Instrumentation

The graphql.execution.instrumentation.Instrumentation interface allows you to inject code that can observe the execution of a query and also change the runtime behaviour.

The primary use case for this is to allow say performance monitoring and custom logging but it could be used for many different purposes.

When you build the Graphql object you can specify what Instrumentation to use (if any).

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        GraphQL.newGraphQL(schema)
                .instrumentation(new TracingInstrumentation())
                .build();

Custom Instrumentation

An implementation of Instrumentation needs to implement the “begin” step methods that represent the execution of a graphql query.

Each step must give back a non null graphql.execution.instrumentation.InstrumentationContext object which will be called back when the step completes, and will be told that it succeeded or failed with a Throwable.

The following is a basic custom Instrumentation that measures overall execution time and puts it into a stateful object.

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    class CustomInstrumentationState implements InstrumentationState {
        private Map<String, Object> anyStateYouLike = new HashMap<>();

        void recordTiming(String key, long time) {
            anyStateYouLike.put(key, time);
        }
    }

    class CustomInstrumentation extends SimpleInstrumentation {
        @Override
        public InstrumentationState createState() {
            //
            // instrumentation state is passed during each invocation of an Instrumentation method
            // and allows you to put stateful data away and reference it during the query execution
            //
            return new CustomInstrumentationState();
        }

        @Override
        public InstrumentationContext<ExecutionResult> beginExecution(InstrumentationExecutionParameters parameters) {
            long startNanos = System.nanoTime();
            return new SimpleInstrumentationContext<ExecutionResult>() {
                @Override
                public void onCompleted(ExecutionResult result, Throwable t) {
                    CustomInstrumentationState state = parameters.getInstrumentationState();
                    state.recordTiming(parameters.getQuery(), System.nanoTime() - startNanos);
                }
            };
        }

        @Override
        public DataFetcher<?> instrumentDataFetcher(DataFetcher<?> dataFetcher, InstrumentationFieldFetchParameters parameters) {
            //
            // this allows you to intercept the data fetcher used to fetch a field and provide another one, perhaps
            // that enforces certain behaviours or has certain side effects on the data
            //
            return dataFetcher;
        }

        @Override
        public CompletableFuture<ExecutionResult> instrumentExecutionResult(ExecutionResult executionResult, InstrumentationExecutionParameters parameters) {
            //
            // this allows you to instrument the execution result some how.  For example the Tracing support uses this to put
            // the `extensions` map of data in place
            //
            return CompletableFuture.completedFuture(executionResult);
        }
    }

Chaining Instrumentation

You can combine multiple Instrumentation objects together using the graphql.execution.instrumentation.ChainedInstrumentation class which accepts a list of Instrumentation objects and calls them in that defined order.

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        List<Instrumentation> chainedList = new ArrayList<>();
        chainedList.add(new FooInstrumentation());
        chainedList.add(new BarInstrumentation());
        ChainedInstrumentation chainedInstrumentation = new ChainedInstrumentation(chainedList);

        GraphQL.newGraphQL(schema)
                .instrumentation(chainedInstrumentation)
                .build();

Apollo Tracing Instrumentation

graphql.execution.instrumentation.tracing.TracingInstrumentation is an Instrumentation implementation that creates tracing information about the query that is being executed.

It follows the Apollo proposed tracing format defined at https://github.com/apollographql/apollo-tracing <https://github.com/apollographql/apollo-tracing>_

A detailed tracing map will be created and placed in the extensions section of the result.

So given a query like

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    query {
      hero {
        name
        friends {
          name
        }
      }
    }

It would return a result like

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    {
      "data": {
        "hero": {
          "name": "R2-D2",
          "friends": [
            {
              "name": "Luke Skywalker"
            },
            {
              "name": "Han Solo"
            },
            {
              "name": "Leia Organa"
            }
          ]
        }
      },
      "extensions": {
        "tracing": {
          "version": 1,
          "startTime": "2017-08-14T23:13:39.362Z",
          "endTime": "2017-08-14T23:13:39.497Z",
          "duration": 135589186,
          "execution": {
            "resolvers": [
              {
                "path": [
                  "hero"
                ],
                "parentType": "Query",
                "returnType": "Character",
                "fieldName": "hero",
                "startOffset": 105697585,
                "duration": 79111240
              },
              {
                "path": [
                  "hero",
                  "name"
                ],
                "parentType": "Droid",
                "returnType": "String",
                "fieldName": "name",
                "startOffset": 125010028,
                "duration": 20213
              },
              {
                "path": [
                  "hero",
                  "friends"
                ],
                "parentType": "Droid",
                "returnType": "[Character]",
                "fieldName": "friends",
                "startOffset": 133352819,
                "duration": 7927560
              },
              {
                "path": [
                  "hero",
                  "friends",
                  0,
                  "name"
                ],
                "parentType": "Human",
                "returnType": "String",
                "fieldName": "name",
                "startOffset": 134105887,
                "duration": 6783
              },
              {
                "path": [
                  "hero",
                  "friends",
                  1,
                  "name"
                ],
                "parentType": "Human",
                "returnType": "String",
                "fieldName": "name",
                "startOffset": 134725922,
                "duration": 7016
              },
              {
                "path": [
                  "hero",
                  "friends",
                  2,
                  "name"
                ],
                "parentType": "Human",
                "returnType": "String",
                "fieldName": "name",
                "startOffset": 134875089,
                "duration": 6342
              }
            ]
          }
        }
      }
    }

Field Validation Instrumentation

graphql.execution.instrumentation.fieldvalidation.FieldValidationInstrumentation is an Instrumentation implementation that can be used to validate fields and their arguments before query execution. If errors are returned during this process then the query execution is aborted and the errors will be in the query result.

You can make you own custom implementation of FieldValidation or you can use the SimpleFieldValidation class to add simple per field checks rules.

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        ExecutionPath fieldPath = ExecutionPath.parse("/user");
        FieldValidation fieldValidation = new SimpleFieldValidation()
                .addRule(fieldPath, new BiFunction<FieldAndArguments, FieldValidationEnvironment, Optional<GraphQLError>>() {
                    @Override
                    public Optional<GraphQLError> apply(FieldAndArguments fieldAndArguments, FieldValidationEnvironment environment) {
                        String nameArg = fieldAndArguments.getFieldArgument("name");
                        if (nameArg.length() > 255) {
                            return Optional.of(environment.mkError("Invalid user name", fieldAndArguments));
                        }
                        return Optional.empty();
                    }
                });

        FieldValidationInstrumentation instrumentation = new FieldValidationInstrumentation(
                fieldValidation
        );

        GraphQL.newGraphQL(schema)
                .instrumentation(instrumentation)
                .build();