bpo-41625: Expose the splice() system call in the os module (GH-21947)

2 files changed, 182 insertions, 2 deletions

diff --git a/Modules/clinic/posixmodule.c.h b/Modules/clinic/posixmodule.c.h
index f5826e3681..ee4ee8ceac 100644
--- a/Modules/clinic/posixmodule.c.h
+++ b/Modules/clinic/posixmodule.c.h
@@ -5674,6 +5674,106 @@ exit:
 
 #endif /* defined(HAVE_COPY_FILE_RANGE) */
 
+#if defined(HAVE_SPLICE)
+
+PyDoc_STRVAR(os_splice__doc__,
+"splice($module, /, src, dst, count, offset_src=None, offset_dst=None,\n"
+"       flags=0)\n"
+"--\n"
+"\n"
+"Transfer count bytes from one pipe to a descriptor or vice versa.\n"
+"\n"
+"  src\n"
+"    Source file descriptor.\n"
+"  dst\n"
+"    Destination file descriptor.\n"
+"  count\n"
+"    Number of bytes to copy.\n"
+"  offset_src\n"
+"    Starting offset in src.\n"
+"  offset_dst\n"
+"    Starting offset in dst.\n"
+"  flags\n"
+"    Flags to modify the semantics of the call.\n"
+"\n"
+"If offset_src is None, then src is read from the current position;\n"
+"respectively for offset_dst. The offset associated to the file\n"
+"descriptor that refers to a pipe must be None.");
+
+#define OS_SPLICE_METHODDEF    \
+    {"splice", (PyCFunction)(void(*)(void))os_splice, METH_FASTCALL|METH_KEYWORDS, os_splice__doc__},
+
+static PyObject *
+os_splice_impl(PyObject *module, int src, int dst, Py_ssize_t count,
+               PyObject *offset_src, PyObject *offset_dst,
+               unsigned int flags);
+
+static PyObject *
+os_splice(PyObject *module, PyObject *const *args, Py_ssize_t nargs, PyObject *kwnames)
+{
+    PyObject *return_value = NULL;
+    static const char * const _keywords[] = {"src", "dst", "count", "offset_src", "offset_dst", "flags", NULL};
+    static _PyArg_Parser _parser = {NULL, _keywords, "splice", 0};
+    PyObject *argsbuf[6];
+    Py_ssize_t noptargs = nargs + (kwnames ? PyTuple_GET_SIZE(kwnames) : 0) - 3;
+    int src;
+    int dst;
+    Py_ssize_t count;
+    PyObject *offset_src = Py_None;
+    PyObject *offset_dst = Py_None;
+    unsigned int flags = 0;
+
+    args = _PyArg_UnpackKeywords(args, nargs, NULL, kwnames, &_parser, 3, 6, 0, argsbuf);
+    if (!args) {
+        goto exit;
+    }
+    src = _PyLong_AsInt(args[0]);
+    if (src == -1 && PyErr_Occurred()) {
+        goto exit;
+    }
+    dst = _PyLong_AsInt(args[1]);
+    if (dst == -1 && PyErr_Occurred()) {
+        goto exit;
+    }
+    {
+        Py_ssize_t ival = -1;
+        PyObject *iobj = _PyNumber_Index(args[2]);
+        if (iobj != NULL) {
+            ival = PyLong_AsSsize_t(iobj);
+            Py_DECREF(iobj);
+        }
+        if (ival == -1 && PyErr_Occurred()) {
+            goto exit;
+        }
+        count = ival;
+    }
+    if (!noptargs) {
+        goto skip_optional_pos;
+    }
+    if (args[3]) {
+        offset_src = args[3];
+        if (!--noptargs) {
+            goto skip_optional_pos;
+        }
+    }
+    if (args[4]) {
+        offset_dst = args[4];
+        if (!--noptargs) {
+            goto skip_optional_pos;
+        }
+    }
+    if (!_PyLong_UnsignedInt_Converter(args[5], &flags)) {
+        goto exit;
+    }
+skip_optional_pos:
+    return_value = os_splice_impl(module, src, dst, count, offset_src, offset_dst, flags);
+
+exit:
+    return return_value;
+}
+
+#endif /* defined(HAVE_SPLICE) */
+
 #if defined(HAVE_MKFIFO)
 
 PyDoc_STRVAR(os_mkfifo__doc__,
@@ -8864,6 +8964,10 @@ exit:
     #define OS_COPY_FILE_RANGE_METHODDEF
 #endif /* !defined(OS_COPY_FILE_RANGE_METHODDEF) */
 
+#ifndef OS_SPLICE_METHODDEF
+    #define OS_SPLICE_METHODDEF
+#endif /* !defined(OS_SPLICE_METHODDEF) */
+
 #ifndef OS_MKFIFO_METHODDEF
     #define OS_MKFIFO_METHODDEF
 #endif /* !defined(OS_MKFIFO_METHODDEF) */
@@ -9059,4 +9163,4 @@ exit:
 #ifndef OS_WAITSTATUS_TO_EXITCODE_METHODDEF
     #define OS_WAITSTATUS_TO_EXITCODE_METHODDEF
 #endif /* !defined(OS_WAITSTATUS_TO_EXITCODE_METHODDEF) */
-/*[clinic end generated code: output=49b7ed768242ef7c input=a9049054013a1b77]*/
+/*[clinic end generated code: output=8a59e91178897267 input=a9049054013a1b77]*/
diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
index 0764453f41..ecab147d2f 100644
--- a/Modules/posixmodule.c
+++ b/Modules/posixmodule.c
@@ -6521,7 +6521,6 @@ os_spawnve_impl(PyObject *module, int mode, path_t *path, PyObject *argv,
 
 #endif /* HAVE_SPAWNV */
 
-
 #ifdef HAVE_FORK
 
 /* Helper function to validate arguments.
@@ -10370,6 +10369,75 @@ os_copy_file_range_impl(PyObject *module, int src, int dst, Py_ssize_t count,
 }
 #endif /* HAVE_COPY_FILE_RANGE*/
 
+#ifdef HAVE_SPLICE
+/*[clinic input]
+
+os.splice
+    src: int
+        Source file descriptor.
+    dst: int
+        Destination file descriptor.
+    count: Py_ssize_t
+        Number of bytes to copy.
+    offset_src: object = None
+        Starting offset in src.
+    offset_dst: object = None
+        Starting offset in dst.
+    flags: unsigned_int = 0
+        Flags to modify the semantics of the call.
+
+Transfer count bytes from one pipe to a descriptor or vice versa.
+
+If offset_src is None, then src is read from the current position;
+respectively for offset_dst. The offset associated to the file
+descriptor that refers to a pipe must be None.
+[clinic start generated code]*/
+
+static PyObject *
+os_splice_impl(PyObject *module, int src, int dst, Py_ssize_t count,
+               PyObject *offset_src, PyObject *offset_dst,
+               unsigned int flags)
+/*[clinic end generated code: output=d0386f25a8519dc5 input=047527c66c6d2e0a]*/
+{
+    off_t offset_src_val, offset_dst_val;
+    off_t *p_offset_src = NULL;
+    off_t *p_offset_dst = NULL;
+    Py_ssize_t ret;
+    int async_err = 0;
+
+    if (count < 0) {
+        PyErr_SetString(PyExc_ValueError, "negative value for 'count' not allowed");
+        return NULL;
+    }
+
+    if (offset_src != Py_None) {
+        if (!Py_off_t_converter(offset_src, &offset_src_val)) {
+            return NULL;
+        }
+        p_offset_src = &offset_src_val;
+    }
+
+    if (offset_dst != Py_None) {
+        if (!Py_off_t_converter(offset_dst, &offset_dst_val)) {
+            return NULL;
+        }
+        p_offset_dst = &offset_dst_val;
+    }
+
+    do {
+        Py_BEGIN_ALLOW_THREADS
+        ret = splice(src, p_offset_src, dst, p_offset_dst, count, flags);
+        Py_END_ALLOW_THREADS
+    } while (ret < 0 && errno == EINTR && !(async_err = PyErr_CheckSignals()));
+
+    if (ret < 0) {
+        return (!async_err) ? posix_error() : NULL;
+    }
+
+    return PyLong_FromSsize_t(ret);
+}
+#endif /* HAVE_SPLICE*/
+
 #ifdef HAVE_MKFIFO
 /*[clinic input]
 os.mkfifo
@@ -14550,6 +14618,7 @@ static PyMethodDef posix_methods[] = {
     OS_POSIX_SPAWNP_METHODDEF
     OS_READLINK_METHODDEF
     OS_COPY_FILE_RANGE_METHODDEF
+    OS_SPLICE_METHODDEF
     OS_RENAME_METHODDEF
     OS_REPLACE_METHODDEF
     OS_RMDIR_METHODDEF
@@ -15072,6 +15141,13 @@ all_ins(PyObject *m)
     if (PyModule_AddIntConstant(m, "RWF_APPEND", RWF_APPEND)) return -1;
 #endif
 
+/* constants for splice */
+#ifdef HAVE_SPLICE
+    if (PyModule_AddIntConstant(m, "SPLICE_F_MOVE", SPLICE_F_MOVE)) return -1;
+    if (PyModule_AddIntConstant(m, "SPLICE_F_NONBLOCK", SPLICE_F_NONBLOCK)) return -1;
+    if (PyModule_AddIntConstant(m, "SPLICE_F_MORE", SPLICE_F_MORE)) return -1;
+#endif
+
 /* constants for posix_spawn */
 #ifdef HAVE_POSIX_SPAWN
     if (PyModule_AddIntConstant(m, "POSIX_SPAWN_OPEN", POSIX_SPAWN_OPEN)) return -1;