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    <title>MongoDB Jira</title>
    <link>https://jira.mongodb.org</link>
    <description>This file is an XML representation of an issue</description>
    <language>en-us</language>    <build-info>
        <version>9.7.1</version>
        <build-number>970001</build-number>
        <build-date>13-04-2023</build-date>
    </build-info>


<item>
            <title>[GODRIVER-836] zLib compression does not work</title>
                <link>https://jira.mongodb.org/browse/GODRIVER-836</link>
                <project id="14289" key="GODRIVER">Go Driver</project>
                    <description>&lt;p&gt;It looks like zLib compression is broken.&lt;/p&gt;

&lt;p&gt;Running the tests with `MONGO_GO_DRIVER_COMPRESSOR=zlib` causes failures. To recreate this first set up a mongod with `--networkMessageCompressors=&quot;zlib&quot;`. Many tests fail, but here is one example:&lt;/p&gt;
&lt;p/&gt;
&lt;div id=&quot;syntaxplugin&quot; class=&quot;syntaxplugin&quot; style=&quot;border: 1px dashed #bbb; border-radius: 5px !important; overflow: auto; max-height: 30em;&quot;&gt;
&lt;table cellspacing=&quot;0&quot; cellpadding=&quot;0&quot; border=&quot;0&quot; width=&quot;100%&quot; style=&quot;font-size: 1em; line-height: 1.4em !important; font-weight: normal; font-style: normal; color: black;&quot;&gt;
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					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;  margin-top: 10px;   margin-bottom: 10px;  width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;TOPOLOGY=server MONGO_GO_DRIVER_COMPRESSOR=zlib go test -v ./x/network/integration -run TestCompression&lt;/span&gt;&lt;/pre&gt;
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		&lt;/tr&gt;
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&lt;/table&gt;
&lt;/div&gt;
&lt;p/&gt;
&lt;p&gt;And the result:&lt;/p&gt;
&lt;p/&gt;
&lt;div id=&quot;syntaxplugin&quot; class=&quot;syntaxplugin&quot; style=&quot;border: 1px dashed #bbb; border-radius: 5px !important; overflow: auto; max-height: 30em;&quot;&gt;
&lt;table cellspacing=&quot;0&quot; cellpadding=&quot;0&quot; border=&quot;0&quot; width=&quot;100%&quot; style=&quot;font-size: 1em; line-height: 1.4em !important; font-weight: normal; font-style: normal; color: black;&quot;&gt;
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				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;  margin-top: 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;=== RUN   TestCompression&lt;/span&gt;&lt;/pre&gt;
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		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;--- FAIL: TestCompression (&lt;/span&gt;&lt;span style=&quot;color: #009900; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;0&lt;/span&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;.01s)&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;        Error Trace:    config.go:&lt;/span&gt;&lt;span style=&quot;color: #009900; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;192&lt;/span&gt;&lt;/pre&gt;
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		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;                        once.go:&lt;/span&gt;&lt;span style=&quot;color: #009900; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;44&lt;/span&gt;&lt;/pre&gt;
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				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;                        config.go:&lt;/span&gt;&lt;span style=&quot;color: #009900; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;175&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;                        compressor_test.go:&lt;/span&gt;&lt;span style=&quot;color: #009900; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;30&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;        Error:          Received unexpected error:&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;                        connection(localhost:&lt;/span&gt;&lt;span style=&quot;color: #009900; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;27017&lt;/span&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;[-&lt;/span&gt;&lt;span style=&quot;color: #009900; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;2&lt;/span&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;]) unable to decode message length: EOF&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
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				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;FAIL&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   margin-bottom: 10px;  width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;FAIL    github.com/mongodb/mongo-go-driver/x/network/integration        &lt;/span&gt;&lt;span style=&quot;color: #009900; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;0&lt;/span&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;.029s&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
			&lt;/tbody&gt;
&lt;/table&gt;
&lt;/div&gt;
&lt;p/&gt;
&lt;p&gt;I believe there are three underlying problems with the zLib compression.&lt;/p&gt;

&lt;p&gt;Firstly, `(z *ZlibCompressor) CompressBytes()` will always return an empty slice. This is because the `dest` slice is copied into a writer as the `buf` value. This `buf` is resliced as it is written to by the zLib compressor. So although the underlying array of dest is being updated, `dest`&apos;s length is not being updated. So returning `dest` just returns a slice of zero elements.&#160;&lt;/p&gt;

&lt;p&gt;Secondly, `(z *ZlibCompressor) UncompressBytes()` will also always return an empty slice. `io.ReadFull(zlibReader, dest)` reads exactly `len(dest)` bytes from `zlibReader` into `dest`. Since `c.uncompressBuf` is passed into `UncompressBytes` as a zero element slice, zlibReader will never read anything into dest. See &lt;a href=&quot;#L294&quot; target=&quot;_blank&quot; rel=&quot;noopener&quot;&gt;connection.go&lt;/a&gt;&#160;for context.&lt;/p&gt;

&lt;p&gt;Thirdly, the way compressors are initialized leads to race conditions for the zLib compressor. Currently, a single compressor is initialized by `topology.WithConnString()` and is used for every connection (see &lt;a href=&quot;#L196&quot; target=&quot;_blank&quot; rel=&quot;noopener&quot;&gt;topology_options.go&lt;/a&gt;). This is fine for Snappy. But for zLib, if multiple connections use the same zLib writer at the same time, they will all be accessing and modifying the writer&apos;s internal buffers. I think initializing a new compressor per connection is probably the way to go.&lt;/p&gt;

&lt;p&gt;I&apos;m submitting a PR to address these three issues. Would love some more eyes to ensure I haven&apos;t misunderstood anything here.&lt;br/&gt;
 &#160;&lt;/p&gt;</description>
                <environment></environment>
        <key id="699907">GODRIVER-836</key>
            <summary>zLib compression does not work</summary>
                <type id="1" iconUrl="https://jira.mongodb.org/secure/viewavatar?size=xsmall&amp;avatarId=14703&amp;avatarType=issuetype">Bug</type>
                                            <priority id="3" iconUrl="https://jira.mongodb.org/images/icons/priorities/major.svg">Major - P3</priority>
                        <status id="6" iconUrl="https://jira.mongodb.org/images/icons/statuses/closed.png" description="The issue is considered finished, the resolution is correct. Issues which are closed can be reopened.">Closed</status>
                    <statusCategory id="3" key="done" colorName="success"/>
                                    <resolution id="13201">Fixed</resolution>
                                        <assignee username="tim.fogarty@mongodb.com">Tim Fogarty</assignee>
                                    <reporter username="tim.fogarty@mongodb.com">Tim Fogarty</reporter>
                        <labels>
                    </labels>
                <created>Tue, 19 Feb 2019 00:16:40 +0000</created>
                <updated>Sat, 28 Oct 2023 11:39:05 +0000</updated>
                            <resolved>Thu, 7 Mar 2019 20:26:00 +0000</resolved>
                                    <version>0.3.0</version>
                                    <fixVersion>1.0.0-rc2</fixVersion>
                                    <component>Core API</component>
                                        <votes>0</votes>
                                    <watches>1</watches>
                                                                                                                <comments>
                            <comment id="2174977" author="xgen-internal-githook" created="Thu, 7 Mar 2019 20:26:14 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{&apos;name&apos;: &apos;Tim Fogarty&apos;, &apos;username&apos;: &apos;tfogo&apos;, &apos;email&apos;: &apos;tim.fogarty@mongodb.com&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/GODRIVER-836&quot; title=&quot;zLib compression does not work&quot; class=&quot;issue-link&quot; data-issue-key=&quot;GODRIVER-836&quot;&gt;&lt;del&gt;GODRIVER-836&lt;/del&gt;&lt;/a&gt; Fix zLib compression&lt;/p&gt;

&lt;p&gt;Fixes the CompressBytes method of ZlibCompressor to correctly&lt;br/&gt;
return a slice of compressed bytes. Also ensuresUncompressBytes&lt;br/&gt;
will correctly return a slice of uncompressed bytes. Previously&lt;br/&gt;
both methods would return slices of length 0.&lt;/p&gt;

&lt;p&gt;New Compressors are initialized for every connection to avoid&lt;br/&gt;
race conditions with the zLib compressor.&lt;/p&gt;

&lt;p&gt;Evergreen config is updated to run zlib tests for mongo&lt;br/&gt;
versions &amp;gt; 3.4. Snappy tests now only run for versions &amp;gt; 3.2.&lt;br/&gt;
Unit tests are added for compressors.&lt;/p&gt;

&lt;p&gt;Change-Id: I4524027a1ed85eb698a75e528b56cfe56a4d6167&lt;br/&gt;
Branch: master&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo-go-driver/commit/930d5ebf05c44dc699403343280c8010993c1ec6&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo-go-driver/commit/930d5ebf05c44dc699403343280c8010993c1ec6&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="2155036" author="tim.fogarty" created="Tue, 19 Feb 2019 00:29:02 +0000"  >&lt;p&gt;Just submitted a patch here:&#160;&lt;a href=&quot;https://review.gerrithub.io/c/mongodb/mongo-go-driver/+/445192&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://review.gerrithub.io/c/mongodb/mongo-go-driver/+/445192&lt;/a&gt;&lt;/p&gt;</comment>
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