This commit ensures the `TorControlConnection::m_message` buffer doesn't
grow unbounded and exhaust memory, by limiting the number of lines
handled by `TorControlConnection::ProcessBuffer()` to `MAX_LINE_COUNT =
1000`. Now the most memory that can be occupied by `m_message` is on the
order of `MAX_LINE_LENGTH * MAX_LINE_COUNT= 100MB`
Although this is not compliant with the tor control protocol in general,
where commands like `GETINFO ns/all` will likely return thousands of
lines, it is more than sufficient for handling the replies from the
commands that are used by a node:
`AUTHENTICATE`: 1 line:
The server responds with 250 OK on success or 515 Bad
authentication if the authentication cookie is incorrect. Tor closes
the connection on an authentication failure.
https://spec.torproject.org/control-spec/commands.html#authenticate
`GETINFO net/listener/socks`: 2 lines
A quoted, space-separated list of the locations where Tor is
listening...
https://spec.torproject.org/control-spec/commands.html#getinfo
`AUTHCHALLENGE SAFECOOKIE`: 1 line
If the server accepts the command, the server reply format is:
```
"250 AUTHCHALLENGE" SP "SERVERHASH=" ServerHash SP "SERVERNONCE="
ServerNonce CRLF
```
https://spec.torproject.org/control-spec/commands.html#authenticate
`PROTOCOLINFO`: 4-5 lines
The server reply format is:
```
250-PROTOCOLINFO" SP PIVERSION CRLF \*InfoLine "250 OK" CRLF
InfoLine = AuthLine / VersionLine / OtherLine
```
(https://spec.torproject.org/control-spec/commands.html#protocolinfo)
`ADD_ONION`: 2-3 lines for Bitcoin Core's tor control client.
The server reply format is:
```
"250-ServiceID=" ServiceID CRLF
["250-PrivateKey=" KeyType ":" KeyBlob CRLF]
*("250-ClientAuth=" ClientName ":" ClientBlob CRLF)
"250 OK" CRLF
```
...
The server response will only include a private key if the server
was requested to generate a new keypair
...
If client authorization is enabled using the “BasicAuth” flag (which
is v2 only), the service will not be accessible to clients without
valid authorization data (configured with the “HidServAuth” option).
The list of authorized clients is specified with one or more
“ClientAuth” parameters. If “ClientBlob” is not specified for a
client, a new credential will be randomly generated and returned."
https://spec.torproject.org/control-spec/commands.html#add_onion
We don't set the `BasicAuth` flag, so the response will not include any
`ClientAuthLines`.
Adds a check that at the boundary of MAX_LINE_LENGTH, no disconnect
occurs.
Also makes the overlength test message exactly MAX_LINE_LENGTH + 1 to
test the boundary.
Drops the redundant node liveness check, which is covered by the later
check that the node reconnects.
