From 6beeb1b708550be0d4a53b272283e17e5e35fe17 Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Sun, 7 Apr 2024 17:01:30 +0200 Subject: Adding upstream version 2.4.57. Signed-off-by: Daniel Baumann --- docs/manual/mod/mod_deflate.html.en | 442 ++++++++++++++++++++++++++++++++++++ 1 file changed, 442 insertions(+) create mode 100644 docs/manual/mod/mod_deflate.html.en (limited to 'docs/manual/mod/mod_deflate.html.en') diff --git a/docs/manual/mod/mod_deflate.html.en b/docs/manual/mod/mod_deflate.html.en new file mode 100644 index 0000000..57b988d --- /dev/null +++ b/docs/manual/mod/mod_deflate.html.en @@ -0,0 +1,442 @@ + + + + + +mod_deflate - Apache HTTP Server Version 2.4 + + + + + + + +
+

Modules | Directives | FAQ | Glossary | Sitemap

+

Apache HTTP Server Version 2.4

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+ +
+

Apache Module mod_deflate

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+

Available Languages:  en  | + fr  | + ja  | + ko 

+
+ + + +
Description:Compress content before it is delivered to the +client
Status:Extension
Module Identifier:deflate_module
Source File:mod_deflate.c
+

Summary

+ +

The mod_deflate module provides + the DEFLATE output filter that allows output from + your server to be compressed before being sent to the client over + the network.

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+

Supported Encodings

+

The gzip encoding is the only one supported to ensure complete compatibility + with old browser implementations. The deflate encoding is not supported, + please check the zlib's documentation + for a complete explanation. +

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+

Sample Configurations

+

Compression and TLS

+

Some web applications are vulnerable to an information disclosure + attack when a TLS connection carries deflate compressed data. For more + information, review the details of the "BREACH" family of attacks.

+
+

This is a simple configuration that compresses common text-based content types.

+ +

Compress only a few types

AddOutputFilterByType DEFLATE text/html text/plain text/xml text/css text/javascript application/javascript
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+ +
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+

Enabling Compression

+

Compression and TLS

+

Some web applications are vulnerable to an information disclosure + attack when a TLS connection carries deflate compressed data. For more + information, review the details of the "BREACH" family of attacks.

+
+ +

Output Compression

+

Compression is implemented by the DEFLATE + filter. The following directive + will enable compression for documents in the container where it + is placed:

+ + 
SetOutputFilter DEFLATE
+SetEnvIfNoCase Request_URI "\.(?:gif|jpe?g|png)$" no-gzip
+ + +

If you want to restrict the compression to particular MIME types + in general, you may use the AddOutputFilterByType directive. Here is an example of + enabling compression only for the html files of the Apache + documentation:

+ + 
<Directory "/your-server-root/manual">
+    AddOutputFilterByType DEFLATE text/html
+</Directory>
+ + +

Note

+ The DEFLATE filter is always inserted after RESOURCE + filters like PHP or SSI. It never touches internal subrequests. +
+

Note

+ There is an environment variable force-gzip, + set via SetEnv, which + will ignore the accept-encoding setting of your browser and will + send compressed output. +
+ + +

Output Decompression

+

The mod_deflate module also provides a filter for + inflating/uncompressing a gzip compressed response body. In order to activate + this feature you have to insert the INFLATE filter into + the output filter chain using SetOutputFilter or AddOutputFilter, for example:

+ + 
<Location "/dav-area">
+    ProxyPass "http://example.com/"
+    SetOutputFilter INFLATE
+</Location>
+ + +

This Example will uncompress gzip'ed output from example.com, so other + filters can do further processing with it. +

+ + +

Input Decompression

+

The mod_deflate module also provides a filter for + decompressing a gzip compressed request body . In order to activate + this feature you have to insert the DEFLATE filter into + the input filter chain using SetInputFilter or AddInputFilter, for example:

+ + 
<Location "/dav-area">
+    SetInputFilter DEFLATE
+</Location>
+ + +

Now if a request contains a Content-Encoding: + gzip header, the body will be automatically decompressed. + Few browsers have the ability to gzip request bodies. However, + some special applications actually do support request + compression, for instance some WebDAV clients.

+ +

Note on Content-Length

+

If you evaluate the request body yourself, don't trust + the Content-Length header! + The Content-Length header reflects the length of the + incoming data from the client and not the byte count of + the decompressed data stream.

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+

Dealing with proxy servers

+ +

The mod_deflate module sends a Vary: + Accept-Encoding HTTP response header to alert proxies that + a cached response should be sent only to clients that send the + appropriate Accept-Encoding request header. This + prevents compressed content from being sent to a client that will + not understand it.

+ +

If you use some special exclusions dependent + on, for example, the User-Agent header, you must + manually configure an addition to the Vary header + to alert proxies of the additional restrictions. For example, + in a typical configuration where the addition of the DEFLATE + filter depends on the User-Agent, you should add:

+ + 
Header append Vary User-Agent
+ + +

If your decision about compression depends on other information + than request headers (e.g. HTTP version), you have to set the + Vary header to the value *. This prevents + compliant proxies from caching entirely.

+ +

Example

Header set Vary *
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+

Serving pre-compressed +content

+ +

Since mod_deflate re-compresses content each + time a request is made, some performance benefit can be derived by + pre-compressing the content and telling mod_deflate to serve them + without re-compressing them. This may be accomplished using a + configuration like the following:

+ + 
<IfModule mod_headers.c>
+    # Serve gzip compressed CSS and JS files if they exist
+    # and the client accepts gzip.
+    RewriteCond "%{HTTP:Accept-encoding}" "gzip"
+    RewriteCond "%{REQUEST_FILENAME}\.gz" -s
+    RewriteRule "^(.*)\.(css|js)"         "$1\.$2\.gz" [QSA]
+
+    # Serve correct content types, and prevent mod_deflate double gzip.
+    RewriteRule "\.css\.gz$" "-" [T=text/css,E=no-gzip:1]
+    RewriteRule "\.js\.gz$"  "-" [T=text/javascript,E=no-gzip:1]
+
+
+    <FilesMatch "(\.js\.gz|\.css\.gz)$">
+      # Serve correct encoding type.
+      Header append Content-Encoding gzip
+
+      # Force proxies to cache gzipped &
+      # non-gzipped css/js files separately.
+      Header append Vary Accept-Encoding
+    </FilesMatch>
+</IfModule>
+ + +
+
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+

DeflateBufferSize Directive

+ + + + + + + +
Description:Fragment size to be compressed at one time by zlib
Syntax:DeflateBufferSize value
Default:DeflateBufferSize 8096
Context:server config, virtual host
Status:Extension
Module:mod_deflate
+

The DeflateBufferSize directive specifies + the size in bytes of the fragments that zlib should compress at one + time. If the compressed response size is bigger than the one specified + by this directive then httpd will switch to chunked encoding + (HTTP header Transfer-Encoding set to Chunked), with the + side effect of not setting any Content-Length HTTP header. This is particularly + important when httpd works behind reverse caching proxies or when httpd is configured with + mod_cache and mod_cache_disk because + HTTP responses without any Content-Length header might not be cached. +

+ +
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+

DeflateCompressionLevel Directive

+ + + + + + + +
Description:How much compression do we apply to the output
Syntax:DeflateCompressionLevel value
Default:Zlib's default
Context:server config, virtual host
Status:Extension
Module:mod_deflate
+

The DeflateCompressionLevel directive specifies + what level of compression should be used, the higher the value, + the better the compression, but the more CPU time is required to + achieve this.

+

The value must between 1 (less compression) and 9 (more compression).

+ +
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+

DeflateFilterNote Directive

+ + + + + + +
Description:Places the compression ratio in a note for logging
Syntax:DeflateFilterNote [type] notename
Context:server config, virtual host
Status:Extension
Module:mod_deflate
+

The DeflateFilterNote directive + specifies that a note about compression ratios should be attached + to the request. The name of the note is the value specified for + the directive. You can use that note for statistical purposes by + adding the value to your access log.

+ +

Example

DeflateFilterNote ratio
+
+LogFormat '"%r" %b (%{ratio}n) "%{User-agent}i"' deflate
+CustomLog "logs/deflate_log" deflate
+
+ +

If you want to extract more accurate values from your logs, you + can use the type argument to specify the type of data + left as a note for logging. type can be one of:

+ +
+
Input
+
Store the byte count of the filter's input stream in the note.
+ +
Output
+
Store the byte count of the filter's output stream in the note.
+ +
Ratio
+
Store the compression ratio (output/input * 100) + in the note. This is the default, if the type argument + is omitted.
+
+ +

Thus you may log it this way:

+ +

Accurate Logging

DeflateFilterNote Input instream
+DeflateFilterNote Output outstream
+DeflateFilterNote Ratio ratio
+
+LogFormat '"%r" %{outstream}n/%{instream}n (%{ratio}n%%)' deflate
+CustomLog "logs/deflate_log" deflate
+
+ +

See also

+ +
+
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+

DeflateInflateLimitRequestBody Directive

+ + + + + + + + +
Description:Maximum size of inflated request bodies
Syntax:DeflateInflateLimitRequestBody value
Default:None, but LimitRequestBody applies after deflation
Context:server config, virtual host, directory, .htaccess
Status:Extension
Module:mod_deflate
Compatibility:2.4.10 and later
+

The DeflateInflateLimitRequestBody directive + specifies the maximum size of an inflated request body. If it is unset, + LimitRequestBody is applied to the + inflated body.

+ +
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DeflateInflateRatioBurst Directive

+ + + + + + + + +
Description:Maximum number of times the inflation ratio for request bodies + can be crossed
Syntax:DeflateInflateRatioBurst value
Default:DeflateInflateRatioBurst 3
Context:server config, virtual host, directory, .htaccess
Status:Extension
Module:mod_deflate
Compatibility:2.4.10 and later
+

The DeflateInflateRatioBurst directive + specifies the maximum number of times the + DeflateInflateRatioLimit can + be crossed before terminating the request.

+ +
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+

DeflateInflateRatioLimit Directive

+ + + + + + + + +
Description:Maximum inflation ratio for request bodies
Syntax:DeflateInflateRatioLimit value
Default:DeflateInflateRatioLimit 200
Context:server config, virtual host, directory, .htaccess
Status:Extension
Module:mod_deflate
Compatibility:2.4.10 and later
+

The DeflateInflateRatioLimit directive + specifies the maximum ratio of deflated to inflated size of an + inflated request body. This ratio is checked as the body is + streamed in, and if crossed more than + DeflateInflateRatioBurst + times, the request will be terminated.

+ +
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DeflateMemLevel Directive

+ + + + + + + +
Description:How much memory should be used by zlib for compression
Syntax:DeflateMemLevel value
Default:DeflateMemLevel 9
Context:server config, virtual host
Status:Extension
Module:mod_deflate
+

The DeflateMemLevel directive specifies + how much memory should be used by zlib for compression + (a value between 1 and 9).

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DeflateWindowSize Directive

+ + + + + + + +
Description:Zlib compression window size
Syntax:DeflateWindowSize value
Default:DeflateWindowSize 15
Context:server config, virtual host
Status:Extension
Module:mod_deflate
+

The DeflateWindowSize directive specifies the + zlib compression window size (a value between 1 and 15). Generally, the + higher the window size, the higher can the compression ratio be expected.

+ +
+
+
+

Available Languages:  en  | + fr  | + ja  | + ko 

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Comments

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