Restructure modules

Modules are now separated into a fashion where the library can be used
for most use cases, without needing to compile the rest.

The core of serenity, with no features enabled, contains only the
struct (model) definitions, constants, and prelude. Models do not have
most functions compiled in, as that is separated into the `model`
feature.

The `client` module has been split into 3 modules: `client`, `gateway`,
and `http`.

`http` contains functions to interact with the REST API. `gateway`
contains the Shard to interact with the gateway, requiring `http` for
retrieving the gateway URL. `client` requires both of the other features
and acts as an abstracted interface over both the gateway and REST APIs,
handling the event loop.

The `builder` module has been separated from `utils`, and can now be
optionally compiled in. It and the `http` feature are required by the
`model` feature due to a large number of methods requiring access to
them.

`utils` now contains a number of utilities, such as the Colour struct, the
`MessageBuilder`, and mention parsing functions.

Each of the original `ext` modules are still featured, with `cache` not
requiring any feature to be enabled, `framework` requiring the `client`,
`model`, and `utils`, and `voice` requiring `gateway`.

In total the features and their requirements are:

- `builder`: none
- `cache`: none
- `client`: `gateway`, `http`
- `framework`: `client`, `model`, `utils`
- `gateway`: `http`
- `http`: none
- `model`: `builder`, `http`
- `utils`: none
- `voice`: `gateway`

The default features are `builder`, `cache`, `client`, `framework`,
`gateway`, `model`, `http`, and `utils`.

To help with forwards compatibility, modules have been re-exported from
their original locations.

1 files changed, 44 insertions, 0 deletions

diff --git a/src/gateway/error.rs b/src/gateway/error.rs
new file mode 100644
index 0000000..57fa1cf
--- /dev/null
+++ b/src/gateway/error.rs
@@ -0,0 +1,44 @@
+use std::error::Error as StdError;
+use std::fmt::{self, Display};
+
+/// An error that occurred while attempting to deal with the gateway.
+///
+/// Note that - from a user standpoint - there should be no situation in which
+/// you manually handle these.
+#[derive(Clone, Debug)]
+pub enum Error {
+    /// There was an error building a URL.
+    BuildingUrl,
+    /// The connection closed, potentially uncleanly.
+    Closed(Option<u16>, String),
+    /// Expected a Hello during a handshake
+    ExpectedHello,
+    /// Expected a Ready or an InvalidateSession
+    InvalidHandshake,
+    /// An indicator that an unknown opcode was received from the gateway.
+    InvalidOpCode,
+    /// When a session Id was expected (for resuming), but was not present.
+    NoSessionId,
+    /// Failed to reconnect after a number of attempts.
+    ReconnectFailure,
+}
+
+impl Display for Error {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.write_str(self.description())
+    }
+}
+
+impl StdError for Error {
+    fn description(&self) -> &str {
+        match *self {
+            Error::BuildingUrl => "Error building url",
+            Error::Closed(_, _) => "Connection closed",
+            Error::ExpectedHello => "Expected a Hello",
+            Error::InvalidHandshake => "Expected a valid Handshake",
+            Error::InvalidOpCode => "Invalid OpCode",
+            Error::NoSessionId => "No Session Id present when required",
+            Error::ReconnectFailure => "Failed to Reconnect",
+        }
+    }
+}