From d48f8fce64d6496a18b442c74021829554151823 Mon Sep 17 00:00:00 2001
From: Steven Allen <steven@stebalien.com>
Date: Tue, 10 Sep 2019 18:07:48 -0700
Subject: [PATCH] file: implement ReadAt

This commit was moved from ipfs/go-ipfs-http-client@88a9b615205816ea20ea38fbee170b3256e51b94
---
 client/httpapi/apifile.go | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/client/httpapi/apifile.go b/client/httpapi/apifile.go
index afd9934e6..ec2f7588d 100644
--- a/client/httpapi/apifile.go
+++ b/client/httpapi/apifile.go
@@ -82,6 +82,25 @@ func (f *apiFile) Read(p []byte) (int, error) {
 	return n, err
 }
 
+func (f *apiFile) ReadAt(p []byte, off int64) (int, error) {
+	// Always make a new request. This method should be parallel-safe.
+	resp, err := f.core.Request("cat", f.path.String()).
+		Option("offset", off).Option("length", len(p)).Send(f.ctx)
+	if err != nil {
+		return 0, err
+	}
+	if resp.Error != nil {
+		return 0, resp.Error
+	}
+	defer resp.Output.Close()
+
+	n, err := io.ReadFull(resp.Output, p)
+	if err == io.ErrUnexpectedEOF {
+		err = io.EOF
+	}
+	return n, err
+}
+
 func (f *apiFile) Seek(offset int64, whence int) (int64, error) {
 	switch whence {
 	case io.SeekEnd: