Add plugins

definition.go

@@ -597,6 +597,7 @@ type ResolveInfo struct {
 	RootValue      interface{}
 	Operation      ast.Definition
 	VariableValues map[string]interface{}
+	ArgumentValues map[string]interface{}
 }
 
 type Fields map[string]*Field

executor.go

@@ -103,13 +103,14 @@ type buildExecutionCtxParams struct {
 }
 
 type executionContext struct {
-	Schema         Schema
-	Fragments      map[string]ast.Definition
-	Root           interface{}
-	Operation      ast.Definition
-	VariableValues map[string]interface{}
-	Errors         []gqlerrors.FormattedError
-	Context        context.Context
+	Schema             Schema
+	Fragments          map[string]ast.Definition
+	Root               interface{}
+	Operation          ast.Definition
+	VariableValues     map[string]interface{}
+	Errors             []gqlerrors.FormattedError
+	Context            context.Context
+	PluginExecRegistry *PluginExecutionRegistry
 }
 
 func buildExecutionContext(p buildExecutionCtxParams) (*executionContext, error) {
@@ -155,6 +156,7 @@ func buildExecutionContext(p buildExecutionCtxParams) (*executionContext, error)
 	eCtx.Operation = operation
 	eCtx.VariableValues = variableValues
 	eCtx.Context = p.Context
+	eCtx.PluginExecRegistry = NewPluginExecRegistry()
 	return eCtx, nil
 }
 
@@ -279,8 +281,13 @@ func executeFields(p executeFieldsParams) *Result {
 
 	dethunkMapWithBreadthFirstTraversal(finalResults)
 
+	finalModified, errs := p.ExecutionContext.PluginExecRegistry.Execute(p.ExecutionContext.Context, finalResults)
+	if len(errs) > 0 {
+		p.ExecutionContext.Errors = append(p.ExecutionContext.Errors, errs...)
+	}
+
 	return &Result{
-		Data:   finalResults,
+		Data:   finalModified,
 		Errors: p.ExecutionContext.Errors,
 	}
 }
@@ -637,6 +644,7 @@ func resolveField(eCtx *executionContext, parentType *Object, source interface{}
 		RootValue:      eCtx.Root,
 		Operation:      eCtx.Operation,
 		VariableValues: eCtx.VariableValues,
+		ArgumentValues: args,
 	}
 
 	var resolveFnError error
@@ -663,6 +671,9 @@ func resolveField(eCtx *executionContext, parentType *Object, source interface{}
 	}
 
 	completed := completeValueCatchingError(eCtx, returnType, fieldASTs, info, path, result)
+
+	handlePluginsResolveFieldFinished(eCtx, info)
+
 	return completed, resultState
 }
 

plugins.go

@@ -0,0 +1,81 @@
+package graphql
+
+import (
+	"context"
+	"fmt"
+	"strings"
+
+	"github.com/graphql-go/graphql/gqlerrors"
+)
+
+// Plugin is an interface for custom post-processing based on the execution context
+// all the pre-processing happens in Resolve*()
+// plugins differs from extensions by the time of execution and by how they modify the result
+// in resolve func plugin analyzes execution context for each field in order to collect information of
+// what to process during execution
+// execution happens once query resolve is fully finished
+type Plugin interface {
+	// Name returns name of the plugin
+	Name() string
+	// IsCompatible tests whether current field is compatible with the plugin
+	IsCompatible(ctx context.Context, i ResolveInfo) bool
+	// Execute runs plugin processing on the data accessed by provided json pointer
+	Execute(ctx context.Context, pointer string, data interface{}, i ResolveInfo) (interface{}, error)
+}
+
+func handlePluginsResolveFieldFinished(eCtx *executionContext, info ResolveInfo) {
+	for _, p := range info.Schema.plugins {
+		if p.IsCompatible(eCtx.Context, info) {
+			eCtx.PluginExecRegistry.Register(PluginExecutable{
+				info:   info,
+				plugin: p,
+			})
+		}
+	}
+}
+
+type PluginExecutionRegistry struct {
+	plugins []PluginExecutable
+}
+
+func NewPluginExecRegistry() *PluginExecutionRegistry {
+	return &PluginExecutionRegistry{
+		plugins: make([]PluginExecutable, 0),
+	}
+}
+
+type PluginExecutable struct {
+	info   ResolveInfo
+	plugin Plugin
+}
+
+func (pr *PluginExecutionRegistry) Register(pe PluginExecutable) {
+	pr.plugins = append(pr.plugins, pe)
+}
+
+func (pr *PluginExecutionRegistry) Execute(ctx context.Context, data interface{}) (interface{}, []gqlerrors.FormattedError) {
+	var plgErrs []gqlerrors.FormattedError
+	var err error
+	for _, p := range pr.plugins {
+		elPath := constructPointer(p.info.Path.AsArray())
+		data, err = p.plugin.Execute(ctx, elPath, data, p.info)
+		if err != nil {
+			plgErrs = append(plgErrs, gqlerrors.FormatError(
+				fmt.Errorf("%s.PluginExecution: %v", p.plugin.Name(), err)))
+		}
+	}
+
+	return data, plgErrs
+}
+
+func constructPointer(path []interface{}) string {
+	var buf = strings.Builder{}
+	buf.WriteString("/")
+	for i := 0; i < len(path); i++ {
+		buf.WriteString(fmt.Sprintf("%v", path[i]))
+		if i != len(path)-1 {
+			buf.WriteString("/")
+		}
+	}
+	return buf.String()
+}

schema.go

@@ -7,6 +7,7 @@ type SchemaConfig struct {
 	Types        []Type
 	Directives   []*Directive
 	Extensions   []Extension
+	Plugins      []Plugin
 }
 
 type TypeMap map[string]Type
@@ -41,6 +42,7 @@ type Schema struct {
 	implementations  map[string][]*Object
 	possibleTypeMap  map[string]map[string]bool
 	extensions       []Extension
+	plugins          []Plugin
 }
 
 func NewSchema(config SchemaConfig) (Schema, error) {
@@ -142,6 +144,11 @@ func NewSchema(config SchemaConfig) (Schema, error) {
 		schema.extensions = config.Extensions
 	}
 
+	// Add plugins from config
+	if len(config.Plugins) != 0 {
+		schema.plugins = config.Plugins
+	}
+
 	return schema, nil
 }
 
@@ -267,6 +274,11 @@ func (gq *Schema) AddExtensions(e ...Extension) {
 	gq.extensions = append(gq.extensions, e...)
 }
 
+// AddPlugins can be used to add additional plugins to the schema
+func (gq *Schema) AddPlugins(p ...Plugin) {
+	gq.plugins = append(gq.plugins, p...)
+}
+
 // map-reduce
 func typeMapReducer(schema *Schema, typeMap TypeMap, objectType Type) (TypeMap, error) {
 	var err error