1 files changed, 114 insertions, 0 deletions
diff --git a/js/io.ts b/js/io.ts
new file mode 100644
index 000000000..710722f42
--- /dev/null
+++ b/js/io.ts
@@ -0,0 +1,114 @@
+// Interfaces 100% copied from Go.
+// Documentation liberally lifted from them too.
+// Thank you! We love Go!
+
+// The bytes read during an I/O call and a boolean indicating EOF.
+export interface ReadResult {
+  nread: number;
+  eof: boolean;
+}
+
+// Reader is the interface that wraps the basic read() method.
+// https://golang.org/pkg/io/#Reader
+export interface Reader {
+  // read() reads up to p.byteLength bytes into p. It returns the number of
+  // bytes read (0 <= n <= p.byteLength) and any error encountered. Even if
+  // read() returns n < p.byteLength, it may use all of p as scratch space
+  // during the call. If some data is available but not p.byteLength bytes,
+  // read() conventionally returns what is available instead of waiting for
+  // more.
+  //
+  // When read() encounters an error or end-of-file condition after successfully
+  // reading n > 0 bytes, it returns the number of bytes read. It may return the
+  // (non-nil) error from the same call or return the error (and n == 0) from a
+  // subsequent call. An instance of this general case is that a Reader
+  // returning a non-zero number of bytes at the end of the input stream may
+  // return either err == EOF or err == nil. The next read() should return 0,
+  // EOF.
+  //
+  // Callers should always process the n > 0 bytes returned before considering
+  // the EOF. Doing so correctly handles I/O errors that happen after reading
+  // some bytes and also both of the allowed EOF behaviors.
+  //
+  // Implementations of read() are discouraged from returning a zero byte count
+  // with a nil error, except when p.byteLength == 0. Callers should treat a
+  // return of 0 and nil as indicating that nothing happened; in particular it
+  // does not indicate EOF.
+  //
+  // Implementations must not retain p.
+  read(p: ArrayBufferView): Promise<ReadResult>;
+}
+
+// Writer is the interface that wraps the basic write() method.
+// https://golang.org/pkg/io/#Writer
+export interface Writer {
+  // write() writes p.byteLength bytes from p to the underlying data stream. It
+  // returns the number of bytes written from p (0 <= n <= p.byteLength) and any
+  // error encountered that caused the write to stop early. write() must return
+  // a non-nil error if it returns n < p.byteLength. write() must not modify the
+  // slice data, even temporarily.
+  //
+  // Implementations must not retain p.
+  write(p: ArrayBufferView): Promise<number>;
+}
+
+// https://golang.org/pkg/io/#Closer
+export interface Closer {
+  // The behavior of Close after the first call is undefined. Specific
+  // implementations may document their own behavior.
+  close(): void;
+}
+
+// https://golang.org/pkg/io/#Seeker
+export interface Seeker {
+  // Seek sets the offset for the next read() or write() to offset, interpreted
+  // according to whence: SeekStart means relative to the start of the file,
+  // SeekCurrent means relative to the current offset, and SeekEnd means
+  // relative to the end. Seek returns the new offset relative to the start of
+  // the file and an error, if any.
+  //
+  // Seeking to an offset before the start of the file is an error. Seeking to
+  // any positive offset is legal, but the behavior of subsequent I/O operations
+  // on the underlying object is implementation-dependent.
+  seek(offset: number, whence: number): Promise<void>;
+}
+
+// https://golang.org/pkg/io/#ReadCloser
+export interface ReaderCloser extends Reader, Closer {}
+
+// https://golang.org/pkg/io/#WriteCloser
+export interface WriteCloser extends Writer, Closer {}
+
+// https://golang.org/pkg/io/#ReadSeeker
+export interface ReadSeeker extends Reader, Seeker {}
+
+// https://golang.org/pkg/io/#WriteSeeker
+export interface WriteSeeker extends Writer, Seeker {}
+
+// https://golang.org/pkg/io/#ReadWriteCloser
+export interface ReadWriteCloser extends Reader, Writer, Closer {}
+
+// https://golang.org/pkg/io/#ReadWriteSeeker
+export interface ReadWriteSeeker extends Reader, Writer, Seeker {}
+
+// copy() copies from src to dst until either EOF is reached on src or an error
+// occurs. It returns the number of bytes copied and the first error encountered
+// while copying, if any.
+//
+// Because copy() is defined to read from src until EOF, it does not treat an
+// EOF from read() as an error to be reported.
+//
+// https://golang.org/pkg/io/#Copy
+export async function copy(dst: Writer, src: Reader): Promise<number> {
+  let n = 0;
+  const b = new Uint8Array(1024);
+  let gotEOF = false;
+  while (gotEOF === false) {
+    const result = await src.read(b);
+    if (result.eof) {
+      gotEOF = true;
+    }
+    n += await dst.write(b.subarray(0, result.nread));
+  }
+  return n;
+}