| #LyX 1.3 created this file. For more info see http://www.lyx.org/ |
| \lyxformat 221 |
| \textclass book |
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| %\renewcommand{\sectionmark}[1]{\markright{\MakeUppercase{\thesection.\ #1}}} |
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| \language english |
| \inputencoding latin1 |
| \fontscheme times |
| \graphics default |
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| \spacing single |
| \papersize Default |
| \paperpackage a4 |
| \use_geometry 0 |
| \use_amsmath 0 |
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| \paperorientation portrait |
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| \quotes_language swedish |
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| \papersides 2 |
| \paperpagestyle fancy |
| |
| \layout Title |
| |
| Using the Free ASN.1 Compiler |
| \layout Author |
| |
| Lev Walkin < |
| \begin_inset LatexCommand \url{vlm@lionet.info} |
| |
| \end_inset |
| |
| > |
| \layout Standard |
| |
| |
| \begin_inset ERT |
| status Open |
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| \layout Standard |
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| \backslash |
| extramarks{Document revision $Revision$}{} |
| \end_inset |
| |
| |
| \layout Standard |
| |
| |
| \begin_inset LatexCommand \tableofcontents{} |
| |
| \end_inset |
| |
| |
| \layout Standard |
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| |
| \begin_inset ERT |
| status Collapsed |
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| \layout Standard |
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| \backslash |
| pagestyle{headings} |
| \end_inset |
| |
| |
| \layout Part |
| |
| ASN.1 Basics |
| \layout Chapter |
| |
| Abstract Syntax Notation: ASN.1 |
| \layout Standard |
| |
| |
| \emph on |
| This chapter defines some basic ASN.1 concepts and describes several most |
| widely used types. |
| It is by no means an authoritative or complete reference. |
| For more complete ASN.1 description, please refer to Olivier Dubuisson's |
| book |
| \begin_inset LatexCommand \cite{Dub00} |
| |
| \end_inset |
| |
| or the ASN.1 body of standards itself |
| \begin_inset LatexCommand \cite{ITU-T/ASN.1} |
| |
| \end_inset |
| |
| . |
| \layout Standard |
| |
| The Abstract Syntax Notation One is used to formally describe the semantics |
| of data transmitted across the network. |
| Two communicating parties may have different formats of their native data |
| types (i.e. |
| number of bits in the integer type), thus it is important to have a way |
| to describe the data in a manner which is independent from the particular |
| machine's representation. |
| The ASN.1 specifications is used to achieve one or more of the following: |
| \layout Itemize |
| |
| The specification expressed in the ASN.1 notation is a formal and precise |
| way to communicate the data semantics to human readers; |
| \layout Itemize |
| |
| The ASN.1 specifications may be used as input for automatic compilers which |
| produce the code for some target language (C, C++, Java, etc) to encode |
| and decode the data according to some encoding rules (which are also defined |
| by the ASN.1 standard). |
| \layout Standard |
| |
| Consider the following example: |
| \layout LyX-Code |
| |
| Rectangle ::= SEQUENCE { |
| \layout LyX-Code |
| |
| height INTEGER, |
| \layout LyX-Code |
| |
| width INTEGER |
| \layout LyX-Code |
| |
| } |
| \layout Standard |
| |
| This ASN.1 specification describes a constructed type, |
| \emph on |
| Rectangle |
| \emph default |
| , containing two integer fields. |
| This specification may tell the reader that there is this kind of data |
| structure and that some entity may be prepared to send or receive it. |
| The question on |
| \emph on |
| how |
| \emph default |
| that entity is going to send or receive the |
| \emph on |
| encoded data |
| \emph default |
| is outside the scope of ASN.1. |
| For example, this data structure may be encoded according to some encoding |
| rules and sent to the destination using the TCP protocol. |
| The ASN.1 specifies several ways of encoding (or |
| \begin_inset Quotes sld |
| \end_inset |
| |
| serializing |
| \begin_inset Quotes srd |
| \end_inset |
| |
| , or |
| \begin_inset Quotes sld |
| \end_inset |
| |
| marshaling |
| \begin_inset Quotes srd |
| \end_inset |
| |
| ) the data: BER, CER, DER and XER, some of them which will be described |
| later. |
| \layout Standard |
| |
| The complete specification must be wrapped in a module, which looks like |
| this: |
| \layout LyX-Code |
| |
| UsageExampleModule1 |
| \layout LyX-Code |
| |
| { iso org(3) dod(6) internet(1) private(4) |
| \layout LyX-Code |
| |
| enterprise(1) spelio(9363) software(1) |
| \layout LyX-Code |
| |
| asn1c(5) docs(2) usage(1) 1 } |
| \layout LyX-Code |
| |
| DEFINITIONS AUTOMATIC TAGS ::= |
| \layout LyX-Code |
| |
| BEGIN |
| \layout LyX-Code |
| |
| |
| \layout LyX-Code |
| |
| -- This is a comment which describes nothing. |
| \layout LyX-Code |
| |
| Rectangle ::= SEQUENCE { |
| \layout LyX-Code |
| |
| height INTEGER, -- Height of the rectangle |
| \layout LyX-Code |
| |
| width INTEGER -- Width of the rectangle |
| \layout LyX-Code |
| |
| } |
| \layout LyX-Code |
| |
| |
| \layout LyX-Code |
| |
| END |
| \layout Standard |
| |
| The module header consists of module name (UsageExampleModule1), the module |
| object identifier ({...}), a keyword |
| \begin_inset Quotes sld |
| \end_inset |
| |
| DEFINITIONS |
| \begin_inset Quotes srd |
| \end_inset |
| |
| , a set of module flags (AUTOMATIC TAGS) and |
| \begin_inset Quotes sld |
| \end_inset |
| |
| ::= BEGIN |
| \begin_inset Quotes srd |
| \end_inset |
| |
| . |
| The module ends with an |
| \begin_inset Quotes sld |
| \end_inset |
| |
| END |
| \begin_inset Quotes srd |
| \end_inset |
| |
| statement. |
| \layout Section |
| |
| Some of the ASN.1 Basic Types |
| \layout Subsection |
| |
| The BOOLEAN type |
| \layout Standard |
| |
| The BOOLEAN type models the simple binary TRUE/FALSE, YES/NO, ON/OFF or |
| a similar kind of two-way choice. |
| \layout Subsection |
| |
| The INTEGER type |
| \layout Standard |
| |
| The INTEGER type is a signed natural number type without any restrictions |
| on its size. |
| If the automatic checking on INTEGER value bounds are necessary, the subtype |
| constraints must be used. |
| \layout LyX-Code |
| |
| SimpleInteger ::= INTEGER |
| \layout LyX-Code |
| |
| |
| \layout LyX-Code |
| |
| -- An integer with a very limited range |
| \layout LyX-Code |
| |
| SmallInt ::= INTEGER (0..127) |
| \layout LyX-Code |
| |
| |
| \layout LyX-Code |
| |
| -- Integer, negative |
| \layout LyX-Code |
| |
| NegativeInt ::= INTEGER (MIN..0) |
| \layout Subsection |
| |
| The ENUMERATED type |
| \layout Standard |
| |
| The ENUMERATED type is semantically equivalent to the INTEGER type with |
| some integer values explicitly named. |
| \layout LyX-Code |
| |
| FruitId ::= ENUMERATED { apple(1), orange(2) } |
| \layout LyX-Code |
| |
| |
| \layout LyX-Code |
| |
| -- The numbers in braces are optional, |
| \layout LyX-Code |
| |
| -- the enumeration can be performed |
| \layout LyX-Code |
| |
| -- automatically by the compiler |
| \layout LyX-Code |
| |
| ComputerOSType ::= ENUMERATED { |
| \layout LyX-Code |
| |
| FreeBSD, -- will be 0 |
| \layout LyX-Code |
| |
| Windows, -- will be 1 |
| \layout LyX-Code |
| |
| Solaris(5), -- will remain 5 |
| \layout LyX-Code |
| |
| Linux, -- will be 6 |
| \layout LyX-Code |
| |
| MacOS -- will be 7 |
| \layout LyX-Code |
| |
| } |
| \layout Subsection |
| |
| The OCTET STRING type |
| \layout Standard |
| |
| This type models the sequence of 8-bit bytes. |
| This may be used to transmit some opaque data or data serialized by other |
| types of encoders (i.e. |
| video file, photo picture, etc). |
| \layout Subsection |
| |
| The OBJECT IDENTIFIER type |
| \layout Standard |
| |
| The OBJECT IDENTIFIER is used to represent the unique identifier of any |
| object, starting from the very root of the registration tree. |
| If your organization needs to uniquely identify something (a router, a |
| room, a person, a standard, or whatever), you are encouraged to get your |
| own identification subtree at |
| \begin_inset LatexCommand \htmlurl{http://www.iana.org/protocols/forms.htm} |
| |
| \end_inset |
| |
| . |
| \layout Standard |
| |
| For example, the very first ASN.1 module in this document has the following |
| OBJECT IDENTIFIER: 1 3 6 1 4 1 9363 1 5 2 1 1. |
| \layout LyX-Code |
| |
| ExampleOID ::= OBJECT IDENTIFIER |
| \layout LyX-Code |
| |
| |
| \layout LyX-Code |
| |
| usageExampleModule1-oid ExampleOID |
| \layout LyX-Code |
| |
| ::= { 1 3 6 1 4 1 9363 1 5 2 1 1 } |
| \layout LyX-Code |
| |
| |
| \layout LyX-Code |
| |
| -- An identifier of the Internet. |
| \layout LyX-Code |
| |
| internet-id OBJECT IDENTIFIER |
| \layout LyX-Code |
| |
| ::= { iso(1) identified-organization(3) |
| \layout LyX-Code |
| |
| dod(6) internet(1) } |
| \layout Standard |
| |
| As you see, names are optional. |
| \layout Subsection |
| |
| The RELATIVE-OID type |
| \layout Standard |
| |
| The RELATIVE-OID type has the semantics of a subtree of an OBJECT IDENTIFIER. |
| There may be no need to repeat the whole sequence of numbers from the root |
| of the registration tree where the only thing of interest is some of the |
| tree's subsequence. |
| \layout LyX-Code |
| |
| this-document RELATIVE-OID ::= { docs(2) usage(1) } |
| \layout LyX-Code |
| |
| |
| \layout LyX-Code |
| |
| this-example RELATIVE-OID ::= { |
| \layout LyX-Code |
| |
| this-document assorted-examples(0) this-example(1) } |
| \layout Section |
| |
| Some of the ASN.1 String Types |
| \layout Subsection |
| |
| The IA5String type |
| \layout Standard |
| |
| This is essentially the ASCII, with 128 character codes available (7 lower |
| bits of an 8-bit byte). |
| \layout Subsection |
| |
| The UTF8String type |
| \layout Standard |
| |
| This is the character string which encodes the full Unicode range (4 bytes) |
| using multibyte character sequences. |
| \layout Subsection |
| |
| The NumericString type |
| \layout Standard |
| |
| This type represents the character string with the alphabet consisting of |
| numbers ( |
| \begin_inset Quotes sld |
| \end_inset |
| |
| 0 |
| \begin_inset Quotes srd |
| \end_inset |
| |
| to |
| \begin_inset Quotes sld |
| \end_inset |
| |
| 9 |
| \begin_inset Quotes srd |
| \end_inset |
| |
| ) and a space. |
| \layout Subsection |
| |
| The PrintableString type |
| \layout Standard |
| |
| The character string with the following alphabet: space, |
| \begin_inset Quotes sld |
| \end_inset |
| |
| |
| \series bold |
| ' |
| \series default |
| |
| \begin_inset Quotes srd |
| \end_inset |
| |
| (single quote), |
| \begin_inset Quotes sld |
| \end_inset |
| |
| |
| \series bold |
| ( |
| \series default |
| |
| \begin_inset Quotes sld |
| \end_inset |
| |
| , |
| \begin_inset Quotes sld |
| \end_inset |
| |
| |
| \series bold |
| ) |
| \series default |
| |
| \begin_inset Quotes srd |
| \end_inset |
| |
| , |
| \begin_inset Quotes sld |
| \end_inset |
| |
| |
| \series bold |
| + |
| \series default |
| |
| \begin_inset Quotes srd |
| \end_inset |
| |
| , |
| \begin_inset Quotes sld |
| \end_inset |
| |
| , |
| \begin_inset Quotes srd |
| \end_inset |
| |
| (comma), |
| \begin_inset Quotes sld |
| \end_inset |
| |
| |
| \series bold |
| - |
| \series default |
| |
| \begin_inset Quotes srd |
| \end_inset |
| |
| , |
| \begin_inset Quotes sld |
| \end_inset |
| |
| |
| \series bold |
| . |
| \series default |
| |
| \begin_inset Quotes srd |
| \end_inset |
| |
| , |
| \begin_inset Quotes sld |
| \end_inset |
| |
| |
| \series bold |
| / |
| \series default |
| |
| \begin_inset Quotes srd |
| \end_inset |
| |
| , digits ( |
| \begin_inset Quotes sld |
| \end_inset |
| |
| 0 |
| \begin_inset Quotes srd |
| \end_inset |
| |
| to |
| \begin_inset Quotes sld |
| \end_inset |
| |
| 9 |
| \begin_inset Quotes srd |
| \end_inset |
| |
| ), |
| \begin_inset Quotes sld |
| \end_inset |
| |
| |
| \series bold |
| : |
| \series default |
| |
| \begin_inset Quotes srd |
| \end_inset |
| |
| , |
| \begin_inset Quotes sld |
| \end_inset |
| |
| |
| \series bold |
| = |
| \series default |
| |
| \begin_inset Quotes srd |
| \end_inset |
| |
| , |
| \begin_inset Quotes sld |
| \end_inset |
| |
| |
| \series bold |
| ? |
| \series default |
| |
| \begin_inset Quotes srd |
| \end_inset |
| |
| , upper-case and lower-case letters ( |
| \begin_inset Quotes sld |
| \end_inset |
| |
| A |
| \begin_inset Quotes srd |
| \end_inset |
| |
| to |
| \begin_inset Quotes sld |
| \end_inset |
| |
| Z |
| \begin_inset Quotes srd |
| \end_inset |
| |
| and |
| \begin_inset Quotes sld |
| \end_inset |
| |
| a |
| \begin_inset Quotes srd |
| \end_inset |
| |
| to |
| \begin_inset Quotes sld |
| \end_inset |
| |
| z |
| \begin_inset Quotes srd |
| \end_inset |
| |
| ) |
| \layout Subsection |
| |
| The VisibleString type |
| \layout Standard |
| |
| The character string with the alphabet which is more or less a subset of |
| ASCII between space and |
| \begin_inset Quotes sld |
| \end_inset |
| |
| |
| \series bold |
| ~ |
| \series default |
| |
| \begin_inset Quotes srd |
| \end_inset |
| |
| (tilde). |
| Alternatively, the alphabet may be described as the PrintableString alphabet |
| presented earlier, plus the following characters: |
| \begin_inset Quotes sld |
| \end_inset |
| |
| |
| \series bold |
| ! |
| \series default |
| |
| \begin_inset Quotes srd |
| \end_inset |
| |
| , |
| \begin_inset Quotes sld |
| \end_inset |
| |
| |
| \series bold |
| |
| \begin_inset Quotes srd |
| \end_inset |
| |
| |
| \series default |
| |
| \begin_inset Quotes srd |
| \end_inset |
| |
| , |
| \begin_inset Quotes sld |
| \end_inset |
| |
| |
| \series bold |
| # |
| \series default |
| |
| \begin_inset Quotes srd |
| \end_inset |
| |
| , |
| \begin_inset Quotes sld |
| \end_inset |
| |
| |
| \series bold |
| $ |
| \series default |
| |
| \begin_inset Quotes srd |
| \end_inset |
| |
| , |
| \begin_inset Quotes sld |
| \end_inset |
| |
| |
| \series bold |
| % |
| \series default |
| |
| \begin_inset Quotes srd |
| \end_inset |
| |
| , |
| \begin_inset Quotes sld |
| \end_inset |
| |
| |
| \series bold |
| & |
| \series default |
| |
| \begin_inset Quotes srd |
| \end_inset |
| |
| , |
| \begin_inset Quotes sld |
| \end_inset |
| |
| |
| \series bold |
| * |
| \series default |
| |
| \begin_inset Quotes srd |
| \end_inset |
| |
| , |
| \begin_inset Quotes sld |
| \end_inset |
| |
| |
| \series bold |
| ; |
| \series default |
| |
| \begin_inset Quotes srd |
| \end_inset |
| |
| , |
| \begin_inset Quotes sld |
| \end_inset |
| |
| |
| \series bold |
| < |
| \series default |
| |
| \begin_inset Quotes srd |
| \end_inset |
| |
| , |
| \begin_inset Quotes sld |
| \end_inset |
| |
| |
| \series bold |
| > |
| \series default |
| |
| \begin_inset Quotes srd |
| \end_inset |
| |
| , |
| \begin_inset Quotes sld |
| \end_inset |
| |
| |
| \series bold |
| [ |
| \series default |
| |
| \begin_inset Quotes srd |
| \end_inset |
| |
| , |
| \begin_inset Quotes sld |
| \end_inset |
| |
| |
| \series bold |
| |
| \backslash |
| |
| \series default |
| |
| \begin_inset Quotes srd |
| \end_inset |
| |
| , |
| \begin_inset Quotes sld |
| \end_inset |
| |
| |
| \series bold |
| ] |
| \series default |
| |
| \begin_inset Quotes srd |
| \end_inset |
| |
| , |
| \begin_inset Quotes sld |
| \end_inset |
| |
| |
| \series bold |
| ^ |
| \series default |
| |
| \begin_inset Quotes srd |
| \end_inset |
| |
| , |
| \begin_inset Quotes sld |
| \end_inset |
| |
| |
| \series bold |
| _ |
| \series default |
| |
| \begin_inset Quotes srd |
| \end_inset |
| |
| , |
| \begin_inset Quotes sld |
| \end_inset |
| |
| |
| \series bold |
| ` |
| \series default |
| |
| \begin_inset Quotes srd |
| \end_inset |
| |
| (single left quote), |
| \begin_inset Quotes sld |
| \end_inset |
| |
| |
| \series bold |
| { |
| \series default |
| |
| \begin_inset Quotes srd |
| \end_inset |
| |
| , |
| \begin_inset Quotes sld |
| \end_inset |
| |
| |
| \series bold |
| | |
| \series default |
| |
| \begin_inset Quotes srd |
| \end_inset |
| |
| , |
| \begin_inset Quotes sld |
| \end_inset |
| |
| |
| \series bold |
| } |
| \series default |
| |
| \begin_inset Quotes srd |
| \end_inset |
| |
| , |
| \begin_inset Quotes sld |
| \end_inset |
| |
| |
| \series bold |
| ~ |
| \series default |
| |
| \begin_inset Quotes srd |
| \end_inset |
| |
| . |
| \layout Section |
| |
| ASN.1 Constructed Types |
| \layout Subsection |
| |
| The SEQUENCE type |
| \layout Standard |
| |
| This is an ordered collection of other simple or constructed types. |
| The SEQUENCE constructed type resembles the C |
| \begin_inset Quotes sld |
| \end_inset |
| |
| struct |
| \begin_inset Quotes srd |
| \end_inset |
| |
| statement. |
| \layout LyX-Code |
| |
| Address ::= SEQUENCE { |
| \layout LyX-Code |
| |
| -- The apartment number may be omitted |
| \layout LyX-Code |
| |
| apartmentNumber NumericString OPTIONAL, |
| \layout LyX-Code |
| |
| streetName PrintableString, |
| \layout LyX-Code |
| |
| cityName PrintableString, |
| \layout LyX-Code |
| |
| stateName PrintableString, |
| \layout LyX-Code |
| |
| -- This one may be omitted too |
| \layout LyX-Code |
| |
| zipNo NumericString OPTIONAL |
| \layout LyX-Code |
| |
| } |
| \layout Subsection |
| |
| The SET type |
| \layout Standard |
| |
| This is a collection of other simple or constructed types. |
| Ordering is not important. |
| The data may arrive in the order which is different from the order of specifica |
| tion. |
| Data is encoded in the order not necessarily corresponding to the order |
| of specification. |
| \layout Subsection |
| |
| The CHOICE type |
| \layout Standard |
| |
| This type is just a choice between the subtypes specified in it. |
| The CHOICE type contains at most one of the subtypes specified, and it |
| is always implicitly known which choice is being decoded or encoded. |
| This one resembles the C |
| \begin_inset Quotes sld |
| \end_inset |
| |
| union |
| \begin_inset Quotes srd |
| \end_inset |
| |
| statement. |
| \layout Standard |
| |
| The following type defines a response code, which may be either an integer |
| code or a boolean |
| \begin_inset Quotes sld |
| \end_inset |
| |
| true |
| \begin_inset Quotes srd |
| \end_inset |
| |
| / |
| \begin_inset Quotes srd |
| \end_inset |
| |
| false |
| \begin_inset Quotes srd |
| \end_inset |
| |
| code. |
| \layout LyX-Code |
| |
| ResponseCode ::= CHOICE { |
| \layout LyX-Code |
| |
| intCode INTEGER, |
| \layout LyX-Code |
| |
| boolCode BOOLEAN |
| \layout LyX-Code |
| |
| } |
| \layout LyX-Code |
| |
| \layout Subsection |
| |
| The SEQUENCE OF type |
| \layout Standard |
| |
| This one is the list (array) of simple or constructed types: |
| \layout LyX-Code |
| |
| -- Example 1 |
| \layout LyX-Code |
| |
| ManyIntegers ::= SEQUENCE OF INTEGER |
| \layout LyX-Code |
| |
| |
| \layout LyX-Code |
| |
| -- Example 2 |
| \layout LyX-Code |
| |
| ManyRectangles ::= SEQUENCE OF Rectangle |
| \layout LyX-Code |
| |
| |
| \layout LyX-Code |
| |
| -- More complex example: |
| \layout LyX-Code |
| |
| -- an array of structures defined in place. |
| \layout LyX-Code |
| |
| ManyCircles ::= SEQUENCE OF SEQUENCE { |
| \layout LyX-Code |
| |
| radius INTEGER |
| \layout LyX-Code |
| |
| } |
| \layout Subsection |
| |
| The SET OF type |
| \layout Standard |
| |
| The SET OF type models the bag of structures. |
| It resembles the SEQUENCE OF type, but the order is not important: i.e. |
| the elements may arrive in the order which is not necessarily the same |
| as the in-memory order on the remote machines. |
| \layout LyX-Code |
| |
| -- A set of structures defined elsewhere |
| \layout LyX-Code |
| |
| SetOfApples :: SET OF Apple |
| \layout LyX-Code |
| |
| |
| \layout LyX-Code |
| |
| -- Set of integers encoding the kind of a fruit |
| \layout LyX-Code |
| |
| FruitBag ::= SET OF ENUMERATED { apple, orange } |
| \layout Part |
| |
| Using the ASN.1 Compiler |
| \layout Chapter |
| |
| Introduction to the ASN.1 Compiler |
| \layout Standard |
| |
| The purpose of the ASN.1 compiler, of which this document is part, is to |
| convert the ASN.1 specifications to some other target language (currently, |
| only C is supported |
| \begin_inset Foot |
| collapsed false |
| |
| \layout Standard |
| |
| C++ is |
| \begin_inset Quotes sld |
| \end_inset |
| |
| supported |
| \begin_inset Quotes srd |
| \end_inset |
| |
| too, as long as an class-based approach is not a definitive factor. |
| \end_inset |
| |
| ). |
| The compiler reads the specification and emits a series of target language |
| structures and surrounding maintenance code. |
| For example, the C structure which may be created by compiler to represent |
| the simple |
| \emph on |
| Rectangle |
| \emph default |
| specification defined earlier in this document, may look like this |
| \begin_inset Foot |
| collapsed false |
| |
| \layout Standard |
| |
| |
| \emph on |
| -fnative-integers |
| \emph default |
| compiler option is used to produce basic C |
| \emph on |
| int |
| \emph default |
| types instead of infinite width INTEGER_t structures. |
| See Table |
| \begin_inset LatexCommand \vref{cap:asn1c-cmdopts} |
| |
| \end_inset |
| |
| . |
| \end_inset |
| |
| : |
| \layout LyX-Code |
| |
| typedef struct Rectangle_s { |
| \layout LyX-Code |
| |
| int height; |
| \layout LyX-Code |
| |
| int width; |
| \layout LyX-Code |
| |
| } Rectangle_t; |
| \layout Standard |
| |
| This would not be of much value for such a simple specification, so the |
| compiler goes further and actually produces the code which fills in this |
| structure by parsing the opaque binary |
| \begin_inset Foot |
| collapsed true |
| |
| \layout Standard |
| |
| BER, CER and DER encodings are binary. |
| However, the XER encoding is text (XML) based. |
| \end_inset |
| |
| data provided in some buffer. |
| It also produces the code that takes this structure as an argument and |
| performs structure serialization by emitting a series of bytes. |
| \layout Chapter |
| |
| Quick start |
| \layout Standard |
| |
| After building and installing the compiler, the |
| \emph on |
| asn1c |
| \begin_inset Foot |
| collapsed false |
| |
| \layout Standard |
| |
| The 1 symbol in asn |
| \series bold |
| 1 |
| \series default |
| c is a digit, not an |
| \begin_inset Quotes sld |
| \end_inset |
| |
| ell |
| \begin_inset Quotes srd |
| \end_inset |
| |
| letter. |
| \end_inset |
| |
| |
| \emph default |
| command may be used to compile the ASN.1 specification |
| \begin_inset Foot |
| collapsed false |
| |
| \layout Standard |
| |
| This is probably |
| \series bold |
| not |
| \series default |
| what you want to try out right now -- read through the rest of this chapter |
| to find out about |
| \series bold |
| -P |
| \series default |
| and |
| \series bold |
| -R |
| \series default |
| options. |
| \end_inset |
| |
| : |
| \layout LyX-Code |
| |
| asn1c |
| \emph on |
| <spec.asn1> |
| \layout Standard |
| |
| If several specifications contain interdependencies, all of the files must |
| be specified altogether: |
| \layout LyX-Code |
| |
| asn1c |
| \emph on |
| <spec1.asn1> <spec2.asn1> ... |
| \layout Standard |
| |
| The compiler |
| \series bold |
| -E |
| \series default |
| and |
| \series bold |
| -EF |
| \series default |
| options are used for testing the parser and the semantic fixer, respectively. |
| These options will instruct the compiler to dump out the parsed (and fixed, |
| if |
| \series bold |
| -F |
| \series default |
| is involved) ASN.1 specification as it was "understood" by the compiler. |
| It might be useful to check whether a particular syntactic construction |
| is properly supported by the compiler. |
| \layout LyX-Code |
| |
| asn1c |
| \series bold |
| -EF |
| \series default |
| |
| \emph on |
| <spec-to-test.asn1> |
| \layout Standard |
| |
| The |
| \series bold |
| -P |
| \series default |
| option is used to dump the compiled output on the screen instead of creating |
| a bunch of .c and .h files on disk in the current directory. |
| You would probably want to start with |
| \series bold |
| -P |
| \series default |
| option instead of creating a mess in your current directory. |
| Another option, |
| \series bold |
| -R |
| \series default |
| , asks compiler to only generate the files which need to be generated, and |
| supress linking in the numerous support files. |
| \layout Standard |
| |
| Print the compiled output instead of creating multiple source files: |
| \layout LyX-Code |
| |
| asn1c |
| \series bold |
| -P |
| \series default |
| |
| \emph on |
| <spec-to-compile-and-print.asn1> |
| \layout LyX-Code |
| |
| \layout Chapter |
| |
| Using the ASN.1 Compiler |
| \layout Section |
| |
| Command-line options |
| \layout Standard |
| |
| The Table |
| \begin_inset LatexCommand \vref{cap:asn1c-cmdopts} |
| |
| \end_inset |
| |
| summarizes various options affecting the compiler's behavior. |
| \layout Standard |
| |
| |
| \begin_inset Float table |
| wide false |
| collapsed true |
| |
| \layout Standard |
| |
| |
| \begin_inset Tabular |
| <lyxtabular version="3" rows="20" columns="2"> |
| <features> |
| <column alignment="left" valignment="top" leftline="true" width="0"> |
| <column alignment="block" valignment="top" leftline="true" rightline="true" width="3in"> |
| <row topline="true" bottomline="true"> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \layout Standard |
| |
| |
| \series bold |
| Overall Options |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \layout Standard |
| |
| |
| \series bold |
| Description |
| \end_inset |
| </cell> |
| </row> |
| <row topline="true"> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \layout Standard |
| |
| -E |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \layout Standard |
| |
| |
| \size small |
| Stop after the parsing stage and print the reconstructed ASN.1 specification |
| code to the standard output. |
| \end_inset |
| </cell> |
| </row> |
| <row topline="true"> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \layout Standard |
| |
| -F |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \layout Standard |
| |
| |
| \size small |
| Used together with -E, instructs the compiler to stop after the ASN.1 syntax |
| tree fixing stage and dump the reconstructed ASN.1 specification to the |
| standard output. |
| \end_inset |
| </cell> |
| </row> |
| <row topline="true"> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \layout Standard |
| |
| -P |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \layout Standard |
| |
| |
| \size small |
| Dump the compiled output to the standard output instead of cre- ating the |
| target language files on disk. |
| \end_inset |
| </cell> |
| </row> |
| <row topline="true"> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \layout Standard |
| |
| -R |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \layout Standard |
| |
| |
| \size small |
| Restrict the compiler to generate only the ASN.1 tables, omit- ting the usual |
| support code. |
| \end_inset |
| </cell> |
| </row> |
| <row topline="true"> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \layout Standard |
| |
| -S |
| \emph on |
| <directory> |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \layout Standard |
| |
| |
| \size small |
| Use the specified directory with ASN.1 skeleton files. |
| \end_inset |
| </cell> |
| </row> |
| <row topline="true" bottomline="true"> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \layout Standard |
| |
| -t |
| \emph on |
| <data-string> |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \layout Standard |
| |
| |
| \size small |
| Interpret the data-string as a sequence of hexadecimal values representing |
| the start of BER TLV encoding. |
| Print the human readable explanation. |
| \end_inset |
| </cell> |
| </row> |
| <row topline="true"> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \layout Standard |
| |
| |
| \series bold |
| Warning Options |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \layout Standard |
| |
| |
| \series bold |
| Description |
| \end_inset |
| </cell> |
| </row> |
| <row topline="true"> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \layout Standard |
| |
| -Werror |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \layout Standard |
| |
| |
| \size small |
| Treat warnings as errors; abort if any warning is produced. |
| \end_inset |
| </cell> |
| </row> |
| <row topline="true"> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \layout Standard |
| |
| -Wdebug-lexer |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \layout Standard |
| |
| |
| \size small |
| Enable lexer debugging during the ASN.1 parsing stage. |
| \end_inset |
| </cell> |
| </row> |
| <row topline="true"> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \layout Standard |
| |
| -Wdebug-fixer |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \layout Standard |
| |
| |
| \size small |
| Enable ASN.1 syntax tree fixer debugging during the fixing stage. |
| \end_inset |
| </cell> |
| </row> |
| <row topline="true" bottomline="true"> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \layout Standard |
| |
| -Wdebug-compiler |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \layout Standard |
| |
| |
| \size small |
| Enable debugging during the actual compile time. |
| \end_inset |
| </cell> |
| </row> |
| <row topline="true"> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \layout Standard |
| |
| |
| \series bold |
| Language Options |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \layout Standard |
| |
| |
| \series bold |
| Description |
| \end_inset |
| </cell> |
| </row> |
| <row topline="true"> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \layout Standard |
| |
| -fbless-SIZE |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \layout Standard |
| |
| |
| \size small |
| Allow SIZE() constraint for INTEGER, ENUMERATED, and other types for which |
| this constraint is normally prohibited by the standard. |
| This is a violation of an ASN.1 standard and compiler may fail to produce |
| the meaningful code. |
| \end_inset |
| </cell> |
| </row> |
| <row topline="true"> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \layout Standard |
| |
| -fnative-integers |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \layout Standard |
| |
| |
| \size small |
| Use native machine's integer types whenever possible, instead of the complex |
| ASN.1 INTEGER and ENUMERATED types. |
| |
| \end_inset |
| </cell> |
| </row> |
| <row topline="true"> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \layout Standard |
| |
| -funnamed-unions |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \layout Standard |
| |
| |
| \size small |
| Enable unnamed unions in the definitions of target language's structures. |
| \end_inset |
| </cell> |
| </row> |
| <row topline="true" bottomline="true"> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \layout Standard |
| |
| -ftypes88 |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \layout Standard |
| |
| |
| \size small |
| Use only ASN.1:1988 embedded types. |
| \end_inset |
| </cell> |
| </row> |
| <row topline="true"> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \layout Standard |
| |
| |
| \series bold |
| Output Options |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \layout Standard |
| |
| |
| \series bold |
| Description |
| \end_inset |
| </cell> |
| </row> |
| <row topline="true"> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \layout Standard |
| |
| -print-constraints |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \layout Standard |
| |
| |
| \size small |
| When -EF are also specified, this option forces the compiler to explain |
| its internal understanding of subtype constraints. |
| \end_inset |
| </cell> |
| </row> |
| <row topline="true" bottomline="true"> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none"> |
| \begin_inset Text |
| |
| \layout Standard |
| |
| -print-lines |
| \end_inset |
| </cell> |
| <cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none"> |
| \begin_inset Text |
| |
| \layout Standard |
| |
| |
| \size small |
| Generate "-- #line" comments in -E output. |
| \end_inset |
| </cell> |
| </row> |
| </lyxtabular> |
| |
| \end_inset |
| |
| |
| \layout Caption |
| |
| |
| \begin_inset LatexCommand \label{cap:asn1c-cmdopts} |
| |
| \end_inset |
| |
| The list of asn1c command line options |
| \end_inset |
| |
| |
| \layout Section |
| |
| Recognizing compiler output |
| \layout Standard |
| |
| After compiling, the following entities will be created in your current |
| directory: |
| \layout Itemize |
| |
| A set of .c and .h files, generally a single pair for each type defined in |
| the ASN.1 specifications. |
| These files will be named similarly to the ASN.1 types ( |
| \emph on |
| Rectangle.c |
| \emph default |
| and |
| \emph on |
| Rectangle.h |
| \emph default |
| for the specification defined in the beginning of this document). |
| \layout Itemize |
| |
| A set of helper .c and .h files which contain generic encoders, decoders and |
| other useful routines. |
| There will be quite a few of them, some of them even are not always necessary, |
| but the overall amount of code after compiling will be rather small anyway. |
| \layout Standard |
| |
| It is your responsibility to create .c file with the |
| \emph on |
| int main() |
| \emph default |
| routine and the Makefile (if needed). |
| Compiler helps you with the latter by creating the Makefile.am.sample, containing |
| the skeleton definition for the automake, should you want to use autotools. |
| \layout Standard |
| |
| In other words, after compiling the Rectangle module, you have the following |
| set of files: { Makefile.am.sample, Rectangle.c, Rectangle.h, |
| \series bold |
| \SpecialChar \ldots{} |
| |
| \series default |
| }, where |
| \series bold |
| |
| \begin_inset Quotes sld |
| \end_inset |
| |
| \SpecialChar \ldots{} |
| |
| \begin_inset Quotes srd |
| \end_inset |
| |
| |
| \series default |
| stands for the set of additional |
| \begin_inset Quotes sld |
| \end_inset |
| |
| helper |
| \begin_inset Quotes srd |
| \end_inset |
| |
| files created by the compiler. |
| If you add the simple file with the |
| \emph on |
| int main() |
| \emph default |
| routine, it would even be possible to compile everything with the single |
| instruction: |
| \layout LyX-Code |
| |
| cc -o rectangle *.c # It could be |
| \emph on |
| that |
| \emph default |
| simple |
| \begin_inset Foot |
| collapsed false |
| |
| \layout Standard |
| |
| Provided that you've also created a .c file with the |
| \emph on |
| int main() |
| \emph default |
| routine. |
| \end_inset |
| |
| |
| \layout Section |
| |
| Invoking the ASN.1 helper code from the application |
| \layout Standard |
| |
| First of all, you should to include one or more header files into your applicati |
| on. |
| For our Rectangle module, including the Rectangle.h file is enough: |
| \layout LyX-Code |
| |
| #include <Rectangle.h> |
| \layout Standard |
| |
| The header files defines the C structure corresponding to the ASN.1 definition |
| of a rectangle and the declaration of the ASN.1 type descriptor, which is |
| used as an argument to most of the functions provided by the ASN.1 module. |
| For example, here is the code which frees the Rectangle_t structure: |
| \layout LyX-Code |
| |
| Rectangle_t *rect = ...; |
| \layout LyX-Code |
| |
| |
| \layout LyX-Code |
| |
| asn1_DEF_Rectangle->free_struct(&asn1_DEF_Rectangle, |
| \layout LyX-Code |
| |
| rect, 0); |
| \layout Standard |
| |
| This code defines a |
| \emph on |
| rect |
| \emph default |
| pointer which points to the Rectangle_t structure which needs to be freed. |
| The second line invokes the generic free_struct routine created specifically |
| for this Rectangle_t structure. |
| The |
| \emph on |
| asn1_DEF_Rectangle |
| \emph default |
| is the type descriptor, which holds a collection of generic routines to |
| deal with the Rectangle_t structure. |
| \layout Standard |
| |
| There are several generic functions available: |
| \layout Description |
| |
| check_constraints Check that the contents of the target structure are semantical |
| ly valid and constrained to appropriate implicit or explicit subtype constraints. |
| Please refer to Section |
| \begin_inset LatexCommand \vref{sub:Validating-the-target} |
| |
| \end_inset |
| |
| . |
| \layout Description |
| |
| ber_decoder This is the generic |
| \emph on |
| restartable |
| \begin_inset Foot |
| collapsed false |
| |
| \layout Standard |
| |
| Restartable means that if the decoder encounters the end of the buffer, |
| it will fail, but may later be invoked again with the rest of the buffer |
| to continue decoding. |
| \end_inset |
| |
| |
| \emph default |
| BER decoder (Basic Encoding Rules). |
| This decoder would create and/or fill the target structure for you. |
| Please refer to Section |
| \begin_inset LatexCommand \ref{sub:Decoding-BER} |
| |
| \end_inset |
| |
| . |
| \layout Description |
| |
| der_encoder This is the generic DER encoder (Distinguished Encoding Rules). |
| This decoder will take the target structure and encode it into a series |
| of bytes. |
| Please refer to Section |
| \begin_inset LatexCommand \ref{sub:Encoding-DER} |
| |
| \end_inset |
| |
| . |
| \layout Description |
| |
| print_struct This function convert the contents of the passed target structure |
| into human readable form. |
| This form is not formal and cannot be converted back into the structure, |
| but it may turn out to be useful for debugging or quick-n-dirty printing. |
| Please refer to Section |
| \begin_inset LatexCommand \ref{sub:Printing-the-target} |
| |
| \end_inset |
| |
| . |
| \layout Description |
| |
| free_struct This is a generic disposal which frees the target structure. |
| Please refer to Section |
| \begin_inset LatexCommand \ref{sub:Freeing-the-target} |
| |
| \end_inset |
| |
| . |
| \layout Standard |
| |
| Each of the above function takes the type descriptor ( |
| \emph on |
| asn1_DEF_\SpecialChar \ldots{} |
| |
| \emph default |
| ) and the target structure ( |
| \emph on |
| rect |
| \emph default |
| , in the above example). |
| The target structure is typically created by the generic BER decoder or |
| by the application itself. |
| \layout Standard |
| |
| Here is how the buffer can be deserialized into the structure: |
| \layout LyX-Code |
| |
| Rectangle_t * |
| \layout LyX-Code |
| |
| simple_deserializer(const void *buffer, size_t buf_size) { |
| \layout LyX-Code |
| |
| Rectangle_t *rect = 0; /* Note this 0! */ |
| \layout LyX-Code |
| |
| ber_dec_rval_t rval; |
| \layout LyX-Code |
| |
| |
| \layout LyX-Code |
| |
| rval = asn1_DEF_Rectangle->ber_decoder( |
| \layout LyX-Code |
| |
| &asn1_DEF_Rectangle, |
| \layout LyX-Code |
| |
| (void **)&rect, |
| \layout LyX-Code |
| |
| buffer, buf_size, |
| \layout LyX-Code |
| |
| 0); |
| \layout LyX-Code |
| |
| |
| \layout LyX-Code |
| |
| if(rval |
| \series bold |
| .code |
| \series default |
| == RC_OK) { |
| \layout LyX-Code |
| |
| return rect; /* Decoding succeeded */ |
| \layout LyX-Code |
| |
| } else { |
| \layout LyX-Code |
| |
| /* Free partially decoded rect */ |
| \layout LyX-Code |
| |
| asn1_DEF_Rectangle->free_struct( |
| \layout LyX-Code |
| |
| &asn1_DEF_Rectangle, rect, 0); |
| \layout LyX-Code |
| |
| return 0; |
| \layout LyX-Code |
| |
| } |
| \layout LyX-Code |
| |
| } |
| \layout Standard |
| |
| The code above defines a function, |
| \emph on |
| simple_deserializer |
| \emph default |
| , which takes a buffer and its length and expected to return a pointer to |
| the Rectangle_t structure. |
| Inside, it tries to convert the bytes passed into the target structure |
| (rect) using the generic BER decoder and returns the rect pointer afterwards. |
| If the structure cannot be deserialized, it frees the memory which might |
| be left allocated by the unfinished |
| \emph on |
| ber_decoder |
| \emph default |
| routine and returns NULL. |
| |
| \series bold |
| This freeing is necessary |
| \series default |
| because the ber_decoder is a restartable procedure, and may fail just because |
| there is more data needs to be provided before decoding could be finalized. |
| The code above obviously does not take into account the way the |
| \emph on |
| ber_decoder |
| \emph default |
| failed, so the freeing is necessary because the part of the buffer may |
| already be decoded into the structure by the time something goes wrong. |
| \layout Standard |
| |
| Restartable decoding is a little bit trickier: you need to provide the old |
| target structure pointer (which might be already half-decoded) and react |
| on RC_WMORE return code. |
| This will be explained later in Section |
| \begin_inset LatexCommand \vref{sub:Decoding-BER} |
| |
| \end_inset |
| |
| |
| \layout Subsection |
| |
| |
| \begin_inset LatexCommand \label{sub:Decoding-BER} |
| |
| \end_inset |
| |
| Decoding BER |
| \layout Standard |
| |
| The Basic Encoding Rules describe the basic way how the structure can be |
| encoded and decoded. |
| Several other encoding rules (CER, DER) define a more restrictive versions |
| of BER, so the generic BER parser is also capable of decoding the data |
| encoded by CER and DER encoders. |
| The opposite is not true. |
| \layout Standard |
| |
| The ASN.1 compiler provides the generic BER decoder which is implicitly capable |
| of decoding BER, CER and DER encoded data. |
| \layout Standard |
| |
| The decoder is restartable (stream-oriented), which means that in case the |
| buffer has less data than it is expected, the decoder will process whatever |
| it is available and ask for more data to be provided. |
| Please note that the decoder may actually process less data than it is |
| given in the buffer, which means that you should be able to make the next |
| buffer contain the unprocessed part of the previous buffer. |
| \layout Standard |
| |
| Suppose, you have two buffers of encoded data: 100 bytes and 200 bytes. |
| \layout Itemize |
| |
| You may concatenate these buffers and feed the BER decoder with 300 bytes |
| of data, or |
| \layout Itemize |
| |
| You may feed it the first buffer of 100 bytes of data, realize that the |
| ber_decoder consumed only 95 bytes from it and later feed the decoder with |
| 205 bytes buffer which consists of 5 unprocessed bytes from the first buffer |
| and the latter 200 bytes from the second buffer. |
| \layout Standard |
| |
| This is not as convenient as it could be (like, the BER encoder would consume |
| the whole 100 bytes and keep these 5 bytes in some temporary storage), |
| but in case of stream-based processing it might actually be OK. |
| Suggestions are welcome. |
| \layout Standard |
| |
| There are two ways to invoke a BER decoder. |
| The first one is a direct reference of the type-specific decoder. |
| This way was shown in the previous example of |
| \emph on |
| simple_deserializer |
| \emph default |
| function. |
| The second way is to invoke a |
| \emph on |
| ber_decode |
| \emph default |
| function, which is just a simple wrapper of the former approach into a |
| less wordy notation: |
| \layout LyX-Code |
| |
| rval = ber_decode(&asn1_DEF_Rectangle, (void **)&rect, |
| \layout LyX-Code |
| |
| buffer, buf_size); |
| \layout Standard |
| |
| Note that the initial (asn1_DEF_Rectangle->ber_decoder) reference is gone, |
| and also the last argument (0) is no longer necessary. |
| \layout Standard |
| |
| These two ways of invocations are fully equivalent. |
| \layout Standard |
| |
| The BER de |
| \emph on |
| coder |
| \emph default |
| may fail because ( |
| \emph on |
| the following RC_\SpecialChar \ldots{} |
| codes are defined in ber_decoder.h |
| \emph default |
| ): |
| \layout Itemize |
| |
| RC_WMORE: There is more data expected than it is provided (stream mode continuat |
| ion feature); |
| \layout Itemize |
| |
| RC_FAIL: General failure to decode the buffer; |
| \layout Itemize |
| |
| \SpecialChar \ldots{} |
| other codes may be defined as well. |
| \layout Standard |
| |
| Together with the return code (.code) the ber_dec_rval_t type contains the |
| number of bytes which is consumed from the buffer. |
| In the previous hypothetical example of two buffers (of 100 and 200 bytes), |
| the first call to ber_decode() would return with .code = RC_WMORE and .consumed |
| = 95. |
| The .consumed field of the BER decoder return value is |
| \series bold |
| always |
| \series default |
| valid, even if the decoder succeeds or fails with any other return code. |
| \layout Standard |
| |
| Please look into ber_decoder.h for the precise definition of ber_decode() |
| and related types. |
| \layout Subsection |
| |
| |
| \begin_inset LatexCommand \label{sub:Encoding-DER} |
| |
| \end_inset |
| |
| Encoding DER |
| \layout Standard |
| |
| The Distinguished Encoding Rules is the variant of BER encoding rules which |
| is oriented on representing the structures with length known beforehand. |
| This is probably exactly how you want to encode: either after a BER decoding |
| or after a manual fill-up, the target structure contains the data which |
| size is implicitly known before encoding. |
| The DER encoding is used, for example, to encode X.509 certificates. |
| \layout Standard |
| |
| As with BER decoder, the DER encoder may be invoked either directly from |
| the ASN.1 type descriptor (asn1_DEF_Rectangle) or from the stand-alone function, |
| which is somewhat simpler: |
| \layout LyX-Code |
| |
| /* |
| \layout LyX-Code |
| |
| * This is a custom function which writes the |
| \layout LyX-Code |
| |
| * encoded output into some FILE stream. |
| \layout LyX-Code |
| |
| */ |
| \layout LyX-Code |
| |
| static int |
| \layout LyX-Code |
| |
| write_stream(const void *buffer, size_t size, void *app_key) { |
| \layout LyX-Code |
| |
| FILE *ostream = app_key; |
| \layout LyX-Code |
| |
| size_t wrote; |
| \layout LyX-Code |
| |
| |
| \layout LyX-Code |
| |
| wrote = fwrite(buffer, 1, size, ostream); |
| \layout LyX-Code |
| |
| |
| \layout LyX-Code |
| |
| return (wrote == size) ? 0 : -1; |
| \layout LyX-Code |
| |
| } |
| \layout LyX-Code |
| |
| |
| \layout LyX-Code |
| |
| /* |
| \layout LyX-Code |
| |
| * This is the serializer itself, |
| \layout LyX-Code |
| |
| * it supplies the DER encoder with the |
| \layout LyX-Code |
| |
| * pointer to the custom output function. |
| \layout LyX-Code |
| |
| */ |
| \layout LyX-Code |
| |
| ssize_t |
| \layout LyX-Code |
| |
| simple_serializer(FILE *ostream, Rectangle_t *rect) { |
| \layout LyX-Code |
| |
| der_enc_rval_t rval; /* Return value */ |
| \layout LyX-Code |
| |
| |
| \layout LyX-Code |
| |
| rval = der_encode(&asn1_DEF_Rect, rect, |
| \layout LyX-Code |
| |
| write_stream, ostream); |
| \layout LyX-Code |
| |
| if(rval |
| \series bold |
| .encoded |
| \series default |
| == -1) { |
| \layout LyX-Code |
| |
| /* |
| \layout LyX-Code |
| |
| * Failure to encode the rectangle data. |
| \layout LyX-Code |
| |
| */ |
| \layout LyX-Code |
| |
| fprintf(stderr, |
| \begin_inset Quotes sld |
| \end_inset |
| |
| Cannot encode %s: %s |
| \backslash |
| n |
| \begin_inset Quotes srd |
| \end_inset |
| |
| , |
| \layout LyX-Code |
| |
| rval |
| \series bold |
| .failed_type |
| \series default |
| ->name, |
| \layout LyX-Code |
| |
| strerror(errno)); |
| \layout LyX-Code |
| |
| return -1; |
| \layout LyX-Code |
| |
| } else { |
| \layout LyX-Code |
| |
| /* Return the number of bytes */ |
| \layout LyX-Code |
| |
| return rval.encoded; |
| \layout LyX-Code |
| |
| } |
| \layout LyX-Code |
| |
| } |
| \layout Standard |
| |
| As you see, the DER encoder does not write into some sort of buffer or something. |
| It just invokes the custom function (possible, multiple times) which would |
| save the data into appropriate storage. |
| The optional argument |
| \emph on |
| app_key |
| \emph default |
| is opaque for the DER encoder code and just used by |
| \emph on |
| _write_stream() |
| \emph default |
| as the pointer to the appropriate output stream to be used. |
| \layout Standard |
| |
| If the custom write function is not given (passed as 0), then the DER encoder |
| will essentially do the same thing (i.e., encode the data) but no callbacks |
| will be invoked (so the data goes nowhere). |
| It may prove useful to determine the size of the structure's encoding before |
| actually doing the encoding |
| \begin_inset Foot |
| collapsed false |
| |
| \layout Standard |
| |
| It is actually faster too: the encoder might skip over some computations |
| which aren't important for the size determination. |
| \end_inset |
| |
| . |
| \layout Standard |
| |
| Please look into der_encoder.h for the precise definition of der_encode() |
| and related types. |
| \layout Subsection |
| |
| |
| \begin_inset LatexCommand \label{sub:Validating-the-target} |
| |
| \end_inset |
| |
| Validating the target structure |
| \layout Standard |
| |
| Sometimes the target structure needs to be validated. |
| For example, if the structure was created by the application (as opposed |
| to being decoded from some external source), some important information |
| required by the ASN.1 specification might be missing. |
| On the other hand, the successful decoding of the data from some external |
| source does not necessarily mean that the data is fully valid either. |
| It might well be the case that the specification describes some subtype |
| constraints that were not taken into account during decoding, and it would |
| actually be useful to perform the last check when the data is ready to |
| be encoded or when the data has just been decoded to ensure its validity |
| according to some stricter rules. |
| \layout Standard |
| |
| The asn_check_constraints() function checks the type for various implicit |
| and explicit constraints. |
| It is recommended to use asn_check_constraints() function after each decoding |
| and before each encoding. |
| \layout Standard |
| |
| Please look into constraints.h for the precise definition of asn_check_constraint |
| s() and related types. |
| \layout Subsection |
| |
| |
| \begin_inset LatexCommand \label{sub:Printing-the-target} |
| |
| \end_inset |
| |
| Printing the target structure |
| \layout Standard |
| |
| There are two ways to print the target structure: either invoke the print_struct |
| member of the ASN.1 type descriptor, or using the asn_fprint() function, |
| which is a simpler wrapper of the former: |
| \layout LyX-Code |
| |
| asn_fprint(stdout, &asn1_DEF_Rectangle, rect); |
| \layout Standard |
| |
| Please look into constr_TYPE.h for the precise definition of asn_fprint() |
| and related types. |
| \layout Subsection |
| |
| |
| \begin_inset LatexCommand \label{sub:Freeing-the-target} |
| |
| \end_inset |
| |
| Freeing the target structure |
| \layout Standard |
| |
| Freeing the structure is slightly more complex than it may seem to. |
| When the ASN.1 structure is freed, all the members of the structure and |
| their submembers etc etc are recursively freed too. |
| But it might not be feasible to free the structure itself. |
| Consider the following case: |
| \layout LyX-Code |
| |
| struct my_figure { /* The custom structure */ |
| \layout LyX-Code |
| |
| int flags; /* <some custom member> */ |
| \layout LyX-Code |
| |
| /* The type is generated by the ASN.1 compiler */ |
| \layout LyX-Code |
| |
| |
| \emph on |
| Rectangle_t rect; |
| \layout LyX-Code |
| |
| /* other members of the structure */ |
| \layout LyX-Code |
| |
| }; |
| \layout Standard |
| |
| In this example, the application programmer defined a custom structure with |
| one ASN.1-derived member (rect). |
| This member is not a reference to the Rectangle_t, but an in-place inclusion |
| of the Rectangle_t structure. |
| If the freeing is necessary, the usual procedure of freeing everything |
| must not be applied to the &rect pointer itself, because it does not point |
| to the memory block directly allocated by memory allocation routine, but |
| instead lies within such a block allocated for my_figure structure. |
| \layout Standard |
| |
| To solve this problem, the free_struct routine has the additional argument |
| (besides the intuitive type descriptor and target structure pointers), |
| which is the flag specifying whether the outer pointer itself must be freed |
| (0, default) or it should be left intact (non-zero value). |
| \layout LyX-Code |
| |
| /* Rectangle_t is defined within my_figure */ |
| \layout LyX-Code |
| |
| struct my_figure *mf = |
| \series bold |
| ... |
| \series default |
| ; |
| \layout LyX-Code |
| |
| /* |
| \layout LyX-Code |
| |
| * Freeing the Rectangle_td |
| \layout LyX-Code |
| |
| * without freeing the mf->rect pointer |
| \layout LyX-Code |
| |
| */ |
| \layout LyX-Code |
| |
| asn1_DEF_Rectangle->free_struct( |
| \layout LyX-Code |
| |
| &asn1_DEF_Rectangle, &mf->rect, |
| \emph on |
| 1 |
| \emph default |
| /* !free */); |
| \layout LyX-Code |
| |
| |
| \layout LyX-Code |
| |
| /* Rectangle_t is a stand-alone pointer */ |
| \layout LyX-Code |
| |
| Rectangle_t *rect = |
| \series bold |
| ... |
| \series default |
| ; |
| \layout LyX-Code |
| |
| /* |
| \layout LyX-Code |
| |
| * Freeing the Rectangle_t |
| \layout LyX-Code |
| |
| * and freeing the rect pointer |
| \layout LyX-Code |
| |
| */ |
| \layout LyX-Code |
| |
| asn1_DEF_Rectangle->free_struct( |
| \layout LyX-Code |
| |
| &asn1_DEF_Rectangle, rect, |
| \emph on |
| 0 |
| \emph default |
| /* free the pointer too */); |
| \layout Standard |
| |
| It is safe to invoke the |
| \emph on |
| free_struct |
| \emph default |
| function with the target structure pointer set to 0 (NULL), the function |
| will do nothing. |
| \layout Bibliography |
| \bibitem [ASN1C]{ASN1C} |
| |
| Free ASN.1 Compiler. |
| |
| \begin_inset LatexCommand \htmlurl{http://lionet.info/asn1/} |
| |
| \end_inset |
| |
| |
| \layout Bibliography |
| \bibitem [Dub00]{Dub00} |
| |
| Olivier Dubuisson -- |
| \emph on |
| ASN.1 Communication between heterogeneous systems |
| \emph default |
| -- Morgan Kaufmann Publishers, 2000. |
| |
| \begin_inset LatexCommand \htmlurl{http://asn1.elibel.tm.fr/en/book/} |
| |
| \end_inset |
| |
| . |
| ISBN:0-12-6333361-0. |
| \layout Bibliography |
| \bibitem [ITU-T/ASN.1]{ITU-T/ASN.1} |
| |
| ITU-T Study Group 17 -- Languages for Telecommunication Systems |
| \begin_inset LatexCommand \url{http://www.itu.int/ITU-T/studygroups/com17/languages/} |
| |
| \end_inset |
| |
| |
| \the_end |