imapclient: first step towards making package usable as imap client with other imap servers, and minor imapserver bug fix

The imapclient needs more changes, like more strict parsing, before it can be a
generally usable IMAP client, these are a few steps towards that.

- Fix a bug in the imapserver METADATA responses for TOOMANY and MAXSIZE.
- Split low-level IMAP protocol handling (new Proto type) from the higher-level
  client command handling (existing Conn type). The idea is that some simple
  uses of IMAP can get by with just using these commands, while more intricate
  uses of IMAP (like a synchronizing client that needs to talk to all kinds of
  servers with different behaviours and implemented extensions) can write custom
  commands and read untagged responses or command completion results
  explicitly. The lower-level method names have clearer names now, like
  ReadResponse instead of Response.
- Merge the untagged responses and (command completion) "Result" into a new
  type Response. Makes function signatures simpler. And make Response implement
  the error interface, and change command methods to return the Response as error
  if the result is NO or BAD. Simplifies error handling, and still provides the
  option to continue after a NO or BAD.
- Add UIDSearch/MSNSearch commands, with a custom "search program", so mostly
  to indicate these commands exist.
- More complete coverage of types for response codes, for easier handling.
- Automatically handle any ENABLED or CAPABILITY untagged response or response
  code for IMAP command methods on type Conn.
- Make difference between MSN vs UID versions of
  FETCH/STORE/SEARCH/COPY/MOVE/REPLACE commands more clear. The original MSN
  commands now have MSN prefixed to their name, so they are grouped together in
  the documentation.
- Document which capabilities are needed for a command.

imapserver/append_test.go

@@ -50,14 +50,14 @@ func testAppend(t *testing.T, uidonly bool) {
 	tc2.client.Select("inbox")
 
 	tc2.transactf("no", "append nobox (\\Seen) \" 1-Jan-2022 10:10:00 +0100\" {1}")
-	tc2.xcode("TRYCREATE")
+	tc2.xcodeWord("TRYCREATE")
 
 	tc2.transactf("no", "append expungebox (\\Seen) {1}")
-	tc2.xcode("TRYCREATE")
+	tc2.xcodeWord("TRYCREATE")
 
 	tc2.transactf("ok", "append inbox (\\Seen Label1 $label2) \" 1-Jan-2022 10:10:00 +0100\" {1+}\r\nx")
 	tc2.xuntagged(imapclient.UntaggedExists(1))
-	tc2.xcodeArg(imapclient.CodeAppendUID{UIDValidity: 1, UIDs: xparseUIDRange("1")})
+	tc2.xcode(imapclient.CodeAppendUID{UIDValidity: 1, UIDs: xparseUIDRange("1")})
 
 	tc.transactf("ok", "noop")
 	flags := imapclient.FetchFlags{`\Seen`, "$label2", "label1"}
@@ -67,11 +67,11 @@ func testAppend(t *testing.T, uidonly bool) {
 
 	tc2.transactf("ok", "append inbox (\\Seen) \" 1-Jan-2022 10:10:00 +0100\" UTF8 (~{47+}\r\ncontent-type: just completely invalid;;\r\n\r\ntest)")
 	tc2.xuntagged(imapclient.UntaggedExists(2))
-	tc2.xcodeArg(imapclient.CodeAppendUID{UIDValidity: 1, UIDs: xparseUIDRange("2")})
+	tc2.xcode(imapclient.CodeAppendUID{UIDValidity: 1, UIDs: xparseUIDRange("2")})
 
 	tc2.transactf("ok", "append inbox (\\Seen) \" 1-Jan-2022 10:10:00 +0100\" UTF8 (~{31+}\r\ncontent-type: text/plain;\n\ntest)")
 	tc2.xuntagged(imapclient.UntaggedExists(3))
-	tc2.xcodeArg(imapclient.CodeAppendUID{UIDValidity: 1, UIDs: xparseUIDRange("3")})
+	tc2.xcode(imapclient.CodeAppendUID{UIDValidity: 1, UIDs: xparseUIDRange("3")})
 
 	// Messages that we cannot parse are marked as application/octet-stream. Perhaps
 	// the imap client knows how to deal with them.
@@ -92,7 +92,7 @@ func testAppend(t *testing.T, uidonly bool) {
 	tc.transactf("ok", "noop") // Flush pending untagged responses.
 	tc.transactf("ok", "append inbox {6+}\r\ntest\r\n ~{6+}\r\ntost\r\n")
 	tc.xuntagged(imapclient.UntaggedExists(5))
-	tc.xcodeArg(imapclient.CodeAppendUID{UIDValidity: 1, UIDs: xparseUIDRange("4:5")})
+	tc.xcode(imapclient.CodeAppendUID{UIDValidity: 1, UIDs: xparseUIDRange("4:5")})
 
 	// Cancelled with zero-length message.
 	tc.transactf("no", "append inbox {6+}\r\ntest\r\n {0+}\r\n")
@@ -106,7 +106,7 @@ func testAppend(t *testing.T, uidonly bool) {
 	tclimit.xuntagged(imapclient.UntaggedExists(1))
 	// Second message would take account past limit.
 	tclimit.transactf("no", "append inbox (\\Seen Label1 $label2) \" 1-Jan-2022 10:10:00 +0100\" {1+}\r\nx")
-	tclimit.xcode("OVERQUOTA")
+	tclimit.xcodeWord("OVERQUOTA")
 
 	// Empty mailbox.
 	if uidonly {
@@ -119,10 +119,10 @@ func testAppend(t *testing.T, uidonly bool) {
 	// Multiappend with first message within quota, and second message with sync
 	// literal causing quota error. Request should get error response immediately.
 	tclimit.transactf("no", "append inbox {1+}\r\nx {100000}")
-	tclimit.xcode("OVERQUOTA")
+	tclimit.xcodeWord("OVERQUOTA")
 
 	// Again, but second message now with non-sync literal, which is fully consumed by server.
-	tclimit.client.Commandf("", "append inbox {1+}\r\nx {4000+}")
+	tclimit.client.WriteCommandf("", "append inbox {1+}\r\nx {4000+}")
 	buf := make([]byte, 4000, 4002)
 	for i := range buf {
 		buf[i] = 'x'
@@ -131,5 +131,5 @@ func testAppend(t *testing.T, uidonly bool) {
 	_, err := tclimit.client.Write(buf)
 	tclimit.check(err, "write append message")
 	tclimit.response("no")
-	tclimit.xcode("OVERQUOTA")
+	tclimit.xcodeWord("OVERQUOTA")
 }