int aws_hpack_decode_string()

in source/hpack.c [955:1049]

• 67 lines of code
• 14 McCabe index (conditional complexity)

int aws_hpack_decode_string(
    struct aws_hpack_context *context,
    struct aws_byte_cursor *to_decode,
    struct aws_byte_buf *output,
    bool *complete) {

    AWS_PRECONDITION(context);
    AWS_PRECONDITION(to_decode);
    AWS_PRECONDITION(output);
    AWS_PRECONDITION(complete);

    struct hpack_progress_string *progress = &context->progress_string;

    while (to_decode->len) {
        switch (progress->state) {
            case HPACK_STRING_STATE_INIT: {
                /* Do init stuff */
                progress->state = HPACK_STRING_STATE_LENGTH;
                progress->use_huffman = *to_decode->ptr >> 7;
                aws_huffman_decoder_reset(&context->decoder);
                /* fallthrough, since we didn't consume any data */
            }
            /* FALLTHRU */
            case HPACK_STRING_STATE_LENGTH: {
                bool length_complete = false;
                if (aws_hpack_decode_integer(context, to_decode, 7, &progress->length, &length_complete)) {
                    return AWS_OP_ERR;
                }

                if (!length_complete) {
                    goto handle_ongoing;
                }

                if (progress->length == 0) {
                    goto handle_complete;
                }

                if (progress->length > SIZE_MAX) {
                    return aws_raise_error(AWS_ERROR_OVERFLOW_DETECTED);
                }

                progress->state = HPACK_STRING_STATE_VALUE;
            } break;

            case HPACK_STRING_STATE_VALUE: {
                /* Take either as much data as we need, or as much as we can */
                size_t to_process = aws_min_size((size_t)progress->length, to_decode->len);
                progress->length -= to_process;

                struct aws_byte_cursor chunk = aws_byte_cursor_advance(to_decode, to_process);

                if (progress->use_huffman) {
                    if (aws_huffman_decode(&context->decoder, &chunk, output)) {
                        HPACK_LOGF(ERROR, context, "Error from Huffman decoder: %s", aws_error_name(aws_last_error()));
                        return AWS_OP_ERR;
                    }

                    /* Decoder should consume all bytes we feed it.
                     * EOS (end-of-string) symbol could stop it early, but HPACK says to treat EOS as error. */
                    if (chunk.len != 0) {
                        HPACK_LOG(ERROR, context, "Huffman encoded end-of-string symbol is illegal");
                        return aws_raise_error(AWS_ERROR_INVALID_ARGUMENT);
                    }
                } else {
                    if (aws_byte_buf_append_dynamic(output, &chunk)) {
                        return AWS_OP_ERR;
                    }
                }

                /* If whole length consumed, we're done */
                if (progress->length == 0) {
                    /* #TODO Validate any padding bits left over in final byte of string.
                     * "A padding not corresponding to the most significant bits of the
                     * code for the EOS symbol MUST be treated as a decoding error" */

                    /* #TODO impose limits on string length */

                    goto handle_complete;
                }
            } break;
        }
    }

handle_ongoing:
    /* Fell out of to_decode loop, must still be in progress */
    AWS_ASSERT(to_decode->len == 0);
    *complete = false;
    return AWS_OP_SUCCESS;

handle_complete:
    AWS_ASSERT(context->progress_string.length == 0);
    AWS_ZERO_STRUCT(context->progress_string);
    *complete = true;
    return AWS_OP_SUCCESS;
}