Replace ExternalStream with new ByteStream type (#12774)

# Description
This PR introduces a `ByteStream` type which is a `Read`-able stream of
bytes. Internally, it has an enum over three different byte stream
sources:
```rust
pub enum ByteStreamSource {
    Read(Box<dyn Read + Send + 'static>),
    File(File),
    Child(ChildProcess),
}
```

This is in comparison to the current `RawStream` type, which is an
`Iterator<Item = Vec<u8>>` and has to allocate for each read chunk.

Currently, `PipelineData::ExternalStream` serves a weird dual role where
it is either external command output or a wrapper around `RawStream`.
`ByteStream` makes this distinction more clear (via `ByteStreamSource`)
and replaces `PipelineData::ExternalStream` in this PR:
```rust
pub enum PipelineData {
    Empty,
    Value(Value, Option<PipelineMetadata>),
    ListStream(ListStream, Option<PipelineMetadata>),
    ByteStream(ByteStream, Option<PipelineMetadata>),
}
```

The PR is relatively large, but a decent amount of it is just repetitive
changes.

This PR fixes #7017, fixes #10763, and fixes #12369.

This PR also improves performance when piping external commands. Nushell
should, in most cases, have competitive pipeline throughput compared to,
e.g., bash.
| Command | Before (MB/s) | After (MB/s) | Bash (MB/s) |
| -------------------------------------------------- | -------------:|
------------:| -----------:|
| `throughput \| rg 'x'` | 3059 | 3744 | 3739 |
| `throughput \| nu --testbin relay o> /dev/null` | 3508 | 8087 | 8136 |

# User-Facing Changes
- This is a breaking change for the plugin communication protocol,
because the `ExternalStreamInfo` was replaced with `ByteStreamInfo`.
Plugins now only have to deal with a single input stream, as opposed to
the previous three streams: stdout, stderr, and exit code.
- The output of `describe` has been changed for external/byte streams.
- Temporary breaking change: `bytes starts-with` no longer works with
byte streams. This is to keep the PR smaller, and `bytes ends-with`
already does not work on byte streams.
- If a process core dumped, then instead of having a `Value::Error` in
the `exit_code` column of the output returned from `complete`, it now is
a `Value::Int` with the negation of the signal number.

# After Submitting
- Update docs and book as necessary
- Release notes (e.g., plugin protocol changes)
- Adapt/convert commands to work with byte streams (high priority is
`str length`, `bytes starts-with`, and maybe `bytes ends-with`).
- Refactor the `tee` code, Devyn has already done some work on this.

---------

Co-authored-by: Devyn Cairns <devyn.cairns@gmail.com>

crates/nu-plugin-engine/src/context.rs

@@ -108,7 +108,7 @@ impl<'a> PluginExecutionContext for PluginExecutionCommandContext<'a> {
                     Value::Closure { val, .. } => {
                         ClosureEvalOnce::new(&self.engine_state, &self.stack, *val)
                             .run_with_input(PipelineData::Empty)
-                            .map(|data| data.into_value(span))
+                            .and_then(|data| data.into_value(span))
                             .unwrap_or_else(|err| Value::error(err, self.call.head))
                     }
                     _ => value.clone(),

crates/nu-plugin-engine/src/init.rs

@@ -26,7 +26,7 @@ use crate::{
 
 /// This should be larger than the largest commonly sent message to avoid excessive fragmentation.
 ///
-/// The buffers coming from external streams are typically each 8192 bytes, so double that.
+/// The buffers coming from byte streams are typically each 8192 bytes, so double that.
 pub(crate) const OUTPUT_BUFFER_SIZE: usize = 16384;
 
 /// Spawn the command for a plugin, in the given `mode`. After spawning, it can be passed to

crates/nu-plugin-engine/src/interface/mod.rs

@@ -519,8 +519,8 @@ impl InterfaceManager for PluginInterfaceManager {
                     .map_data(|data| {
                         let ctrlc = self.get_ctrlc(id)?;
 
-                        // Register the streams in the response
-                        for stream_id in data.stream_ids() {
+                        // Register the stream in the response
+                        if let Some(stream_id) = data.stream_id() {
                             self.recv_stream_started(id, stream_id);
                         }
 
@@ -602,7 +602,7 @@ impl InterfaceManager for PluginInterfaceManager {
                     meta,
                 ))
             }
-            PipelineData::Empty | PipelineData::ExternalStream { .. } => Ok(data),
+            PipelineData::Empty | PipelineData::ByteStream(..) => Ok(data),
         }
     }
 
@@ -953,7 +953,7 @@ impl PluginInterface {
 
         let call = PluginCall::CustomValueOp(value.map(|cv| cv.without_source()), op);
         match self.plugin_call(call, None)? {
-            PluginCallResponse::PipelineData(out_data) => Ok(out_data.into_value(span)),
+            PluginCallResponse::PipelineData(out_data) => out_data.into_value(span),
             PluginCallResponse::Error(err) => Err(err.into()),
             _ => Err(ShellError::PluginFailedToDecode {
                 msg: format!("Received unexpected response to custom value {op_name}() call"),
@@ -1091,7 +1091,7 @@ impl Interface for PluginInterface {
                     meta,
                 ))
             }
-            PipelineData::Empty | PipelineData::ExternalStream { .. } => Ok(data),
+            PipelineData::Empty | PipelineData::ByteStream(..) => Ok(data),
         }
     }
 }

crates/nu-plugin-engine/src/interface/tests.rs

@@ -9,10 +9,10 @@ use crate::{
 use nu_plugin_core::{interface_test_util::TestCase, Interface, InterfaceManager};
 use nu_plugin_protocol::{
     test_util::{expected_test_custom_value, test_plugin_custom_value},
-    CallInfo, CustomValueOp, EngineCall, EngineCallResponse, EvaluatedCall, ExternalStreamInfo,
+    ByteStreamInfo, CallInfo, CustomValueOp, EngineCall, EngineCallResponse, EvaluatedCall,
     ListStreamInfo, PipelineDataHeader, PluginCall, PluginCallId, PluginCallResponse,
-    PluginCustomValue, PluginInput, PluginOutput, Protocol, ProtocolInfo, RawStreamInfo,
-    StreamData, StreamMessage,
+    PluginCustomValue, PluginInput, PluginOutput, Protocol, ProtocolInfo, StreamData,
+    StreamMessage,
 };
 use nu_protocol::{
     ast::{Math, Operator},
@@ -154,16 +154,9 @@ fn manager_consume_all_propagates_message_error_to_readers() -> Result<(), Shell
     test.add(invalid_output());
 
     let stream = manager.read_pipeline_data(
-        PipelineDataHeader::ExternalStream(ExternalStreamInfo {
+        PipelineDataHeader::ByteStream(ByteStreamInfo {
+            id: 0,
             span: Span::test_data(),
-            stdout: Some(RawStreamInfo {
-                id: 0,
-                is_binary: false,
-                known_size: None,
-            }),
-            stderr: None,
-            exit_code: None,
-            trim_end_newline: false,
         }),
         None,
     )?;
@@ -378,7 +371,7 @@ fn manager_consume_call_response_registers_streams() -> Result<(), ShellError> {
         fake_plugin_call(&mut manager, n);
     }
 
-    // Check list streams, external streams
+    // Check list streams, byte streams
     manager.consume(PluginOutput::CallResponse(
         0,
         PluginCallResponse::PipelineData(PipelineDataHeader::ListStream(ListStreamInfo {
@@ -388,23 +381,9 @@ fn manager_consume_call_response_registers_streams() -> Result<(), ShellError> {
     ))?;
     manager.consume(PluginOutput::CallResponse(
         1,
-        PluginCallResponse::PipelineData(PipelineDataHeader::ExternalStream(ExternalStreamInfo {
+        PluginCallResponse::PipelineData(PipelineDataHeader::ByteStream(ByteStreamInfo {
+            id: 1,
             span: Span::test_data(),
-            stdout: Some(RawStreamInfo {
-                id: 1,
-                is_binary: false,
-                known_size: None,
-            }),
-            stderr: Some(RawStreamInfo {
-                id: 2,
-                is_binary: false,
-                known_size: None,
-            }),
-            exit_code: Some(ListStreamInfo {
-                id: 3,
-                span: Span::test_data(),
-            }),
-            trim_end_newline: false,
         })),
     ))?;
 
@@ -423,22 +402,20 @@ fn manager_consume_call_response_registers_streams() -> Result<(), ShellError> {
         "plugin_call_input_streams[0] should be Some(0)"
     );
 
-    // ExternalStream should have three
+    // ByteStream should have one
     if let Some(sub) = manager.plugin_call_states.get(&1) {
         assert_eq!(
-            3, sub.remaining_streams_to_read,
-            "ExternalStream remaining_streams_to_read should be 3"
+            1, sub.remaining_streams_to_read,
+            "ByteStream remaining_streams_to_read should be 1"
         );
     } else {
-        panic!("failed to find subscription for ExternalStream (1), maybe it was removed");
-    }
-    for n in [1, 2, 3] {
-        assert_eq!(
-            Some(&1),
-            manager.plugin_call_input_streams.get(&n),
-            "plugin_call_input_streams[{n}] should be Some(1)"
-        );
+        panic!("failed to find subscription for ByteStream (1), maybe it was removed");
     }
+    assert_eq!(
+        Some(&1),
+        manager.plugin_call_input_streams.get(&1),
+        "plugin_call_input_streams[1] should be Some(1)"
+    );
 
     Ok(())
 }
@@ -1087,7 +1064,7 @@ fn interface_run() -> Result<(), ShellError> {
 
     assert_eq!(
         Value::test_int(number),
-        result.into_value(Span::test_data())
+        result.into_value(Span::test_data())?,
     );
     assert!(test.has_unconsumed_write());
     Ok(())
@@ -1136,7 +1113,7 @@ fn interface_prepare_pipeline_data_accepts_normal_values() -> Result<(), ShellEr
         match interface.prepare_pipeline_data(PipelineData::Value(value.clone(), None), &state) {
             Ok(data) => assert_eq!(
                 value.get_type(),
-                data.into_value(Span::test_data()).get_type()
+                data.into_value(Span::test_data())?.get_type(),
             ),
             Err(err) => panic!("failed to accept {value:?}: {err}"),
         }