ecpp - Man Page
template language for tntnet(8)
Description
ecpp 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 tntnet.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 - generate 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, with 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::QueryParams. Normally you use a <%args> block to specify the parameters, but there are special cases, where it is useful to access these directly.
component addressing
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 sub components. The name of the internal sub component is appended to the class name 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.
errorhandling
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 output stream. The characters <, >, , "
and ', which have special meanings in html, are translated to the
corresponding html entities.
<$$ expr $>
Print expressions expr without translating characters with special meaning in
html to html entities to the output stream.
<? cond ? expr ?>
Conditional output. Print expression expr to the output stream, 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 output stream, 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
output stream. If the component name does not start with a letter, the
ecpp compiler treats it as a expression, 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 normally 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 argument list is treated as a variable of type
cxxtools::QueryParams and a copy is passed to the component. 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|shared|global" ] >...</%application>
Variables defined here, have the lifetime of the application.
Application scope is automatically locked.
<%args>...</%args>
Defines GET or POST parameters received by the component.
Each argument has a name and optionally a default value. The default value is
delimited by '=' from the name. A single argument 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 cxxtools
deserialization operator. If the argument can't be converted, the default
value is set.
Argument names 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 converted to the target type.
<%attr>...</%attr>
Components may define attributes, which can be queried from other components.
These values are strings and are defined by specifying a name followed by '='
and the string value. No type is allowed here.
A other component can the fetch a reference to the component using
fetchComp(name). fetchComp is a member of the base class
tnt::EcppComponent of components built with ecpp.
The component has then a member method getAttribute(name), which returns the
attribute or a empty string when not found. A different default string can be
passed as a second parameter to getAttribute.
Example
A content component specifies a title:
<%attr> title = "my title"; </%attr>
A component webmain want to add a title depending on a content component:
<head>
<title>
<$ fetchComp("theContent").getAttribute("title", "default title") $>
</title>
...To separte the C++ code from the html, the actual doing can be moved to a C++
section. The component can then be also called later to generate the content:
<%cpp>
tnt::Component theContent = fetchComp("theContent");
std::string title = theContent.getAttribute("title", "default title");
</%cpp>
<head>
<title><$ title $></title>
...
<div id="contnent">
<{ theContent(request, reply, qparam); }>
</div><%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.
This tag is deprecated and should not be used any more.
<%config>...</%config>
Often web applications need some configuration like database names or
login information to the database. These configuration variables can be read
from the tntnet.xml. Variable names ended with a semicolon are defined as
static std::string variables 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 sub component 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.
<%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 syntax (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 <$$ ... $>. Prints the contained C++ expression expr.
<%post>...</%post>
Works like a <%args> block but receives only POST parameters.
<%pre>...</%pre>
Defines C++ code, which is placed outside the C++ class and outside the
namespace definition. This is a good place to define #include directives.
<%request [ scope="component|page|shared|global" ] >...</%request>
Define request scope variables. Variables defined here, has the lifetime of
the request.
<%session [ scope="component|page|shared|global" ] >...</%session>
Variables defined here, has the lifetime of the session.
Sessions are identified with cookies. If a <%session> block is defined
somewhere in a component, a session cookie is sent to the client.
Sessions are automatically locked.
<%securesession [ scope="component|page|shared|global" ] >...</%securesession>
Secure session is just like session but a secure cookie is used to identify
the session. Secure cookies are transferred only over a ssl connection from
the browser and hence the variables are only kept in a ssl secured
application.
If a variable defined here is used in a non ssl page, the variable values are
lost after the current request.
<%sout> expr </%sout>
Same as <$ ... $>. 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|shared|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 tntnet. 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 <%application>. 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 <%session>. 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 sub components in a <%def> block. Variables,
defined in page scope are shared between these sub components.
global or shared
Variables are shared between all components. If you define the same variable
with shared 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. The global and shared are just synonyms.
Variables are automatically locked as needed. If you use session 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 separated 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 shared 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 database connection, 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="shared"> tntdb::Connection conn(dburl); </%thread>
Author
This manual page was written by Tommi Mäkitalo ⟨tommi@tntnet.org⟩.
See Also
Referenced By
ecppc(1), tntnet(8), tntnet-defcomp(1).