[issue5804] Add an 'offset' argument to zlib.decompress

Modules/zlibmodule.c

 /* zlibmodule.c -- gzip-compatible data compression */
 /* See http://www.gzip.org/zlib/ */
 
 /* Windows users:  read Python's PCbuild\readme.txt */
 
 
 #include "Python.h"
 #include "zlib.h"
 
 #ifdef WITH_THREAD
@@ skipping 168 matching lines @@
     else
         zlib_error(zst, err, "while finishing compression");
 
  error:
     free(output);
 
     return ReturnVal;
 }
 
 PyDoc_STRVAR(decompress__doc__,
-"decompress(string[, wbits[, bufsize]]) -- Return decompressed string.\n"
+"decompress(string[, wbits[, bufsize[, offset]]]) -- Return decompressed string.\n"
 "\n"
 "Optional arg wbits is the window buffer size.  Optional arg bufsize is\n"
-"the initial output buffer size.");
+"the initial output buffer size.  Optional arg offset specifies\n"
+"the start position in the string to start decompresion and, if spceified,\n"

[gregory.p.smith, 2009/05/10 21:05:27]

typo: specified.

+"causes the return value to be a tuple, with the second element being\n"
+"the position in the string just afer the last piece of compressed data.");
 
 static PyObject *
-PyZlib_decompress(PyObject *self, PyObject *args)
+PyZlib_decompress(PyObject *self, PyObject *args, PyObject *kw)
 {
     PyObject *result_str;
     Byte *input;
     int length, err;
     int wsize=DEF_WBITS;
     Py_ssize_t r_strlen=DEFAULTALLOC;
+    Py_ssize_t offset = -1;
     z_stream zst;
+    char *keywords[] = {"string", "wbits", "bufsize", "offset", 0};
 
-    if (!PyArg_ParseTuple(args, "s#|in:decompress",
-                          &input, &length, &wsize, &r_strlen))
+    if (!PyArg_ParseTupleAndKeywords(args, kw, "s#|inn:decompress", keywords,
+                          &input, &length, &wsize, &r_strlen, &offset))
         return NULL;
-
     if (r_strlen <= 0)
         r_strlen = 1;
+
+    /* if specified, don't start at the beginning of the input string */
+    if (offset > 0) {
+        if (offset > length)
+            offset = length;
+        length -= offset;
+        input += offset;
+    }
 
     zst.avail_in = length;
     zst.avail_out = r_strlen;
 
     if (!(result_str = PyString_FromStringAndSize(NULL, r_strlen)))
         return NULL;
 
     zst.zalloc = (alloc_func)NULL;
     zst.zfree = (free_func)Z_NULL;
     zst.next_out = (Byte *)PyString_AS_STRING(result_str);
@@ skipping 52 matching lines @@
         }
     } while (err != Z_STREAM_END);
 
     err = inflateEnd(&zst);
     if (err != Z_OK) {
         zlib_error(zst, err, "while finishing data decompression");
         goto error;
     }
 
     _PyString_Resize(&result_str, zst.total_out);
+    if (result_str != NULL && offset >= 0) {
+        /* compute new offset to current pos */
+        offset = length-zst.avail_in+offset;

[gregory.p.smith, 2009/05/10 21:05:27]

leave spaces around your - and + operators and this becomes easier to read.

+        return Py_BuildValue("Nn", result_str, offset);
+    }
     return result_str;
 
  error:
     Py_XDECREF(result_str);
     return NULL;
 }
 
 static PyObject *
 PyZlib_compressobj(PyObject *selfptr, PyObject *args)
 {
@@ skipping 642 matching lines @@
 static PyMethodDef zlib_methods[] =
 {
     {"adler32", (PyCFunction)PyZlib_adler32, METH_VARARGS,
                 adler32__doc__},
     {"compress", (PyCFunction)PyZlib_compress,  METH_VARARGS,
                  compress__doc__},
     {"compressobj", (PyCFunction)PyZlib_compressobj, METH_VARARGS,
                     compressobj__doc__},
     {"crc32", (PyCFunction)PyZlib_crc32, METH_VARARGS,
               crc32__doc__},
-    {"decompress", (PyCFunction)PyZlib_decompress, METH_VARARGS,
+    {"decompress", (PyCFunction)PyZlib_decompress, METH_KEYWORDS,
                    decompress__doc__},
     {"decompressobj", (PyCFunction)PyZlib_decompressobj, METH_VARARGS,
                    decompressobj__doc__},
     {NULL, NULL}
 };
 
 static PyTypeObject Comptype = {
     PyVarObject_HEAD_INIT(0, 0)
     "zlib.Compress",
     sizeof(compobject),
@@ skipping 75 matching lines @@
     ver = PyString_FromString(ZLIB_VERSION);
     if (ver != NULL)
         PyModule_AddObject(m, "ZLIB_VERSION", ver);
 
     PyModule_AddStringConstant(m, "__version__", "1.0");
 
 #ifdef WITH_THREAD
     zlib_lock = PyThread_allocate_lock();
 #endif /* WITH_THREAD */
 }