The emphasis of this server is on dynamically generated content,
rather than fetching it from a filesystem. To do this the handler
functions make calls to fprintf() and
fputs(). Such handler functions would end up a
mass of print calls, with the actual structure of the HTML page hidden
in the format strings and arguments, making maintenance and debugging
very difficult. Such an approach would also result in the definition
of many, often only slightly different, format strings, leading to
unnecessary bloat.
In an effort to expose the structure of the HTML in the structure of
the C code, and to maximize the sharing of string constants, the
cyg/httpd/httpd.h header file defines a set of
helper functions and macros. Most of these are wrappers for predefined
print calls on the client stream passed to the
hander function. For examples of their use, see the System Monitor
example.
Note: All arguments to macros are pointers to strings, unless otherwise
stated. In general, wherever a function or macro has an
attr or __attr
parameter, then the contents of this string will be inserted into the
tag being defined as HTML attributes. If it is a NULL or empty string
it will be ignored.
The function cyg_http_start() generates a simple
HTTP response header containing the value of
CYGDAT_HTTPD_SERVER_ID in the "Server" field, and the
values of content_type and
content_length in the "Content-type"
and "Content-length" field respectively. The function
cyg_http_finish() just adds an extra newline to
the end of the output and then flushes it to force the data out to the
client.
The macro html_begin() generates an HTTP header
with a "text/html" content type followed by an opening
"<html>" tag. html_end() generates
a closing "</html>" tag and calls
cyg_http_finish().
The function cyg_html_tag_begin() generates an
opening tag with the given name. The function
cyg_html_tag_end() generates a closing tag with
the given name. The macros html_tag_begin() and
html_tag_end are just wrappers for these functions.
The macro html_head() generates an HTML header
section with __title as the title. The
__meta argument defines any meta tags that will
be inserted into the header. html_body_begin() and
html_body_end generate HTML body begin and end
tags.
html_heading() generates a complete HTML header
where __level is a numerical level, between 1
and 6, and __heading is the heading
text. html_para_begin() generates a paragraph
break.
html_url() inserts a URL where
__text is the displayed text and
__link is the URL of the linked
page. html_image() inserts an image tag where
__source is the URL of the image to be
included and __alt is the alternative text for
when the image is not displayed.
html_table_begin() starts a table and
html_table_end() end
it. html_table_header() generates a simple table
column header containg the string __content.
html_table_row_begin() and
html_table_row_end() begin and end a table row,
and similarly html_table_data_begin() and
html_table_data_end() begin and end a table
entry.
html_form_begin() begins a form, the
__url argument is the value for the
action
attribute. html_form_end() ends the form.
html_form_input() defines a general form input
element with the given type, name and
value. html_form_input_radio creates a radio button
with the given name and value; the __checked
argument is a boolean expression that is used to determine whether the
checked attribute is added to the tag. Similarly
html_form_input_checkbox() defines a checkbox
element. html_form_input_hidden() defines a hidden
form element with the given name and value.
html_form_select_begin() begins a multiple choice
menu with the given name. html_form_select_end()
end it. html_form_option() defines a menu entry
with the given value and label; the __selected
argument is a boolean expression controlling whether the
selected attribute is added to the tag.
cyg_formdata_parse() converts a form response
string into an NULL-terminated array of
"name=value" entries. The data
argument is the string as passed to the handler function; note that
this string is not copied and will be updated in place to form the
list entries. list is a pointer to an array of
character pointers, and is size elements long.
cyg_formlist_find() searches a list generated by
cyg_formdata_parse() and returns a pointer to the
value part of the string whose name part matches
name; if there is no match it will return
NULL.
The HTTP server defines a couple of predefined handers to make it
easier to deliver simple, static content.
cyg_httpd_send_html() takes a
NULL-terminated string as the argument and sends it
to the client with an HTTP header indicating that it is HTML. The
following is an example of its use:
char cyg_html_message[] = "<head><title>Welcome</title></head>\n"
"<body><h2>Welcome to my Web Page</h2></body>\n"
CYG_HTTPD_TABLE_ENTRY( cyg_html_message_entry,
"/message.html",
cyg_httpd_send_html,
cyg_html_message );
cyg_httpd_send_data() Sends arbitrary data to the
client. The argument is a pointer to a cyg_httpd_data
structure that defines the content type and length of the data, and a
pointer to the data itself. The CYG_HTTPD_DATA()
macro automates the definition of the structure. Here is a typical
example of its use:
