com.google.streamhtmlparser.util

Class HtmlUtils

java.lang.Object

com.google.streamhtmlparser.util.HtmlUtils

public final class HtmlUtils
extends Object

Utility functions for HTML and Javascript that are most likely not interesting to users outside this package.

The HtmlParser will be open-sourced hence we took the decision to keep these utilities in this package as well as not to leverage others that may exist in the google3 code base.

The functionality exposed is designed to be 100% compatible with the corresponding logic in the C-version of the HtmlParser as such we are particularly concerned with cross-language compatibility.

Note: The words Javascript and ECMAScript are used interchangeably unless otherwise noted.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	HtmlUtils.META_REDIRECT_TYPE Indicates the type of content contained in the content HTML attribute of the meta HTML tag.

Method Summary

Modifier and Type	Method and Description
static String	encodeCharForAscii(char chr) Encodes the specified character using Ascii for convenient insertion into a single-quote enclosed String.
static boolean	isAttributeJavascript(String attribute) Determines if the HTML attribute specified expects javascript for its value.
static boolean	isAttributeStyle(String attribute) Determines if the HTML attribute specified expects a style for its value.
static boolean	isAttributeUri(String attribute) Determines if the HTML attribute specified expects a URI for its value.
static boolean	isHtmlSpace(char chr) Determines if the specified character is an HTML whitespace character.
static boolean	isJavascriptIdentifier(char chr) Determines if the specified character is a valid character in an ECMAScript identifier.
static boolean	isJavascriptRegexpPrefix(String input) Determines if the input token provided is a valid token prefix to a javascript regular expression.
static boolean	isJavascriptWhitespace(char chr) Determines if the specified character is an ECMAScript whitespace or line terminator character.
static HtmlUtils.META_REDIRECT_TYPE	parseContentAttributeForUrl(String value) Parses the given String to determine if it contains a URL in the format followed by the content attribute of the meta HTML tag.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

isAttributeJavascript

public static boolean isAttributeJavascript(String attribute)

Determines if the HTML attribute specified expects javascript for its value. Such is the case for example with the onclick attribute.

Currently returns true for any attribute name that starts with "on" which is not exactly correct but we trust a developer to not use non-spec compliant attribute names (e.g. onbogus).

Parameters:

attribute - the name of an HTML attribute

Returns:

false if the input is null or is not an attribute that expects javascript code; true

isAttributeStyle

public static boolean isAttributeStyle(String attribute)

Determines if the HTML attribute specified expects a style for its value. Currently this is only true for the style HTML attribute.

Parameters:

attribute - the name of an HTML attribute

Returns:

true iff the attribute name is one that expects a style for a value; otherwise false

isAttributeUri

public static boolean isAttributeUri(String attribute)

Determines if the HTML attribute specified expects a URI for its value. For example, both href and src expect a URI but style does not. Returns false if the attribute given was null.

Parameters:

attribute - the name of an HTML attribute

Returns:

true if the attribute name is one that expects a URI for a value; otherwise null

See Also:

ATTRIBUTE_EXPECTS_URI

isHtmlSpace

public static boolean isHtmlSpace(char chr)

Determines if the specified character is an HTML whitespace character. A character is an HTML whitespace character if and only if it is one of the characters below.

• A Space character
• A Tab character
• A Line feed character
• A Carriage Return character
• A Zero-Width Space character

Note: The list includes the zero-width space (​) which is not included in the C version.

Parameters:

chr - the char to check

Returns:

true if the character is an HTML whitespace character White space

isJavascriptWhitespace

public static boolean isJavascriptWhitespace(char chr)

Determines if the specified character is an ECMAScript whitespace or line terminator character. A character is a whitespace or line terminator if and only if it is one of the characters below:

• A white-space character (Tab, Vertical Tab, Form Feed, Space, No-break space)
• A line terminator character (Line Feed, Carriage Return, Line separator, Paragraph Separator).

Encompasses the characters in sections 7.2 and 7.3 of ECMAScript 3, in particular, this list is quite different from that in Character.isWhitespace. ECMAScript Language Specification

Parameters:

chr - the char to check

Returns:

true or false

isJavascriptIdentifier

public static boolean isJavascriptIdentifier(char chr)

Determines if the specified character is a valid character in an ECMAScript identifier. This determination is currently not exact, in particular:

• It does not accept Unicode letters, only ASCII ones.
• It does not distinguish between the first character of an identifier (which cannot contain numbers) and subsequent characters.

We are considering leveraging Character.isJavaIdentifierStart and Character.isJavaIdentifierPart given that Java and Javascript follow similar identifier naming rules but we lose compatibility with the C-version.

Parameters:

chr - char to check

Returns:

true if the chr is a Javascript whitespace character; otherwise false

isJavascriptRegexpPrefix

public static boolean isJavascriptRegexpPrefix(String input)

Determines if the input token provided is a valid token prefix to a javascript regular expression. The token argument is compared against a Set of identifiers that can precede a regular expression in the javascript grammar, and returns true if the provided String is in that Set.

Parameters:

input - the String token to check

Returns:

true iff the token is a valid prefix of a regexp

encodeCharForAscii

public static String encodeCharForAscii(char chr)

Encodes the specified character using Ascii for convenient insertion into a single-quote enclosed String. Printable characters are returned as-is. Carriage Return, Line Feed, Horizontal Tab, back-slash and single quote are all backslash-escaped. All other characters are returned hex-encoded.

Parameters:

chr - char to encode

Returns:

an Ascii-friendly encoding of the given char

parseContentAttributeForUrl

public static HtmlUtils.META_REDIRECT_TYPE parseContentAttributeForUrl(String value)

Parses the given String to determine if it contains a URL in the format followed by the content attribute of the meta HTML tag.

This function expects to receive the value of the content HTML attribute. This attribute takes on different meanings depending on the value of the http-equiv HTML attribute of the same meta tag. Since we may not have access to the http-equiv attribute, we instead rely on parsing the given value to determine if it contains a URL. The specification of the meta HTML tag can be found in: http://dev.w3.org/html5/spec/Overview.html#attr-meta-http-equiv-refresh

We return HtmlUtils.META_REDIRECT_TYPE indicating whether the value contains a URL and whether we are at the start of the URL or past the start. We are at the start of the URL if and only if one of the two conditions below is true:

• The given input does not contain any characters from the URL proper. Example "5; URL=".
• The given input only contains the optional leading single or double quote leading the URL. Example "5; URL='".

Examples:

• Example of a complete meta tag where the content attribute contains a URL [we are not at the start of the URL]:

   <meta http-equiv="refresh" content="5; URL=http://www.google.com">
   

• Example of a complete meta tag where the content attribute contains a URL [we are at the start of the URL]:

   <meta http-equiv="refresh" content="5; URL=">
   

• Example of a complete meta tag where the content attribute does not contain a URL:

   <meta http-equiv="content-type" content="text/html">
   

Parameters:

value - String to parse

Returns:

HtmlUtils.META_REDIRECT_TYPE indicating the presence of a URL in the given value