Add HTMLLayout fuzzer

[AdamKorcz]

Adds a fuzzer for HTMLLayout.

[swebb2066]

I believe you need to provide a maximum length to ConsumeRandomLengthString or all subsequent calls will return an empty string.

[AdamKorcz]

That is not the case. The fuzzer determines the length of the string in a deterministic manner. It can consist of the entire test case, but those odd cases are fine. Ref the doc:

"ConsumeRandomLengthString method returns a std::string as well, but its length is derived from the fuzz input and typically is hard to predict, though always deterministic. The caller can provide the max length argument."

https://github.com/google/fuzzing/blob/master/docs/split-inputs.md#methods-for-extracting-sequences-of-bytes

I also tested it locally and found that the non-first invocations of fdp.ConsumeRandomLengthString() do indeed generate strings.

The one that should always be last is ConsumeRemainingBytesAsString(). If it is not, then the remaining attempts to generate strings will yield empty strings like you say.

[swebb2066]

Unfortunately the documentation (and the ConsumeRandomLengthString function name) is missleading. When I build XMLLayoutFuzzer with an extra line log4cxx::helpers::LogLog::debug(result); I get this result (for example):

log4cxx: <log4j:event logger="com.example.bar" timestamp="1737242190330" level="INFO" thread="0x728374e74000">
<log4j:message><![CDATA[]]></log4j:message>
<log4j:NDC><![CDATA[<envelope><faultstring><![CDATA[The EffectiveDate]]>]]&gt;<![CDATA[</faultstring><envelope>]]></log4j:NDC>
<log4j:locationInfo class="" method="LLVMFuzzerTestOneInput" file="/home/stephen/source/logging-log4cxx/src/fuzzers/cpp/XMLLayoutFuzzer.cpp" line="45"/>
<log4j:properties>
<log4j:data name=";▒" value=""/>
<log4j:data name=";▒" value=""/>
</log4j:properties>
</log4j:event>

Note also there is bug in XMLLayoutFuzzer. I believe

        // Set MDC
        log4cxx::MDC::put(key1, key2);

was supposed to be:

        // Set MDC
        log4cxx::MDC::put(key2, val2);