ecpp(7) Tntnet users guide ecpp(7)NAMEecpp - template-language for tntnet(8)DESCRIPTIONecpp is the template-language used by the tntnet-system to generate
dynamic content.
A template consists of normal content (normally html-data) enriched
with special tags, which trigger some special handling.
One ecpp-file is compiled into a C++-class. The C++-class is placed
into the namespace component. A ecpp-file compiled into a C++-class is
called component. The name of the class is the basename of the file.
request, reply, qparam
Each component has 3 parameters: request, reply and qparam. request
holds information about the client-request like http headers and the
url, but also additional parameters specified in the config-file tnt‐
net.xml(7). The type of request is tnt::HttpRequest.
reply receives the answer from the component. The component can set
additional http-headers here, set cookies and - most important - gener‐
ate output. The most important methods here are reply.out() and
reply.sout(). Both return a std::ostream, which receives the output of
the component. reply.sout() has a filter installed, which translates
some characters, whith special meanings in html to the corresponding
html-entities. The characters are <, >, &, " and '. This is useful for
printing values from variables to the html-code.
qparam holds the query-parameters parsed from GET- or POST-parameters
or received from other components. The type of qparam is
tnt::query_params. Normally you use a <%args>-block to specify the
parameters, but there are special cases, where it is useful to access
these directly.
component adressing
Each component has a unique name. The name is composed from the
class-name, the character '@' and the name of the shared library, it is
located. Components can have internal subcomponents. The name of the
internal subcomponent is appended to the classname separated by a dot
(.).
special rule for line feeds after a </%something>-tag
A line feed immediately after a closing tag for all <%something>-blocks
are ignored. Hence blocks followed immediately one after another does
not generate white space in output, which is often undesirable.
error-handling
Error-handling is done by exception. Tntnet catches all exceptions
thrown by components and handles them properly. Exceptions must be
derived from std::exception. Exceptions derived from tnt::HttpError,
are handled separately. They carry a http-return-code, which is sent to
the client. Other exceptions derived from std::exception, result in a
http error code 500 (Internal Server Error).
TAGS
<$ expr $>
Print expressions expr to the outputstream. The characters <, >,
&, " and ', which have special meanings in html, are translated
to the corresponding html-entities.
<$$ expr $>
Print expressions expr without translating characters with spe‐
cial meaning in html to html entities to the output stream.
<? cond ? expr ?>
Conditional output. Print expression expr to the outputstream,
if cond evaluates to true. Characters with special meaning in
html are translated to the corresponding html-entities.
<?? cond ? expr ?>
Conditional output. Print expression expr to the outputstream,
if cond evaluates to true. Characters with special meaning in
html are not translated to the corresponding html-entities.
<& component [ arguments ] >
Call the specified component. The output of the component is
printed into the outputstream. If the component-name does not
start with a letter, the ecpp-compiler treats it as a expres‐
sion, which returns the name of the component. You must surround
the expression in brackets, if it contains spaces.
The arguments-part specify the parameters, the component will
receive. Arguments are name-value-pairs separated by '='. They
are put in the qparam-parameter of the component and are nor‐
mally declared in the <%args>-block. Values can be specified in
3 forms:
As a plain word without spaces
As a string enclosed in quotation marks
As a expression enclosed in brackets
A single plain word in the argumentlist is treated as a variable
of type cxxtools::query_params and a copy is passed to the com‐
ponent. Other parameters are added to this copy. If you want to
pass all parameters of the current component put the variable
qparam as a plain word in the argument list.
</&component>
Closing-tag for a component-call. When components are called,
this closing-tag might occur later. The code in <%close>-block
is placed here.
<{...}>
C++-inline-processing-block. The code in this block is copied
into the C++-class unchanged.
A linefeed after the closing tag is not ignored.
<#...#>
Comment-block. Everything in this block is ignored.
<%application [ scope="component|page|global" ] >...</%application>
Variables defined here, have the lifetime of the application.
Application-scope is automatically locked.
<%args>...</%args>
Defines GET- or POST-parameters recieved by the component.
Each argument has a name and optionally a defaul-value. The
default-value is delimited by '=' from the name. A single argu‐
ment-definition followed by a semicolon (;). In the component a
variable with the same name of type std::string is defined,
which receives the value.
A argument-name can be prefixed by a type-definition. The
ecpp-compiler generates code, which tries to convert the value
with the input-stream-operator. This means, that each type,
which can be read from a input-stream (std::istream) can be
used. If the argument can't be converted, a exception is thrown.
Argumentnames can be postfixed by empty square-brackets. This
defines a std::vector with the specified type or std::string, if
no type is specified. This way multiple values with the same
name can be received. If a type is specified, each value is con‐
verted to the target-type.
<%close>...</%close>
Code in these tags is placed into the calling component, when a
closing tag </&component> is found.
The <%close> receives the same parameters like the corresponding
normal component call.
<%config>...</%config>
Often webapplications need some configuration like data‐
base-names or login-information to the database. These configu‐
ratioin-variables can be read from the tntnet.xml. Variablenames
ended with a semicolon are defined as static std::string-vari‐
ables and filled from tntnet.xml. A variable can be prepended by
a type. The value from tntnet.xml is then converted with a
std::istream.
You can also specify a default value by appending a '=' and the
value to the variable.
Example:
<%config>
dburl = "sqlite:db=mydbfile.sqlite";
int maxvalue = 10;
</%config>
tntnet.xml:
<dburl>postgresql:dbname=mydb</dburl>
<%cpp>...</%cpp>
C++-processing-block. The code between these tags are copied
into the C++-class unchanged.
A linefeed after the closing tag is ignored.
<%def name>...</%def>
Defines a internal subcomponent with the name name, which can be
called like other components.
<%doc>...</%doc>
Comment-block. Everything in this block is ignored.
A linefeed after the closing tag is ignored.
<%get>...</%get>
Works like a <%args> block but receives only GET parameters.
<%i18n>...</%i18n>
Encloses a block of text-data, which is to be translated. See
ecppl(1) and ecppll(1) for details.
<%include>filename</%include>
The specified file is read and compiled.
<%param>...</%param>
Defines parameter received from calling components. In contrast
to query-parameters these variables can be of any type. The syn‐
tax (and the underlying technology) is the same like in scoped
variables. See the description about scoped variables to see how
to define parameters. The main difference is, that a parameter
variable has no scope, since the parameter is always local to
the component.
<%out> expr </%out>
Same as <$$ ... $>. Prints the contained C++ expression expr.
<%post>...</%post>
Works like a <%args> block but receives only POST parameters.
<%pre>...</%pre>
Defines C++-code, which is placed outside the C++-class and out‐
side the namespace-definition. This is a good place to define
#include-directives.
<%request [ scope="component|page|global" ] >...</%request>
Define request-scope variables. Variables defined here, has the
lifetime of the request.
<%session [ scope="component|page|global" ] >...</%session>
Variables defined here, has the lifetime of the session.
Sessions are identified with cookies. If a <%session>-block is
defined somewhere in a component, a session-cookie is sent to
the client.
Sessions are automatically locked.
<%securesession [ scope="component|page|global" ] >...</%securesession>
Secure session is just like session but a secure cookie is used
to identify the session. Secure cookies are transfered only over
a ssl connection from the browser and hence the variables are
only kept in a ssl secured application.
If a variable defined here is used in a non ssl page, the vari‐
able values are lost after the current request.
<%sout> expr </%sout>
Same as <$ ... $>. Prints the contained C++ expression expr. The
characters <, >, &, " and ', which have special meanings in
html, are translated to the corresponding html-entities.
<%thread [ scope="component|page|global" ] >...</%thread>
Variables defined here, has the lifetime of the thread. Each
thread has his own instance of these variables.
Thread-scope-variables do not need to be locked at all, because
they are only valid in the current thread.
SCOPED VARIABLES
Scoped variables are c++-variables, whose lifetime is handled by tnt‐
net. These variables has a lifetime and a scope. The lifetime is
defined by the tag, used to declare the variable and the scope is
passed as a parameter to the tag.
There are 5 different lifetimes for scoped variables:
request
The variable is valid in the current request. The tag is
<%request>.
application
The variable is valid in the application. The tag is <%applica‐
tion>. The application is specified by the shared-library of the
top-level component.
session
The variable is valid for the current session. The tag is <%ses‐
sion>. If at least session-variable is declared in the current
request, a session-cookie is sent to the client.
thread The variable is valid in the current thread. The tag is
<%thread>.
param The variable receives parameters. The tag is <%param>.
And 3 scopes:
component
The variable is only valid in the same component. This is the
default scope.
page The variable is shared between the components in a single
ecpp-file. You can specify multiple internal subcomponents in a
%def-block. Variables, defined in page-scope are shared between
these subcomponents.
global Variables are shared between all components. If you define the
same variable with global-scope in different components, they
must have the same type. This is achieved most easily defining
them in a separate file and include them with a
<%include>-block.
Variables are automatically locked as needed. If you use ses‐
sion-variables, tntnet ensures, that all requests of the same
session are serialized. If you use application-variables, tntnet
serializes all requests to the same application-scope. Request-
and thread-scope variables do not need to be locked at all,
because they are not shared between threads.
Syntax of scoped variables
Scoped variables are declared with exactly the same syntax as normal
variables in c++-code. They can be of any type and are instantiated,
when needed. Objects, which do not have default constructors, need to
be specified with proper constructor-parameters in brackets or sepa‐
rated by '='. The parameters are only used, if the variable need to be
instantiated. This means, that parameters to e.g. application-scope
variables are only used once. When the same component is called later
in the same or another request, the parameters are not used any more.
Examples
Specify a application-specific global variable, which is initialized
with 0:
<%application>
unsigned count = 0;
</%application>
Specify a variable with a user-defined type, which holds the state of
the session:
<%session>
MyClass sessionState;
</%session>
Specify a persistent databaseconnection, which is initialized, when
first needed and hold for the lifetime of the current thread. This
variable may be used in other components:
<%thread scope="global">
tntdb::Connection conn(dburl);
</%thread>
AUTHOR
This manual page was written by Tommi Mäkitalo ⟨tommi@tntnet.org⟩.
SEE ALSOtntnet(1), ecppc(1)Tntnet 2006-07-23 ecpp(7)
