have to add a zero byte.  If it doesn't
                 *      overflow the current attribute, then just add
                 *      it in.
                 */
                if (attr_len < UINT8_MAX) {
                        attr_len++;
                        FR_DBUFF_IN_BYTES_RETURN(&work_dbuff, 0x00);
 
                        fr_dbuff_set(&frag_hdr, &hdr);
                        fr_dbuff_in(&frag_hdr, (uint8_t) attr_len); /* there's no fr_dbuff_in_no_advance() */
                        continue;
                }
 
                /*
                 *      The zero byte causes the current attribute to
                 *      overflow.  Create a new header with the zero
                 *      byte already populated, and keep going.
                 */
                fr_dbuff_marker(&hdr, &work_dbuff);
                fr_dbuff_advance(&hdr, 1);
                FR_DBUFF_IN_BYTES_RETURN(&work_dbuff, (uint8_t)vp->da->attr, 0x00, 0x00);
                attr_len = 3;
        }
 
        vp = fr_dcursor_current(cursor);
        fr_proto_da_stack_build(da_stack, vp ? vp->da : NULL);
 
        return fr_dbuff_set(dbuff, &work_dbuff);
}
 
/** Encode an RFC standard attribute 1..255
 *
 *  This function is not the same as encode_child(), because this
 *  one treats some "top level" attributes as special.  e.g.
 *  Message-Authenticator.
 */
static ssize_t encode_rfc(fr_dbuff_t *dbuff, fr_da_stack_t *da_stack, unsigned int depth,
                              fr_dcursor_t *cursor, void *encode_ctx)
{
        fr_pair_t const *vp = fr_dcursor_current(cursor);
        fr_dbuff_t              work_dbuff = FR_DBUFF(dbuff);
        fr_dbuff_marker_t       start;
        fr_radius_encode_ctx_t  *packet_ctx = encode_ctx;
 
        fr_dbuff_marker(&start, &work_dbuff);
 
        /*
         *      Sanity checks
         */
        PAIR_VERIFY(vp);
        FR_PROTO_STACK_PRINT(da_stack, depth);
 
        switch (da_stack->da[depth]->type) {
        case FR_TYPE_TLV:
        case FR_TYPE_VSA:
        case FR_TYPE_VENDOR:
                /* FR_TYPE_STRUCT is actually allowed... */
                fr_strerror_printf("%s: Expected leaf type got \"%s\"", __FUNCTION__,
                                   fr_type_to_str(da_stack->da[depth]->type));
                return PAIR_ENCODE_FATAL_ERROR;
 
        default:
                /*
                 *      Attribute 0 is fine as a TLV leaf, or VSA, but not
                 *      in the original standards space.
                 */
                if (((fr_dict_vendor_num_by_da(da_stack->da[depth]) == 0) && (da_stack->da[depth]->attr == 0)) ||
                    (da_stack->da[depth]->attr > UINT8_MAX)) {
                        fr_strerror_printf("%s: Called with non-standard attribute %u", __FUNCTION__, vp->da->attr);
                        return 0;
                }
                break;
        }
 
        /*
         *      Only CUI is allowed to have zero length.
         *      Thank you, WiMAX!
         */
        if ((vp->da == attr_chargeable_user_identity) && (vp->vp_length == 0)) {
                fr_dbuff_in_bytes(&work_dbuff, (uint8_t)vp->da->attr, 0x02);
 
                FR_PROTO_HEX_DUMP(fr_dbuff_current(&start), 2, "header rfc");
 
                vp = fr_dcursor_next(cursor);
                fr_proto_da_stack_build(da_stack, vp ? vp->da : NULL);
                return fr_dbuff_set(dbuff, &work_dbuff);
        }
 
        /*
         *      Message-Authenticator is hard-coded.
         */
        if (vp->da == attr_message_authenticator) {
                if (!packet_ctx->seen_message_authenticator) {
                        FR_DBUFF_IN_BYTES_RETURN(&work_dbuff, (uint8_t)vp->da->attr, 18);
                        FR_DBUFF_MEMSET_RETURN(&work_dbuff, 0, RADIUS_MESSAGE_AUTHENTICATOR_LENGTH);
 
                        FR_PROTO_HEX_DUMP(fr_dbuff_current(&start) + 2, RADIUS_MESSAGE_AUTHENTICATOR_LENGTH,
                                          "message-authenticator");
                        FR_PROTO_HEX_DUMP(fr_dbuff_current(&start), 2, "header rfc");
 
                        packet_ctx->seen_message_authenticator = true;
                }
 
                vp = fr_dcursor_next(cursor);
                fr_proto_da_stack_build(da_stack, vp ? vp->da : NULL);
                return fr_dbuff_set(dbuff, &work_dbuff);
        }
 
        /*
         *      NAS-Filter-Rule has a stupid format in order to save
         *      one byte per attribute.
         */
        if (vp->da == attr_nas_filter_rule) {
                return encode_nas_filter_rule(dbuff, da_stack, depth, cursor, encode_ctx);
        }
 
        /*
         *      Once we've checked for various top-level magic, RFC attributes are just TLVs.
         */
        return encode_child(dbuff, da_stack, depth, cursor, encode_ctx);
}
 
/** Encode a data structure into a RADIUS attribute
 *
 * This is the main entry point into the encoder.  It sets up the encoder array
 * we use for tracking our TLV/VSA nesting and then calls the appropriate
 * dispatch function.
 *
 * @param[out] dbuff            Where to write encoded data.
 * @param[in] cursor            Specifying attribute to encode.
 * @param[in] encode_ctx        Additional data such as the shared secret to use.
 * @return
 *      - >0 The number of bytes written to out.
 *      - 0 Nothing to encode (or attribute skipped).
 *      - <0 an error occurred.
 */
ssize_t fr_radius_encode_pair(fr_dbuff_t *dbuff, fr_dcursor_t *cursor, void *encode_ctx)
{
        fr_pair_t const         *vp;
        ssize_t                 slen;
        fr_dbuff_t              work_dbuff = FR_DBUFF(dbuff);
 
        fr_da_stack_t           da_stack;
        fr_dict_attr_t const    *da = NULL;
 
        if (!cursor) return PAIR_ENCODE_FATAL_ERROR;
 
        vp = fr_dcursor_current(cursor);
        if (!vp) return 0;
 
        PAIR_VERIFY(vp);
 
        if (vp->da->depth > FR_DICT_MAX_TLV_STACK) {
                fr_strerror_printf("%s: Attribute depth %u exceeds maximum nesting depth %i",
                                   __FUNCTION__, vp->da->depth, FR_DICT_MAX_TLV_STACK);
                return PAIR_ENCODE_FATAL_ERROR;
        }
 
        /*
         *      Tags are *top-level*, and are never nested.
         */
        if ((vp->vp_type == FR_TYPE_GROUP) && vp->da->flags.internal &&
            (vp->da->attr > FR_TAG_BASE) && (vp->da->attr < (FR_TAG_BASE + 0x20))) {
                fr_radius_encode_ctx_t  *packet_ctx = encode_ctx;
 
                packet_ctx->tag = vp->da->attr - FR_TAG_BASE;
                fr_assert(packet_ctx->tag > 0);
                fr_assert(packet_ctx->tag < 0x20);
 
                // recurse to encode the children of this attribute
                slen = encode_pairs(&work_dbuff, &vp->vp_group, encode_ctx);
                packet_ctx->tag = 0;
                if (slen < 0) return slen;
 
                fr_dcursor_next(cursor); /* skip the tag attribute */
                return fr_dbuff_set(dbuff, &work_dbuff);
        }
 
        /*
         *      Check for zero-length attributes.
         */
        switch (vp->vp_type) {
        default:
                break;
 
                /*
                 *      Only variable length data types can be
                 *      variable sized.  All others have fixed size.
                 */
        case FR_TYPE_STRING:
        case FR_TYPE_OCTETS:
                /*
                 *      Zero-length strings are allowed for CUI
                 *      (thanks WiMAX!), and for
                 *      Message-Authenticator, because we will
                 *      automagically generate that one ourselves.
                 */
                if ((vp->vp_length == 0) &&
                    (vp->da != attr_chargeable_user_identity) &&
                    (vp->da != attr_message_authenticator)) {
                        fr_dcursor_next(cursor);
                        fr_strerror_const("Zero length string attributes not allowed");
                        return 0;
                }
                break;
        }
 
        /*
         *      Nested structures of attributes can't be longer than
         *      255 bytes, so each call to an encode function can
         *      only use 255 bytes of buffer space at a time.
         */
 
        /*
         *      Fast path for the common case.
         */
        if (vp->da->parent->flags.is_root && fr_radius_flag_encrypted(vp->da)) {
                switch (vp->vp_type) {
                case FR_TYPE_LEAF:
                        da_stack.da[0] = vp->da;
                        da_stack.da[1] = NULL;
                        da_stack.depth = 1;
                        FR_PROTO_STACK_PRINT(&da_stack, 0);
                        slen = encode_rfc(&work_dbuff, &da_stack, 0, cursor, encode_ctx);
                        if (slen < 0) return slen;
                        return fr_dbuff_set(dbuff, &work_dbuff);
 
                default:
                        break;
                }
        }
 
        /*
         *      Do more work to set up the stack for the complex case.
         */
        fr_proto_da_stack_build(&da_stack, vp->da);
        FR_PROTO_STACK_PRINT(&da_stack, 0);
 
        /*
         *      Top-level attributes get treated specially.  Things
         *      like VSAs inside of extended attributes are handled
         *      inside of type-specific encoders.
         */
        da = da_stack.da[0];
        switch (da->type) {
        case FR_TYPE_OCTETS:
                if (fr_radius_flag_concat(da)) {
                        /*
                         *      Attributes like EAP-Message are marked as
                         *      "concat", which means that they are fragmented
                         *      using a different scheme than the "long
                         *      extended" one.
                         */
                        slen = encode_concat(&work_dbuff, &da_stack, 0, cursor, encode_ctx);
                        if (slen < 0) return slen;
                        break;
                }
                FALL_THROUGH;
 
        default:
                slen = encode_rfc(&work_dbuff, &da_stack, 0, cursor, encode_ctx);
                if (slen < 0) return slen;
                break;
 
        case FR_TYPE_VSA:
                slen = encode_vsa(&work_dbuff, &da_stack, 0, cursor, encode_ctx);
                if (slen < 0) return slen;
                break;
 
        case FR_TYPE_TLV:
                if (!fr_radius_flag_extended(da)) {
                        slen = encode_child(&work_dbuff, &da_stack, 0, cursor, encode_ctx);
 
                } else if (vp->da != da) {
                        fr_strerror_printf("extended attributes must be nested");
                        return PAIR_ENCODE_FATAL_ERROR;
 
                } else {
                        slen = encode_extended_nested(&work_dbuff, &da_stack, 0, cursor, encode_ctx);
                }
                if (slen < 0) return slen;
                break;
 
        case FR_TYPE_NULL:
        case FR_TYPE_VENDOR:
        case FR_TYPE_MAX:
                fr_strerror_printf("%s: Cannot encode attribute %s", __FUNCTION__, vp->da->name);
                return PAIR_ENCODE_FATAL_ERROR;
        }
 
        /*
         *      We couldn't do it, so we didn't do anything.
         */
        if (fr_dcursor_current(cursor) == vp) {
                fr_strerror_printf("%s: Nested attribute structure too large to encode", __FUNCTION__);
                return PAIR_ENCODE_FATAL_ERROR;
        }
 
        return fr_dbuff_set(dbuff, &work_dbuff);
}
 
ssize_t fr_radius_encode_foreign(fr_dbuff_t *dbuff, fr_pair_list_t const *list)
{
        fr_radius_ctx_t common_ctx = {};
        fr_radius_encode_ctx_t encode_ctx = {
                .common = &common_ctx,
        };
 
        /*
         *      Just in case we need random numbers.
         */
        encode_ctx.rand_ctx.a = fr_rand();
        encode_ctx.rand_ctx.b = fr_rand();
 
        /*
         *      Encode the pairs.
         */
        return encode_pairs(dbuff, list, &encode_ctx);
}
 
 
static int encode_test_ctx(void **out, TALLOC_CTX *ctx, UNUSED fr_dict_t const *dict,
                           UNUSED fr_dict_attr_t const *root_da)
{
        static uint8_t vector[RADIUS_AUTH_VECTOR_LENGTH] = {
                0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
                0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f };
 
        fr_radius_encode_ctx_t  *test_ctx;
        fr_radius_ctx_t         *common;
 
        test_ctx = talloc_zero(ctx, fr_radius_encode_ctx_t);
        if (!test_ctx) return -1;
 
        test_ctx->common = common = talloc_zero(test_ctx, fr_radius_ctx_t);
 
        common->secret = talloc_strdup(test_ctx->common, "testing123");
        common->secret_length = talloc_array_length(test_ctx->common->secret) - 1;
 
        /*
         *      We don't want to automatically add Message-Authenticator
         */
        common->secure_transport = true;
 
        test_ctx->request_authenticator = vector;
        test_ctx->rand_ctx.a = 6809;
        test_ctx->rand_ctx.b = 2112;
 
        *out = test_ctx;
 
        return 0;
}
 
static ssize_t fr_radius_encode_proto(TALLOC_CTX *ctx, fr_pair_list_t *vps, uint8_t *data, size_t data_len, void *proto_ctx)
{
        fr_radius_encode_ctx_t  *packet_ctx = talloc_get_type_abort(proto_ctx, fr_radius_encode_ctx_t);
        int packet_type = FR_RADIUS_CODE_ACCESS_REQUEST;
        fr_pair_t *vp;
        ssize_t slen;
        uint8_t const *request_authenticator = NULL;
 
        vp = fr_pair_find_by_da(vps, NULL, attr_packet_type);
        if (vp) {
                packet_type = vp->vp_uint32;
 
                if (!FR_RADIUS_PACKET_CODE_VALID(packet_type)) {
                        fr_strerror_printf("Invalid packet code %u", packet_type);
                        return -1;
                }
        }
 
        /*
         *      Force specific values for testing.
         */
        if ((packet_type == FR_RADIUS_CODE_ACCESS_REQUEST) || (packet_type == FR_RADIUS_CODE_STATUS_SERVER)) {
                vp = fr_pair_find_by_da(vps, NULL, attr_packet_authentication_vector);
                if (!vp) {
                        fr_pair_list_append_by_da_len(ctx, vp, vps, attr_packet_authentication_vector,
                                                      packet_ctx->request_authenticator, RADIUS_AUTH_VECTOR_LENGTH, false);
                }
        }
 
        packet_ctx->code = packet_type;
        packet_ctx->request_code = allowed_replies[packet_type];
        if (packet_ctx->request_code) request_authenticator = packet_ctx->request_authenticator;
 
        /*
         *      @todo - pass in packet_ctx to this function, so that we
         *      can leverage a consistent random number generator.
         */
        slen = fr_radius_encode(&FR_DBUFF_TMP(data, data_len), vps, packet_ctx);
        if (slen <= 0) return slen;
 
        if (fr_radius_sign(data, request_authenticator,
                           (uint8_t const *) packet_ctx->common->secret, talloc_array_length(packet_ctx->common->secret) - 1) < 0) {
                return -1;
        }
 
        return slen;
}
 
/*
 *      No one else should be using this.
 */
extern void *fr_radius_next_encodable(fr_dcursor_t *cursor, void *to_eval, void *uctx);
 
/*
 *      Test points
 */
extern fr_test_point_pair_encode_t radius_tp_encode_pair;
fr_test_point_pair_encode_t radius_tp_encode_pair = {
        .test_ctx       = encode_test_ctx,
        .func           = fr_radius_encode_pair,
        .next_encodable = fr_radius_next_encodable,
};
 
 
extern fr_test_point_proto_encode_t radius_tp_encode_proto;
fr_test_point_proto_encode_t radius_tp_encode_proto = {
        .test_ctx       = encode_test_ctx,
        .func           = fr_radius_encode_proto
};