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This is a detailed overview of the gSOAP XML data bindings concepts and implementation. At the end of this document two examples are given to illustrate the application of data bindings.
The first example address.cpp
shows how to use wsdl2h to bind an XML schema to C++. The C++ application reads and writes an XML file into and from a C++ "address book" data structure. The C++ data structure is an STL vector of address objects.
The second example graph.cpp
shows how XML is serialized as a tree, digraph, and cyclic graph. The digraph and cyclic graph serialization rules are similar to SOAP 1.1/1.2 encoded multi-ref elements with id-ref attributes to link elements through IDREF XML "pointers".
These examples demonstrate XML data bindings only for relatively simple data structures and types. The gSOAP tools support more than just these type of structures, which we will explain in the next sections. Support for XML schema components is practically unlimited. The wsdl2h tool maps schemas to C and C++ using built-in intuitive mapping rules, while allowing the mappings to be customized using a typemap.dat
file with mapping instructions for wsdl2h.
The information in this document is applicable to gSOAP 2.8.24 and higher, which supports C++11 features. However, C++11 is not required to use this material and follow the example, unless we need smart pointers and scoped enumerations. While most of the examples in this document are given in C++, the concepts also apply to C with the exception of containers, smart pointers, classes and their methods. None of these exceptions limit the use of the gSOAP tools for C in any way.
The data binding concepts described in this document have somewhat changed and improved over the years since the first version of gSOAP was developed in 1999 (the project was called a "XML/SOAP stub/skeleton compiler" back then). However, the principle of mapping XSD components to C/C++ types and vice versa was envisioned and implemented early on in research conducted by Dr. van Engelen at the Florida State University and subsequently adopted by other tools, including Java web services and in C# WCF.
To convert WSDL and XML schemas (XSD files), we use the wsdl2h command to generate the data binding interface code in a special gSOAP header file:
wsdl2h [options] -o file.h ... XSD and WSDL files ...
This converts WSDL and XSD files to C++ (or pure C with wsdl2h option -c
) and saves a special file.h
data binding interface file.
The WSDL 1.1/2.0, SOAP 1.1/1.2, and XSD 1.0/1.1 standards are supported by the gSOAP tools. In addition, the most popular WS specifications are also supported, including WS-Addressing, WS-ReliableMessaging, WS-Discovery, WS-Security, WS-Policy, WS-SecurityPolicy, and WS-SecureConversation.
This document focusses on XML data bindings and mapping C/C++ to XML 1.0/1.1 and XSD 1.0/1.1. This covers all of the following standard XSD components with their optional [ attributes ]
properties:
any [minOccurs, maxOccurs] anyAttribute all choice [minOccurs, maxOccurs] sequence [minOccurs, maxOccurs] group [name, ref] attributeGroup [name, ref] attribute [name, ref, type, use, default, fixed, form, wsdl:arrayType] element [name, ref, type, default, fixed, form, nillable, abstract, substitutionGroup, minOccurs, maxOccurs] simpleType [name] complexType [name, abstract, mixed]
And also the following standard XSD components:
import imports a schema into the importing schema for referencing include include schema component definitions into a schema override override by replacing schema component definitions redefine extend or restrict schema component definitions annotation annotates a component
The XSD facets and their mappings to C/C++ are:
enumeration maps to enum simpleContent maps to class/struct wrapper with __item member complexContent maps to class/struct list maps to enum* bitmask (enum* enumerates up to 64 bit masks) extension through inheritance restriction partly through inheritance and redeclaration length restricts content length minLength restricst content length maxLength restricst content length minInclusive restricts numerical value range maxInclusive restricts numerical value range minExclusive restricts numerical value range maxExclusive restricts numerical value range precision maps to float/double but constraint is not validated scale maps to float/double but constraint is not validated totalDigits maps to float/double but constraint is not validated fractionDigits maps to float/double but constraint is not validated pattern must define `soap::fsvalidate` callback to validate patterns union maps to string of values
All primitive XSD types are supported, including but not limited to the following XSD types:
anyType maps to _XML string with literal XML content (or DOM with wsdl2h option -d) anyURI maps to string string maps to string (char*/wchar_t*/std::string/std::wstring) boolean maps to bool (C++) or enum xsd__boolean (C) byte maps to char (int8_t) short maps to short (int16_t) int maps to int (int32_t) long maps to LONG64 (long long and int64_t) unsignedByte maps to unsigned char (uint8_t) unsignedShort maps to unsigned short (uint16_t) unsignedInt maps to unsigned int (uint32_t) unsignedLong maps to ULONG64 (unsigned long long and uint64_t) float maps to float double maps to double integer maps to string decimal maps to string, or use "#import "custom/long_double.h" precisionDecimal maps to string duration maps to string, or use "#import "custom/duration.h" dateTime maps to time_t, or use "#import "custom/struct_tm.h" time maps to string, or use "#import "custom/long_time.h" date maps to string, or use "#import "custom/struct_tm_date.h" hexBinary maps to class/struct xsd__hexBinary base64Bianry maps to class/struct xsd__base64Binary QName maps to _QName (URI normalization rules are applied)
All other primitive XSD types not listed above are mapped to strings, by generating a typedef. For example, xsd:token is bound to a C++ or C string, which associates a value space to the type with the appropriate XSD type name used by the soapcpp2-generated serializers:
typedef std::string xsd__token; // C++ typedef char *xsd__token; // C (wsdl2h option -c)
It is possible to remap types by adding the appropriate mapping rules to typemap.dat
as explained in the next section.
We use a typemap.dat
file to redefine namespace prefixes and to customize type bindings for the the generated header files produced by the wsdl2h tool. The typemap.dat
is the default file processed by wsdl2h. Use wsdl2h option -t
to specify an alternate file.
Declarations in typemap.dat
can be broken up over multiple lines by continuing on the next line by ending each line to be continued with a backslash \
.
The wsdl2h tool generates C/C++ type declarations that use ns1
, ns2
, etc. as URI schema-binding prefixes. These default prefixes are generated somewhat arbitrarily for each schema URI, meaning that their ordering may change depending on the WSDL and XSD order of processing with wsdl2h.
It is strongly recommended to declare your own prefix for each schema URI to enhance maintaince of your code. This is to anticipate possible changes of the schema(s) and/or the binding URI(s) and/or the tooling procedures.
Therefore, the first and foremost important thing to do is to define prefix-URI bindings for our C/C++ code by adding the following line(s) to our typemap.dat
or make a copy of this file and add the line(s) that bind our choice of prefix name to each URI:
prefix = "URI"
For example:
g = "urn:graph"
This produces g__name
C/C++ type names that are bound to the "urn:graph" schema by association of g
to the C/C++ types.
This means that <g:name xmlns:g="urn:graph">
is parsed as an instance of a g__name
C/C++ type. Also <x:name xmlns:x="urn:graph">
parses as an instance of g__name
, because the prefix x
has the same URI value urn:graph
. Prefixes in XML have local scopes (like variables in a block).
The first run of wsdl2h will reveal the URIs, so we do not need to search WSDLs and XSD files for all of the target namespaces.
Custom C/C++ type bindings can be declared in typemap.dat
to associate C/C++ types with specific schema types. These type bindings have four parts:
prefix__type = declaration | use | ptruse
where
prefix__type
is the schema type to be customized (the prefix__type
name uses the common double underscore naming convention);declaration
declares the C/C++ type in the wsdl2h-generated header file. This part can be empty if no explicit declaration is needed;use
is an optional part that specifies how the C/C++ type is used in the code. When omitted, it is the same as prefix__type
;ptruse
is an optional part that specifies how the type is used as a pointer type. By default it is the use
type name with a *
or C++11 std::shared_ptr<>
(see further below).For example, to map xsd:duration to a long long
(LONG64
) milliseconds value, we can use the custom serializer declared in custom/duration.h
by adding the following line to typemap.dat
:
xsd__duration = #import "custom/duration.h" | xsd__duration
Here, we could have omitted the second field, because xsd__duration
is the name that wsdl2h uses to identify this type.
To map xsd:string to wchar_t*
wide strings:
xsd__string = | wchar_t* | wchar_t*
Note that the first field is empty, because wchar_t
is a C type and does not need to be declared. A ptruse
field is given so that we do not end up generating the wrong pointer types, such as wchar_t**
and std::shared_ptr<wchar_t>
.
When the auto-generated declaration should be preserved but the use
or ptruse
fields replaced, then we use an ellipsis for the declaration part:
prefix__type = ... | use | ptruse
This is useful to map schema polymorphic types to C types for example, where we need to be able to both handle a base type and its extensions as per schema extensibility. Say we have a base type called ns:base that is extended, then we can remap this to a C type that permits referening the extended types via a void*
as follows:
ns__base = ... | int __type_base; void*
such that __type_base
and void*
are used to (de)serialize any data type, including base and its derived types.
All generated classes and structs can be augmented with additional members such as methods, constructors and destructors, and private members:
prefix__type = $ member-declaration
For example, we can add method declarations and private members to a class, say ns__record
as follows:
ns__record = $ ns__record(const ns__record &); // copy constructor ns__record = $ void print(); // a print method ns__record = $ private: int status; // a private member
Note that method declarations cannot include any code, because soapcpp2's input permits only type declarations, not code.
Type replacements can be given to replace one type entirely with another given type:
prefix__type1 == prefix__type2
This replaces all prefix__type1
by prefix__type2
in the wsdl2h output. However, care muse be taken not to agressively replace types, because this can cause XML validation to fail when a value-type mismatch is encountered in the XML input. Therefore, only replace similar types with other similar types that are wider (e.g. short
by int
and float
by double
).
The typemap.dat
$CONTAINER
variable defines the container to emit in the generated declarations, which is std::vector
by default. For example:
$CONTAINER = std::list
The typemap.dat
$POINTER
variable defines the smart pointer to emit in the generated declarations, which replaces the use of *
pointers. For example:
$POINTER = std::shared_ptr
Not all pointers in the generated output can be replaced by smart pointers when standard pointers are used as union members and pointers to arrays.
Any other content to be generated by wsdl2h can be included in typemap.dat
by enclosing it within brackets [
and ]
. These brackets MUST appear at the start of a new line.
For example, we can add an #import "wsa5.h"
directive to the wsdl2h-generated output:
[ #import "wsa5.h" ]
which emits the #import "wsa5.h"
literally at the start of the wsdl2h-generated header file.
The soapcpp2 command generates the data binding implementation code from a data binding interface file.h
:
soapcpp2 [options] file.h
where file.h
is a gSOAP header file that declares the XML data binding interface. The file.h
is typically generated by wsdl2h, but we can also declare one ourself. If so, we add gSOAP directives and declare in this file all our C/C++ types we want to serialize in XML. We can also declare functions that will be converted to service operations by soapcpp2.
Global function declarations define service operations, which are of the form:
int ns__name(arg1, arg2, ..., argn, result);
where arg1
, arg2
, ..., argn
are formal argument declarations of the input and result
is a formal argument for the output, which must be a pointer or reference to the result object to be populated. More information can be found in the gSOAP user guide.
The following C/C++ types are supported by soapcpp2 and mapped to XSD types and constructs. See the subsections below for more details or follow the links.
List of C++ bool and C alternative
bool C++ bool enum xsd__boolean C alternative bool
List of enumerations and bitmasks
enum enumeration enum class C++11 scoped enumeration (soapcpp2 -c++11) enum* a bitmask that enumerates values 1, 2, 4, 8, ... enum* class C++11 scoped enumeration (soapcpp2 -c++11)
List of numerical types
char byte short 16 bit integer int 32 bit integer long 32 bit integer LONG64 64 bit integer long long same as LONG64 unsigned char unsigned byte unsigned short unsigned 16 bit integer unsigned int unsigned 32 bit integer unsigned long unsigned 32 bit integer ULONG64 unsigned 64 bit integer unsigned long long same as ULONG64 int8_t same as char int16_t same as short int32_t same as int int64_t same as LONG64 uint8_t same as unsigned char uint16_t same as unsigned short uint32_t same as unsigned int uint64_t same as ULONG64 size_t transient type (not serializable) float 32 bit float double 64 bit float long double 128 bit float, use #import "custom/long_double.h" typedef declares a type name, may restrict numeric range
List of string types
char* string wchar_t* wide string std::string C++ string std::wstring C++ wide string char[N] fixed-size string, requires soapcpp2 option -b _QName normalized QName content _XML literal XML string content typedef declares a type name, may restrict string length
List of date and time types
time_t date and time point since epoch struct tm date and time point, use #import "custom/struct_tm.h" struct tm date point, use #import "custom/struct_tm_date.h" struct timeval date and time point, use #import "custom/struct_timeval.h" unsigned long long time point in microseconds, use #import "custom/long_time.h" std::chrono::system_clock::time_point date and time point, use #import "custom/chrono_time_point.h"
List of time duration types
long long duration in milliseconds, use #import "custom/duration.h" std::chrono::nanoseconds duration in nanoseconds, use #import "custom/chrono_duration.h"
List of classes and structs
class C++ class with single inheritance only struct C struct or C++ struct without inheritance T* pointer to type T T[N] fixed-size array of type T std::shared_ptr<T> C++11 smart shared pointer std::unique_ptr<T> C++11 smart pointer std::auto_ptr<T> C++ smart pointer std::deque<T> use #import "stldeque.h" std::list<T> use #import "stllist.h" std::vector<T> use #import "stlvector.h" std::set<T> use #import "stlset.h" template<T> class a container with begin(), end(), size(), clear(), and insert() methods union requires a discriminant member void* requires a __type member to indicate the type of object pointed to
List of special classes and structs
Array single and multidimensional SOAP Arrays xsd__hexBinary binary content xsd__base64Binary binary content and optional MIME/MTOM attachments Wrapper complexTypes with simpleContent
To bind C/C++ type names to XSD types, a simple form of name prefixing is used by the gSOAP tools by prepending the XML namespace prefix to the C/C++ type name with a pair of undescrores. This also ensures that name clashes cannot occur when multiple WSDL and XSD files are converted to C/C++. Also, C++ namespaces are not sufficiently rich to capture XML schema namespaces accurately, for example when class members are associated with schema elements defined in another XML namespace and thus the XML namespace scope of the member's name is relevant, not just its type.
However, from a C/C++ centric point of view this can be cumbersome. Therefore, colon notation is an alternative to physically augmenting C/C++ names with prefixes.
For example, the following class uses colon notation to bind the record
class to the urn:types
schema:
//gsoap ns schema namespace: urn:types class ns:record // binding 'ns:' to a type name { public: std::string name; uint64_t SSN; ns:record *spouse; // using 'ns:' with the type name ns:record(); // using 'ns:' here too ~ns:record(); // and here };
The colon notation is stripped away by soapcpp2 when generating the data binding implementation code for our project. So the final code just uses record
to identify this class and its constructor/destructor.
When using colon notation we have to be consistent as we cannot use both forms together. That is, ns:record
differs from ns__record
as a name.
The C++ bool
type is bound to built-in XSD type xsd:boolean.
The C alternative is to define an enumeration:
enum xsd__boolean { false_, true_ };
or by defining an enumeration in C with pseudo-scoped enumeration values:
enum xsd__boolean { xsd__boolean__false, xsd__boolean__true };
The XML value space of these types is false
and true
, but also accepts 0
and 1
as values.
To prevent name clashes, false_
and true_
have an underscore which are removed in the XML value space.
Enumerations are mapped to XSD simpleType enumeration restrictions of xsd:string, xsd:QName, and xsd:long.
Consider for example:
enum ns__Color { RED, WHITE, BLUE };
which maps to a simpleType restriction of xsd:string in the soapcpp2-generated schema:
<simpleType name="Color"> <restriction base="xsd:string"> <enumeration value="RED"/> <enumeration value="WHITE"/> <enumeration value="BLUE"/> </restriction> </simpleType>
Enumeration name constants can be pseudo-scoped to prevent name clashes, because enumeration name constants have a global scope in C and C++:
enum ns__Color { ns__Color__RED, ns__Color__WHITE, ns__Color__BLUE };
We can also use C++11 scoped enumerations to prevent name clashes:
enum class ns__Color : int { RED, WHITE, BLUE };
Here, the type part : int
is optional. In place of int
in the example above, we can also use int8_t
, int16_t
, int32_t
, or int64_t
.
The XML value space of the enumertions defined above is RED
, WHITE
, and BLUE
.
Prefix-qualified enumeration name constants are mapped to simpleType restrictions of xsd:QName, for example:
enum ns__types { xsd__int, xsd__float };
which maps to a simpleType restriction of xsd:QName in the soapcpp2-generated schema:
<simpleType name="types"> <restriction base="xsd:QName"> <enumeration value="xsd:int"/> <enumeration value="xsd:float"/> </restriction> </simpleType>
Enumeration name constants can be pseudo-numeric as follows:
enum ns__Primes { _3 = 3, _5 = 5, _7 = 7, _11 = 11 };
which maps to a simpleType restriction of xsd:long
:
<simpleType name="Color"> <restriction base="xsd:long"> <enumeration value="3"/> <enumeration value="5"/> <enumeration value="7"/> <enumeration value="11"/> </restriction> </simpleType>
The XML value space of this type is 3
, 5
, 7
, and 11
.
Besides (pseudo-) scoped enumerations, another way to prevent name clashes accross enumerations is to start an enumeration name constant with one underscore or followed it by any number of underscores, which makes it unique. The leading and trailing underscores are removed in the XML value space.
enum ns__ABC { A, B, C }; enum ns__BA { B, A }; // BAD: B = 1 but B is already defined as 2 enum ns__BA_ { B_, A_ }; // OK
The gSOAP soapcpp2 tool permits reusing enumeration name constants in other (non-scoped) enumerations as long as these values are assigned the same constant. Therefore, the following is permitted:
enum ns__Primes { _3 = 3, _5 = 5, _7 = 7, _11 = 11 }; enum ns__Throws { _1 = 1, _2 = 2, _3 = 3, _4 = 4, _5 = 5, _6 = 6 };
A bitmask type is an enum*
"product" enumeration with a geometric, power-of-two sequence of values assigned to the name constants:
enum* ns__Options { SSL3, TLS10, TLS11, TLS12 };
where the product enum assigns 1 to SSL3
, 2 to TLS10
, 4 to TLS11
, and 8 to TLS12
, which allows the enumeration values to be used in composing bitmasks with |
(bitwise or) &
(bitwise and), and ~
(bitwise not):
enum ns__Options options = (enum ns__Options)(SSL3 | TLS10 | TLS11 | TLS12); if (options & SSL3) // if SSL3 is an option, warn and remove from options { warning(); options &= ~SSL3; }
The bitmask type maps to a simpleType list restriction of xsd:string in the soapcpp2-generated schema:
<simpleType name="Options"> <list> <restriction base="xsd:string"> <enumeration value="SSL3"/> <enumeration value="TLS10"/> <enumeration value="TLS11"/> <enumeration value="TLS12"/> </restriction> </list> </simpleType>
The XML value space of this type consists of all 16 possible subsets of the four values, represented by an XML string with space-separated values. For example, the bitmask TLS10 | TLS11 | TLS12
equals 14 and is represented in by the XML string TLS10 TLS11 TLS12
.
To convert enum
name constants to string, we use the soapcpp2 auto-generated const char *soap_T2s(soap, enum T)
function.
To convert a string to an enum
name constant, we use the soapcpp2 auto-generated int soap_s2T(soap, const char *str, enum T*)
function.
Integer and floating point types are mapped to the equivalent built-in XSD types with the same sign and bit width.
The size_t
type is transient (not serializable) because its width is platform dependent. We recommend to use uint64_t
instead.
The XML value space of integer types are their decimal representations without loss of precision.
The XML value space of floating point types are their decimal representations. The decimal representations are formatted with the printf format string "%.9G" for floats and the printf format string "%.17lG" for double. The value space includes the values INF
, -INF
, and NAN
. To change the format string, we can change one of these struct soap
context data members:
const char * soap::float_format const char * soap::double_format
Note that decimal conversions may result in a loss of precision of the least significant decimal.
A long double
128 bit floating point value requires a custom serializer:
#import "custom/long_double.h" typedef long double xsd__decimal;
Compile and link your code with custom/long_double.c
.
The range of a numerical type can be restricted with a typedef:
typedef int ns__narrow -10:10;
which maps to a simpleType restriction of xsd:int in the soapcpp2-generated schema:
<simpleType name="narrow"> <restriction base="xsd:int"> <minInclusive value="-10"/> <maxInclusive value="10"/> </restriction> </simpleType>
The range of a float type can only be restricted within integral bounds. This restriction may be dropped in future releases.
String types are mapped to the built-in xsd:string and xsd:QName XSD types.
The wide strings wchar_t*
and std::wstring
may contain Unicode that is preserved in the XML value space.
Strings char*
and std::string
can only contain extended Latin, but we can store UTF-8 content that is preserved in the XML value space when the struct soap
context is initialized with the flag XML_C_UTFSTRING
.
Beware that many XML 1.0 parsers reject all control characters (those between #x1
and #x1F
) except #x9
, #xA
, and #xD
. With the newer XML 1.1 parsers (including gSOAP) you should be fine.
The length of a string type can be restricted with a typedef:
typedef std::string ns__password 6:16;
which maps to a simpleType restriction of xsd:string in the soapcpp2-generated schema:
<simpleType name="password"> <restriction base="xsd:string"> <minLength value="6"/> <maxLength value="16"/> </restriction> </simpleType>
In addition, an XSD regex pattern restriction can be associated with a string typedef:
typedef std::string ns__password "([a-zA-Z]|[0-9]|-)+" 6:16;
which maps to a simpleType restriction of xsd:string in the soapcpp2-generated schema:
<simpleType name="password"> <restriction base="xsd:string"> <pattern value="([a-zA-Z0-9]|-)+"/> <minLength value="6"/> <maxLength value="16"/> </restriction> </simpleType>
Fixed-size strings (char[N]
) are rare occurrences in the wild, but apparently still used in some projects to store strings. To facilitate fixed-size string serialization, use soapcpp2 option -b
:
typedef char ns__buffer[10]; // requires soapcpp2 option -b
which maps to a simpleType restriction of xsd:string in the soapcpp2-generated schema:
<simpleType name="buffer"> <restriction base="xsd:string"> <maxLength value="9"/> </restriction> </simpleType>
Note that fixed-size strings MUST contain NUL-terminated text and SHOULD NOT contain raw binary data. Also, the length limitation is more restrictive for UTF-8 content (enabled with the SOAP_C_UTFSTRING
) that requires multibyte character encodings. As a consequence, UTF-8 content may be truncated to fit.
Note that raw binary data can be stored in a xsd__base64Binary
or xsd__hexBinary
structure, or transmitted as a MIME attachment.
The built-in _QName
type is a regular C string type (char*
) that maps to xsd:QName but has the added advantage that it holds normalized qualified names. There are actually two forms of normalized QName content, to ensure any QName is represented accurately and uniquely:
prefix:name "URI":name
where the first form is used when the prefix (and the binding URI) is defined in the namespace table and is bound to a URI (see the .nsmap file). The second form is used when the URI is not defined in the namespace table and therefore no prefix is available to bind and normalize the URI to.
A _QName
string may contain a sequence of space-separated QName values, not just one, and all QName values are normalized to the format shown above.
To define a std::string
base type for xsd:QName, we use a typedef:
typedef std::string xsd__QName;
The xsd__QName
string content is normalized, just as with the _QName
normalization.
To serialize strings that contain literal XML content to be reproduced in the XML value space, use the built-in _XML
string type, which is a regular C string type (char*
) that maps to plain XML CDATA.
To define a std::string
base type for literal XML content, use a typedef:
typedef std::string XML;
Strings can hold any of the values of the XSD built-in primitive types. We can use a string typedef to declare the use of the string type as a XSD built-in type:
typedef std::string xsd__token;
We MUST ensure that the string values we populate in this type conform to the XML standard, which in case of xsd:token is: the lexical and value spaces of xsd:token are the sets of all strings after whitespace replacement of any occurrence of #x9
, #xA
, and #xD
by #x20
and collapsing.
The C/C++ time_t
type is mapped to the built-in xsd:dateTime XSD type that represents a date and time within a time zone (typically UTC).
The XML value space contains ISO 8601 Gregorian time instances of the form [-]CCYY-MM-DDThh:mm:ss.sss[Z|(+|-)hh:mm]
, where Z
is the UTC time zone or a time zone offset (+|-)hh:mm]
from UTC is used.
A time_t
value is considered and represented in UTC by the serializer.
Because the time_t
value range is restricted to dates after 01/01/1970, care must be taken to ensure the range of xsd:dateTime values in XML exchanges do not exceed the time_t
range.
This restriction does not hold for struct tm
(<time.h>
), which we can use to store and communicate a date and time in UTC without date range restrictions. The serializer uses the tm
data members directly for conversion to/from the XML value space of xsd:dateTime:
struct tm { int tm_sec; // seconds (0 - 60) int tm_min; // minutes (0 - 59) int tm_hour; // hours (0 - 23) int tm_mday; // day of month (1 - 31) int tm_mon; // month of year (0 - 11) int tm_year; // year - 1900 int tm_wday; // day of week (Sunday = 0) (NOT USED) int tm_yday; // day of year (0 - 365) (NOT USED) int tm_isdst; // is summer time in effect? char* tm_zone; // abbreviation of timezone (NOT USED) };
The struct tm
type is mapped to the built-in xsd:dateTime XSD type and serialized with the custom serializer custom/struct_tm.h
that declares a xsd__dateTime
type:
#import "custom/struct_tm.h" // import typedef struct tm xsd__dateTime; ... use xsd__dateTime ...
Compile and link your code with custom/struct_tm.c
.
The struct tm
type is mapped to the built-in xsd:date XSD type and serialized with the custom serializer custom/struct_tm_date.h
that declares a xsd__date
type:
#import "custom/struct_tm_date.h" // import typedef struct tm xsd__date; ... use xsd__date ...
Compile and link your code with custom/struct_tm_date.c
.
The XML value space of xsd:date are Gregorian calendar dates of the form [-]CCYY-MM-DD[Z|(+|-)hh:mm]
.
The struct timeval
(<sys/time.h>
) type is mapped to the built-in xsd:dateTime XSD type and serialized with the custom serializer custom/struct_timeval.h
that declares a xsd__dateTime
type:
#import "custom/struct_timeval.h" // import typedef struct timeval xsd__dateTime; ... use xsd__dateTime ...
Compile and link your code with custom/struct_timeval.c
.
Note that the same value range restrictions apply to struct timeval
as they apply to time_t
. The added benefit of struct timeval
is the addition of a microsecond-precise clock:
struct timeval { time_t tv_sec; // seconds since Jan. 1, 1970 suseconds_t tv_usec; // and microseconds };
An unsigned long long
(ULONG64
or uint64_t
) type that contains a 24 hour time in microseconds UTC is mapped to the built-in xsd:time XSD type and serialized with the custom serializer custom/long_time.h
that declares a xsd__time
type:
#import "custom/long_time.h" // import typedef unsigned long long xsd__time; ... use xsd__time ...
Compile and link your code with custom/long_time.c
.
The XML value space of xsd:time are points in time recurring each day of the form hh:mm:ss.sss[Z|(+|-)hh:mm]
, where Z
is the UTC time zone or a time zone offset from UTC is used. The xsd__time
value is always considered and represented in UTC by the serializer.
A C++11 std::chrono::system_clock::time_point
type is mapped to the built-in xsd:dateTime XSD type and serialized with the custom serializer custom/chrono_time_point.h
that declares a xsd__dateTime
type:
#import "custom/chrono_time_point.h" // import typedef std::chrono::system_clock::time_point xsd__dateTime; ... use xsd__dateTime ...
Compile and link your code with custom/chrono_time_point.cpp
.
The XML value space of xsd:duration are values of the form PnYnMnDTnHnMnS
where the capital letters are delimiters. Delimiters may be omitted when the corresponding member is not used.
A long long
(LONG64
or int64_t
) type that contains a duration (time lapse) in milliseconds is mapped to the built-in xsd:duration XSD type and serialized with the custom serializer custom/duration.h
that declares a xsd__duration
type:
#import "custom/duration.h" // import typedef long long xsd__duration; ... use xsd__duration ...
Compile and link your code with custom/duration.c
.
The duration type xsd__duration
can represent 106,751,991,167 days forward and backward with millisecond precision.
A C++11 std::chrono::nanoseconds
type is mapped to the built-in xsd:duration XSD type and serialized with the custom serializer custom/chrono_duration.h
that declares a xsd__duration
type:
#import "custom/chrono_duration.h" // import typedef std::chrono::duration xsd__duration; ... use xsd__duration ...
Compile and link your code with custom/chrono_duration.cpp
.
Classes and structs are mapped to XSD complexTypes. The XML value space consists of XML elements with attributes and subelements, possibly constrained by validation rules that enforce element and attribute occurrence contraints, numerical value range constraints, and string length and pattern constraints.
Classes that are declared with the gSOAP tools are limited to single inheritence only. Structs cannot be inherited.
The class and struct name is bound to an XML namespace by means of the prefix naming convention or by using colon notation:
//gsoap ns schema namespace: urn:types class ns__record { public: std::string name; uint64_t SSN; ns__record *spouse; ns__record(); ~ns__record(); protected: struct soap *soap; };
In the example above, we also added a context pointer to the struct soap
that manages this instance. It is set when the instance is created in the engine's context, for example when deserialized and populated by the engine.
The class maps to a complexType in the soapcpp2-generated schema:
<complexType name="record"> <sequence> <element name="name" type="xsd:string" minOccurs="1" maxOccurs="1"/> <element name="SSN" type="xsd:unsignedLong" minOccurs="1" maxOccurs="1"/> <element name="spouse" type="ns:record" minOccurs="0" maxOccurs="1" nillable="true"/> </sequence> </complexType>
Public data members of a class or struct are serialized. Private and protected members are transient and not serializable.
Also const
and static
members are not serializable, with the exception of const char*
and const wchar_t*
.
Types and specific class/struct members can be made transient by using the extern
qualifier:
extern class std::ostream; // declare 'std::ostream' transient class ns__record { public: extern int num; // not serialized std::ostream out; // not serialized static const int MAX = 1024; // not serialized };
By declaring std::ostream
transient we can use this type where we need it and without soapcpp2 complaining that this class is not defined.
Classes and structs can be declared volatile
with the gSOAP tools. This means that they are already declared elsewhere in our project's source code. We do not want soapcpp2 to generate a second definition for these types.
For example, struct tm
is declared in <time.h>
. We want it serializable and serialize only a selection of its data members:
volatile struct tm { int tm_sec; // seconds (0 - 60) int tm_min; // minutes (0 - 59) int tm_hour; // hours (0 - 23) int tm_mday; // day of month (1 - 31) int tm_mon; // month of year (0 - 11) int tm_year; // year - 1900 };
We can declare classes and structs volatile
for any such types we want to serialize by only providing the public data members we want to serialize.
Colon notation comes in handy to bind an existing class or struct to a schema. For example, we can change the tm
name as follows without affecting the code that uses struct tm
generated by soapcpp2:
volatile struct ns:tm { ... }
This struct maps to a complexType in the soapcpp2-generated schema:
<complexType name="tm"> <sequence> <element name="tm-sec" type="xsd:int" minOccurs="1" maxOccurs="1"/> <element name="tm-min" type="xsd:int" minOccurs="1" maxOccurs="1"/> <element name="tm-hour" type="xsd:int" minOccurs="1" maxOccurs="1"/> <element name="tm-mday" type="xsd:int" minOccurs="1" maxOccurs="1"/> <element name="tm-mon" type="xsd:int" minOccurs="1" maxOccurs="1"/> <element name="tm-year" type="xsd:int" minOccurs="1" maxOccurs="1"/> </sequence> </complexType>
Classes and structs can be declared mutable
with the gSOAP tools. This means that their definition can be spread out over the source code. This promotes the concept of a class or struct as a row of named values, also known as a named tuple, that can be extended as needed with additional entries. Because these types differ from the traditional object-oriented principles of classes and objects, constructors and destructors cannot be defined (also because we cannot guarantee merging these into one such that all members will be initialized). A default constructor, copy constructor, assignment operation, and destructor will be assigned.
mutable struct ns__tuple { @std::string id; }; mutable struct ns__tuple { std::string name; std::string value; };
The members are collected into one definition generated by soapcpp2. Members may be repeated from one definition to another, but only if their associated types are identical. So a third extension with a value
member with a different type fails:
mutable struct ns__tuple { duuble value; // BAD: value is already declared std::string };
The mutable
concept has proven to be very useful when declaring and collecting SOAP Headers for multiple services, which are collected into one struct SOAP_ENV__Header
by the soapcpp2 tool.
Class and struct data members may be declared with a default initialization value that is provided "inline" with the declaration of the member:
class ns__record { public: std::string name = "Joe";
These initializations are made by the default constructor that is added by soapcpp2 to each class and struct. A constructor is only added when a default constructor is not already defined with the class declaration.
Initializations can only be provided for members that have primitive types (bool
, enum
, time_t
, numeric and string types).
Class and struct data members can be declared as XML attributes by annotating their type with a @
with the declaration of the member:
class ns__record { public: @std::string name; @uint64_t SSN; ns__record *spouse; };
This class maps to a complexType in the soapcpp2-generated schema:
<complexType name="record"> <sequence> <element name="spouse" type="ns:record" minOccurs="0" maxOccurs="1" nillable="true"/> </sequence> <attribute name="name" type="xsd:string" use="required"/> <attribute name="SSN" type="xsd:unsignedLong" use="required"/> </complexType>
An example XML instance of ns__record
is:
<ns:record xmlns:ns="urn:types" name="Joe" SSN="1234567890"> <spouse> <name>Jane</name> <SSN>1987654320</SSN> </spouse> </ns:record>
Attribute data members are restricted to primitive types (bool
, enum
, time_t
, numeric and string types), xsd__hexBinary
, xsd__base64Binary
, and custom serializers, such as xsd__dateTime
. Custom serializers for types that may be used as attributes MUST define soap_s2T
and soap_T2s
functions that convert values of type T
to strings and back.
Attribute data members can be pointers and smart pointers to these types, which permits attributes to be optional.
A public pointer-typed data member is serialized by following its (smart) pointer(s) to the value pointed to.
Pointers that are NULL and smart pointers that are empty are serialized to produce omitted element and attribute values, unless an element is required and is nillable.
To control the occurrence requirements of pointer-based data members, occurrence constraints are associated with data members in the form of a range minOccurs : maxOccurs
. For non-repeatable (meaning, not a container or array) data members, there are only three reasonable occurrence constraints:
0:0
means that this element or attribute is prohibited.0:1
means that this element or attribute is optional.1:1
means that this element or attribute is required.Pointer-based data members have a default 0:1
occurrence constraint, making them optional, and their XSD schema local element/attribute definition is marked as nillable. Non-pointer data members have a default 1:1
occurence constraint, making them required.
A pointer data member that is explicitly marked as required with 1:1
will be serialized as an element with an xsi:nil attribute, thus effectively revealing the NULL property of its value.
A non-pointer data member that is explicitly marked as optional with 0:1
will be set to its default value when no XML value is presented to the deserializer. A default value can be assigned to data members that have primitive types.
Consider for example:
class ns__record { public: std::shared_ptr<std::string> name; // optional (0:1) uint64_t SSN 0:1 = 999; // forced this to be optional with default 999 ns__record *spouse 1:1; // forced this to be required (only married people) };
This class maps to a complexType in the soapcpp2-generated schema:
<complexType name="record"> <sequence> <element name="name" type="xsd:string" minOccurs="0" maxOccurs="1" nillable="true"/> <element name="SSN" type="xsd:unsignedLong" minOccurs="0" maxOccurs="1" default="999"/> <element name="spouse" type="ns:record" minOccurs="1" maxOccurs="1" nillable="true"/> </sequence> </complexType>
An example XML instance of ns__record
with its name
string value set to Joe
, SSN
set to its default, and spouse
set to NULL:
<ns:record xmlns:ns="urn:types"> <name>Joe</name> <SSN>999</SSN> <spouse xsi:nil="true"/> </ns:record>
Class and struct data members declared as a container std::deque
, std::list
, std::set
, and std::vector
are serialized as a collection of values:
class ns__record { public: std::vector<std::string> names; uint64_t SSN; };
To practically limit the number of names within reasonable bounds, occurrence constraints are associated with the container. Occurrence constraints are of the form minOccurs : maxOccurs
:
class ns__record { public: std::vector<std::string> names 1:10; uint64_t SSN; };
This class maps to a complexType in the soapcpp2-generated schema:
<complexType name="record"> <sequence> <element name="name" type="xsd:string" minOccurs="1" maxOccurs="10"/> <element name="SSN" type="xsd:unsignedLong" minOccurs="1" maxOccurs="1""/> </sequence> </complexType>
Because C does not support a container template library, we can use a dynamically-sized array of values. This array is declared as a size-pointer member pair:
struct ns__record { $int sizeofnames; // array size char* *names; // array of char* names uint64_t SSN; };
where the marker $
with int
denotes a special type that is used to store the array size and to indicate that this is a size-pointer member pair that declares a dynamically-sized array.
This class maps to a complexType in the soapcpp2-generated schema:
<complexType name="record"> <sequence> <element name="name" type="xsd:string" minOccurs="0" maxOccurs="unbounded" nillable="true"/> <element name="SSN" type="xsd:unsignedLong" minOccurs="1" maxOccurs="1""/> </sequence> </complexType>
To limit the number of names in the array within reasonable bounds, occurrence constraints are associated with the array size member. Occurrence constraints are of the form minOccurs : maxOccurs
:
struct ns__record { $int sizeofnames 1:10; // array size 1..10 char* *names; // array of one to ten char* names uint64_t SSN; };
This class maps to a complexType in the soapcpp2-generated schema:
<complexType name="record"> <sequence> <element name="name" type="xsd:string" minOccurs="1" maxOccurs="10" nillable="true"/> <element name="SSN" type="xsd:unsignedLong" minOccurs="1" maxOccurs="1""/> </sequence> </complexType>
A union member in a class or in a struct cannot be serialized unless a discriminating variant selector is provided that tells the serializer which union field to serialize.
The variant selector is associated with the union as a selector-union member pair, where the variant selector is a special $int
member:
class ns__record { public: $int xORnORs; // variant selector union choice { float x; int n; char *s; } u; std::string name; };
The variant selector values are auto-generated based on the union name choice
and the names of its members x
, n
, and s
:
xORnORs = SOAP_UNION_choice_x
when u.x
is valid.xORnORs = SOAP_UNION_choice_n
when u.n
is valid.xORnORs = SOAP_UNION_choice_s
when u.s
is valid.xORnORs = 0
when none are valid (should only be used with great care, because XML content validation may fail when content is required but absent).This class maps to a complexType with a sequence and choice in the soapcpp2-generated schema:
<complexType name="record"> <sequence> <choice> <element name="x" type="xsd:float" minOccurs="1" maxOccurs="1"/> <element name="n" type="xsd:int" minOccurs="1" maxOccurs="1"/> <element name="s" type="xsd:string" minOccurs="0" maxOccurs="1" nillable="true"/> </choice> <element name="names" type="xsd:string" minOccurs="1" maxOccurs="10" nillable="true"/> </sequence> </complexType>
A public get
method may be added to a class or struct, which will be triggered by the deserializer. This method will be invoked right after the instance is populated by the deserializer. The get
method can be used to update or verify deserialized content. It should return SOAP_OK
or set soap::error
to a nonzero error code and return it.
A public set
method may be added to a class or struct, which will be triggered by the serializer. The method will be invoked just before the instance is serialized. Likewise, the set
method should return SOAP_OK
or set set soap::error
to a nonzero error code and return it.
For example, adding a set
and get
method to a class declaration:
class ns__record { public: int set(struct soap*); // triggered before serialization int get(struct soap*); // triggered after deserialization
To add these and othe rmethods to classes and structs with wsdl2h and typemap.dat
, please see section class and struct addition.
To define and reference XML document root elements we use type names that start with an underscore:
class _ns__record
Alternatively, we can use a typedef to define a document root element with a given type:
typedef ns__record _ns__record;
This typedef maps to a global root element that is added to the soapcpp2-generated schema:
<element name="record" type="ns:record"/>
An example XML instance of _ns__record
is:
<ns:record xmlns:ns="urn:types"> <name>Joe</name> <SSN>1234567890</SSN> <spouse> <name>Jane</name> <SSN>1987654320</SSN> </spouse> </ns:record>
Global-level element/attribute definitions are also referenced and/or added to the generated schema when serializable data members reference these by their qualified name:
typedef std::string _ns__name 1:100; class _ns__record { public: @_QName xsi__type; // built-in XSD attribute xsi:type _ns__name ns__name; // ref to global ns:name element uint64_t SSN; _ns__record *spouse; };
These types map to the following comonents in the soapcpp2-generated schema:
<simpleType name="name"> <restriction base="xsd:string"> <minLength value="1"/> <maxLength value="100"/> </restriction> </simpleType> <element name="name" type="ns:name"/> <complexType name="record"> <sequence> <element ref="ns:name" minOccurs="1" maxOccurs="1"/> <element name="SSN" type="xsd:unsignedLong" minOccurs="1" maxOccurs="1"/> <element name="spouse" type="ns:record" minOccurs="0" maxOccurs="1" nillable="true"/> </sequence> <attribute ref="xsi:type" use="optional"/> </complexType> <element name="record" type="ns:record"/>
However, we must warn against using qualified member names when their types do not match their definitions:
class _ns__record { public: int ns__name; // BAD: element ns:name is NOT of an int type
Therefore, we recommend to avoid qualified member names and only use them when referring to standard XSD elements and attributes, such as xsi__type
, and xsd__lang
. The soapcpp2 tool does not prevent abuse of this mechanism.
The following functions/macros are generated by soapcpp2 for each type T
, which should make it easier to send, receive, and copy XML data in C and in C++:
int soap_write_T(struct soap*, T*)
writes an instance of T
to a FILE (via FILE *soap::sendfd)
) or to a stream (via std::ostream *soap::os
). Returns SOAP_OK
on success or an error code, also stored in soap->error
.int soap_read_T(struct soap*, T*)
reads an instance of T
from a FILE (via FILE *soap::recvfd)
) or from a stream (via std::istream *soap::is
). Returns SOAP_OK
on success or an error code, also stored in soap->error
.void soap_default_T(struct soap*, T*)
sets an instance T
to its default value, resetting members of a struct to their initial values (for classes we use method T::soap_default
, see below).T * soap_dup_T(struct soap*, T *dst, const T *src)
(soapcpp2 option -Ec
) deep copy src
into dst
, replicating all deep cycles and shared pointers when a managing soap context is provided as argument. When dst
is NULL, allocates space for dst
. Deep copy is a tree when argument is NULL, but the presence of deep cycles will lead to non-termination. Use flag SOAP_XML_TREE
with managing context to copy into a tree without cycles and pointers to shared objects. Returns dst
(or allocated space when dst
is NULL).void soap_del_T(const T*)
(soapcpp2 option -Ed
) deletes all heap-allocated members of this object by deep deletion ONLY IF this object and all of its (deep) members are not managed by a soap context AND the deep structure is a tree (no cycles and co-referenced objects by way of multiple (non-smart) pointers pointing to the same data). Can be safely used after soap_dup(NULL)
to delete the deep copy. Does not delete the object itself.When in C++ mode, soapcpp2 tool adds several methods to classes and structs, in addition to adding a default constructor and destructor (when these were not explicitly declared).
The public methods added to a class/struct T
:
virtual int T::soap_type(void)
returns a unique type ID (SOAP_TYPE_T
). This numeric ID can be used to distinguish base from derived instances.virtual void T::soap_default(struct soap*)
sets all data members to default values.virtual void T::soap_serialize(struct soap*) const
serializes object to prepare for SOAP 1.1/1.2 encoded output (or with SOAP_XML_GRAPH
) by analyzing its (cyclic) structures.virtual int T::soap_put(struct soap*, const char *tag, const char *type) const
emits object in XML, compliant with SOAP 1.1 encoding style, return error code or SOAP_OK
. Requires soap_begin_send(soap)
and soap_end_send(soap)
.virtual int T::soap_out(struct soap*, const char *tag, int id, const char *type) const
emits object in XML, with tag and optional id attribute and xsi:type, return error code or SOAP_OK
. Requires soap_begin_send(soap)
and soap_end_send(soap)
.virtual void * T::soap_get(struct soap*, const char *tag, const char *type)
Get object from XML, compliant with SOAP 1.1 encoding style, return pointer to object or NULL on error. Requires soap_begin_recv(soap)
and soap_end_recv(soap)
.virtual void *soap_in(struct soap*, const char *tag, const char *type)
Get object from XML, with matching tag and type (NULL matches any tag and type), return pointer to object or NULL on error. Requires soap_begin_recv(soap)
and soap_end_recv(soap)
virtual T * T::soap_alloc(void) const
returns a new object of type T
, default initialized and not managed by a soap context.virtual T * T::soap_dup(struct soap*) const
(soapcpp2 option -Ec
) returns a duplicate of this object by deep copying, replicating all deep cycles and shared pointers when a managing soap context is provided as argument. Deep copy is a tree when argument is NULL, but the presence of deep cycles will lead to non-termination. Use flag SOAP_XML_TREE
with managing context to copy into a tree without cycles and pointers to shared objects.virtual void T::soap_del() const
(soapcpp2 option -Ed
) deletes all heap-allocated members of this object by deep deletion ONLY IF this object and all of its (deep) members are not managed by a soap context AND the deep structure is a tree (no cycles and co-referenced objects by way of multiple (non-smart) pointers pointing to the same data).Can be safely used after soap_dup(NULL)
to delete the deep copy. Does not delete the object itself.A class or struct with the following layout is a one-dimensional SOAP Array type:
class Array { public: T *__ptr; // array pointer int __size; // array size };
where T
is the array element type. A multidimensional SOAP Array is:
class Array { public: T *__ptr; // array pointer int __size[N]; // array size of each dimension };
where N
is the constant number of dimensions. The pointer points to an array of __size[0]*__size[1]* ... * __size[N-1]
elements.
A special case of a one-dimensional array is used to define xsd:hexBinary and xsd:base64Binary types when the pointer type is unsigned char
:
class xsd__hexBinary { public: unsigned char *__ptr; // points to raw binary data int __size; // size of data };
and
class xsd__base64Binary { public: unsigned char *__ptr; // points to raw binary data int __size; // size of data };
A class or struct with a binary content layout can be extended to support MIME/MTOM (and older DIME) attachments, such as in xop:Include elements:
//gsoap xop schema import: http://www.w3.org/2004/08/xop/include class _xop__Include { public: unsigned char *__ptr; // points to raw binary data int __size; // size of data char *id; // NULL to generate an id, or set to a unique UUID char *type; // MIME type of the data char *options; // optional description of MIME attachment };
Attachments are beyond the scope of this document and we refer to the gSOAP user guide for more details.
A class or struct with the following layout is a complexType with simpleContent wrapper:
class ns__simple { public: T __item; };
A wrapper class/struct may have any number of attributes declared with @
.
Memory management with the soap
context enables us to allocate data in context-managed heap space that can be collectively deleted. All deserialized data is placed on the context-managed heap by the gSOAP engine.
In C (wsdl2h option -c
and soapcpp2 option -c
), the gSOAP engine allocates data on a context-managed heap with:
void *soap_malloc(struct soap*, size_t len)
.The soap_malloc
function is a wrapper around malloc
, but which also allows the struct soap
context to track all heap allocations for collective deletion with soap_end(soap)
:
#include "soapH.h" #include "ns.nsmap" ... struct soap *soap = soap_new(); // new context ... struct ns__record *record = soap_malloc(soap, sizeof(struct ns__record)); soap_default_ns__record(soap, record); ... soap_destroy(soap); // only for C++, see section on C++ below soap_end(soap); // delete record and all other heap allocations soap_free(soap); // delete context
The soapcpp2 auto-generated deserializers in C use soap_malloc
to allocate and populate deserialized structures, which are managed by the context for collective deletion.
To make char*
and wchar_t*
string copies to the context-managed heap, we can use the functions:
char *soap_strdup(struct soap*, const char*)
andwchar_t *soap_wstrdup(struct soap*, const wchar_t*)
.We use the soapcpp2 auto-generated soap_dup_T
functions to duplicate data into another context (this requires soapcpp2 option -Ec
to generate), here shown for C:
struct soap *other_soap = soap_new(); // another context struct ns__record *other_record = soap_dup_ns__record(other_soap, NULL, record); ... soap_destroy(other_soap); // only for C++, see section on C++ below soap_end(other_soap); // delete other_record and all of its deep data soap_free(other_soap); // delete context
Note that the only reason to use another context and not to use the primary context is when the primary context must be destroyed together with all of the objects it manages while some of the objects must be kept alive. If the objects that are kept alive contain deep cycles then this is the only option we have, because deep copy with a managing context detects and preserves these cycles unless the SOAP_XML_TREE
flag is used with the context:
struct soap *other_soap = soap_new1(SOAP_XML_TREE); // another context struct ns__record *other_record = soap_dup_ns__record(other, NULL, record);
The resulting deep copy will be a full copy of the source data structure as a tree without co-referenced data (i.e. no digraph) and without cycles. Cycles are pruned and (one of the) pointers that forms a cycle is repaced by NULL.
We can also deep copy into unmanaged space and use the auto-generated soap_del_T()
function (requires soapcpp2 option -Ed
to generate) to delete it later, but we MUST NOT do this for any data that we suspect has deep cycles:
struct ns__record *other_record = soap_dup_ns__record(NULL, NULL, record); ... soap_del_ns__record(other_record); // deep delete record data members free(other_record); // delete the record
Cycles in the data structure will lead to non-termination when making unmanaged deep copies. Consider for example:
struct ns__record { const char *name; uint64_t SSN; ns__record *spouse; };
Our code to populate a structure with a mutual spouse relationship:
struct soap *soap = soap_new(); ... struct ns__record pers1, pers2; soap_default_ns__record(soap, &pers1); soap_default_ns__record(soap, &pers2); pers1.name = "Joe"; // OK to serialize static data pers1.SSN = 1234567890; pers1.spouse = &pers2; pers2.name = soap_strdup(soap, "Jane"); // allocates and copies a string pers2.SSN = 1987654320; pers2.spouse = &pers1; ... struct ns__record *pers3 = soap_dup_ns__record(NULL, NULL, &pers1); // BAD struct ns__record *pers4 = soap_dup_ns__record(soap, NULL, &pers1); // OK soap_set_mode(soap, SOAP_XML_TREE); struct ns__record *pers5 = soap_dup_ns__record(soap, NULL, &pers1); // OK
As we can see, the gSOAP serializer can serialize any heap, stack, or static allocated data, such as in our code above. So we can serialize the stack-allocated pers1
record as follows:
soap->sendfd = fopen("record.xml", "w"); soap_set_mode(soap, SOAP_XML_GRAPH); // support id-ref w/o requiring SOAP soap_clr_mode(soap, SOAP_XML_TREE); // if set, clear soap_write_ns__record(soap, &pers1); fclose(soap->sendfd); soap->sendfd = NULL;
which produces an XML document record.xml that is similar to:
<ns:record xmlns:ns="urn:types" id="Joe"> <name>Joe</name> <SSN>1234567890</SSN> <spouse id="Jane"> <name>Jane</name> <SSN>1987654320</SSN> <spouse ref="#Joe"/> </spouse> </ns:record>
Deserialization of an XML document with a SOAP 1.1/1.2 encoded id-ref graph leads to the same non-termination problem when we later try to copy the data into unmanaged space:
struct soap *soap = soap_new1(SOAP_XML_GRAPH); // support id-ref w/o SOAP ... struct ns__record pers1; soap->recvfd = fopen("record.xml", "r"); soap_read_ns__record(soap, &pers1); fclose(soap->recvfd); soap->recvfd = NULL; ... struct ns__record *pers3 = soap_dup_ns__record(NULL, NULL, &pers1); // BAD struct ns__record *pers4 = soap_dup_ns__record(soap, NULL, &pers1); // OK soap_set_mode(soap, SOAP_XML_TREE); struct ns__record *pers5 = soap_dup_ns__record(soap, NULL, &pers1); // OK
Copying data with soap_dup_T(soap)
into managed space is always safe. Copying into unmanaged space requires diligence. But deleting unmanaged data is easy with soap_del_T()
.
We can also use soap_del_T()
to delete structures that we created in C, but only if these structures are created with malloc
and do NOT contain pointers to stack and static data.
In C++, the gSOAP engine allocates data on a managed heap using a combination of void *soap_malloc(struct soap*, size_t len)
and soap_new_T()
, where T
is the name of a class, struct, or class template (container or smart pointer). Heap allocation is tracked by the struct soap
context for collective deletion with soap_destroy(soap)
and soap_end(soap)
.
Only structs, classes, and class templates are allocated with new
via soap_new_T(struct soap*)
and mass-deleted with soap_destroy(soap)
.
There are four variations of soap_new_T
for class/struct/template type T
that soapcpp2 auto-generates to create instances on a context-managed heap:
T* soap_new_T(struct soap*)
returns a new instance of T
with default data member initializations that are set with the soapcpp2 auto-generated void T::soap_default(struct soap*)
method), but ONLY IF the soapcpp2 auto-generated default constructor is used that invokes soap_default()
and was not replaced by a user-defined default constructor.T* soap_new_T(struct soap*, int n)
returns an array of n
new instances of T
. Similar to the above, instances are initialized.T* soap_new_req_T(struct soap*, ...)
returns a new instance of T
and sets the required data members to the values specified in ...
. The required data members are those with minOccurs > 0, see the subsection on occurrence constraints in Classes and structs.T* soap_new_set_T(struct soap*, ...)
returns a new instance of T
and sets the public/serializable data members to the values specified in ...
.The above functions can be invoked with a NULL soap
context, but we will be responsible to use delete T
to remove this instance from the unmanaged heap.
Primitive types and arrays of these are allocated with soap_malloc
by the gSOAP engine. As we stated above, all types except for classes, structs, class templates (containers and smart pointers) are allocated with soap_malloc
for reasons of efficiency.
We can use a C++ template to simplify the managed allocation and initialization of primitive values as follows (this is for primitive types only, because we should allocate structs and classes with soap_new_T
):
template<class T> T* soap_make(struct soap *soap, T val) { T *p = (T*)soap_malloc(soap, sizeof(T)); if (p) *p = val; return p; }
For example, assuming we have the following class:
class ns__record { public: std::string name; // required name uint64_t *SSN; // optional SSN ns__record *spouse; // optional spouse };
We can instantiate a record by using the auto-generated soap_new_set_ns__record
and our soap_make
to create a SSN value on the managed heap:
soap *soap = soap_new(); // new context ... ns__record *record = soap_new_set_ns__record( soap, "Joe", soap_make<uint64_t>(soap, 1234567890), NULL); ... soap_destroy(soap); // delete record and all other managed instances soap_end(soap); // delete managed soap_malloc'ed heap data soap_free(soap); // delete context
Note however that the gSOAP serializer can serialize any heap, stack, or static allocated data. So we can also create a new record as follows:
uint64_t SSN = 1234567890; ns__record *record = soap_new_set_ns__record(soap, "Joe", &SSN, NULL);
which will be fine to serialize this record as long as the local SSN
stack-allocated value remains in scope when invoking the serializer and/or using record
. It does not matter if soap_destroy
and soap_end
are called beyond the scope of SSN
.
To facilitate our class methods to access the managing context, we can add a soap context pointer to a class/struct:
class ns__record { ... void create_more(); // needs a context to create more internal data protected: struct soap *soap; // the context that manages this instance, or NULL };
The context is set when invoking soap_new_T
(and similar) with a non-NULL context argument.
We use the soapcpp2 auto-generated soap_dup_T
functions to duplicate data into another context (this requires soapcpp2 option -Ec
to generate):
soap *other_soap = soap_new(); // another context ns__record *other_record = soap_dup_ns__record(other, NULL, record); ... soap_destroy(other_soap); // delete record and other managed instances soap_end(other_soap); // delete other data (the SSNs on the heap) soap_free(other_soap); // delete context
To duplicate derived instances when a base class instance is provided, use the auto-generated method T* T::soap_dup(struct soap*)
:
soap *other_soap = soap_new(); // another context ns__record *other_record = soap_dup_ns__record(other_soap, NULL, record); ... soap_destroy(other_soap); // delete record and other managed instances soap_end(other_soap); // delete other data (the SSNs on the heap) soap_free(other_soap); // delete context
Note that the only reason to use another context and not to use the primary context is when the primary context must be destroyed together with all of the objects it manages while some of the objects must be kept alive. If the objects that are kept alive contain deep cycles then this is the only option we have, because deep copy with a managing context detects and preserves these cycles unless the SOAP_XML_TREE
flag is used with the context:
soap *other_soap = soap_new1(SOAP_XML_TREE); // another context ns__record *other_record = record->soap_dup(other_soap);
The resulting deep copy will be a full copy of the source data structure as a tree without co-referenced data (i.e. no digraph) and without cycles. Cycles are pruned and (one of the) pointers that forms a cycle is repaced by NULL.
We can also deep copy into unmanaged space and use the auto-generated soap_del_T()
function or the T::soap_del()
method (requires soapcpp2 option -Ed
to generate) to delete it later, but we MUST NOT do this for any data that we suspect has deep cycles:
ns__record *other_record = record->soap_dup(NULL); ... other_record->soap_del(); // deep delete record data members delete other_record; // delete the record
Cycles in the data structure will lead to non-termination when making unmanaged deep copies. Consider for example:
class ns__record { const char *name; uint64_t SSN; ns__record *spouse; };
Our code to populate a structure with a mutual spouse relationship:
soap *soap = soap_new(); ... ns__record pers1, pers2; pers1.name = "Joe"; pers1.SSN = 1234567890; pers1.spouse = &pers2; pers2.name = "Jane"; pers2.SSN = 1987654320; pers2.spouse = &pers1; ... ns__record *pers3 = soap_dup_ns__record(NULL, NULL, &pers1); // BAD ns__record *pers4 = soap_dup_ns__record(soap, NULL, &pers1); // OK soap_set_mode(soap, SOAP_XML_TREE); ns__record *pers5 = soap_dup_ns__record(soap, NULL, &pers1); // OK
Note that the gSOAP serializer can serialize any heap, stack, or static allocated data, such as in our code above. So we can serialize the stack-allocated pers1
record as follows:
soap->sendfd = fopen("record.xml", "w"); soap_set_mode(soap, SOAP_XML_GRAPH); // support id-ref w/o requiring SOAP soap_clr_mode(soap, SOAP_XML_TREE); // if set, clear soap_write_ns__record(soap, &pers1); fclose(soap->sendfd); soap->sendfd = NULL;
which produces an XML document record.xml that is similar to:
<ns:record xmlns:ns="urn:types" id="Joe"> <name>Joe</name> <SSN>1234567890</SSN> <spouse id="Jane"> <name>Jane</name> <SSN>1987654320</SSN> <spouse ref="#Joe"/> </spouse> </ns:record>
Deserialization of an XML document with a SOAP 1.1/1.2 encoded id-ref graph leads to the same non-termination problem when we later try to copy the data into unmanaged space:
soap *soap = soap_new1(SOAP_XML_GRAPH); // support id-ref w/o SOAP ... ns__record pers1; soap->recvfd = fopen("record.xml", "r"); soap_read_ns__record(soap, &pers1); fclose(soap->recvfd); soap->recvfd = NULL; ... ns__record *pers3 = soap_dup_ns__record(NULL, NULL, &pers1); // BAD ns__record *pers4 = soap_dup_ns__record(soap, NULL, &pers1); // OK soap_set_mode(soap, SOAP_XML_TREE); ns__record *pers5 = soap_dup_ns__record(soap, NULL, &pers1); // OK
Copying data with soap_dup_T(soap)
into managed space is always safe. Copying into unmanaged space requires diligence. But deleting unmanaged data is easy with soap_del_T()
.
We can also use soap_del_T()
to delete structures in C++, but only if these structures are created with new
(and new []
for arrays when applicable) for classes, structs, and class templates and with malloc
for anything else, and the structures do NOT contain pointers to stack and static data.
There are several context initialization flags and mode flags to control XML serialization at runtime:
SOAP_XML_STRICT
: strictly validates XML while deserializing. Should not be used together with SOAP 1.1/1.2 encoding style of messaging.SOAP_XML_INDENT
: produces indented XML.SOAP_XML_CANONICAL
: c14n canonocalization, removes unnecessary xmlns
bindings and adds them to appropriate places by applying c14n normalization rules. Should not be used together with SOAP 1.1/1.2 encoding style of messaging.SOAP_XML_TREE
: write tree XML without id-ref, pruning data structure cycles to prevent nontermination.SOAP_XML_GRAPH
: write graph (digraph and cyclic graphs with shared pointers to objects) using id-ref attributes. That is, XML with SOAP multi-ref encoded id-ref elements. This is a structure-preserving serialization format, because co-referenced data and also cyclic relations are accurately represented.SOAP_XML_DEFAULTNS
: uses xmlns default bindings, assuming that the schema element form is "qualified" by default (be warned if it is not!).SOAP_XML_NOTYPE
: removes all xsi:type attribuation. This may affect the quality of the deserializer, which relies on xsi:type attributes to distinguish base class instances from derived class instanced.SOAP_C_UTFSTRING
: enables all std::string
and char*
strings to contain UTF-8 content.Additional notes with respect to the wsdl2h and soapcpp2 tools:
#import "file.h"
instead of #include
to import other header files in a gSOAP header file for soapcpp2. The #include
and #define
directives are accepted, but deferred to the generated code.-0
.-qname
. Or add a namespace name { ... }
to the header file, but the { ... }
MUST cover the entire header file content from begin to end.-d
for DOM support and compile and link with dom.c
or dom.cpp
.The soapcpp2 tool generates a .nsmap
file that includes two bindings for SOAP namespaces. We can remove all SOAP namespaces (and SOAP processing logic) with soapcpp2 option -0
or by simply setting the two entries to NULL:
SOAP_NMAC struct Namespace namespaces[] = { {"SOAP-ENV", NULL, NULL, NULL}, {"SOAP-ENC", NULL, NULL, NULL}, ...
Note that once the .nsmap
is generated, we can copy-paste the content into our project code. However, if we rerun wsdl2h on updated WSDL/XSD files or typemap.dat
declarations then we need to use the updated table.
Select the project files below to peruse the source code examples.
address.xsd
Address book schemaaddress.cpp
Address book app (reads/writes address.xml file)addresstypemap.dat
Schema namespace prefix name preference for wsdl2hgraph.h
Graph data binding (tree, digraph, cyclic graph)graph.cpp
Test graph serialization as tree, digraph, and cyclicaddress.h
gSOAP-specific data binding definitions from address.xsdaddressStub.h
C++ data binding definitionsaddressH.h
SerializersaddressC.cpp
Serializersaddress.xml
Address book data generated by address appgraphStub.h
C++ data binding definitionsgraphH.h
SerializersgraphC.cpp
Serializersg.xsd
XSD schema with g:Graph
complexTypeg.nsmap
xmlns bindings namespace mapping tableBuilding the AddressBook example:
wsdl2h -g -t addresstypemap.dat address.xsd soapcpp2 -0 -CS -I../../import -p address address.h c++ -I../.. address.cpp addressC.cpp -o address -lgsoap++
Building the graph serialization example:
soapcpp2 -CS -I../../import -p graph graph.h c++ -I../.. graph.cpp graphC.cpp -o graph -lgsoap++
To compile without using the libgsoap++
library: simply compile stdsoap2.cpp
together with the above.
To execute the AddressBook example:
./address
To execute the Graph serialization example:
./graph