feat(qsl): credit line at the foot of the default QSL e-mail

"Designed & sent by OpsLog — https://github.com/GregTroar/OpsLog/releases/latest"
now closes the default body, so a fresh install sends it without being asked.

Put in the TEMPLATE, not appended at send time. Two consequences, both of them
the point: an operator who does not want it deletes the line once and it is
gone, and one who has already written their own body never sees it appear —
a stored template is returned verbatim and the default is only the fallback.
Appending it at send would have made it unremovable, which is not a thing to do
to somebody's outgoing mail.

The link is the human release page. updateCheckURL sits next to it in update.go
and answers JSON, which is the easy mistake here — a correspondent who clicks
the credit gets a download page, and a test says so.

app_qsl_designer.go

@@ -45,9 +45,20 @@ const appQSLCardSentField = "APP_OPSLOG_QSL_SENT"
 // (please send one). Independent of ADIF qsl_rcvd, like the sent field.
 const appQSLCardRcvdField = "APP_OPSLOG_QSL_RCVD"
 
+// qslCredit closes the default QSL e-mail: who made the card, and where the
+// recipient can get the same program.
+//
+// A DEFAULT, not a signature. It lives in the body template like every other
+// line, so an operator who does not want it deletes it once and it is gone —
+// and one who has already written their own body never sees it appear, because
+// a stored template is returned verbatim and the default is only the fallback.
+// Appending it at send time instead would have made it unremovable, which is
+// not a thing to do to someone's outgoing mail.
+const qslCredit = "--\nDesigned & sent by OpsLog — " + releasesPageURL
+
 const (
 	defaultQSLEmailSubject = "eQSL — {CALL} de {MYCALL}"
-	defaultQSLEmailBody    = "Hi,\n\nThank you for our QSO! Please find attached your eQSL card.\n\n{DATE}  ·  {BAND}  ·  {MODE}\n\n73,\n{MYCALL}"
+	defaultQSLEmailBody    = "Hi,\n\nThank you for our QSO! Please find attached your eQSL card.\n\n{DATE}  ·  {BAND}  ·  {MODE}\n\n73,\n{MYCALL}\n\n" + qslCredit
 )
 
 // qslDir is the root of all designer artifacts: templates/<id>/ and outbox/.

changelog.json

@@ -4,11 +4,13 @@
     "date": "",
     "en": [
       "Right-click: update the US county of the selected contacts from the ULS database, replacing a county since renamed or abolished.",
-      "A QSO logged from WSJT-X, MSHV or a net now appears in Recent QSOs at once, instead of waiting for a delayed auto-upload to send it."
+      "A QSO logged from WSJT-X, MSHV or a net now appears in Recent QSOs at once, instead of waiting for a delayed auto-upload to send it.",
+      "New installs: the default QSL e-mail ends with a credit line and a link to OpsLog. It is part of the template, so delete it if you'd rather not."
     ],
     "fr": [
       "Clic droit : mettre à jour le comté US des contacts sélectionnés depuis la base ULS, pour remplacer un comté renommé ou supprimé.",
-      "Un QSO logué depuis WSJT-X, MSHV ou un net apparaît aussitôt dans les QSO récents, sans attendre l’envoi d’un upload automatique différé."
+      "Un QSO logué depuis WSJT-X, MSHV ou un net apparaît aussitôt dans les QSO récents, sans attendre l’envoi d’un upload automatique différé.",
+      "Nouvelles installations : le mail QSL par défaut se termine par une ligne de crédit et un lien vers OpsLog. Elle fait partie du modèle, supprimable."
     ]
   },
   {

qslcredit_test.go

@@ -0,0 +1,39 @@
+package main
+
+import (
+	"strings"
+	"testing"
+)
+
+// The default QSL e-mail closes with a credit line carrying the download page.
+//
+// It is part of the BODY TEMPLATE, deliberately: an operator who does not want
+// it deletes it once, and one who already wrote their own body never sees it,
+// because a stored template is returned verbatim and the default is only the
+// fallback. Appending it at send time would have made it unremovable.
+func TestQSLCreditIsInTheDefaultBody(t *testing.T) {
+	if !strings.HasSuffix(defaultQSLEmailBody, qslCredit) {
+		t.Errorf("the default QSL e-mail does not end with the credit line:\n%q", defaultQSLEmailBody)
+	}
+	// The body still has to be a usable template — the credit is added to it,
+	// not in place of it.
+	for _, v := range []string{"{DATE}", "{BAND}", "{MODE}", "{MYCALL}"} {
+		if !strings.Contains(defaultQSLEmailBody, v) {
+			t.Errorf("the default QSL e-mail lost %s", v)
+		}
+	}
+}
+
+// The link must be the page a person can read. updateCheckURL sits beside it and
+// answers JSON — sending a correspondent there is the easy mistake to make.
+func TestQSLCreditLinksTheHumanPage(t *testing.T) {
+	if !strings.Contains(qslCredit, releasesPageURL) {
+		t.Errorf("credit %q does not carry the releases page", qslCredit)
+	}
+	if strings.Contains(qslCredit, "api.github.com") {
+		t.Errorf("credit %q points at the update API, which answers JSON to whoever clicks it", qslCredit)
+	}
+	if !strings.Contains(qslCredit, "OpsLog") {
+		t.Errorf("credit %q does not name OpsLog", qslCredit)
+	}
+}

update.go

@@ -23,6 +23,11 @@ import (
 // build (the exe lives there; source stays on Gitea). Adjust the repo if needed.
 const updateCheckURL = "https://api.github.com/repos/GregTroar/OpsLog/releases/latest"
 
+// releasesPageURL is the same release, for people rather than for the updater:
+// the API address above answers JSON, so it is not something to put in front of
+// an operator who followed a link out of a QSL e-mail.
+const releasesPageURL = "https://github.com/GregTroar/OpsLog/releases/latest"
+
 // UpdateInfo is the result of the version check.
 type UpdateInfo struct {
 	Current     string `json:"current"`      // this build's version (appVersion)