1 files changed, 57 insertions, 0 deletions
diff --git a/src/base/bufio/seek.c b/src/base/bufio/seek.c
new file mode 100644
index 0000000..5d25173
--- /dev/null
+++ b/src/base/bufio/seek.c
@@ -0,0 +1,57 @@
+#include "internal.h"
+
+int
+bio·seek(io·Header *io, intptr offset, int whence, intptr *pos)
+{
+    intptr n,d,cap;
+
+    switch(io->state){
+    default:
+        fmt·fprint(2, "seek: unknown state %d\n", io->state);
+        return io·BufEof;
+    case io·BufEnd:
+        io->state = io·BufRdr;
+        io->ilen = 0;
+        io->g = io->e;
+        /* fallthrough */
+    case io·BufRdr:
+        n = offset;
+        if(whence == sys·SeekCur){
+            n += bio·offset(io);
+            whence = sys·SeekSet;
+        }
+
+        /* can we seek inside our buffer */
+        if(whence == sys·SeekSet){
+            d = n - bio·offset(io);
+            cap = io->e - io->g;
+            if(-cap <= d && d <= cap){
+                io->ilen += d;
+                if(d >= 0){
+                    if(io->ilen <= 0){
+                        *pos = n;
+                        return 0;
+                    }
+                }else{
+                    if(io->e - io->g >= -io->ilen){
+                        *pos = n;
+                        return 0;
+                    }
+                }
+            }
+        }
+
+        /* nope, call the kernel to do it for us */
+        sys·seek(io->fd, offset, whence, &n);
+        io->ilen = 0;
+        io->g = io->e;
+        break;
+
+    case io·BufWtr:
+        bio·flush(io);
+        sys·seek(io->fd, offset, whence, &n);
+        break;
+    }
+    io->pos = *pos = n;
+    return 0;
+}