refactor: move slack url creation to its own package

.cursor/.gitignore

@@ -0,0 +1 @@
+plans/

.gitignore

@@ -5,3 +5,4 @@
 /amtool
 /data/
 /vendor
+.idea

notify/slack/internal/apiurl/apiurl.go

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+// Copyright 2019 Prometheus Team
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package apiurl resolves Slack notifier api_url / api_url_file into outbound HTTP URLs.
+package apiurl
+
+import (
+	"fmt"
+	"os"
+	"strings"
+
+	amcommoncfg "github.com/prometheus/alertmanager/config/common"
+)
+
+// Resolver turns Slack notifier config (api_url or api_url_file) into the actual HTTP
+// URL for each outgoing request (initial post, chat.update, etc.).
+type Resolver struct {
+	apiURL     *amcommoncfg.SecretURL
+	apiURLFile string
+}
+
+// NewResolver captures api_url / api_url_file from config when the notifier is built.
+//
+// APIURLFile is stored as a path only. The file is read from disk on every call to
+// URLForMethod when apiURL is nil—there is no in-memory cache of the URL string.
+// That way changes to the file (rotation, out-of-band updates) apply to the next
+// notification without restarting Alertmanager, matching historical behavior.
+func NewResolver(apiURL *amcommoncfg.SecretURL, apiURLFile string) *Resolver {
+	return &Resolver{apiURL: apiURL, apiURLFile: apiURLFile}
+}
+
+func (r *Resolver) URLForMethod(method string) (string, error) {
+	if method == "" {
+		if r.apiURL != nil {
+			apiURLStr := r.apiURL.String()
+			if apiURLStr != "" {
+				return apiURLStr, nil
+			}
+			return "", fmt.Errorf("slack api url is empty")
+		}
+
+		// Read api_url_file on each resolution; see New.
+		parsed, err := r.getURLFromFile()
+		if err != nil {
+			return "", err
+		}
+		return parsed.String(), nil
+	}
+
+	var baseURL *amcommoncfg.SecretURL
+	if r.apiURL != nil {
+		baseURL = r.apiURL
+	} else {
+		// Read api_url_file on each resolution; see New.
+		parsed, err := r.getURLFromFile()
+		if err != nil {
+			return "", err
+		}
+		secret := amcommoncfg.SecretURL(*parsed)
+		baseURL = &secret
+	}
+
+	return webAPIMethodURL(baseURL, method)
+}
+
+func (r *Resolver) getURLFromFile() (*amcommoncfg.URL, error) {
+	content, err := os.ReadFile(r.apiURLFile)
+	if err != nil {
+		return nil, err
+	}
+	raw := strings.TrimSpace(string(content))
+	return amcommoncfg.ParseURL(raw)
+}
+
+// webAPIMethodURL returns a Slack Web API URL for the given method, using the same
+// Scheme and host as postMessageURL. postMessageURL must be a URL whose path ends
+// with a method name (e.g. .../api/chat.postMessage).
+func webAPIMethodURL(postMessageURL *amcommoncfg.SecretURL, method string) (string, error) {
+	if postMessageURL == nil || postMessageURL.URL == nil {
+		return "", fmt.Errorf("slack api url is nil")
+	}
+
+	// Work on a copy so we never mutate the original URL.
+	u := *postMessageURL.URL
+	if u.Scheme == "" || u.Host == "" {
+		return "", fmt.Errorf("slack api url %q is missing scheme or host", u.String())
+	}
+
+	pathWithoutTrailingSlash := strings.TrimSuffix(u.Path, "/")
+	lastSlashIndex := strings.LastIndex(pathWithoutTrailingSlash, "/")
+	if lastSlashIndex < 0 {
+		return "", fmt.Errorf("slack api url %q has no path segment to replace", u.String())
+	}
+	u.Path = pathWithoutTrailingSlash[:lastSlashIndex+1] + method
+	u.RawQuery = ""
+	u.Fragment = ""
+	return u.String(), nil
+}

notify/slack/internal/apiurl/apiurl_test.go

@@ -0,0 +1,176 @@
+// Copyright The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package apiurl
+
+import (
+	"net/url"
+	"os"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	amcommoncfg "github.com/prometheus/alertmanager/config/common"
+)
+
+const (
+	baseURL                = "https://slack.com"
+	defaultURLWithAPIPath  = baseURL + "/api/chat.postMessage"
+	defaultURLWithFilePath = baseURL + "/file/chat.postMessage"
+
+	addReactionsMethod = "reactions.add"
+	updateChatMethod   = "chat.update"
+)
+
+func TestResolver_URLForMethod_ValidScenarios(t *testing.T) {
+	t.Parallel()
+
+	defaultAPIURLFile := createTempAPIURLFile(t, "test_url_for_method", defaultURLWithFilePath)
+
+	tests := []struct {
+		name       string
+		apiURL     *amcommoncfg.SecretURL
+		apiURLFile string
+		method     string
+		want       string
+	}{
+		{
+			name:       "empty method with apiURL",
+			apiURL:     getSecretURL(t, defaultURLWithAPIPath),
+			apiURLFile: "",
+			method:     "",
+			want:       defaultURLWithAPIPath,
+		},
+		{
+			name:       "empty method without apiURL but with apiURLFile",
+			apiURL:     nil,
+			apiURLFile: defaultAPIURLFile.Name(),
+			method:     "",
+			want:       defaultURLWithFilePath,
+		},
+		{
+			name:       "empty method with apiURL and apiURLFile, should use apiURL",
+			apiURL:     getSecretURL(t, defaultURLWithAPIPath),
+			apiURLFile: defaultAPIURLFile.Name(),
+			method:     "",
+			want:       defaultURLWithAPIPath,
+		},
+		{
+			name:       "method chat.update with apiURL",
+			apiURL:     getSecretURL(t, defaultURLWithAPIPath),
+			apiURLFile: defaultAPIURLFile.Name(),
+			method:     updateChatMethod,
+			want:       baseURL + "/api/" + updateChatMethod,
+		},
+		{
+			name:       "method chat.update with apiURL with trailing slash",
+			apiURL:     getSecretURL(t, defaultURLWithAPIPath+"/"),
+			apiURLFile: defaultAPIURLFile.Name(),
+			method:     updateChatMethod,
+			want:       baseURL + "/api/" + updateChatMethod,
+		},
+		{
+			name:       "method reactions.add with apiURLFile",
+			apiURL:     nil,
+			apiURLFile: defaultAPIURLFile.Name(),
+			method:     addReactionsMethod,
+			want:       baseURL + "/file/" + addReactionsMethod,
+		},
+		{
+			name:       "method reactions.add with apiURLFile with empty spaces",
+			apiURL:     nil,
+			apiURLFile: createTempAPIURLFile(t, "test_url_for_method_with_new_lines_and_spaces", defaultURLWithFilePath+"\n    \n").Name(),
+			method:     addReactionsMethod,
+			want:       baseURL + "/file/" + addReactionsMethod,
+		},
+		{
+			name:       "method reactions.add with apiURLFile with trailing slash",
+			apiURL:     nil,
+			apiURLFile: createTempAPIURLFile(t, "test_url_for_method_with_trailing_slash", defaultURLWithFilePath+"/").Name(),
+			method:     addReactionsMethod,
+			want:       baseURL + "/file/" + addReactionsMethod,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			resolver := NewResolver(tt.apiURL, tt.apiURLFile)
+
+			got, err := resolver.URLForMethod(tt.method)
+			require.NoError(t, err)
+			require.Equal(t, tt.want, got)
+		})
+	}
+}
+
+func TestResolver_URLForMethod_InvalidScenarios(t *testing.T) {
+	t.Parallel()
+
+	invalidURL := amcommoncfg.SecretURL{
+		URL: &url.URL{},
+	}
+	tests := []struct {
+		name             string
+		apiURL           *amcommoncfg.SecretURL
+		apiURLFile       string
+		method           string
+		expectedErrorMsg string
+	}{
+		{
+			name:             "invalid URL",
+			apiURL:           &invalidURL,
+			apiURLFile:       "",
+			method:           "",
+			expectedErrorMsg: "slack api url is empty",
+		},
+		{
+			name:             "no apiURL nor apiURLFile",
+			apiURL:           nil,
+			apiURLFile:       "unknown",
+			method:           "",
+			expectedErrorMsg: "open unknown: no such file or directory",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			resolver := NewResolver(tt.apiURL, tt.apiURLFile)
+
+			_, err := resolver.URLForMethod(tt.method)
+			require.Error(t, err)
+			require.Contains(t, err.Error(), tt.expectedErrorMsg)
+		})
+	}
+}
+
+func getSecretURL(t *testing.T, raw string) *amcommoncfg.SecretURL {
+	t.Helper()
+	u, err := amcommoncfg.ParseURL(raw)
+	require.NoError(t, err)
+	s := amcommoncfg.SecretURL(*u)
+	return &s
+}
+
+func createTempAPIURLFile(t *testing.T, pattern, url string) *os.File {
+	t.Helper()
+	apiURLFileWithNewLines, err := os.CreateTemp(t.TempDir(), pattern)
+	require.NoError(t, err)
+	_, err = apiURLFileWithNewLines.WriteString(url)
+	require.NoError(t, err)
+	require.NoError(t, apiURLFileWithNewLines.Close())
+	return apiURLFileWithNewLines
+}