read the exposure scope from the compose file, drop the _EXPOSE variable

The variable declared an intent and changed nothing: it fed the report and
never the binding, so it could say public while the file published on the
loopback, or the reverse. A declaration that cannot be wrong is better than one
that has to be kept in step.

The scope is now which binding the file asks for, read from the compose files
as written: ${MYOS_BIND_PUBLIC} is public, a hand-written address is pinned,
and a bare '- 80' or '9000:9000' is unbound, meaning docker opens it on every
address and nobody chose that. --strict fails on those.

Reading the resolved configuration instead would lose the distinction: every
form ends up as a plain address, and an unbound port looks exactly like a
deliberate public one.

What is left to configure per host is the address of each scope, which is the
part that belongs to the host rather than to the stack.

spec/unit/expose_spec.sh

@@ -54,26 +54,47 @@ Describe 'lib/expose.sh'
     End
   End
 
-  Describe 'myos_expose_scope'
-    It 'is private unless the stack says otherwise'
-      When call myos_expose_scope HOST_FTPS ftps 21
-      The output should equal "private"
+  Describe 'myos_expose_declared'
+    setup() { MYOS_TMP=$(mktemp -d "${TMPDIR:-/tmp}/myos-exp.XXXXXX"); }
+    cleanup() { rm -rf "$MYOS_TMP"; }
+    BeforeEach setup
+    AfterEach cleanup
+
+    # The scope is not declared on the side: it is which binding the compose
+    # file asks for. Reading the resolved configuration instead would lose the
+    # difference, since every form ends up as a plain address.
+    It 'reads the scope out of the binding each port asks for'
+      printf 'services:\n  a:\n    ports:\n' > "$MYOS_TMP/c.yml"
+      printf '      - "${MYOS_BIND_PUBLIC}:443:443"\n' >> "$MYOS_TMP/c.yml"
+      printf '      - "${MYOS_BIND_PRIVATE}::8080"\n' >> "$MYOS_TMP/c.yml"
+      printf '      - "${MYOS_BIND_MESH}::7946"\n' >> "$MYOS_TMP/c.yml"
+      printf '      - "127.0.0.1:5432:5432"\n' >> "$MYOS_TMP/c.yml"
+      printf '      - 80\n' >> "$MYOS_TMP/c.yml"
+      When call myos_expose_declared "$MYOS_TMP/c.yml"
+      The line 1 should equal "a|443|public"
+      The line 2 should equal "a|8080|private"
+      The line 3 should equal "a|7946|mesh"
+      The line 4 should equal "a|5432|pinned"
+      The line 5 should equal "a|80|unbound"
     End
-    It 'reads the scope of one port'
-      HOST_FTPS_SERVICE_21_EXPOSE=public
-      When call myos_expose_scope HOST_FTPS ftps 21
-      The output should equal "public"
+
+    It 'calls a plain host:container mapping unbound, because it is'
+      printf 'services:\n  a:\n    ports:\n      - "9000:9000"\n      - 25:25\n' > "$MYOS_TMP/c.yml"
+      When call myos_expose_declared "$MYOS_TMP/c.yml"
+      The line 1 should equal "a|9000|unbound"
+      The line 2 should equal "a|25|unbound"
     End
-    It 'reads the scope of a whole stack'
-      HOST_FTPS_SERVICE_EXPOSE=mesh
-      When call myos_expose_scope HOST_FTPS ftps 21
-      The output should equal "mesh"
+
+    It 'keeps the protocol out of the port'
+      printf 'services:\n  a:\n    ports:\n      - 4001/udp\n' > "$MYOS_TMP/c.yml"
+      When call myos_expose_declared "$MYOS_TMP/c.yml"
+      The output should equal "a|4001|unbound"
     End
-    It 'prefers the port over the stack'
-      HOST_FTPS_SERVICE_EXPOSE=mesh
-      HOST_FTPS_SERVICE_21_EXPOSE=public
-      When call myos_expose_scope HOST_FTPS ftps 21
-      The output should equal "public"
+
+    It 'reports nothing for a service that publishes nothing'
+      printf 'services:\n  a:\n    image: alpine\n' > "$MYOS_TMP/c.yml"
+      When call myos_expose_declared "$MYOS_TMP/c.yml"
+      The output should equal ""
     End
   End
 End