ogen-fixerror

README

ogen-fixerror

Fixes ogen-generated code to preserve error response bodies.

Problem

When an ogen-generated client receives an unexpected HTTP status code (e.g., 400, 403, 500), the error contains the *http.Response but the body is already closed by the time you try to read it.

This happens because:

1. The client code has defer resp.Body.Close()
2. The response decoder returns UnexpectedStatusCodeWithResponse(resp) without reading the body
3. When the function returns, the defer runs and closes the body
4. By the time you call ogenerror.Parse() or try to read the body, it's already closed

Result: You get the status code but lose the error message:

Status: 403
Body: (empty)

Solution

This tool modifies the response decoders to buffer the body before returning the error.

Before:

return res, validate.UnexpectedStatusCodeWithResponse(resp)

After:

// Buffer the response body so it survives resp.Body.Close()
body, _ := io.ReadAll(resp.Body)
resp.Body = io.NopCloser(bytes.NewReader(body))
return res, validate.UnexpectedStatusCodeWithResponse(resp)

Result: Error details are now accessible:

Status: 400
Message: An invalid ID has been received: 'invalid-voice-id'. Make sure to provide a correct one.
Detail: invalid_uid

Installation

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

Usage

Run after ogen code generation:

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

# Fix error body preservation
ogen-fixerror internal/api/oas_response_decoders_gen.go

Or use go run without installing:

go run github.com/agentplexus/ogen-tools/cmd/ogen-fixerror@latest internal/api/oas_response_decoders_gen.go

Integration with generate.sh

#!/bin/bash
set -e

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

# Fix ogen bugs
go run github.com/agentplexus/ogen-tools/cmd/ogen-fixnull@latest internal/api/oas_json_gen.go
go run github.com/agentplexus/ogen-tools/cmd/ogen-fixerror@latest internal/api/oas_response_decoders_gen.go

# Verify build
go build ./...

Reading Error Details

Use the ogenerror package to extract error details:

import "github.com/agentplexus/ogen-tools/ogenerror"

resp, err := client.SomeMethod(ctx, req)
if err != nil {
    if status := ogenerror.Parse(err); status != nil {
        fmt.Printf("Status: %d\n", status.StatusCode)
        fmt.Printf("Body: %s\n", status.Body)
    }
}

Example Output

$ ogen-fixerror internal/api/oas_response_decoders_gen.go
Fixed 204 UnexpectedStatusCode returns in internal/api/oas_response_decoders_gen.go

If no fixes are needed:

$ ogen-fixerror internal/api/oas_response_decoders_gen.go
No UnexpectedStatusCode returns needed fixing in internal/api/oas_response_decoders_gen.go

Documentation

Overview

Command ogen-fixerror fixes ogen-generated code to preserve error response bodies.

This tool addresses an issue where ogen's UnexpectedStatusCodeError contains the http.Response but the body gets closed by defer before callers can read it.

Usage:

ogen-fixerror <oas_response_decoders_gen.go>

The tool modifies the file in place, changing:

return res, validate.UnexpectedStatusCodeWithResponse(resp)

To read and buffer the body before returning:

body, _ := io.ReadAll(resp.Body)
resp.Body = io.NopCloser(bytes.NewReader(body))
return res, validate.UnexpectedStatusCodeWithResponse(resp)

This ensures the error body is preserved and can be read by error handlers.