109 lines
4.6 KiB
Plaintext
109 lines
4.6 KiB
Plaintext
[[modules-scripting-painless-debugging]]
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=== Painless Debugging
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experimental[The Painless scripting language is new and is still marked as experimental. The syntax or API may be changed in the future in non-backwards compatible ways if required.]
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==== Debug.Explain
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Painless doesn't have a
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https://en.wikipedia.org/wiki/Read%E2%80%93eval%E2%80%93print_loop[REPL]
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and while it'd be nice for it to have one one day, it wouldn't tell you the
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whole story around debugging painless scripts embedded in Elasticsearch because
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the data that the scripts have access to or "context" is so important. For now
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the best way to debug embedded scripts is by throwing exceptions at choice
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places. While you can throw your own exceptions
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(`throw new Exception('whatever')`), Painless's sandbox prevents you from
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accessing useful information like the type of an object. So Painless has a
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utility method, `Debug.explain` which throws the exception for you. For
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example, you can use the <<search-explain>> to explore the context available to
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a <<query-dsl-script-query>>.
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[source,js]
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---------------------------------------------------------
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PUT /hockey/player/1?refresh
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{"first":"johnny","last":"gaudreau","goals":[9,27,1],"assists":[17,46,0],"gp":[26,82,1]}
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POST /hockey/player/1/_explain
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{
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"query": {
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"script": {
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"script": "Debug.explain(doc.goals)"
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}
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}
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}
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---------------------------------------------------------
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// CONSOLE
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// TEST[s/_explain/_explain?error_trace=false/ catch:/painless_explain_error/]
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// The test system sends error_trace=true by default for easier debugging so
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// we have to override it to get a normal shaped response
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Which shows that the class of `doc.first` is
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`org.elasticsearch.index.fielddata.ScriptDocValues$Longs` by responding with:
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[source,js]
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---------------------------------------------------------
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{
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"error": {
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"type": "script_exception",
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"class": "org.elasticsearch.index.fielddata.ScriptDocValues$Longs",
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"to_string": "[1, 9, 27]",
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...
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},
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"status": 500
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}
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---------------------------------------------------------
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// TESTRESPONSE[s/\.\.\./"script_stack": $body.error.script_stack, "script": $body.error.script, "lang": $body.error.lang, "caused_by": $body.error.caused_by, "root_cause": $body.error.root_cause, "reason": $body.error.reason/]
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You can use the same trick to see that `_source` is a `java.util.LinkedHashMap`
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in the `_update` API:
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[source,js]
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---------------------------------------------------------
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POST /hockey/player/1/_update
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{
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"script": "Debug.explain(ctx._source)"
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}
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---------------------------------------------------------
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// CONSOLE
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// TEST[continued s/_update/_update?error_trace=false/ catch:/painless_explain_error/]
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The response looks like:
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[source,js]
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---------------------------------------------------------
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{
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"error" : {
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"root_cause": ...,
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"type": "illegal_argument_exception",
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"reason": "failed to execute script",
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"caused_by": {
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"type": "script_exception",
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"class": "java.util.LinkedHashMap",
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"to_string": "{gp=[26, 82, 1], last=gaudreau, assists=[17, 46, 0], first=johnny, goals=[9, 27, 1]}",
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...
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}
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},
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"status": 400
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}
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---------------------------------------------------------
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// TESTRESPONSE[s/"root_cause": \.\.\./"root_cause": $body.error.root_cause/]
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// TESTRESPONSE[s/\.\.\./"script_stack": $body.error.caused_by.script_stack, "script": $body.error.caused_by.script, "lang": $body.error.caused_by.lang, "caused_by": $body.error.caused_by.caused_by, "reason": $body.error.caused_by.reason/]
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// TESTRESPONSE[s/"to_string": ".+"/"to_string": $body.error.caused_by.to_string/]
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// TODO we should build some javadoc like mashup so people don't have to jump through these hoops.
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Once you have the class of an object you can go
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https://github.com/elastic/elasticsearch/tree/{branch}/modules/lang-painless/src/main/resources/org/elasticsearch/painless[here]
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and check the available methods. Painless uses a strict whitelist to prevent
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scripts that don't work well with Elasticsearch and all whitelisted methods
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are listed in a file named after the package of the object (everything before
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the last `.`). So `java.util.Map` is listed in a file named `java.util.txt`
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starting on the line that looks like `class Map -> java.util.Map {`.
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With the list of whitelisted methods in hand you can turn to either
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https://docs.oracle.com/javase/8/docs/api/[Javadoc],
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https://github.com/elastic/elasticsearch/tree/{branch}[Elasticsearch's source tree]
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or, for whitelisted methods ending in `*`, the
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https://github.com/elastic/elasticsearch/blob/{branch}/modules/lang-painless/src/main/java/org/elasticsearch/painless/Augmentation.java[Augmentation]
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class.
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