Cesar Rodriguez created SOLR-13181:
--------------------------------------

             Summary: NullPointerException in 
org.apache.solr.request.macro.MacroExpander
                 Key: SOLR-13181
                 URL: https://issues.apache.org/jira/browse/SOLR-13181
             Project: Solr
          Issue Type: Bug
      Security Level: Public (Default Security Level. Issues are Public)
    Affects Versions: master (9.0)
         Environment: h1. Steps to reproduce

* Use a Linux machine.
*  Build commit {{ea2c8ba}} of Solr as described in the section below.
* Build the films collection as described below.
* Start the server using the command {{./bin/solr start -f -p 8983 -s 
/tmp/home}}
* Request the URL given in the bug description.

h1. Compiling the server

{noformat}
git clone https://github.com/apache/lucene-solr
cd lucene-solr
git checkout ea2c8ba
ant compile
cd solr
ant server
{noformat}

h1. Building the collection

We followed [Exercise 
2|http://lucene.apache.org/solr/guide/7_5/solr-tutorial.html#exercise-2] from 
the [Solr Tutorial|http://lucene.apache.org/solr/guide/7_5/solr-tutorial.html]. 
The attached file ({{home.zip}}) gives the contents of folder {{/tmp/home}} 
that you will obtain by following the steps below:

{noformat}
mkdir -p /tmp/home
echo '<?xml version="1.0" encoding="UTF-8" ?><solr></solr>' > /tmp/home/solr.xml
{noformat}

In one terminal start a Solr instance in foreground:
{noformat}
./bin/solr start -f -p 8983 -s /tmp/home
{noformat}

In another terminal, create a collection of movies, with no shards and no 
replication, and initialize it:

{noformat}
bin/solr create -c films
curl -X POST -H 'Content-type:application/json' --data-binary '{"add-field": 
{"name":"name", "type":"text_general", "multiValued":false, "stored":true}}' 
http://localhost:8983/solr/films/schema
curl -X POST -H 'Content-type:application/json' --data-binary 
'{"add-copy-field" : {"source":"*","dest":"_text_"}}' 
http://localhost:8983/solr/films/schema
./bin/post -c films example/films/films.json
{noformat}
            Reporter: Cesar Rodriguez
         Attachments: 
0001-Macro-expander-fail-gracefully-on-unsupported-syntax.patch, home.zip

Requesting the following URL causes Solr to return an HTTP 500 error response:

{noformat}
http://localhost:8983/solr/films/select?a=${${b}}
{noformat}

The error response seems to be caused by the following uncaught exception:

{noformat}
java.lang.StringIndexOutOfBoundsException: String index out of range: -4
        at java.lang.String.substring(String.java:1967)
        at 
org.apache.solr.request.macro.MacroExpander._expand(MacroExpander.java:150)
        at 
org.apache.solr.request.macro.MacroExpander.expand(MacroExpander.java:101)
        at 
org.apache.solr.request.macro.MacroExpander.expand(MacroExpander.java:65)
        at 
org.apache.solr.request.macro.MacroExpander.expand(MacroExpander.java:51)
        at 
org.apache.solr.request.json.RequestUtil.processParams(RequestUtil.java:159)
        at 
org.apache.solr.util.SolrPluginUtils.setDefaults(SolrPluginUtils.java:167)
        at 
org.apache.solr.handler.RequestHandlerBase.handleRequest(RequestHandlerBase.java:196)
[...]
{noformat}

Parameter [macro expansion|http://yonik.com/solr-query-parameter-substitution/] 
seems to take place in 
{{org.apache.solr.request.macro.MacroExpander._expand(String val)}}. From 
reading the code of the function it seems that macros are not expanded inside 
curly brackets {{${...}}}, and so the {{${b}}} inside

{noformat}
${${b}}
{noformat}

should not be expanded. But the function seems to fail to detect this specific 
case and graciously refuse to expand it.

A possible fix could be updating the {{idx}} variable when the {{StrParser}} 
detects that no valid identifier can be found inside the brackets. See attached 
file {{0001-Macro-expander-fail-gracefully-on-unsupported-syntax.patch}}.

We found this bug using [Diffblue Microservices 
Testing|https://www.diffblue.com/labs/]. Find more information on this [fuzz 
testing 
campaign|https://www.diffblue.com/blog/2018/12/19/diffblue-microservice-testing-a-sneak-peek-at-our-early-product-and-results].



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