read_byte_stream implemented for ByteStreams

crates/nu-command/src/bytes/at.rs

@@ -1,9 +1,11 @@
+use itertools::Itertools;
 use nu_cmd_base::{
     input_handler::{operate, CmdArgument},
     util,
 };
 use nu_engine::command_prelude::*;
-use nu_protocol::Range;
+use nu_protocol::{Range, Reader};
+use std::io::{Bytes, Read, Write};
 
 #[derive(Clone)]
 pub struct BytesAt;
@@ -83,7 +85,11 @@ impl Command for BytesAt {
             cell_paths,
         };
 
-        operate(action, args, input, call.head, engine_state.signals())
+        if let PipelineData::ByteStream(stream, metadata) = input {
+            handle_byte_stream(&args, stream, call, metadata, engine_state)
+        } else {
+            operate(action, args, input, call.head, engine_state.signals())
+        }
     }
 
     fn examples(&self) -> Vec<Example> {
@@ -127,27 +133,8 @@ impl Command for BytesAt {
 fn action(input: &Value, args: &Arguments, head: Span) -> Value {
     let range = &args.indexes;
     match input {
-        Value::Binary { val, .. } => {
+        Value::Binary { val, .. } => read_bytes(val, range, head),
-            let len = val.len() as isize;
-            let start = if range.0 < 0 { range.0 + len } else { range.0 };
-            let end = if range.1 < 0 { range.1 + len } else { range.1 };
-
-            if start > end {
-                Value::binary(vec![], head)
-            } else {
-                let val_iter = val.iter().skip(start as usize);
-                Value::binary(
-                    if end == isize::MAX {
-                        val_iter.copied().collect::<Vec<u8>>()
-                    } else {
-                        val_iter.take((end - start + 1) as usize).copied().collect()
-                    },
-                    head,
-                )
-            }
-        }
         Value::Error { .. } => input.clone(),
-
         other => Value::error(
             ShellError::UnsupportedInput {
                 msg: "Only binary values are supported".into(),
@@ -159,3 +146,88 @@ fn action(input: &Value, args: &Arguments, head: Span) -> Value {
         ),
     }
 }
+
+fn handle_byte_stream(
+    args: &Arguments,
+    stream: ByteStream,
+    call: &Call,
+    metadata: Option<nu_protocol::PipelineMetadata>,
+    engine_state: &EngineState,
+) -> Result<PipelineData, ShellError> {
+    let idxs = args.indexes;
+    if idxs.0 >= idxs.1 {
+        return Ok(PipelineData::empty());
+    }
+
+    match stream.reader() {
+        Some(reader) => {
+            let iter = reader.bytes();
+
+            if idxs.0 < 0 || idxs.1 < 0 {
+                match iter.try_len() {
+                    Ok(_) => {
+                        let vec = iter.filter_map(Result::ok).collect::<Vec<u8>>();
+                        Ok(read_bytes(&vec, &idxs, call.head).into_pipeline_data_with_metadata(metadata))
+                    }
+                    _ => Err(ShellError::IncorrectValue {
+                        msg:
+                            "Negative range values cannot be used with streams that don't specify a length"
+                                .into(),
+                        val_span: call.head,
+                        call_span: call.arguments_span(),
+                    }),
+                }
+            } else {
+                Ok(read_stream(iter, idxs, call, engine_state, metadata))
+            }
+        }
+        None => Ok(PipelineData::empty()),
+    }
+}
+
+fn read_bytes(val: &[u8], range: &Subbytes, head: Span) -> Value {
+    let len = val.len() as isize;
+    let start = if range.0 < 0 { range.0 + len } else { range.0 };
+    let end = if range.1 < 0 { range.1 + len } else { range.1 };
+
+    if start > end {
+        Value::binary(vec![], head)
+    } else {
+        let val_iter = val.iter().skip(start as usize);
+        Value::binary(
+            if end == isize::MAX {
+                val_iter.copied().collect::<Vec<u8>>()
+            } else {
+                val_iter.take((end - start + 1) as usize).copied().collect()
+            },
+            head,
+        )
+    }
+}
+
+fn read_stream(
+    iter: Bytes<Reader>,
+    range: Subbytes,
+    call: &Call,
+    engine_state: &EngineState,
+    metadata: Option<nu_protocol::PipelineMetadata>,
+) -> PipelineData {
+    let start = range.0 as usize;
+    let end = (range.1 - range.0) as usize;
+    let mut iter = iter.skip(start).take(end);
+
+    let stream = ByteStream::from_fn(
+        call.head,
+        engine_state.signals().clone(),
+        ByteStreamType::Binary,
+        move |buf| match iter.next() {
+            Some(Ok(n)) if n > 0 => match buf.write(&[n]) {
+                Ok(_) => Ok(true),
+                Err(err) => Err(err.into()),
+            },
+            _ => Ok(false),
+        },
+    );
+
+    PipelineData::ByteStream(stream, metadata)
+}