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Diffstat (limited to 'skeletons/ber_decoder.c')
| -rw-r--r-- | skeletons/ber_decoder.c | 230 |
1 files changed, 230 insertions, 0 deletions
diff --git a/skeletons/ber_decoder.c b/skeletons/ber_decoder.c new file mode 100644 index 00000000..135e7910 --- /dev/null +++ b/skeletons/ber_decoder.c @@ -0,0 +1,230 @@ +/*- + * Copyright (c) 2003 Lev Walkin <vlm@lionet.info>. All rights reserved. + * Redistribution and modifications are permitted subject to BSD license. + */ +#include <constr_TYPE.h> +#include <assert.h> + +#define ADVANCE(num_bytes) do { \ + size_t num = num_bytes; \ + ptr += num; \ + size -= num; \ + consumed_myself += num; \ + } while(0) +#define RETURN(_code) do { \ + ber_dec_rval_t rval; \ + rval.code = _code; \ + rval.consumed = consumed_myself; \ + return rval; \ + } while(0) + +/* + * The BER decoder of any type. + */ +ber_dec_rval_t +ber_decode(asn1_TYPE_descriptor_t *type_descriptor, + void **struct_ptr, void *ptr, size_t size) { + + /* + * Invoke type-specific decoder. + */ + return type_descriptor->ber_decoder(type_descriptor, + struct_ptr, /* Pointer to the destination structure */ + ptr, size, /* Buffer and its size */ + 0 /* Default tag mode is 0 */ + ); +} + +/* + * Check the set of <TL<TL<TL...>>> tags matches the definition. + */ +ber_dec_rval_t +ber_check_tags(asn1_TYPE_descriptor_t *head, ber_dec_ctx_t *ctx, + void *ptr, size_t size, int tag_mode, + ber_tlv_len_t *last_length, int *opt_tlv_form) { + ssize_t consumed_myself = 0; + ssize_t tag_len; + ssize_t len_len; + ber_tlv_tag_t tlv_tag; + ber_tlv_len_t tlv_len; + ber_tlv_len_t limit_len = -1; + int expect_00_terminators = 0; + int tlv_constr = -1; /* If CHOICE, opt_tlv_form is not given */ + int tagno; + + /* + * So what does all this tags_impl_skip stuff mean? + * Imagine two types, + * A ::= [5] IMPLICIT T + * B ::= [2] EXPLICIT T + * Where T is defined as + * T ::= [4] IMPLICIT SEQUENCE { ... } + * + * Let's say, we are starting to decode type A, given the + * following TLV stream: <5> <0>. What does this mean? + * It means that the type A contains type T which is, + * in turn, empty. + * Remember though, that we are still in A. We cannot + * just pass control to the type T decoder. Why? Because + * the type T decoder expects <4> <0>, not <5> <0>. + * So, we must make sure we are going to receive <5> while + * still in A, then pass control to the T decoder, indicating + * that the tag <4> was implicitly skipped. The decoder of T + * hence will be prepared to treat <4> as valid tag, and decode + * it appropriately. + */ + + /* + * We have a list of tags that must occur in the stream: + * {A,B,C} + * However, it may be indicated that the type is + * implicitly tagged in the caller, so it really boils down to the + * {I,B,C} or even {I,C} + * This is because the implicit tag at above structure may replace + * zero or more (or every) tags which follow it. We don't care + * about the precise number, as it is already computed for us + * by the ASN.1 compiler and placed into head->tags_impl_skip. + * So let's suppose the only tag left after implicit tagging is {I}. + * Yet, the table we have is {A,B,C} and head->tags_impl_skip=3. + * We need to check at least one tag in the loop, so the loop range + * is modified so it will be invoked at least one time. + */ + tagno = ctx->step /* Continuing where left previously */ + + (tag_mode==-1?(head->tags_impl_skip-1):0) + + (tag_mode==1?-1:0) + ; + //assert(head->tags_count >= 1); ?May not be the case for CHOICE! + assert(tagno < head->tags_count); /* At least one loop */ + for((void)tagno; tagno < head->tags_count; tagno++, ctx->step++) { + + /* + * Fetch and process T from TLV. + */ + tag_len = ber_fetch_tag(ptr, size, &tlv_tag); + ASN_DEBUG("Fetching tag from {%p,%ld} %02X: " + "len %ld, tag %s", + ptr, (long)size, + *(uint8_t *)ptr, (long)tag_len, + ber_tlv_tag_string(tlv_tag)); + switch(tag_len) { + case -1: RETURN(RC_FAIL); + case 0: RETURN(RC_WMORE); + } + + tlv_constr = BER_TLV_CONSTRUCTED(ptr); + + /* + * If {I}, don't check anything. + * If {I,B,C}, check B and C unless we're at I. + */ + if(tag_mode != 0 && ctx->step == 0) { + /* + * We don't expect tag to match here. + * It's just because we don't know how the tag + * is supposed to look like. + */ + } else { + assert(tagno >= 0); /* Guaranteed by the code above */ + if(tlv_tag != head->tags[tagno]) { + /* + * Unexpected tag. Too bad. + */ + ASN_DEBUG("Expected: %s, expectation failed", + ber_tlv_tag_string(head->tags[tagno])); + RETURN(RC_FAIL); + } + } + + /* + * Attention: if there are more tags expected, + * ensure that the current tag is presented + * in constructed form (it contains other tags!). + * If this one is the last one, check that the tag form + * matches the one given in descriptor. + */ + if(tagno < (head->tags_count - 1)) { + if(tlv_constr == 0) { + RETURN(RC_FAIL); + } + } else { + if(head->last_tag_form != tlv_constr + && head->last_tag_form != -1) { + RETURN(RC_FAIL); + } + } + + /* + * Fetch and process L from TLV. + */ + len_len = ber_fetch_length(tlv_constr, + ptr + tag_len, size - tag_len, &tlv_len); + switch(len_len) { + case -1: RETURN(RC_FAIL); + case 0: RETURN(RC_WMORE); + } + + /* + * FIXME + * As of today, the chain of tags + * must either contain several indefinite length TLVs, + * or several definite length ones. + * No mixing is allowed. + */ + if(tlv_len == -1) { + /* + * Indefinite length. + */ + if(limit_len == -1) { + expect_00_terminators++; + } else { + ASN_DEBUG("Unexpected indefinite length " + "in a chain of definite lengths"); + RETURN(RC_FAIL); + } + ADVANCE(tag_len + len_len); + continue; + } else { + if(expect_00_terminators) { + ASN_DEBUG("Unexpected definite length " + "in a chain of indefinite lengths"); + RETURN(RC_FAIL); + } + } + + /* + * Check that multiple TLVs specify ever decreasing length, + * which is consistent. + */ + if(limit_len == -1) { + limit_len = tlv_len + tag_len + len_len; + } else if(limit_len != tlv_len + tag_len + len_len) { + /* + * Inner TLV specifies length which is inconsistent + * with the outer TLV's length value. + */ + ASN_DEBUG("Outer TLV is %d and inner is %d", + limit_len, tlv_len); + RETURN(RC_FAIL); + } + + ADVANCE(tag_len + len_len); + + limit_len -= (tag_len + len_len); + if(size > limit_len) { + /* + * Make sure that we won't consume more bytes + * from the large buffer than the inferred limit. + */ + size = limit_len; + } + } + + if(opt_tlv_form) + *opt_tlv_form = tlv_constr; + if(expect_00_terminators) + *last_length = -expect_00_terminators; + else + *last_length = tlv_len; + + RETURN(RC_OK); +} |