tracing.go

Documentation: github.com/99designs/gqlgen/graphql/handler/apollofederatedtracingv1

     1  package apollofederatedtracingv1
     2  
     3  import (
     4  	"context"
     5  	"encoding/base64"
     6  	"fmt"
     7  
     8  	"google.golang.org/protobuf/proto"
     9  
    10  	"github.com/99designs/gqlgen/graphql"
    11  )
    12  
    13  type (
    14  	Tracer struct {
    15  		ClientName string
    16  		Version    string
    17  		Hostname   string
    18  	}
    19  
    20  	treeBuilderKey string
    21  )
    22  
    23  const (
    24  	key = treeBuilderKey("treeBuilder")
    25  )
    26  
    27  var _ interface {
    28  	graphql.HandlerExtension
    29  	graphql.ResponseInterceptor
    30  	graphql.FieldInterceptor
    31  	graphql.OperationInterceptor
    32  } = &Tracer{}
    33  
    34  // ExtensionName returns the name of the extension
    35  func (Tracer) ExtensionName() string {
    36  	return "ApolloFederatedTracingV1"
    37  }
    38  
    39  // Validate returns errors based on the schema; since this extension doesn't require validation, we return nil
    40  func (Tracer) Validate(graphql.ExecutableSchema) error {
    41  	return nil
    42  }
    43  
    44  func (t *Tracer) shouldTrace(ctx context.Context) bool {
    45  	return graphql.HasOperationContext(ctx) &&
    46  		graphql.GetOperationContext(ctx).Headers.Get("apollo-federation-include-trace") == "ftv1"
    47  }
    48  
    49  func (t *Tracer) getTreeBuilder(ctx context.Context) *TreeBuilder {
    50  	val := ctx.Value(key)
    51  	if val == nil {
    52  		return nil
    53  	}
    54  	if tb, ok := val.(*TreeBuilder); ok {
    55  		return tb
    56  	}
    57  	return nil
    58  }
    59  
    60  // InterceptOperation acts on each Graph operation; on each operation, start a tree builder and start the tree's timer for tracing
    61  func (t *Tracer) InterceptOperation(ctx context.Context, next graphql.OperationHandler) graphql.ResponseHandler {
    62  	if !t.shouldTrace(ctx) {
    63  		return next(ctx)
    64  	}
    65  	return next(context.WithValue(ctx, key, NewTreeBuilder()))
    66  }
    67  
    68  // InterceptField is called on each field's resolution, including information about the path and parent node.
    69  // This information is then used to build the relevant Node Tree used in the FTV1 tracing format
    70  func (t *Tracer) InterceptField(ctx context.Context, next graphql.Resolver) (interface{}, error) {
    71  	if !t.shouldTrace(ctx) {
    72  		return next(ctx)
    73  	}
    74  	if tb := t.getTreeBuilder(ctx); tb != nil {
    75  		tb.WillResolveField(ctx)
    76  	}
    77  
    78  	return next(ctx)
    79  }
    80  
    81  // InterceptResponse is called before the overall response is sent, but before each field resolves; as a result
    82  // the final marshaling is deferred to happen at the end of the operation
    83  func (t *Tracer) InterceptResponse(ctx context.Context, next graphql.ResponseHandler) *graphql.Response {
    84  	if !t.shouldTrace(ctx) {
    85  		return next(ctx)
    86  	}
    87  	tb := t.getTreeBuilder(ctx)
    88  	if tb == nil {
    89  		return next(ctx)
    90  	}
    91  
    92  	tb.StartTimer(ctx)
    93  
    94  	val := new(string)
    95  	graphql.RegisterExtension(ctx, "ftv1", val)
    96  
    97  	// now that fields have finished resolving, it stops the timer to calculate trace duration
    98  	defer func(val *string) {
    99  		tb.StopTimer(ctx)
   100  
   101  		// marshal the protobuf ...
   102  		p, err := proto.Marshal(tb.Trace)
   103  		if err != nil {
   104  			fmt.Print(err)
   105  		}
   106  
   107  		// ... then set the previously instantiated string as the base64 formatted string as required
   108  		*val = base64.StdEncoding.EncodeToString(p)
   109  	}(val)
   110  	resp := next(ctx)
   111  	return resp
   112  }
   113
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