Girish Kumar | 93e9174 | 2020-07-27 16:43:19 +0000 | [diff] [blame] | 1 | // Copyright 2017 Michal Witkowski. All Rights Reserved. |
| 2 | // See LICENSE for licensing terms. |
| 3 | |
| 4 | package grpc_ctxtags |
| 5 | |
| 6 | import ( |
| 7 | "reflect" |
| 8 | ) |
| 9 | |
| 10 | // RequestFieldExtractorFunc is a user-provided function that extracts field information from a gRPC request. |
| 11 | // It is called from tags middleware on arrival of unary request or a server-stream request. |
| 12 | // Keys and values will be added to the context tags of the request. If there are no fields, you should return a nil. |
| 13 | type RequestFieldExtractorFunc func(fullMethod string, req interface{}) map[string]interface{} |
| 14 | |
| 15 | type requestFieldsExtractor interface { |
| 16 | // ExtractRequestFields is a method declared on a Protobuf message that extracts fields from the interface. |
| 17 | // The values from the extracted fields should be set in the appendToMap, in order to avoid allocations. |
| 18 | ExtractRequestFields(appendToMap map[string]interface{}) |
| 19 | } |
| 20 | |
| 21 | // CodeGenRequestFieldExtractor is a function that relies on code-generated functions that export log fields from requests. |
| 22 | // These are usually coming from a protoc-plugin that generates additional information based on custom field options. |
| 23 | func CodeGenRequestFieldExtractor(fullMethod string, req interface{}) map[string]interface{} { |
| 24 | if ext, ok := req.(requestFieldsExtractor); ok { |
| 25 | retMap := make(map[string]interface{}) |
| 26 | ext.ExtractRequestFields(retMap) |
| 27 | if len(retMap) == 0 { |
| 28 | return nil |
| 29 | } |
| 30 | return retMap |
| 31 | } |
| 32 | return nil |
| 33 | } |
| 34 | |
| 35 | // TagBasedRequestFieldExtractor is a function that relies on Go struct tags to export log fields from requests. |
| 36 | // These are usually coming from a protoc-plugin, such as Gogo protobuf. |
| 37 | // |
| 38 | // message Metadata { |
| 39 | // repeated string tags = 1 [ (gogoproto.moretags) = "log_field:\"meta_tags\"" ]; |
| 40 | // } |
| 41 | // |
| 42 | // The tagName is configurable using the tagName variable. Here it would be "log_field". |
| 43 | func TagBasedRequestFieldExtractor(tagName string) RequestFieldExtractorFunc { |
| 44 | return func(fullMethod string, req interface{}) map[string]interface{} { |
| 45 | retMap := make(map[string]interface{}) |
| 46 | reflectMessageTags(req, retMap, tagName) |
| 47 | if len(retMap) == 0 { |
| 48 | return nil |
| 49 | } |
| 50 | return retMap |
| 51 | } |
| 52 | } |
| 53 | |
| 54 | func reflectMessageTags(msg interface{}, existingMap map[string]interface{}, tagName string) { |
| 55 | v := reflect.ValueOf(msg) |
| 56 | // Only deal with pointers to structs. |
| 57 | if v.Kind() != reflect.Ptr || v.Elem().Kind() != reflect.Struct { |
| 58 | return |
| 59 | } |
| 60 | // Deref the pointer get to the struct. |
| 61 | v = v.Elem() |
| 62 | t := v.Type() |
| 63 | for i := 0; i < v.NumField(); i++ { |
| 64 | field := v.Field(i) |
| 65 | kind := field.Kind() |
| 66 | // Only recurse down direct pointers, which should only be to nested structs. |
| 67 | if kind == reflect.Ptr { |
| 68 | reflectMessageTags(field.Interface(), existingMap, tagName) |
| 69 | } |
| 70 | // In case of arrays/splices (repeated fields) go down to the concrete type. |
| 71 | if kind == reflect.Array || kind == reflect.Slice { |
| 72 | if field.Len() == 0 { |
| 73 | continue |
| 74 | } |
| 75 | kind = field.Index(0).Kind() |
| 76 | } |
| 77 | // Only be interested in |
| 78 | if (kind >= reflect.Bool && kind <= reflect.Float64) || kind == reflect.String { |
| 79 | if tag := t.Field(i).Tag.Get(tagName); tag != "" { |
| 80 | existingMap[tag] = field.Interface() |
| 81 | } |
| 82 | } |
| 83 | } |
| 84 | return |
| 85 | } |