| // Copyright 2017 Michal Witkowski. All Rights Reserved. |
| // See LICENSE for licensing terms. |
| |
| package grpc_ctxtags |
| |
| import ( |
| "reflect" |
| ) |
| |
| // RequestFieldExtractorFunc is a user-provided function that extracts field information from a gRPC request. |
| // It is called from tags middleware on arrival of unary request or a server-stream request. |
| // Keys and values will be added to the context tags of the request. If there are no fields, you should return a nil. |
| type RequestFieldExtractorFunc func(fullMethod string, req interface{}) map[string]interface{} |
| |
| type requestFieldsExtractor interface { |
| // ExtractRequestFields is a method declared on a Protobuf message that extracts fields from the interface. |
| // The values from the extracted fields should be set in the appendToMap, in order to avoid allocations. |
| ExtractRequestFields(appendToMap map[string]interface{}) |
| } |
| |
| // CodeGenRequestFieldExtractor is a function that relies on code-generated functions that export log fields from requests. |
| // These are usually coming from a protoc-plugin that generates additional information based on custom field options. |
| func CodeGenRequestFieldExtractor(fullMethod string, req interface{}) map[string]interface{} { |
| if ext, ok := req.(requestFieldsExtractor); ok { |
| retMap := make(map[string]interface{}) |
| ext.ExtractRequestFields(retMap) |
| if len(retMap) == 0 { |
| return nil |
| } |
| return retMap |
| } |
| return nil |
| } |
| |
| // TagBasedRequestFieldExtractor is a function that relies on Go struct tags to export log fields from requests. |
| // These are usually coming from a protoc-plugin, such as Gogo protobuf. |
| // |
| // message Metadata { |
| // repeated string tags = 1 [ (gogoproto.moretags) = "log_field:\"meta_tags\"" ]; |
| // } |
| // |
| // The tagName is configurable using the tagName variable. Here it would be "log_field". |
| func TagBasedRequestFieldExtractor(tagName string) RequestFieldExtractorFunc { |
| return func(fullMethod string, req interface{}) map[string]interface{} { |
| retMap := make(map[string]interface{}) |
| reflectMessageTags(req, retMap, tagName) |
| if len(retMap) == 0 { |
| return nil |
| } |
| return retMap |
| } |
| } |
| |
| func reflectMessageTags(msg interface{}, existingMap map[string]interface{}, tagName string) { |
| v := reflect.ValueOf(msg) |
| // Only deal with pointers to structs. |
| if v.Kind() != reflect.Ptr || v.Elem().Kind() != reflect.Struct { |
| return |
| } |
| // Deref the pointer get to the struct. |
| v = v.Elem() |
| t := v.Type() |
| for i := 0; i < v.NumField(); i++ { |
| field := v.Field(i) |
| kind := field.Kind() |
| // Only recurse down direct pointers, which should only be to nested structs. |
| if kind == reflect.Ptr { |
| reflectMessageTags(field.Interface(), existingMap, tagName) |
| } |
| // In case of arrays/splices (repeated fields) go down to the concrete type. |
| if kind == reflect.Array || kind == reflect.Slice { |
| if field.Len() == 0 { |
| continue |
| } |
| kind = field.Index(0).Kind() |
| } |
| // Only be interested in |
| if (kind >= reflect.Bool && kind <= reflect.Float64) || kind == reflect.String { |
| if tag := t.Field(i).Tag.Get(tagName); tag != "" { |
| existingMap[tag] = field.Interface() |
| } |
| } |
| } |
| return |
| } |