tapir/internal/adapters/transcribe/gateway_test.go

package transcribe_test

import (
	"bytes"
	"context"
	"io"
	"net/http"
	"net/http/httptest"
	"os"
	"path/filepath"
	"testing"

	"github.com/stretchr/testify/assert"
	"github.com/stretchr/testify/require"

	"git.d-ma.be/mathias/tapir/internal/adapters/transcribe"
	"git.d-ma.be/mathias/tapir/internal/domain"
)

// The httptest server stands in for the LiteLLM gateway: it is the process
// boundary, so a fake here is legitimate. The JSON it returns mirrors what the
// real gateway returned for iguana/kb-whisper and berget/kb-whisper on 2026-10-01
// (docs/research/audio-length-ceiling-2026-10-01.md). All text is synthetic.

const verboseJSON = `{
  "text": " God morgon allihopa.\n Vi går igenom läget.\n",
  "language": "swedish",
  "duration": 4.25,
  "segments": [
    {"id": 0, "start": 0.0, "end": 1.0, "text": " God morgon allihopa."},
    {"id": 1, "start": 1.0, "end": 9.0, "text": " Vi går igenom läget."}
  ]
}`

func wavFile(t *testing.T, content string) string {
	t.Helper()
	p := filepath.Join(t.TempDir(), "a.wav")
	require.NoError(t, os.WriteFile(p, []byte(content), 0o600))
	return p
}

type seen struct {
	method, path, auth, expect, contentType string
	contentLength                           int64
	transferEncoding                        []string
	fields                                  map[string]string
	file                                    string
	fileField                               string
	bodyLen                                 int
}

// serve starts a gateway fake that records the request it received and replies
// with status and body.
func serve(t *testing.T, status int, reply string, got *seen) *httptest.Server {
	t.Helper()
	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if got != nil {
			got.method, got.path = r.Method, r.URL.Path
			got.auth = r.Header.Get("Authorization")
			got.expect = r.Header.Get("Expect")
			got.contentType = r.Header.Get("Content-Type")
			got.contentLength = r.ContentLength
			got.transferEncoding = r.TransferEncoding
			raw, _ := io.ReadAll(r.Body)
			got.bodyLen = len(raw)
			r.Body = io.NopCloser(bytes.NewReader(raw))
			require.NoError(t, r.ParseMultipartForm(32<<20))
			got.fields = map[string]string{}
			for k, v := range r.MultipartForm.Value {
				got.fields[k] = v[0]
			}
			for field, fhs := range r.MultipartForm.File {
				got.fileField = field
				f, _ := fhs[0].Open()
				b, _ := io.ReadAll(f)
				got.file = string(b)
			}
		}
		w.WriteHeader(status)
		_, _ = io.WriteString(w, reply)
	}))
	t.Cleanup(srv.Close)
	return srv
}

func TestGateway_SendsTheRequestTheGatewayExpects(t *testing.T) {
	var got seen
	srv := serve(t, 200, verboseJSON, &got)
	g := transcribe.NewGateway(srv.URL+"/v1", "secret-key", "iguana/kb-whisper", srv.Client())

	_, err := g.Transcribe(context.Background(), wavFile(t, "RIFF-synthetic-pcm"))

	require.NoError(t, err)
	assert.Equal(t, http.MethodPost, got.method)
	assert.Equal(t, "/v1/audio/transcriptions", got.path)
	assert.Equal(t, "Bearer secret-key", got.auth)
	assert.Equal(t, "file", got.fileField, "the multipart field is `file`; `audio_file` is rejected as 'Invalid request'")
	assert.Equal(t, "RIFF-synthetic-pcm", got.file)
	assert.Equal(t, "iguana/kb-whisper", got.fields["model"])
	assert.Equal(t, "verbose_json", got.fields["response_format"])
	assert.Equal(t, "sv", got.fields["language"])
	assert.Empty(t, got.expect, "no Expect: 100-continue: it trips the proxy for any body over 1 KB")
}

func TestGateway_SendsAKnownContentLengthNotChunked(t *testing.T) {
	var got seen
	srv := serve(t, 200, verboseJSON, &got)
	g := transcribe.NewGateway(srv.URL+"/v1", "k", "m", srv.Client())

	_, err := g.Transcribe(context.Background(), wavFile(t, "0123456789"))

	require.NoError(t, err)
	assert.Empty(t, got.transferEncoding, "a 90-minute WAV is ~170 MB: stream it with a computed length, not chunked and not buffered")
	assert.Equal(t, int64(got.bodyLen), got.contentLength)
}

func TestGateway_NormalisesTheVerboseJSONResponse(t *testing.T) {
	srv := serve(t, 200, verboseJSON, nil)
	g := transcribe.NewGateway(srv.URL+"/v1", "k", "iguana/kb-whisper", srv.Client())

	got, err := g.Transcribe(context.Background(), wavFile(t, "x"))

	require.NoError(t, err)
	assert.Equal(t, "God morgon allihopa.\n Vi går igenom läget.", got.Text)
	assert.Equal(t, "iguana/kb-whisper", got.Endpoint, "the serving endpoint is part of the result")
	assert.InDelta(t, 4.25, got.AudioSeconds, 1e-9)
	assert.Equal(t, []domain.Segment{
		{Start: 0, End: 1, Text: "God morgon allihopa."},
		// The final segment ended at 9.0 s for 4.25 s of audio: whisper's last
		// window can run past the end. Clamped to the audio duration.
		{Start: 1, End: 4.25, Text: "Vi går igenom läget."},
	}, got.Segments)
}

func TestGateway_ErrorsDoNotDependOnTheBody(t *testing.T) {
	// {"error":"failed to process audio"} has had at least five distinct causes, so
	// no code may branch on it. Two different bodies must be treated identically.
	for _, reply := range []string{`{"error":"failed to process audio"}`, `{"error":"something else entirely"}`} {
		srv := serve(t, 500, reply, nil)
		g := transcribe.NewGateway(srv.URL+"/v1", "k", "m", srv.Client())

		_, err := g.Transcribe(context.Background(), wavFile(t, "x"))

		var se *transcribe.StatusError
		require.ErrorAs(t, err, &se)
		assert.Equal(t, 500, se.Code)
	}
}

func TestGateway_AnEmptyTranscriptIsAFailureNotASuccess(t *testing.T) {
	srv := serve(t, 200, `{"text":"  ","language":"swedish","duration":3,"segments":[]}`, nil)
	g := transcribe.NewGateway(srv.URL+"/v1", "k", "m", srv.Client())

	_, err := g.Transcribe(context.Background(), wavFile(t, "x"))

	assert.ErrorIs(t, err, transcribe.ErrEmptyTranscript)
}

func TestGateway_MalformedJSONIsAnError(t *testing.T) {
	srv := serve(t, 200, `not json`, nil)
	g := transcribe.NewGateway(srv.URL+"/v1", "k", "m", srv.Client())

	_, err := g.Transcribe(context.Background(), wavFile(t, "x"))

	assert.Error(t, err)
}

func TestGateway_MissingAudioFileIsAnError(t *testing.T) {
	g := transcribe.NewGateway("http://127.0.0.1:1/v1", "k", "m", http.DefaultClient)

	_, err := g.Transcribe(context.Background(), filepath.Join(t.TempDir(), "nope.wav"))

	assert.Error(t, err)
}