1 files changed, 71 insertions, 0 deletions
diff --git a/std/io/seekable_stream.zig b/std/io/seekable_stream.zig
index baf479891c..392e135302 100644
--- a/std/io/seekable_stream.zig
+++ b/std/io/seekable_stream.zig
@@ -30,3 +30,74 @@ pub fn SeekableStream(comptime SeekErrorType: type, comptime GetSeekPosErrorType
         }
     };
 }
+
+pub const SliceSeekableInStream = struct {
+    const Self = @This();
+    pub const Error = error{};
+    pub const SeekError = error{EndOfStream};
+    pub const GetSeekPosError = error{};
+    pub const Stream = InStream(Error);
+    pub const SeekableInStream = SeekableStream(SeekError, GetSeekPosError);
+
+    pub stream: Stream,
+    pub seekable_stream: SeekableInStream,
+
+    pos: usize,
+    slice: []const u8,
+
+    pub fn init(slice: []const u8) Self {
+        return Self{
+            .slice = slice,
+            .pos = 0,
+            .stream = Stream{ .readFn = readFn },
+            .seekable_stream = SeekableInStream{
+                .seekToFn = seekToFn,
+                .seekForwardFn = seekForwardFn,
+                .getEndPosFn = getEndPosFn,
+                .getPosFn = getPosFn,
+            },
+        };
+    }
+
+    fn readFn(in_stream: *Stream, dest: []u8) Error!usize {
+        const self = @fieldParentPtr(Self, "stream", in_stream);
+        const size = std.math.min(dest.len, self.slice.len - self.pos);
+        const end = self.pos + size;
+
+        std.mem.copy(u8, dest[0..size], self.slice[self.pos..end]);
+        self.pos = end;
+
+        return size;
+    }
+
+    fn seekToFn(in_stream: *SeekableInStream, pos: u64) SeekError!void {
+        const self = @fieldParentPtr(Self, "seekable_stream", in_stream);
+        const usize_pos = @intCast(usize, pos);
+        if (usize_pos >= self.slice.len) return error.EndOfStream;
+        self.pos = usize_pos;
+    }
+
+    fn seekForwardFn(in_stream: *SeekableInStream, amt: i64) SeekError!void {
+        const self = @fieldParentPtr(Self, "seekable_stream", in_stream);
+
+        if (amt < 0) {
+            const abs_amt = @intCast(usize, -amt);
+            if (abs_amt > self.pos) return error.EndOfStream;
+            self.pos -= abs_amt;
+        } else {
+            const usize_amt = @intCast(usize, amt);
+            if (self.pos + usize_amt >= self.slice.len) return error.EndOfStream;
+            self.pos += usize_amt;
+        }
+    }
+
+    fn getEndPosFn(in_stream: *SeekableInStream) GetSeekPosError!u64 {
+        const self = @fieldParentPtr(Self, "seekable_stream", in_stream);
+        return @intCast(u64, self.slice.len);
+    }
+
+    fn getPosFn(in_stream: *SeekableInStream) GetSeekPosError!u64 {
+        const self = @fieldParentPtr(Self, "seekable_stream", in_stream);
+        return @intCast(u64, self.pos);
+    }
+};