rpc: fix MatchMirror substring ambiguity for exact-match names

rpc/rpc.go

@@ -129,18 +129,40 @@ func (c *CLI) MatchMirror(ctx context.Context, in *MatchRequest) (*MatchReply, e
 		return nil, fmt.Errorf("can't fetch the list of mirrors: %w", err)
 	}
 
-	reply := &MatchReply{}
+	reply := &MatchReply{
+		Mirrors: matchMirrorsByPattern(mirrors, in.Pattern),
+	}
+
+	return reply, nil
+}
+
+// matchMirrorsByPattern returns a list of mirrors:
+// - if the pattern matches a mirror's name exactly, only that mirror is returned
+// - otherwise, all mirrors containing the pattern as a substring are returned
+// - all matches are case-insensitive
+// This allows a mirror whose name is a substring of other mirror names
+// (e.g. "fcix.net" vs. "mirror.fcix.net") to still be matched unambiguously.
+func matchMirrorsByPattern(mirrors map[int]string, pattern string) []*MirrorID {
+	lowerPattern := strings.ToLower(pattern)
 
+	var matches []*MirrorID
 	for id, name := range mirrors {
-		if strings.Contains(strings.ToLower(name), strings.ToLower(in.Pattern)) {
-			reply.Mirrors = append(reply.Mirrors, &MirrorID{
+		lowerName := strings.ToLower(name)
+		if lowerName == lowerPattern {
+			return []*MirrorID{{
+				ID:   int32(id),
+				Name: name,
+			}}
+		}
+		if strings.Contains(lowerName, lowerPattern) {
+			matches = append(matches, &MirrorID{
 				ID:   int32(id),
 				Name: name,
 			})
 		}
 	}
 
-	return reply, nil
+	return matches
 }
 
 func (c *CLI) ChangeStatus(ctx context.Context, in *ChangeStatusRequest) (*empty.Empty, error) {

rpc/rpc_test.go

@@ -0,0 +1,91 @@
+// Copyright (c) 2026 Amit Mishra
+// Licensed under the MIT license
+
+package rpc
+
+import (
+	"sort"
+	"testing"
+)
+
+func names(mirrors []*MirrorID) []string {
+	var out []string
+	for _, m := range mirrors {
+		out = append(out, m.Name)
+	}
+	sort.Strings(out)
+	return out
+}
+
+func TestMatchMirrorsByPattern(t *testing.T) {
+	// Regression test for https://github.com/videolabs/mirrorbits/issues/134
+	tests := []struct {
+		name    string
+		mirrors map[int]string
+		pattern string
+		want    []string
+	}{
+		{
+			name: "exact match takes priority over substring matches",
+			mirrors: map[int]string{
+				1: "fcix.net",
+				2: "mirror.fcix.net",
+				3: "paducahix.mm.fcix.net",
+				4: "forksystems.mm.fcix.net",
+			},
+			pattern: "fcix.net",
+			want:    []string{"fcix.net"},
+		},
+		{
+			name: "exact match is case-insensitive",
+			mirrors: map[int]string{
+				1: "FCIX.net",
+				2: "mirror.fcix.net",
+			},
+			pattern: "fcix.net",
+			want:    []string{"FCIX.net"},
+		},
+		{
+			name: "multiple substring matches returned when no exact match",
+			mirrors: map[int]string{
+				1: "mirror.fcix.net",
+				2: "paducahix.mm.fcix.net",
+			},
+			pattern: "fcix.net",
+			want:    []string{"mirror.fcix.net", "paducahix.mm.fcix.net"},
+		},
+		{
+			name: "no match returns empty",
+			mirrors: map[int]string{
+				1: "alpha",
+				2: "beta",
+			},
+			pattern: "gamma",
+			want:    nil,
+		},
+		{
+			name: "single substring match",
+			mirrors: map[int]string{
+				1: "mirror.example.com",
+				2: "other.example.org",
+			},
+			pattern: "example.com",
+			want:    []string{"mirror.example.com"},
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			got := names(matchMirrorsByPattern(tc.mirrors, tc.pattern))
+
+			if len(got) != len(tc.want) {
+				t.Fatalf("matchMirrorsByPattern(%q) = %v, want %v", tc.pattern, got, tc.want)
+			}
+			for i := range tc.want {
+				if got[i] != tc.want[i] {
+					t.Fatalf("matchMirrorsByPattern(%q) = %v, want %v", tc.pattern, got, tc.want)
+				}
+			}
+		})
+	}
+}