libs/smux/der_encoder.c

   1 /*-
   2  * Copyright (c) 2003, 2004 Lev Walkin <vlm@lionet.info>. All rights reserved.
   3  * Redistribution and modifications are permitted subject to BSD license.
   4  */
   5 #include <asn_internal.h>
   6 #include <errno.h>
   7
   8 static ssize_t der_write_TL(ber_tlv_tag_t tag, ber_tlv_len_t len,
   9         asn_app_consume_bytes_f *cb, void *app_key, int constructed);
  10
  11 /*
  12  * The DER encoder of any type.
  13  */
  14 asn_enc_rval_t
  15 der_encode(const asn_TYPE_descriptor_t *type_descriptor, const void *struct_ptr,
  16            asn_app_consume_bytes_f *consume_bytes, void *app_key) {
  17     ASN_DEBUG("DER encoder invoked for %s",
  18                 type_descriptor->name);
  19
  20         /*
  21          * Invoke type-specific encoder.
  22          */
  23     return type_descriptor->op->der_encoder(
  24         type_descriptor, struct_ptr, /* Pointer to the destination structure */
  25         0, 0, consume_bytes, app_key);
  26 }
  27
  28 /*
  29  * Argument type and callback necessary for der_encode_to_buffer().
  30  */
  31 typedef struct enc_to_buf_arg {
  32         void *buffer;
  33         size_t left;
  34 } enc_to_buf_arg;
  35 static int encode_to_buffer_cb(const void *buffer, size_t size, void *key) {
  36         enc_to_buf_arg *arg = (enc_to_buf_arg *)key;
  37
  38         if(arg->left < size)
  39                 return -1;      /* Data exceeds the available buffer size */
  40
  41         memcpy(arg->buffer, buffer, size);
  42         arg->buffer = ((char *)arg->buffer) + size;
  43         arg->left -= size;
  44
  45         return 0;
  46 }
  47
  48 /*
  49  * A variant of the der_encode() which encodes the data into the provided buffer
  50  */
  51 asn_enc_rval_t
  52 der_encode_to_buffer(const asn_TYPE_descriptor_t *type_descriptor,
  53                      const void *struct_ptr, void *buffer, size_t buffer_size) {
  54     enc_to_buf_arg arg;
  55         asn_enc_rval_t ec;
  56
  57         arg.buffer = buffer;
  58         arg.left = buffer_size;
  59
  60         ec = type_descriptor->op->der_encoder(type_descriptor,
  61                 struct_ptr,     /* Pointer to the destination structure */
  62                 0, 0, encode_to_buffer_cb, &arg);
  63         if(ec.encoded != -1) {
  64                 assert(ec.encoded == (ssize_t)(buffer_size - arg.left));
  65                 /* Return the encoded contents size */
  66         }
  67         return ec;
  68 }
  69
  70
  71 /*
  72  * Write out leading TL[v] sequence according to the type definition.
  73  */
  74 ssize_t
  75 der_write_tags(const asn_TYPE_descriptor_t *sd, size_t struct_length,
  76                int tag_mode, int last_tag_form,
  77                ber_tlv_tag_t tag, /* EXPLICIT or IMPLICIT tag */
  78                asn_app_consume_bytes_f *cb, void *app_key) {
  79 #define ASN1_DER_MAX_TAGS_COUNT 4
  80     ber_tlv_tag_t
  81         tags_buf_scratch[ASN1_DER_MAX_TAGS_COUNT * sizeof(ber_tlv_tag_t)];
  82     ssize_t lens[ASN1_DER_MAX_TAGS_COUNT * sizeof(ssize_t)];
  83     const ber_tlv_tag_t *tags; /* Copy of tags stream */
  84     int tags_count;            /* Number of tags */
  85     size_t overall_length;
  86     int i;
  87
  88     ASN_DEBUG("Writing tags (%s, tm=%d, tc=%d, tag=%s, mtc=%d)",
  89                 sd->name, tag_mode, sd->tags_count,
  90                 ber_tlv_tag_string(tag),
  91                 tag_mode
  92                         ?(sd->tags_count+1
  93                                 -((tag_mode == -1) && sd->tags_count))
  94                         :sd->tags_count
  95         );
  96
  97     if(sd->tags_count + 1 > ASN1_DER_MAX_TAGS_COUNT) {
  98         ASN_DEBUG("System limit %d on tags count", ASN1_DER_MAX_TAGS_COUNT);
  99         return -1;
 100     }
 101
 102         if(tag_mode) {
 103                 /*
 104                  * Instead of doing shaman dance like we do in ber_check_tags(),
 105                  * allocate a small array on the stack
 106                  * and initialize it appropriately.
 107                  */
 108                 int stag_offset;
 109                 ber_tlv_tag_t *tags_buf = tags_buf_scratch;
 110                 tags_count = sd->tags_count
 111                         + 1     /* EXPLICIT or IMPLICIT tag is given */
 112                         - ((tag_mode == -1) && sd->tags_count);
 113                 /* Copy tags over */
 114                 tags_buf[0] = tag;
 115                 stag_offset = -1 + ((tag_mode == -1) && sd->tags_count);
 116                 for(i = 1; i < tags_count; i++)
 117                         tags_buf[i] = sd->tags[i + stag_offset];
 118                 tags = tags_buf;
 119         } else {
 120                 tags = sd->tags;
 121                 tags_count = sd->tags_count;
 122         }
 123
 124         /* No tags to write */
 125         if(tags_count == 0)
 126                 return 0;
 127
 128         /*
 129          * Array of tags is initialized.
 130          * Now, compute the size of the TLV pairs, from right to left.
 131          */
 132         overall_length = struct_length;
 133         for(i = tags_count - 1; i >= 0; --i) {
 134                 lens[i] = der_write_TL(tags[i], overall_length, 0, 0, 0);
 135                 if(lens[i] == -1) return -1;
 136                 overall_length += lens[i];
 137                 lens[i] = overall_length - lens[i];
 138         }
 139
 140         if(!cb) return overall_length - struct_length;
 141
 142         ASN_DEBUG("Encoding %s TL sequence (%d elements)", sd->name,
 143                   tags_count);
 144
 145         /*
 146          * Encode the TL sequence for real.
 147          */
 148         for(i = 0; i < tags_count; i++) {
 149                 ssize_t len;
 150                 int _constr;
 151
 152                 /* Check if this tag happens to be constructed */
 153                 _constr = (last_tag_form || i < (tags_count - 1));
 154
 155                 len = der_write_TL(tags[i], lens[i], cb, app_key, _constr);
 156                 if(len == -1) return -1;
 157         }
 158
 159         return overall_length - struct_length;
 160 }
 161
 162 static ssize_t
 163 der_write_TL(ber_tlv_tag_t tag, ber_tlv_len_t len,
 164                 asn_app_consume_bytes_f *cb, void *app_key,
 165                 int constructed) {
 166         uint8_t buf[32];
 167         size_t size = 0;
 168         int buf_size = cb?sizeof(buf):0;
 169         ssize_t tmp;
 170
 171         /* Serialize tag (T from TLV) into possibly zero-length buffer */
 172         tmp = ber_tlv_tag_serialize(tag, buf, buf_size);
 173         if(tmp == -1 || tmp > (ssize_t)sizeof(buf)) return -1;
 174         size += tmp;
 175
 176         /* Serialize length (L from TLV) into possibly zero-length buffer */
 177         tmp = der_tlv_length_serialize(len, buf+size, buf_size?buf_size-size:0);
 178         if(tmp == -1) return -1;
 179         size += tmp;
 180
 181         if(size > sizeof(buf))
 182                 return -1;
 183
 184         /*
 185          * If callback is specified, invoke it, and check its return value.
 186          */
 187         if(cb) {
 188                 if(constructed) *buf |= 0x20;
 189                 if(cb(buf, size, app_key) < 0)
 190                         return -1;
 191         }
 192
 193         return size;
 194 }