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whitespace.go
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whitespace.go
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/*
Copyright © 2019, 2024 M.Watermann, 10247 Berlin, Germany
All rights reserved
EMail : <support@mwat.de>
*/
package whitespace
/*
* This files provides a function to remove redundant whitespace
* and comments from a HTML page.
*/
import (
"bytes"
"fmt"
"net/http"
"regexp"
)
//lint:file-ignore ST1017 - I prefer Yoda conditions
var (
// `UseRemoveWhitespace` (default: `true`) determines whether the
// removal of whitespace is actually run.
// If set to `false` the `Remove()` function becomes basically a NoOp.
//
// This flag allows you to include the `Wrap()` and/or `Remove()`
// functions in your code and change your program's actual behaviour
// according to some configuration setting or commandline option:
// You'd just change this flag accordingly at runtime without changing
// your source code at all.
UseRemoveWhitespace = true
)
/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
type (
// `tTrimWriter` embeds a `ResponseWriter` and includes
// whitespace removal by overwriting its `Write()` method.
tTrimWriter struct {
http.ResponseWriter // used to construct a HTTP response.
}
)
// `Write` writes the data to the connection as part of an HTTP reply.
//
// Parameters:
// - `aData`: The data (usually text) to send to the remote client.
//
// Returns:
// - `int`: Number of bytes written.
// - `error`: Possible processing error.
func (tw *tTrimWriter) Write(aData []byte) (int, error) {
if UseRemoveWhitespace && (0 < len(aData)) {
if txt := Remove(aData); 0 < len(txt) {
// replace the given text with our trimmed page:
aData = txt
}
}
return tw.ResponseWriter.Write(aData)
} // Write()
/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
type (
tReItem struct {
regEx *regexp.Regexp
replace string
}
)
// Internal list of regular expressions used by
// the `RemoveWhiteSpace()` function.
var (
wsREs = []tReItem{
// comments:
{regexp.MustCompile(`(?s)<!--.*?-->`), ``},
// HTML and HEAD elements:
{regexp.MustCompile(`(?si)\s*(</?(body|\!DOCTYPE|head|html|link|meta|script|style|title)[^>]*>)\s*`), `$1`},
// block elements:
{regexp.MustCompile(`(?si)\s+(</?(article|blockquote|div|footer|h[1-6]|header|nav|p|section)[^>]*>)`), `$1`},
{regexp.MustCompile(`(?si)(</?(article|blockquote|div|footer|h[1-6]|header|nav|p|section)[^>]*>)\s+`), `$1`},
// lists:
{regexp.MustCompile(`(?si)\s+(</?([dou]l|li|d[dt])[^>]*>)`), `$1`},
{regexp.MustCompile(`(?si)(</?([dou]l|li|d[dt])[^>]*>)\s+`), `$1`},
// table elements:
{regexp.MustCompile(`(?si)\s+(</?(col|t(able|body|foot|head|[dhr]))[^>]*>)`), `$1`},
{regexp.MustCompile(`(?si)(</?(col|t(able|body|foot|head|[dhr]))[^>]*>)\s+`), `$1`},
// form elements:
{regexp.MustCompile(`(?si)\s+(</?(form|fieldset|legend|opt(group|ion))[^>]*>)`), `$1`},
{regexp.MustCompile(`(?si)(</?(form|fieldset|legend|opt(group|ion))[^>]*>)\s+`), `$1`},
// BR / HR:
{regexp.MustCompile(`(?i)\s*(<[bh]r[^>]*>)\s*`), `$1`},
// whitespace after opened anchor:
{regexp.MustCompile(`(?si)(<a\s+[^>]*>)\s+`), `$1`},
// preserve empty table cells:
{regexp.MustCompile(`(?i)(<td(\s+[^>]*)?>)\s+(</td>)`), `$1 $3`},
// remove empty paragraphs:
{regexp.MustCompile(`(?i)<(p)(\s+[^>]*)?>\s*</$1>`), ``},
// whitespace before closing GT:
{regexp.MustCompile(`\s+>`), `>`},
}
// RegEx to find PREformatted parts in an HTML page.
wsPreRE = regexp.MustCompile(`(?si)\s*<pre[^>]*>.*?</pre>\s*`)
)
// `Remove` returns `aPage` with HTML comments and
// unnecessary whitespace removed.
//
// Depending of the global `UseRemoveWhitespace` flag this function removes
// all unneeded/redundant whitespace and HTML comments from the given `aPage`.
// This can reduce significantly the amount of data to send to the
// remote user agent thus saving both bandwidth and transfer time.
//
// Parameters:
// - `aPage`: The web page's HTML markup to process.
//
// Returns:
// - `[]byte`: The cleansed page.
func Remove(aPage []byte) []byte {
if !UseRemoveWhitespace {
return aPage
}
// (0) Check whether there are PREformatted parts:
preMatches := wsPreRE.FindAll(aPage, -1)
if (nil == preMatches) || (0 >= len(preMatches)) {
// no PRE hence only the other REs to perform
for _, re := range wsREs {
aPage = re.regEx.ReplaceAll(aPage, []byte(re.replace))
}
return aPage
}
// (1) Make sure PREformatted parts remain as-is.
// Replace the PRE parts with a dummy text:
for lLen, cnt := len(preMatches), 0; cnt < lLen; cnt++ {
search := fmt.Sprintf(`\s*%s\s*`,
regexp.QuoteMeta(string(preMatches[cnt])))
if re, err := regexp.Compile(search); nil == err {
repl := fmt.Sprintf(`</-%d-%d-%d-%d-/>`, cnt, cnt, cnt, cnt)
aPage = re.ReplaceAllLiteral(aPage, []byte(repl))
}
}
// (2) Traverse through all the whitespace REs:
for _, re := range wsREs {
aPage = re.regEx.ReplaceAll(aPage, []byte(re.replace))
}
// (3) Replace the PRE dummies with the real markup:
for lLen, cnt := len(preMatches), 0; cnt < lLen; cnt++ {
search := fmt.Sprintf(`\s*</-%d-%d-%d-%d-/>\s*`, cnt, cnt, cnt, cnt)
if re, err := regexp.Compile(search); nil == err {
aPage = re.ReplaceAllLiteral(aPage,
bytes.TrimSpace(preMatches[cnt]))
}
}
return aPage
} // Remove()
// `Wrap` returns a handler function that removes superfluous whitespace,
// wrapping the given `aHandler` and calling it internally.
//
// Parameters:
// - `aNext`: responds to the actual HTTP request.
//
// Returns:
// - `http.Handler`: The handler function to use by the application.
func Wrap(aNext http.Handler) http.Handler {
return http.HandlerFunc(
func(aWriter http.ResponseWriter, aRequest *http.Request) {
tw := &tTrimWriter{
aWriter,
}
aNext.ServeHTTP(tw, aRequest)
})
} // Wrap()
/* _EoF_ */