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ogen-fixnull

Fixes ogen-generated code to handle null values in Opt* types.

Problem

ogen-go/ogen#1358: When an OpenAPI spec has a nullable $ref field like:

"manual_verification": {
  "$ref": "#/components/schemas/ManualVerificationResponseModel",
  "nullable": true
}

ogen generates Opt* types instead of OptNil* types. The Opt* types don't handle null values, causing JSON decoding errors:

decode ManualVerificationResponseModel: "{" expected: unexpected byte 110 'n'

(byte 110 is n from null)

Solution

This tool adds null handling to all Opt* Decode methods that are missing it.

Before:

func (o *OptManualVerificationResponseModel) Decode(d *jx.Decoder) error {
    if o == nil {
        return errors.New("invalid: unable to decode OptManualVerificationResponseModel to nil")
    }
    o.Set = true
    if err := o.Value.Decode(d); err != nil {
        return err
    }
    return nil
}

After:

func (o *OptManualVerificationResponseModel) Decode(d *jx.Decoder) error {
    if o == nil {
        return errors.New("invalid: unable to decode OptManualVerificationResponseModel to nil")
    }
    if d.Next() == jx.Null {
        if err := d.Null(); err != nil {
            return err
        }
        return nil
    }
    o.Set = true
    if err := o.Value.Decode(d); err != nil {
        return err
    }
    return nil
}

Installation

go install github.com/agentplexus/ogen-tools/cmd/ogen-fixnull@latest

Usage

Run after ogen code generation:

# Generate code with ogen
ogen --package api --target internal/api --clean openapi.json

# Fix null handling
ogen-fixnull internal/api/oas_json_gen.go

Or use go run without installing:

go run github.com/agentplexus/ogen-tools/cmd/ogen-fixnull@latest internal/api/oas_json_gen.go

Integration with generate.sh

#!/bin/bash
set -e

# Check if ogen is installed
if ! command -v ogen &> /dev/null; then
    echo "Error: ogen is not installed."
    echo "Install with: go install github.com/ogen-go/ogen/cmd/ogen@latest"
    exit 1
fi

# Generate API code
echo "Generating API code with ogen..."
ogen --package api --target internal/api --clean openapi.json

# Fix ogen null handling bug (https://github.com/ogen-go/ogen/issues/1358)
echo "Fixing Opt* null handling..."
go run github.com/agentplexus/ogen-tools/cmd/ogen-fixnull@latest internal/api/oas_json_gen.go

# Verify build
echo "Verifying build..."
go build ./...

echo "Done!"

How It Works

The tool uses a regex to find Opt* (non-OptNil*) Decode methods that don't already have null handling, and inserts the null check before o.Set = true.

It's safe to run multiple times - already-fixed methods are skipped.

Example Output

$ ogen-fixnull internal/api/oas_json_gen.go
Fixed 208 Opt* Decode methods in internal/api/oas_json_gen.go

If no fixes are needed:

$ ogen-fixnull internal/api/oas_json_gen.go
No Opt* Decode methods needed fixing in internal/api/oas_json_gen.go