| /*- |
| * 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((ssize_t)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); |
| } |