PageBuilder - HTML assembly aid for ESP8266/ESP32 WebServer

An arduino library to create html string in the sketch for ESP8266/ESP32 WebServer.

PageBuilder is an Arduino library class dedicated to the ESP8266WebServer or the WebServer(ESP32) for easily generating HTML pages and sending them to the client.

Features

Ability to completely separate HTML structure and the web page generation logic in the sketch
No need for inline coding of URI access handler of ESP8266WebServer class or ESP32's WebServer class
Fixed HTML statement parts like template can be allocated as PROGMEM
Its HTML source can be stored SPIFFS and obtain automatically
Arbitrary token can be specified inline HTML statement
Automatically sent to client for HTML page are generated

Ordinary sketch	Sketch by PageBuilder

Works on

For ESP8266
Generic esp8266 module and other representatives works fine. ESP8266 Arduino core 2.4.0 or higher is necessary.
For ESP32
Arduino core for ESP32 supported boards works fine. ESP32 Arduino core 1.0.0 or higher is necessary.

Installation

Download this file as a zip, and extract the resulting folder into your Arduino Libraries folder. See Installing Additional Arduino Libraries.
Required Arduino IDE is current upstream at the 1.8 level or later, and also ESP8266 Arduino core or ESP32 Arduino core.

Example

A most simple example. - No URI handler is needed, only the URI path and html coded.

#include "PageBuilder.h"

// root page
PageElement ROOT_PAGE_ELEMENT("<a href=\"/hello\">hello</a>");
PageBuilder ROOT_PAGE("/", {ROOT_PAGE_ELEMENT});
// /hello page
PageElement HELLO_PAG_ELEMENT("Hello, world!<p><a href=\"/bye\">bye</a></p>");
PageBuilder HELLO_PAGE("/hello", {HELLO_PAG_ELEMENT});
// /bye page
PageElement BYE_PAGE_ELEMENT("Good bye!");
PageBuilder BYE_PAGE("/bye", {BYE_PAGE_ELEMENT});

ROOT_PAGE.insert(Server);     // Add root page
HELLO_PAGE.insert(Server);    // Add /hello page
BYE_PAGE.insert(Server);      // add /bye page

Share multiple elements on different pages.

#include "PageBuilder.h"

static const char _HEAD[] PROGMEM = "<html>" ;
static const char _BODY[] PROGMEM = "<body>This is {{PAGE}}.</body>";
static const char _FOOT[] PROGMEM = "</html>";

String setBody1(PageArgument& args) {
	return String("Page1");
}

String setBody2(PageArgument& args) {
	return String("Page2");
}

PageElement header( _HEAD );
PageElement body1( _BODY, { {"PAGE", setBody1} });
PageElement body2( _BODY, { {"PAGE", setBody2} });
PageElement footer( _FOOT );

PageBuilder Page1( "/page1", {header, body1, footer} );
PageBuilder Page2( "/page2", {header, body2, footer} );

HTML source stored in SPIFFS.

The following screenshot is an example PageBuilder sketch using HTML source stored in SPIFFS. It scan the nearby signal and connect the ESP8266 to the specified access point.
This case is FSPage.ino example sketch in this repository.

Usage

Data structure of PageBuilder

In order to successfully generate an HTML page using PageBuilder please understand the data structure of PageBuilder.
PageBuilder library consists of three objects that are related to each other as the below. PageBuilder inherits RequestHandler provided from ESP8266WebServer (in the ESP8266 arduino core) or WebServer (in the ESP32 arduino core) library and is invoked from ESP8266WebServer/WebServer in response to http requests. PageBuilder owns its URI string and multiple PageElement objects.
Source strings of HTML are owned by PageElement (mold in the figure). Its string contains an identifier called a token. The token appears as {{ }} in the middle of the source HTML string (_token in the figure). The tokens are paired with functions to replace them with actual HTML sentences. When URI access has occurred server from the client, its paired function is invoked by extension of handleClient() method then the token will replace to actual statement to complete the HTML and sends it. PageElement can have multiple tokens (i.e., it can define several tokens in one HTML source element).

To properly generate a web page, you need to code its function that replaces the token with HTML, and its function must return a String.

String AsName(PageArgument& args) {      // User coded function
...    ~~~~~~
  return String("My name");
}
String AsDaytime(PageArgument& args) {   // User coded function
...    ~~~~~~~~~
  return String("afternoon");
}

// Source HTML string
const char html[] = "hello <b>{{NAME}}</b>, <br>Good {{DAYTIME}}.";
...                             ^^^^                   ^^^^^^^
...                             token                  token

PageElement header_elem("<html><body>");
PageElement footer_elem("</body></html>");
PageElement body_elem(html, { {"NAME", AsName}, {"DAYTIME", AsDayTime} });
...                             ^^^^   ~~~~~~     ^^^^^^^   ~~~~~~~~~
...                             token  User coded function to replace the token

PageBuilder page("/hello", { header_elem, body_elem, footer_elem });
...
ESP8266WebServer  webServer;  // in ESP8266 case.
page.insert(webServer);
webServer.begin();
...  // 'on' method is no needed.
webServer.handleClient();

http://your.webserver.address/hello will respond as follows.

<html><body>hello <b>My name</b>, <br>Good afternoon.</body></html>

Invoke the HTML assembly

No need in the sketch. It would be invoked from the instance inherited from the WebServer class which corresponding to the platform ESP8266 or ESP32. Also, like the on method of the WebServer class, you need to register the PageBuilder object with the web server object using the insert method.

String func(PageArgument& args);
PageElement element("mold", {{"token", func}})
PageBuilder page("/uri", { element });

ESP8266WebServer server;  // Probably 'WebServer' in ESP32 case.
page.insert(server);    // This is needed.

server.handleClient();  // Invoke from this.

Arguments of invoked user function

Arguments are passed to the function that should be implemented corresponding to tokens. It is the parameter value as GET or POST at the http request occurred like as url?param=value in HTTP GET, and its parameters are stored in PageArgument object and passed to the function as below.

HTTP GET with http://xxx.xxx.xxx/?param=value
HTTP POST with / HTTP/1.1 Host:xxx.xxx.xxx Connection:keep-alive param=value

String func(PageArgument& args) {
  if (args.hasArg("param"))
    return args.arg("param");
}

PageElement element("hello {{NAME}}.", {{"NAME", func}});

An argument can be accessed with the following method of PageArgument class.

`String PageArgument::arg(String name)`

Returns the value of the parameter specified by name.

`String PageArgument::arg(int i)`

Returns the value of the parameter indexed i.

`String PageArgument::argName(int i)`

Returns parameter name of indexed i.

`int PageArgument::args()`

Get parameters count of the current http request.

`size_t PageArgument::size()`

Same as args().

`bool PageArgument::hasArg(String name)`

Returns whether the name parameter is specified in the current http request.

Declare PageBuilder object and PageElement object

Include directive

#include "PageBuilder.h"

PageBuilder constructor

PageBuilder::PageBuilder();
PageBuilder::PageBuilder(PageElementVT element, HTTPMethod method = HTTP_ANY, TransferEncoding_t chunked = PB_Auto, bool CORS = false);
PageBuilder::PageBuilder(const char* uri, PageElementVT element, HTTPMethod method = HTTP_ANY, TransferEncoding_t chunked = PB_Auto, bool CORS = false);

element : PageElement container wrapper. Normally, use the brackets to specify initializer.
```
PageElement elem1();
PageElement elem2();
PageBuilder page("/", {elem1, elem2});
```
method : Enum value of HTTP method as HTTP_ANY, HTTP_GET, HTTP_POST that page should respond.
uri : A URI string of the page.
chunked : Enumeration type for the transfer-encoding as TransferEncoding_t type. PB_Auto, PB_ByteStream, PB_Chunk can be specified. If PB_Auto is specified, would be determined automatically to switch them the chunk. Its criteria is defined with MAX_CONTENTBLOCK_SIZE macro in PageBuilder.cpp code. If PB_ByteStream is specified, PageBuilder will determine the way of sending either String writing or byte stream according to a size of the content.
CORS : Include a header allowing cross-origin access in the current page response.

PageElement constructor

PageElement::PageElement();
PageElement::PageElement(const char* mold);
PageElement::PageElement(const char* mold, TokenVT source);
PageElement::PageElement(const __FlashStringHelper* mold);
PageElement::PageElement(const __FlashStringHelper* mold, TokenVT source);

mold : A pointer to HTML model string(const char array, PROGMEM available).
source : Container of processable token and handler function. A TokenVT type is std::vector to the structure with the pair of token and func. It prepares with an initializer.
```
String func1(PageArgument& args);
String func2(PageArgument& args);
PageElement elem(html, {{"TOKEN1", func1}, {"TOKEN2", func2}});
```
mold can also use external files placed on LittleFS or SPIFFS. Since HTML consists of more strings, the program area may be smaller in sketches using many pages.
External files can have HTML source specified by mold. That file would be allocated on the LittleFS or SPIFFS file system. This allows you to reduce the sketch size and assign more capacity to the program.
You can specify the HTML source file name by mold parameter in the following format.
```
file:FILE_NAME
```
FILE_NAME is the name of the HTML source file containing /. If prefix file: is specified in mold parameter, the PageElement class reads its file from LittleFS or SPIFFS as HTML source. A sample sketch using this way is an example as FSPage.ino.
For details for how to write HTML source file to SPIFFS of ESP8266, please refer to Uploading files to file system.

Note: For ESP8266, the default file system has been changed to LittleFS since PageBuilder v1.4.2. It is a measure in compliance with the ESP8266 core 2.7.0 or later treating SPIFFS as deprecated.

Methods

PageBuilder Methods

`void PageBuilder::addElement(PageElement& element)`

Add a new PageElement object to the container of PageBuilder.

element : PageElement object.

`void PageBuilder::atNotFound(ESP8266WebServer& server)`
`void PageBuilder::atNotFound(WebServer& server)`

Register the not found page to the ESP8266WebServer. It has the same effect as onNotFound method of ESP8266WebServer/WebServer. The page registered by atNotFound method is response with http code 404.
Note that only the most recently registered PageBuilder object is valid.

server : A reference of ESP8266WebServer (in ESP8266 case) or WebServer (in ESP32 case) object to register the page.

`String PageBuilder::build(void)`

Returns the built html string from const char* mold that processed token by the user function of TokenVT which code as {"token",function_name}. The build method handles all PageElement objects that a PageBuilder contained.

`void PageBuilder::cancel(void)`

Notify to PageBuilder that the generated HTML string should not be send.
PageBuilder internally sends generated HTML with http 200 when invoked as RequestHandler from handleClient(). If the sketch wants to respond only to http response without generating HTML, you need to stop automatic transmission using the cancel method. The following example responds 302 with keep-alive connection. This response does not contain content. So the Token func will have the following code.

  server.sendHeader("Location", redirect-path, true);
  server.sendHeader("Connection", "keep-alive");
  server.send(302, "text/plain", "");
  server.client().stop();

The sketch sends an http response in the Token func then PageBuilder should be stopped 200 response. The cancel method notifies this situation to the PageBuilder. This example is in SendNakedHttp.

  String tokenFunc(PageArgument& args);

  ESP8266WebServer	server;
  PageElement elm("{{RES}}", { {"RES", tokenFunc} });
  PageBuilder page("/", { elm });

  String tokenFunc(PageArgument& args) {
    server.sendHeader("Location", redirect-path, true);
    server.sendHeader("Connection", "keep-alive");
    server.send(302, "text/plain", "");
    server.client().stop();
    page.cancel();
    return "";
  }

`void PageBuilder::clearElements(void)`

Clear enrolled PageElement objects in the PageBuilder.

`void PageBuilder::enableCORS(const bool CORS)`

Include a header allowing Cross-Origin access in the current page response.

`void PageBuilder::exitCanHandle(PrepareFuncT prepareFunc)`

prepareFunc : User function instead of canHandle. This user function would be invoked at all request received.
bool prepareFunc(HTTPMethod method, String uri);
- method : Same as parameter of PageBuilder constructor, HTTP_ANY, HTTP_GET, HTTP_POST.
- uri : A URI string at this time.
- Return : True if this URI request is processed by this PageBuilder, False if it is ignored.
Important notes. The prepareFunc specified by eixtCanHandled is called twice at one http request. See Application hints for details.

`void PageBuilder::insert(ESP8266WebServer& server)`
`void PageBuilder::insert(WebServer& server)`

Register the page and starts handling. It has the same effect as on method of ESP8266WebServer (in ESP8266 case)/WebServer (in ESP32 case).

server : A reference of the ESP8266WebServer or the WebServer object to register the page.

`void PageBuilder::setUri(const char* uri)`

Set URI of this page.

uri : A pointer of URI string.

`const char* PageBuilder::uri()`

Get URI of this page.

`void PageBuilder::transferEncoding(const PageBuilder::TransferEncoding_t encoding)`

Set Transfer-Encoding with chunked, or not. TransferEncoding_t is the enumeration type for the transfer-encoding as following:

Auto : Automatically switch to chunk transmission according to the length of the content.
ByteStream : Chunked transmission, no use the String buffer like stream output.
Chunked : Chunked transfer encoding.

`void PageBuilder::reserve(size_t size)`

Set buffer size for reserved content building buffer.

size : Reservation size. If you do not specify a reserved buffer size by this function, the buffer for the build function will not be reserved. As a result, memory insufficient is likely to occur due to fragmentation.

`void PageBuilder::authentication(const char* username, const char* password, HTTPAuthMethod mode, const char* realm, const String& authFail)`

Enable authentication when the page is accessed. It can take either DIGEST or BASIC as the authentication method, and HTTP authentication will work with the username and password specified along with the URL access.

username : Specify the user name to embed in the sketch for authentication. Specifying a NULL value for the username can de-authorize the page in dynamically.
password : Specify the password to embed in the sketch for authentication.
mode : Specify the authentication method as either BASIC or DIGEST. An enumeration value is BASIC_AUTH for BASIC, DIGEST_AUTH for DIGEST. This parameter can be omitted, and the default value is BASIC_AUTH. It depends on HTTPAuthMethod enumeration.
realm : Specify an authentication realm. This parameter can be omitted, and the default value is "Login Required", which depends on the ESP8266WebServer::requestAuthentication API default value.
authFail : The Content of the HTML response in case of Unauthorized Access.

PageElement methods

`const char* PageElement::mold()`

Get mold string in the PageElement.

`void PageElement::build(String& buffer)`

Build the HTML element string from const char* mold that processed token by the user function of TokenVT.

`void PageElement::setMold(const char* mold)`
`void PageElement::setMold(const __FlashStringHelper* mold)`

Sets the source HTML element string.

`void PageElement::addToken(const char* token, HandleFuncT handler)`
`void PageElement::addToken(const __FlashStringHelper* token, HandlerFuncT handler)`

Add the source HTML element string.

Application hints
to reducing the memory for the HTML source

A usual way, the sketch needs to statically prepare the PageElement object for each element of the web page, so assigning the web contents constructed by multi-page with static const char* (including PROGMEM) strangles the heap area.
However, if the sketch can dynamically create a corresponding page at the time of receiving an HTTP request, you can reduce the number of PageBuilder instances and PageElement instances. By using setMold and addToken method of the PegeElement class, the sketch can construct the multiple pages of web content with just one PageBuilder object and a PageElement object.

Which method is first called from the WebServer when the URL is requested?

In the first place, the request handler described in the ESP8266WerbServer::on (or WebServer::on) method would be registered as the RequestHandler class. The RequestHandler has the canHandle method which purpose is to determine if the handler corresponds to the requested URI. ESP8266WebServer::handleClient (or WebServer::handleClient) method uses the canHandle method of the RequestHandler class for each URI request to determine the handler which should be invoked in all registered handlers. Which means that the canHandle method is the first called, and the PageBuilder has the hook way for the this.

Handling by a single PageBuilder object for all URI requests.

Using that hook way the sketch can aggregate all URI requests into a single PageBuilder object. The exitCanHandle method of PageBuilder specifies the user function to be called which is instead of the canHandle method. That user function overrides the canHandle method.

The function by exitCanHandle.

Declaration of the function.

bool func(HTTPMethod method, String uri);

method : Same as parameter of PageBuilder constructor, HTTP_ANY, HTTP_GET, HTTP_POST.
uri : A URI string at this time.
Return : True if this URI request is processed by this PageBuilder, False if it is ignored.

Generally, the logic of the function to implementation is the follows.

a. Analysis of URI and generation of PageElement object for that page.
b. Setting the HTML mold of that page by setMold method.
c. Registering the token function included in the mold by addToken method.
d. Action to ignore if the same URI of an already generated page is requested.

The function would be called twice at one http request. The cause is the internal logic of ESP8266WebServer (Relating to URI handler detection and URL parameter parsing), so the function specified by exitCanHandle needs to ignore the second call.

An example using this way.

DynamicPage.ino

Significant changes

Since PageBuilder 1.4.2, the default file system has changed SPIFFS to LittleFS. It is a measure to comply with the deprecation of SPIFFS by the core. However, SPIFFS is still available and defines the PB_USE_SPIFFS macro in PageBuilder.h file to enable it as follows:

#define PB_USE_SPIFFS

PB_USE_SPIFFS macro is valid only when the platform is ESP8266 and will be ignored with ESP32 arduino core. (at least until LittleFS is supported by the ESP32 arduino core)

Change log

[1.5.6] 2023-01-30

In ESP8266 core 3.1.0 or later, the default segment length of the chunked encoding has been reduced from 1270 bytes to 510. This measure is to address the situation where ESP8266 core v3.1.0 or later is prone to running out of memory. The default segment length for chunked encoding is defined by the PAGEBUILDER_CONTENTBLOCK_SIZE macro in PageBuilder.h header file.

[1.5.5] 2023-01-05

Fixed memory leak on cancel sending response.

[1.5.4] 2022-12-26

Supports an http response to allow CORS.

[1.5.3] 2022-03-02

Supports LittleFS_esp32 legacy library with ESP32 Arduino core 1.0.6 or less.
Migrate the CI platform to GitHub actions.

[1.5.2] 2021-11-21

Fixed incorrect declaration for Flash string.

[1.5.1] 2021-11-14

Fixed that the content exceeding PAGEBUILDER_CONTENTBLOCK_SIZE is not output.

[1.5.0] 2021-05-25

Improved memory management
Supports PROGMEM natively with PageElement
Supports LittleFS on ESP32.
Supports nested PageElement token

Important note

When building a sketch in the PlatformIO environment, a compile error may appear that says "File system header file not found". This error can be avoided by setting the library search mode (lib_ldf_mode) to the deep in with the platformio.ini file.
The function name for the clearElement has changed to the clearElements from this version.

[1.4.3] 2021-05-20

Supports ESP8266 arduino core 3.0.0.

[1.4.2] 2020-05-28

Supports LittleFS on ESP8266.

[1.4.1] 2020-05-13

Avoid empty-body warning with PB_DEBUG not specified.

[1.4.0] 2020-04-10

Adds BASIC / DIGEST authentication.

[1.3.7] 2020-01-14

Fixed WebLED example sketch crashes.

[1.3.6] 2019-12-19

Fixed a token handler being called twice when building content with more than 1270 bytes. (issue #14)

[1.3.5] 2019-12-04

Fixed losing uri set with setUri. (issue #13)

[1.3.4] 2019-06-27

Fixed PB_DBG_DUMB missing. PR #10

[1.3.3] 2019-04-13

Fixed loss of built content when HTML is large.
Fixed a warning for uninitialized used.

[1.3.2] 2019-02-07

Supports AutoConnect v0.9.7.

[1.3.1] 2019-02-04

Fixed the captive portal not appear.

[1.3.0] 2019-01-29

Adds building buffer reservation option to avoid built content lost.

[1.2.3] 2019-01-22

Fix leaking memory.
Add ArduBadge.

[1.2.2] 2018-12-26

Fix losing built content.

[1.2.1] 2018-12-18

Fixed 4-byte alignment of mold string in flash.

[1.2.0] 2018-12-01

Fixed incomplete transmission of large HTML string. Chunked-encoding has been implemented accordingly.
Fix the destructor PageBuilder can be inherited.

[1.1.0] 2018-08-21

Supports ESP32 platform depends on the WebServer class.
A stable version of arduino-esp32 core version 1.0.0 or higher is required.

[1.0.1] 2018-03-19

Fix WebELD example, no library change.

[1.0.0] 2018-02-17

Supports cancel method in PageBuilder class.
Supports setMold method in PageElement class.
Supports addToken method in PageElement class.

[0.93] 2017-12-19

Supports external file on SPIFFS for PageElement as HTML source data.

[0.92] 2017-12-07

A minor fixes.

[0.91] 2017-12-01

Supports atNotFound method in PageBuilder class.

[0.9] 2017-11-29

Release candidate.

Files

README.md

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