notify: pack Feishu digests against the serialized request body

A Feishu digest sends every item as its own card element. The packing counted the text of each line only, not the element around it (about 52 bytes of JSON per item, plus whatever the encoding escapes) nor the rest of the body beyond a fixed 320-byte reserve. A digest of 500 short lines therefore left as a single request of 41846 bytes, while Feishu rejects a request body over 20 KB as a whole. feishuCard now adds whole items while the request body, measured as it is serialized, stays within feishuMaxCardBytes: each item element by its JSON encoding, the card around the items (header, intro, platform link) by encoding it for the number of items kept, and what Send adds around the card (msg_type, timestamp, sign) as feishuEnvelopeBytes, which the new test pins to the bytes on the wire. Unchanged: the first item of a digest is always kept and its text is truncated to the same budget, single pushes are built as before, and the other channels still pack with packItemCount.
2026-11-13 11:40:53 +08:00 · 2026-11-10 16:28:30 +01:00
parent 3b6eb2fd2c
commit 542582e3bc
2 changed files with 164 additions and 20 deletions
@@ -126,6 +126,12 @@ func feishuSeverityTemplate(severity string) string {
 // clearly below that limit to also cover JSON wrapping overhead.
 const feishuMaxCardBytes = 16000

+// feishuEnvelopeBytes is the size of what Send serializes around the card when a
+// signing secret is configured (without one the request is smaller):
+//
+//	{"card":…,"msg_type":"interactive","sign":"<44 characters>","timestamp":"<10 digits>"}
+const feishuEnvelopeBytes = 113
+
 // feishuCard builds the interactive card and returns it along with the **number
 // of items actually written**. kept serves the same purpose as in markdownBody:
 // only items that actually made it into the card should be marked as sent.
@@ -135,23 +141,51 @@ func feishuCard(m Message) (map[string]any, int) {
 	// TruncateBytes plays in markdownBody. With the summary or asset limit set to
 	// 0 an item has no other bound, and an oversized card loses the whole message.
 	budget := feishuMaxCardBytes - markdownReservedBytes
+	card := map[string]any{
+		"config": map[string]any{"wide_screen_mode": true},
+		"header": map[string]any{"title": map[string]any{"tag": "plain_text", "content": markdownTitle(m)}},
+	}
+	if len(m.Items) > 0 {
+		card["header"].(map[string]any)["template"] = feishuSeverityTemplate(m.Items[0].Severity)
+	}
 	elements := []any{}
 	kept := 0
 	if m.Batch {
-		// Pack whole items first, then assemble the header: the header must state
-		// "the remaining N items will continue in the next message", and N must
-		// come from the number of items that actually fit.
-		kept = packItemCount(m.Items, feishuMaxCardBytes, markdownReservedBytes, "", byteSize, func(it Item, idx int) string {
-			return feishuBatchLine(it, idx+1, lim)
-		})
-		items := m.Items[:kept]
-		elements = append(elements, feishuMarkdownDiv(markdownBatchIntro(m, items, len(m.Items))))
-		for i, it := range items {
-			elements = append(elements, feishuMarkdownDiv(TruncateBytes(feishuBatchLine(it, i+1, lim), budget)))
+		// digest assembles the elements of a digest card around the lines of its
+		// first n items. The intro must state "the remaining N items will continue
+		// in the next message", and N must come from the number of items that
+		// actually fit.
+		digest := func(n int, lines []any) []any {
+			out := []any{feishuMarkdownDiv(markdownBatchIntro(m, m.Items[:n], len(m.Items)))}
+			out = append(out, lines...)
+			if m.HomeURL != "" {
+				out = append(out, feishuButton("View all on the platform", m.HomeURL))
+			}
+			return out
 		}
-		if m.HomeURL != "" {
-			elements = append(elements, feishuButton("View all on the platform", m.HomeURL))
+		// Pack whole items (see packItemCount) against the request body as it will
+		// be serialized, not against the text of the lines. Each line is sent as
+		// its own element: about 52 bytes of JSON around the text, plus whatever
+		// the encoding escapes. Counted as text alone, several hundred short lines
+		// left as one request of more than twice the 20 KB limit. The rest of the
+		// body is measured too: it changes with the number of items kept (the
+		// intro) and with the platform link.
+		//
+		// The first item is always kept: otherwise one oversized item would jam
+		// the whole batch in place. Its text is truncated to budget.
+		var lines []any
+		used := 0
+		for i, it := range m.Items {
+			line := feishuMarkdownDiv(TruncateBytes(feishuBatchLine(it, i+1, lim), budget))
+			used += feishuJSONSize(line) + 1 // the element and its separating comma
+			card["elements"] = digest(i+1, nil)
+			if i > 0 && feishuEnvelopeBytes+feishuJSONSize(card)+used > feishuMaxCardBytes {
+				break
+			}
+			lines = append(lines, line)
 		}
+		kept = len(lines)
+		elements = digest(kept, lines)
 	} else if len(m.Items) > 0 {
 		kept = 1
 		it := m.Items[0]
@@ -161,17 +195,16 @@ func feishuCard(m Message) (map[string]any, int) {
 		}
 	}

-	card := map[string]any{
-		"config":   map[string]any{"wide_screen_mode": true},
-		"header":   map[string]any{"title": map[string]any{"tag": "plain_text", "content": markdownTitle(m)}},
-		"elements": elements,
-	}
-	if len(m.Items) > 0 {
-		card["header"].(map[string]any)["template"] = feishuSeverityTemplate(m.Items[0].Severity)
-	}
+	card["elements"] = elements
 	return card, kept
 }

+// feishuJSONSize returns the number of bytes v takes in the request body.
+func feishuJSONSize(v any) int {
+	raw, _ := json.Marshal(v)
+	return len(raw)
+}
+
 func feishuMarkdownDiv(content string) map[string]any {
 	return map[string]any{"tag": "div", "text": map[string]any{"tag": "lark_md", "content": content}}
 }
@@ -1,6 +1,11 @@
 package notify

 import (
+	"context"
+	"encoding/json"
+	"io"
+	"net/http"
+	"net/http/httptest"
 	"strings"
 	"testing"
 	"unicode/utf8"
@@ -105,6 +110,112 @@ func TestFeishuPackingReportsKept(t *testing.T) {
 	}
 }

+// TestFeishuDigestBodiesStayWithinCardLimit covers digests of many short items.
+//
+// Every digest line is sent as its own card element, which costs about 52 bytes
+// of JSON around the text plus whatever the encoding escapes. The packing used
+// to count the text only, so a digest of several hundred short lines left as one
+// request of more than twice Feishu's 20 KB limit, and Feishu rejects such a
+// request as a whole.
+//
+// The digest is sent the way the delivery engine does it: the items a message
+// did not hold go into the next one. The bodies measured are the real ones sent
+// on the wire, signature included. No item may be lost on the way: across the
+// messages, every item appears exactly once and in order.
+func TestFeishuDigestBodiesStayWithinCardLimit(t *testing.T) {
+	const total = 500
+
+	short := batchMsg(total)
+	for i := range short.Items {
+		short.Items[i].Assets = nil
+	}
+	// The JSON encoding escapes quotes, angle brackets and ampersands, and the
+	// backslashes the lark_md escaping put in before it: these titles take
+	// several times their length once serialized.
+	escaped := batchMsg(total)
+	for i := range escaped.Items {
+		escaped.Items[i].Name = `<a href="x">R&D</a> vuln` + itoa(i+1)
+	}
+
+	cases := []struct {
+		name string
+		m    Message
+	}{
+		{"short lines without assets", short},
+		{"short lines with one asset", batchMsg(total)},
+		{"lines that grow when serialized", escaped},
+	}
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			var raw []byte
+			srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+				raw, _ = io.ReadAll(r.Body)
+				_, _ = io.WriteString(w, `{"code":0,"msg":"success"}`)
+			}))
+			defer srv.Close()
+			cfg := map[string]any{"webhook": srv.URL, "secret": "SECtest123"}
+
+			m := tc.m
+			seen, messages := 0, 0
+			for len(m.Items) > 0 {
+				kept, err := (feishuChannel{}).Send(context.Background(), cfg, m)
+				if err != nil {
+					t.Fatalf("message %d: delivery failed: %v", messages+1, err)
+				}
+				messages++
+				if len(raw) > feishuMaxCardBytes {
+					t.Fatalf("message %d: request body of %d bytes exceeds the limit of %d (%d of %d items left to send)",
+						messages, len(raw), feishuMaxCardBytes, len(m.Items), total)
+				}
+				var body struct {
+					Card json.RawMessage `json:"card"`
+				}
+				var card struct {
+					Elements []struct {
+						Tag  string `json:"tag"`
+						Text struct {
+							Content string `json:"content"`
+						} `json:"text"`
+					} `json:"elements"`
+				}
+				if err := json.Unmarshal(raw, &body); err != nil {
+					t.Fatalf("message %d: request body is not valid JSON: %v", messages, err)
+				}
+				if err := json.Unmarshal(body.Card, &card); err != nil {
+					t.Fatalf("message %d: card is not valid JSON: %v", messages, err)
+				}
+				// The packing counts what Send adds around the card as a constant.
+				if got := len(raw) - len(body.Card); got != feishuEnvelopeBytes {
+					t.Fatalf("message %d: %d bytes around the card, feishuEnvelopeBytes says %d", messages, got, feishuEnvelopeBytes)
+				}
+				// Element 0 is the intro; the button, when present, is not a div.
+				lines := 0
+				for _, el := range card.Elements[1:] {
+					if el.Tag != "div" {
+						continue
+					}
+					lines++
+					if want := "vuln" + itoa(seen+lines) + "**"; !strings.Contains(el.Text.Content, want) {
+						t.Fatalf("message %d: line %d should be item %d (%q), got %q", messages, lines, seen+lines, want, el.Text.Content)
+					}
+				}
+				if kept <= 0 || kept != lines {
+					t.Fatalf("message %d: %d items reported as delivered, the body holds %d", messages, kept, lines)
+				}
+				t.Logf("message %d: %d items, %d bytes", messages, kept, len(raw))
+				seen += kept
+				m.Items = m.Items[kept:]
+			}
+			if seen != total {
+				t.Fatalf("%d items went out across %d messages, want %d", seen, messages, total)
+			}
+			if messages < 2 {
+				t.Fatalf("%d items should not fit one message", total)
+			}
+		})
+	}
+}
+
 func TestWebhookAndEmailReportAllItems(t *testing.T) {
 	// These two channels do not truncate the body; the whole batch counts as
 	// delivered.