1 files changed, 45 insertions, 19 deletions

diff --git a/paramiko/sftp_file.py b/paramiko/sftp_file.py
index 7d9b8f47..f1321018 100644
--- a/paramiko/sftp_file.py
+++ b/paramiko/sftp_file.py
@@ -46,7 +46,6 @@ class SFTPFile (BufferedFile):
         self._prefetching = False
         self._prefetch_done = False
         self._prefetch_so_far = 0
-        self._prefetch_size = 0
         self._prefetch_data = {}
         self._saved_exception = None
 
@@ -89,8 +88,7 @@ class SFTPFile (BufferedFile):
         in the buffer, return None.  otherwise, behaves like a normal read.
         """
         # while not closed, and haven't fetched past the current position, and haven't reached EOF...
-        while (self._prefetch_so_far <= self._realpos) and \
-            (self._prefetch_so_far < self._prefetch_size) and not self._closed:
+        while (self._prefetch_so_far <= self._realpos) and not self._closed:
             if self._prefetch_done:
                 return None
             self.sftp._read_response()
@@ -348,27 +346,36 @@ class SFTPFile (BufferedFile):
         dramatically improve the download speed by avoiding roundtrip latency.
         The file's contents are incrementally buffered in a background thread.
         
+        The prefetched data is stored in a buffer until read via the L{read}
+        method.  Once data has been read, it's removed from the buffer.  The
+        data may be read in a random order (using L{seek}); chunks of the
+        buffer that haven't been read will continue to be buffered.
+
         @since: 1.5.1
         """
         size = self.stat().st_size
         # queue up async reads for the rest of the file
-        self._prefetching = True
-        self._prefetch_done = False
-        self._prefetch_so_far = self._realpos
-        self._prefetch_size = size
-        self._prefetch_data = {}
-        t = threading.Thread(target=self._prefetch)
-        t.setDaemon(True)
-        t.start()
-    
-    def _prefetch(self):
+        chunks = []
         n = self._realpos
-        size = self._prefetch_size
         while n < size:
             chunk = min(self.MAX_REQUEST_SIZE, size - n)
-            self.sftp._async_request(self, CMD_READ, self.handle, long(n), int(chunk))
+            chunks.append((n, chunk))
             n += chunk
-
+        self._start_prefetch(chunks)
+    
+    def readv(self, chunks):
+        # put the offsets in order, since we depend on that for determining
+        # when the reads have finished.
+        ordered_chunks = chunks[:]
+        ordered_chunks.sort(lambda x, y: cmp(x[0], y[0]))
+        self._start_prefetch(ordered_chunks)
+        # now we can just devolve to a bunch of read()s :)
+        out = []
+        for x in chunks:
+            self.seek(x[0])
+            out.append(self.read(x[1]))
+        return out
+    
 
     ###  internals...
 
@@ -379,6 +386,23 @@ class SFTPFile (BufferedFile):
         except:
             return 0
 
+    def _start_prefetch(self, chunks):
+        self._prefetching = True
+        self._prefetch_done = False
+        self._prefetch_so_far = chunks[0][0]
+        self._prefetch_data = {}
+        self._prefetch_reads = chunks
+
+        t = threading.Thread(target=self._prefetch_thread)
+        t.setDaemon(True)
+        t.start()
+        
+    def _prefetch_thread(self):
+        # do these read requests in a temporary thread because there may be
+        # a lot of them, so it may block.
+        for offset, length in self._prefetch_reads:
+            self.sftp._async_request(self, CMD_READ, self.handle, long(offset), int(length))
+
     def _async_response(self, t, msg):
         if t == CMD_STATUS:
             # save exception and re-raise it on next file operation
@@ -390,9 +414,11 @@ class SFTPFile (BufferedFile):
         if t != CMD_DATA:
             raise SFTPError('Expected data')
         data = msg.get_string()
-        self._prefetch_data[self._prefetch_so_far] = data
-        self._prefetch_so_far += len(data)
-        if self._prefetch_so_far == self._prefetch_size:
+        offset, length = self._prefetch_reads.pop(0)
+        assert length == len(data)
+        self._prefetch_data[offset] = data
+        self._prefetch_so_far = offset + length
+        if len(self._prefetch_reads) == 0:
             self._prefetch_done = True
     
     def _check_exception(self):