JSON interface linter

Checks a go module to ensure no data structure containing an interface is being marshaled as json.

This can be used to validate the suitability for a drop-in replacement of a json encoder. Some of these encoders do not allow interfaces being marshaled, for performance reasons.

Running

1. Install it locally

go install github.com/eltonjr/json-interface-linter@latest

1. Run it at the root of the module

Suggestion: don't validate test files

cd <path-to-my-module>
json-interface -test=false ./...

The linter

This module provides two linters that can be used individually or together

• jsontag
• marshal

jsontag

Checks every struct of a module looking for tagged fields json:"...". If some struct has a json tag, it is considered exported, and every field of this struct will be checked not to be an interface.

Fields unexported (starting with lower-case) or marked as json:"-" will not be considered.

This linter can be used individually with the following argument:

json-interface -jsontag ./...

marshal

Checks every value being passed to a Marshal function does not contain an interface within it.

By default, it checks function calls to

json.Marshal         (from encode/json)
json.MarshalIndent   (from encode/json)
json.Encode          (from encode/json.Encoder)

Custom marshalers can also be checked by being specified in a file and informed to the linter

json-interface -marshal.marshalers=file.txt ./...

A custom marshaler can also inform which of the arguments is the value being marshaled. Arguments are optional, positional and zero based, with zero as default.

Example of a marshalers file:

github.com/gin-gonic/gin.JSON
myencoder.Encode[1]

Note: providing a marshalers list will override the default marshalers. To be considered, they must also be in the marshalers file

More examples can be found here

This linter can be used individually with the following argument:

json-interface -marshal ./...

Excluding false-positives

If false-positives were found, they can be ignored by being specified in a file and informed to the linter

json-interface -exclude=exclude.txt

Example of an exclusion file:

errors
any
mypkg.MyInterface

Supported flags

Flag	Description	Default
-test	Specifies whether to validate test files.	true
-jsontag	Runs the jsontag linter.	true
-marshal	Runs the marshal linter.	true
-marshal.marshalers	Specifies a file containing custom marshalers to be checked.	encoding/json.Marshal encoding/json.MarshalIndent encoding/json.Encode
-exclude	Specifies a file containing false-positives to be ignored.
-verbose	Logs every decision made by the linter. Useful for debug.	false