Add Gitea release page transport

2026-10-05 19:46:27 +00:00
parent e98ee0f7b9
commit 717d6d0d04
7 changed files with 756 additions and 8 deletions
--- a/internal/gitea/release.go
+++ b/internal/gitea/release.go
@@ -0,0 +1,367 @@
+// Package gitea implements the internal Gitea REST operations used by delivery.
+package gitea
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+	"strings"
+
+	"gitea.maximumdirect.net/eric/ReleaseKit/internal/versioncontract"
+)
+
+type FailureKind string
+
+const (
+	FailureInvalid      FailureKind = "invalid_request"
+	FailureNotFound     FailureKind = "not_found"
+	FailureUnauthorized FailureKind = "unauthorized"
+	FailureConflict     FailureKind = "conflict"
+	FailureMalformed    FailureKind = "malformed_response"
+	FailureTransport    FailureKind = "transport"
+	FailureRejected     FailureKind = "rejected"
+	FailureUnknown      FailureKind = "unknown"
+)
+
+// Failure describes how a Gitea operation failed. StatusCode is zero when no
+// HTTP response was received.
+type Failure struct {
+	Kind       FailureKind
+	Operation  string
+	StatusCode int
+	Err        error
+}
+
+func (f *Failure) Error() string {
+	if f.StatusCode != 0 {
+		return fmt.Sprintf("gitea %s: %s (HTTP %d)", f.Operation, f.Kind, f.StatusCode)
+	}
+	if f.Err != nil {
+		return fmt.Sprintf("gitea %s: %s: %v", f.Operation, f.Kind, f.Err)
+	}
+	return fmt.Sprintf("gitea %s: %s", f.Operation, f.Kind)
+}
+
+func (f *Failure) Unwrap() error { return f.Err }
+
+type Destination struct {
+	BaseURL    string
+	Owner      string
+	Repository string
+	Token      string
+}
+
+type Request struct {
+	Destination Destination
+	Version     string
+	Commit      string
+	Note        string
+}
+
+type Release struct {
+	ID         int64
+	URL        string
+	TagName    string
+	Title      string
+	Body       string
+	Draft      bool
+	Prerelease bool
+}
+
+type Result struct {
+	Release Release
+	Created bool
+}
+
+type Client struct {
+	HTTPClient *http.Client
+}
+
+type tagResponse struct {
+	Commit struct {
+		SHA string `json:"sha"`
+	} `json:"commit"`
+}
+
+type releaseResponse struct {
+	ID              int64  `json:"id"`
+	HTMLURL         string `json:"html_url"`
+	TagName         string `json:"tag_name"`
+	TargetCommitish string `json:"target_commitish"`
+	Name            string `json:"name"`
+	Body            string `json:"body"`
+	Draft           bool   `json:"draft"`
+	Prerelease      bool   `json:"prerelease"`
+}
+
+type createReleaseRequest struct {
+	TagName         string `json:"tag_name"`
+	TargetCommitish string `json:"target_commitish"`
+	Name            string `json:"name"`
+	Body            string `json:"body"`
+	Draft           bool   `json:"draft"`
+	Prerelease      bool   `json:"prerelease"`
+}
+
+// EnsureRelease verifies the hosted tag and finds or creates its stable release
+// page. It never edits a release that already exists.
+func (c Client) EnsureRelease(ctx context.Context, request Request) (Result, error) {
+	if err := validateRequest(request); err != nil {
+		return Result{}, err
+	}
+	base, err := parseBaseURL(request.Destination.BaseURL)
+	if err != nil {
+		return Result{}, failure(FailureInvalid, "validate destination", 0, err)
+	}
+	client := c.httpClient()
+	apiRoot := strings.TrimRight(base.String(), "/") + "/api/v1/repos/" + url.PathEscape(request.Destination.Owner) + "/" + url.PathEscape(request.Destination.Repository)
+	tagURL := apiRoot + "/tags/" + url.PathEscape(request.Version)
+
+	var tag tagResponse
+	if err := c.getJSON(ctx, client, request.Destination.Token, "get hosted tag", tagURL, &tag); err != nil {
+		return Result{}, err
+	}
+	if tag.Commit.SHA != request.Commit {
+		return Result{}, failure(FailureConflict, "verify hosted tag", 0, fmt.Errorf("tag %q targets %q, want %q", request.Version, tag.Commit.SHA, request.Commit))
+	}
+
+	releaseURL := apiRoot + "/releases/tags/" + url.PathEscape(request.Version)
+	existing, status, err := c.getRelease(ctx, client, request.Destination.Token, releaseURL)
+	if err == nil {
+		return acceptExisting(existing, request)
+	}
+	if status != http.StatusNotFound {
+		return Result{}, err
+	}
+
+	title := noteTitle(request.Note)
+	body, err := json.Marshal(createReleaseRequest{
+		TagName: request.Version, TargetCommitish: request.Commit,
+		Name: title, Body: request.Note,
+	})
+	if err != nil {
+		return Result{}, failure(FailureInvalid, "encode release", 0, err)
+	}
+	created, postStatus, postErr := c.postRelease(ctx, client, request.Destination.Token, apiRoot+"/releases", body)
+	if postErr == nil {
+		return acceptCreated(created, request)
+	}
+	if !shouldReconcileCreate(postStatus, postErr) {
+		return Result{}, postErr
+	}
+
+	// A conflict or interrupted server response may have followed a successful
+	// create. One lookup resolves only a page with the exact selected content.
+	retry, retryStatus, retryErr := c.getRelease(ctx, client, request.Destination.Token, releaseURL)
+	if retryErr == nil {
+		result, matchErr := acceptExisting(retry, request)
+		if matchErr == nil {
+			return result, nil
+		}
+		return Result{}, failure(FailureConflict, "resolve release creation", postStatus, matchErr)
+	}
+	if retryStatus == http.StatusNotFound {
+		if postStatus == http.StatusConflict {
+			return Result{}, failure(FailureConflict, "create release", postStatus, postErr)
+		}
+		return Result{}, failure(FailureUnknown, "resolve release creation", postStatus, postErr)
+	}
+	return Result{}, failure(FailureUnknown, "resolve release creation", postStatus, errors.Join(postErr, retryErr))
+}
+
+func shouldReconcileCreate(status int, err error) bool {
+	if status == http.StatusConflict || status >= 500 || errors.Is(err, context.Canceled) || errors.Is(err, context.DeadlineExceeded) {
+		return true
+	}
+	var failure *Failure
+	return errors.As(err, &failure) && (failure.Kind == FailureTransport || failure.Kind == FailureMalformed)
+}
+
+func (c Client) getRelease(ctx context.Context, client *http.Client, token, endpoint string) (Release, int, error) {
+	request, err := http.NewRequestWithContext(ctx, http.MethodGet, endpoint, nil)
+	if err != nil {
+		return Release{}, 0, failure(FailureInvalid, "find release", 0, err)
+	}
+	request.Header.Set("Authorization", "token "+token)
+	request.Header.Set("Accept", "application/json")
+	response, err := client.Do(request)
+	if err != nil {
+		return Release{}, 0, failure(FailureTransport, "find release", 0, err)
+	}
+	defer response.Body.Close()
+	if response.StatusCode == http.StatusNotFound {
+		return Release{}, response.StatusCode, failure(FailureNotFound, "find release", response.StatusCode, nil)
+	}
+	if response.StatusCode < 200 || response.StatusCode >= 300 {
+		return Release{}, response.StatusCode, responseFailure("find release", response.StatusCode)
+	}
+	var decoded releaseResponse
+	if err := decodeJSON(response.Body, &decoded); err != nil {
+		return Release{}, response.StatusCode, failure(FailureMalformed, "decode release", response.StatusCode, err)
+	}
+	return decoded.Release(), response.StatusCode, nil
+}
+
+func (c Client) getJSON(ctx context.Context, client *http.Client, token, operation, endpoint string, destination any) error {
+	request, err := http.NewRequestWithContext(ctx, http.MethodGet, endpoint, nil)
+	if err != nil {
+		return failure(FailureInvalid, operation, 0, err)
+	}
+	request.Header.Set("Authorization", "token "+token)
+	request.Header.Set("Accept", "application/json")
+	response, err := client.Do(request)
+	if err != nil {
+		return failure(FailureTransport, operation, 0, err)
+	}
+	defer response.Body.Close()
+	if response.StatusCode < 200 || response.StatusCode >= 300 {
+		return responseFailure(operation, response.StatusCode)
+	}
+	if err := decodeJSON(response.Body, destination); err != nil {
+		return failure(FailureMalformed, operation, response.StatusCode, err)
+	}
+	return nil
+}
+
+func (c Client) postRelease(ctx context.Context, client *http.Client, token, endpoint string, body []byte) (Release, int, error) {
+	request, err := http.NewRequestWithContext(ctx, http.MethodPost, endpoint, bytes.NewReader(body))
+	if err != nil {
+		return Release{}, 0, failure(FailureInvalid, "create release", 0, err)
+	}
+	request.Header.Set("Authorization", "token "+token)
+	request.Header.Set("Accept", "application/json")
+	request.Header.Set("Content-Type", "application/json")
+	response, err := client.Do(request)
+	if err != nil {
+		return Release{}, 0, failure(FailureTransport, "create release", 0, err)
+	}
+	defer response.Body.Close()
+	if response.StatusCode < 200 || response.StatusCode >= 300 {
+		return Release{}, response.StatusCode, responseFailure("create release", response.StatusCode)
+	}
+	var decoded releaseResponse
+	if err := decodeJSON(response.Body, &decoded); err != nil {
+		return Release{}, response.StatusCode, failure(FailureMalformed, "decode created release", response.StatusCode, err)
+	}
+	return decoded.Release(), response.StatusCode, nil
+}
+
+func (c Client) httpClient() *http.Client {
+	client := http.DefaultClient
+	if c.HTTPClient != nil {
+		clientCopy := *c.HTTPClient
+		clientCopy.CheckRedirect = func(*http.Request, []*http.Request) error { return http.ErrUseLastResponse }
+		return &clientCopy
+	}
+	clientCopy := *client
+	clientCopy.CheckRedirect = func(*http.Request, []*http.Request) error { return http.ErrUseLastResponse }
+	return &clientCopy
+}
+
+func validateRequest(request Request) error {
+	if !versioncontract.ValidStableVersion(request.Version) {
+		return failure(FailureInvalid, "validate request", 0, errors.New("stable version is required"))
+	}
+	if !validObjectID(request.Commit) {
+		return failure(FailureInvalid, "validate request", 0, errors.New("source commit must be a lowercase Git object ID"))
+	}
+	if strings.TrimSpace(request.Destination.Owner) == "" || strings.ContainsAny(request.Destination.Owner, "/\\") {
+		return failure(FailureInvalid, "validate request", 0, errors.New("Gitea owner is required as one path segment"))
+	}
+	if strings.TrimSpace(request.Destination.Repository) == "" || strings.ContainsAny(request.Destination.Repository, "/\\") {
+		return failure(FailureInvalid, "validate request", 0, errors.New("Gitea repository is required as one path segment"))
+	}
+	if strings.TrimSpace(request.Destination.Token) == "" {
+		return failure(FailureInvalid, "validate request", 0, errors.New("Gitea token is required"))
+	}
+	if noteTitle(request.Note) == "" {
+		return failure(FailureInvalid, "validate request", 0, errors.New("release note must begin with a level-one heading"))
+	}
+	return nil
+}
+
+func parseBaseURL(raw string) (*url.URL, error) {
+	parsed, err := url.Parse(raw)
+	if err != nil {
+		return nil, err
+	}
+	if (parsed.Scheme != "http" && parsed.Scheme != "https") || parsed.Host == "" || parsed.User != nil || parsed.RawQuery != "" || parsed.Fragment != "" {
+		return nil, errors.New("base URL must be an absolute HTTP(S) origin or path without credentials, query, or fragment")
+	}
+	return parsed, nil
+}
+
+func acceptExisting(release Release, request Request) (Result, error) {
+	if release.TagName != request.Version || release.Body != request.Note || release.Draft || release.Prerelease {
+		return Result{}, failure(FailureConflict, "verify existing release", 0, errors.New("existing release does not match the committed note and stable tag"))
+	}
+	return Result{Release: release}, nil
+}
+
+func acceptCreated(release Release, request Request) (Result, error) {
+	if release.ID <= 0 || release.TagName != request.Version || release.Body != request.Note || release.Title != noteTitle(request.Note) || release.Draft || release.Prerelease {
+		return Result{}, failure(FailureMalformed, "verify created release", 0, errors.New("created release response does not match the requested stable release"))
+	}
+	return Result{Release: release, Created: true}, nil
+}
+
+func (response releaseResponse) Release() Release {
+	return Release{ID: response.ID, URL: response.HTMLURL, TagName: response.TagName, Title: response.Name, Body: response.Body, Draft: response.Draft, Prerelease: response.Prerelease}
+}
+
+func noteTitle(note string) string {
+	first := strings.SplitN(note, "\n", 2)[0]
+	if !strings.HasPrefix(first, "# ") {
+		return ""
+	}
+	return strings.TrimSpace(strings.TrimPrefix(first, "# "))
+}
+
+func validObjectID(value string) bool {
+	if len(value) != 40 && len(value) != 64 {
+		return false
+	}
+	for _, r := range value {
+		if !(r >= '0' && r <= '9') && !(r >= 'a' && r <= 'f') {
+			return false
+		}
+	}
+	return true
+}
+
+func responseFailure(operation string, status int) error {
+	kind := FailureRejected
+	switch status {
+	case http.StatusUnauthorized, http.StatusForbidden:
+		kind = FailureUnauthorized
+	case http.StatusConflict:
+		kind = FailureConflict
+	case http.StatusNotFound:
+		kind = FailureNotFound
+	}
+	return failure(kind, operation, status, nil)
+}
+
+func failure(kind FailureKind, operation string, status int, err error) error {
+	return &Failure{Kind: kind, Operation: operation, StatusCode: status, Err: err}
+}
+
+func decodeJSON(reader io.Reader, destination any) error {
+	decoder := json.NewDecoder(reader)
+	if err := decoder.Decode(destination); err != nil {
+		return err
+	}
+	var trailing any
+	if err := decoder.Decode(&trailing); !errors.Is(err, io.EOF) {
+		if err == nil {
+			return errors.New("response contains multiple JSON values")
+		}
+		return err
+	}
+	return nil
+}
--- a/internal/gitea/release_test.go
+++ b/internal/gitea/release_test.go
@@ -0,0 +1,341 @@
+package gitea
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+)
+
+const testCommit = "0123456789012345678901234567890123456789"
+const testNote = "# Example v1.2.3\n\nRelease details.\n"
+const testToken = "fixture-secret-token"
+
+func TestEnsureReleaseFindsMatchingReleaseAndPreservesTitle(t *testing.T) {
+	server, _ := newReleaseServer(t, releaseFixture{title: "Historical title"}, false)
+	result, err := testClient(server).EnsureRelease(context.Background(), testRequest(server.URL))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if result.Created || result.Release.Title != "Historical title" {
+		t.Fatalf("result = %#v", result)
+	}
+}
+
+func TestEnsureReleaseCreatesMissingPageFromCommittedNote(t *testing.T) {
+	server, _ := newReleaseServer(t, releaseFixture{}, true)
+	result, err := testClient(server).EnsureRelease(context.Background(), testRequest(server.URL))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !result.Created || result.Release.Title != "Example v1.2.3" || result.Release.Body != testNote {
+		t.Fatalf("result = %#v", result)
+	}
+}
+
+func TestEnsureReleaseConflictDoesNotEditExistingPage(t *testing.T) {
+	server, state := newReleaseServer(t, releaseFixture{title: "Keep this title", body: "Different body"}, false)
+	_, err := testClient(server).EnsureRelease(context.Background(), testRequest(server.URL))
+	if failureKind(t, err) != FailureConflict {
+		t.Fatalf("error = %v", err)
+	}
+	if got := state.posts; got != 0 {
+		t.Fatalf("release creates = %d, want 0", got)
+	}
+}
+
+func TestEnsureReleaseUnauthorizedIsStructuredAndHidesToken(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		assertRequest(t, r, http.MethodGet, "/api/v1/repos/owner/project/tags/v1.2.3")
+		w.WriteHeader(http.StatusUnauthorized)
+	}))
+	defer server.Close()
+	_, err := testClient(server).EnsureRelease(context.Background(), testRequest(server.URL))
+	if failureKind(t, err) != FailureUnauthorized {
+		t.Fatalf("error = %v", err)
+	}
+	if fmt.Sprint(err) == "" || contains(fmt.Sprint(err), testToken) {
+		t.Fatalf("error exposes unexpected content: %v", err)
+	}
+}
+
+func TestEnsureReleaseMalformedTagResponseStopsBeforeCreate(t *testing.T) {
+	posts := 0
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.Method == http.MethodPost {
+			posts++
+		}
+		assertRequest(t, r, http.MethodGet, "/api/v1/repos/owner/project/tags/v1.2.3")
+		_, _ = w.Write([]byte("{"))
+	}))
+	defer server.Close()
+	_, err := testClient(server).EnsureRelease(context.Background(), testRequest(server.URL))
+	if failureKind(t, err) != FailureMalformed || posts != 0 {
+		t.Fatalf("error = %v, posts = %d", err, posts)
+	}
+}
+
+func TestEnsureReleaseWrongHostedTagStopsBeforeCreate(t *testing.T) {
+	posts := 0
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		assertRequest(t, r, http.MethodGet, "/api/v1/repos/owner/project/tags/v1.2.3")
+		if r.Method == http.MethodPost {
+			posts++
+		}
+		_, _ = fmt.Fprintf(w, `{"commit":{"sha":"%040d"}}`, 7)
+	}))
+	defer server.Close()
+	_, err := testClient(server).EnsureRelease(context.Background(), testRequest(server.URL))
+	if failureKind(t, err) != FailureConflict || posts != 0 {
+		t.Fatalf("error = %v, posts = %d", err, posts)
+	}
+}
+
+func TestEnsureReleaseMissingHostedTagStopsBeforeCreate(t *testing.T) {
+	posts := 0
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		assertRequest(t, r, http.MethodGet, "/api/v1/repos/owner/project/tags/v1.2.3")
+		if r.Method == http.MethodPost {
+			posts++
+		}
+		http.NotFound(w, r)
+	}))
+	defer server.Close()
+	_, err := testClient(server).EnsureRelease(context.Background(), testRequest(server.URL))
+	if failureKind(t, err) != FailureNotFound || posts != 0 {
+		t.Fatalf("error = %v, posts = %d", err, posts)
+	}
+}
+
+func TestEnsureReleaseHonorsContextCancellation(t *testing.T) {
+	called := false
+	server := httptest.NewServer(http.HandlerFunc(func(http.ResponseWriter, *http.Request) { called = true }))
+	defer server.Close()
+	ctx, cancel := context.WithCancel(context.Background())
+	cancel()
+	_, err := testClient(server).EnsureRelease(ctx, testRequest(server.URL))
+	if !errors.Is(err, context.Canceled) || called {
+		t.Fatalf("error = %v, server called = %t", err, called)
+	}
+}
+
+func TestEnsureReleaseResolvesLostCreateAcknowledgmentWithOneLookup(t *testing.T) {
+	created := false
+	lookups := 0
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		assertAuth(t, r)
+		switch r.URL.Path {
+		case "/api/v1/repos/owner/project/tags/v1.2.3":
+			assertRequest(t, r, http.MethodGet, r.URL.Path)
+			writeTag(t, w, testCommit)
+		case "/api/v1/repos/owner/project/releases/tags/v1.2.3":
+			assertRequest(t, r, http.MethodGet, r.URL.Path)
+			lookups++
+			if !created {
+				http.NotFound(w, r)
+				return
+			}
+			writeRelease(t, w, releaseFixture{title: "Example v1.2.3"})
+		case "/api/v1/repos/owner/project/releases":
+			assertRequest(t, r, http.MethodPost, r.URL.Path)
+			var payload createReleaseRequest
+			if err := json.NewDecoder(r.Body).Decode(&payload); err != nil {
+				t.Fatal(err)
+			}
+			if payload.TagName != "v1.2.3" || payload.TargetCommitish != testCommit || payload.Name != "Example v1.2.3" || payload.Body != testNote || payload.Draft || payload.Prerelease {
+				t.Fatalf("create payload = %#v", payload)
+			}
+			created = true
+			hijacker, ok := w.(http.Hijacker)
+			if !ok {
+				t.Fatal("HTTP writer does not support hijacking")
+			}
+			connection, _, err := hijacker.Hijack()
+			if err != nil {
+				t.Fatal(err)
+			}
+			_ = connection.Close()
+		default:
+			t.Fatalf("unexpected request %s %s", r.Method, r.URL.Path)
+		}
+	}))
+	defer server.Close()
+	result, err := testClient(server).EnsureRelease(context.Background(), testRequest(server.URL))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if result.Created || lookups != 2 {
+		t.Fatalf("result = %#v, release lookups = %d", result, lookups)
+	}
+}
+
+func TestEnsureReleaseResolvesCreateConflictWithOneLookup(t *testing.T) {
+	lookups := 0
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		assertAuth(t, r)
+		switch r.URL.Path {
+		case "/api/v1/repos/owner/project/tags/v1.2.3":
+			assertRequest(t, r, http.MethodGet, r.URL.Path)
+			writeTag(t, w, testCommit)
+		case "/api/v1/repos/owner/project/releases/tags/v1.2.3":
+			assertRequest(t, r, http.MethodGet, r.URL.Path)
+			lookups++
+			if lookups == 1 {
+				http.NotFound(w, r)
+				return
+			}
+			writeRelease(t, w, releaseFixture{title: "Created by another request"})
+		case "/api/v1/repos/owner/project/releases":
+			assertRequest(t, r, http.MethodPost, r.URL.Path)
+			w.WriteHeader(http.StatusConflict)
+		default:
+			t.Fatalf("unexpected request %s %s", r.Method, r.URL.Path)
+		}
+	}))
+	defer server.Close()
+	result, err := testClient(server).EnsureRelease(context.Background(), testRequest(server.URL))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if result.Created || result.Release.Title != "Created by another request" || lookups != 2 {
+		t.Fatalf("result = %#v, release lookups = %d", result, lookups)
+	}
+}
+
+func TestEnsureReleaseReportsUnknownWhenAmbiguousCreateCannotBeInspected(t *testing.T) {
+	lookups := 0
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		assertAuth(t, r)
+		switch r.URL.Path {
+		case "/api/v1/repos/owner/project/tags/v1.2.3":
+			assertRequest(t, r, http.MethodGet, r.URL.Path)
+			writeTag(t, w, testCommit)
+		case "/api/v1/repos/owner/project/releases/tags/v1.2.3":
+			assertRequest(t, r, http.MethodGet, r.URL.Path)
+			lookups++
+			if lookups == 1 {
+				http.NotFound(w, r)
+				return
+			}
+			http.Error(w, "temporarily unavailable", http.StatusServiceUnavailable)
+		case "/api/v1/repos/owner/project/releases":
+			assertRequest(t, r, http.MethodPost, r.URL.Path)
+			w.WriteHeader(http.StatusInternalServerError)
+		default:
+			t.Fatalf("unexpected request %s %s", r.Method, r.URL.Path)
+		}
+	}))
+	defer server.Close()
+	_, err := testClient(server).EnsureRelease(context.Background(), testRequest(server.URL))
+	if failureKind(t, err) != FailureUnknown || lookups != 2 {
+		t.Fatalf("error = %v, release lookups = %d", err, lookups)
+	}
+}
+
+type releaseFixture struct {
+	title string
+	body  string
+	draft bool
+	pre   bool
+}
+
+type fixtureState struct{ posts int }
+
+func newReleaseServer(t *testing.T, existing releaseFixture, createMissing bool) (*httptest.Server, *fixtureState) {
+	t.Helper()
+	state := &fixtureState{}
+	handler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		assertAuth(t, r)
+		switch r.URL.Path {
+		case "/api/v1/repos/owner/project/tags/v1.2.3":
+			assertRequest(t, r, http.MethodGet, r.URL.Path)
+			writeTag(t, w, testCommit)
+		case "/api/v1/repos/owner/project/releases/tags/v1.2.3":
+			assertRequest(t, r, http.MethodGet, r.URL.Path)
+			if existing.title == "" && existing.body == "" {
+				http.NotFound(w, r)
+				return
+			}
+			writeRelease(t, w, existing)
+		case "/api/v1/repos/owner/project/releases":
+			assertRequest(t, r, http.MethodPost, r.URL.Path)
+			state.posts++
+			var payload createReleaseRequest
+			if err := json.NewDecoder(r.Body).Decode(&payload); err != nil {
+				t.Fatal(err)
+			}
+			if payload.TagName != "v1.2.3" || payload.TargetCommitish != testCommit || payload.Name != "Example v1.2.3" || payload.Body != testNote || payload.Draft || payload.Prerelease {
+				t.Fatalf("create payload = %#v", payload)
+			}
+			if !createMissing {
+				w.WriteHeader(http.StatusConflict)
+				return
+			}
+			writeRelease(t, w, releaseFixture{title: payload.Name})
+		default:
+			t.Fatalf("unexpected request %s %s", r.Method, r.URL.Path)
+		}
+	})
+	server := httptest.NewServer(handler)
+	return server, state
+}
+
+func writeTag(t *testing.T, w http.ResponseWriter, commit string) {
+	t.Helper()
+	w.Header().Set("Content-Type", "application/json")
+	_, _ = fmt.Fprintf(w, `{"name":"v1.2.3","commit":{"sha":%q}}`, commit)
+}
+
+func writeRelease(t *testing.T, w http.ResponseWriter, fixture releaseFixture) {
+	t.Helper()
+	w.Header().Set("Content-Type", "application/json")
+	w.WriteHeader(http.StatusOK)
+	_ = json.NewEncoder(w).Encode(releaseResponse{ID: 10, HTMLURL: "https://gitea.example/releases/10", TagName: "v1.2.3", Name: fixture.title, Body: fixture.bodyOrDefault(), Draft: fixture.draft, Prerelease: fixture.pre})
+}
+
+func (fixture releaseFixture) bodyOrDefault() string {
+	if fixture.body == "" {
+		return testNote
+	}
+	return fixture.body
+}
+
+func assertRequest(t *testing.T, request *http.Request, method, path string) {
+	t.Helper()
+	if request.Method != method || request.URL.Path != path {
+		t.Fatalf("request = %s %s, want %s %s", request.Method, request.URL.Path, method, path)
+	}
+	assertAuth(t, request)
+}
+
+func assertAuth(t *testing.T, request *http.Request) {
+	t.Helper()
+	if got := request.Header.Get("Authorization"); got != "token "+testToken {
+		t.Fatalf("Authorization = %q", got)
+	}
+}
+
+func testClient(server *httptest.Server) Client {
+	return Client{HTTPClient: server.Client()}
+}
+
+func testRequest(baseURL string) Request {
+	return Request{Destination: Destination{BaseURL: baseURL, Owner: "owner", Repository: "project", Token: testToken}, Version: "v1.2.3", Commit: testCommit, Note: testNote}
+}
+
+func failureKind(t *testing.T, err error) FailureKind {
+	t.Helper()
+	var failure *Failure
+	if !errors.As(err, &failure) {
+		t.Fatalf("error type = %T (%v), want *Failure", err, err)
+	}
+	return failure.Kind
+}
+
+func contains(value, substring string) bool {
+	return len(substring) > 0 && len(value) >= len(substring) && strings.Contains(value, substring)
+}