fixup read_to_end impl

libconfig/src/lib.rs

@@ -1,9 +1,9 @@
 #![no_std]
 extern crate alloc;
 
-use alloc::{rc::Rc, string::FromUtf8Error, string::String, vec::Vec};
+use alloc::{rc::Rc, string::{FromUtf8Error, String}, vec::Vec};
 use sd_reader::SdReader;
-use core::fmt;
+use core::{cmp, fmt};
 use fatfs::{self, Read, Seek, SeekFrom, Write};
 use libboard_zynq::sdio;
 
@@ -57,23 +57,47 @@ impl<'a> From<FromUtf8Error> for Error<'a> {
 }
 
 // Simplified replacements to `read_to_end` and `read_to_string` from core_io
-fn read_to_end<'a>(file: &mut File<'a>, buffer: &mut Vec<u8>) -> Result<'a, ()> {
-    let mut temp_buffer = [0; 1024];
-    loop {
-        let read_bytes = file.read(&mut temp_buffer)?;
-        if read_bytes == 0 {
-            break;
-        }
-        else { 
-            buffer.extend_from_slice(&temp_buffer[..read_bytes]); 
+fn read_to_end<'a>(file: &mut File<'a>, buffer: &mut Vec<u8>) -> Result<'a, usize> {
+    const PROBE_SIZE: usize = 32;
+    const MAX_READ_SIZE: usize = 512; // read max BLOCK_SIZE at a time
+    let start_len = buffer.len();
+    let start_cap = buffer.capacity();
+    fn small_probe_read<'a>(file: &mut File<'a>, buffer: &mut Vec<u8>) -> Result<'a, usize> {
+        let mut probe = [0u8; PROBE_SIZE];
+        let n = file.read(&mut probe)?;
+        buffer.extend_from_slice(&probe[..n]);
+        Ok(n)
+    }
+    if start_cap - start_len < PROBE_SIZE {
+        let read = small_probe_read(file, buffer)?;
+        if read == 0 {
+            return Ok(0);
         }
     }
-    Ok(())
+    loop {
+        if buffer.len() == buffer.capacity() && buffer.capacity() == start_cap {
+            let read = small_probe_read(file, buffer)?;
+            if read == 0 {
+                return Ok(buffer.len() - start_len);
+            }
+        }
+        if buffer.len() == buffer.capacity() {
+            buffer.try_reserve(PROBE_SIZE).unwrap();
+        }
+        let mut read_buf = [0u8; MAX_READ_SIZE];
+        let buf_len = cmp::min(MAX_READ_SIZE, buffer.capacity() - buffer.len());
+        let mut read_buf_mut = &mut read_buf[..buf_len];
+        let bytes_read = file.read(&mut read_buf_mut)?;
+        if bytes_read == 0 {
+            return Ok(buffer.len() - start_len);
+        }
+        buffer.extend_from_slice(&read_buf_mut[..bytes_read]);
+    }
 }
 
 fn read_to_string<'a>(file: &mut File<'a>) -> Result<'a, String> {
     let mut buffer: Vec<u8> = Vec::new();
-    read_to_end(file, &mut buffer)?;
+    read_to_end(file, &mut buffer).map(|_| ())?;
     Ok(String::from_utf8(buffer)?)
 }
 
@@ -128,7 +152,7 @@ impl Config {
             let root_dir = fs.root_dir();
             let mut buffer: Vec<u8> = Vec::new();
             match root_dir.open_file(&["/CONFIG/", key, ".BIN"].concat()) {
-                Ok(mut f) => read_to_end( &mut f, &mut buffer)?,
+                Ok(mut f) => read_to_end( &mut f, &mut buffer).map(|_| ())?,
                 Err(_) => match root_dir.open_file("/CONFIG.TXT") {
                     Ok(f) => parse_config(key, &mut buffer, f)?,
                     Err(_) => return Err(Error::KeyNotFoundError(key)),