implement a detach() method for BufferedIOBase and TextIOBase #5883

2 files changed, 99 insertions, 8 deletions

diff --git a/Modules/_io/bufferedio.c b/Modules/_io/bufferedio.c
index 3d175c7..2c65207 100644
--- a/Modules/_io/bufferedio.c
+++ b/Modules/_io/bufferedio.c
@@ -73,6 +73,18 @@ BufferedIOBase_unsupported(const char *message)
     return NULL;
 }
 
+PyDoc_STRVAR(BufferedIOBase_detach_doc,
+    "Disconnect this buffer from its underlying raw stream and return it.\n"
+    "\n"
+    "After the raw stream has been detached, the buffer is in an unusable\n"
+    "state.\n");
+
+static PyObject *
+BufferedIOBase_detach(PyObject *self)
+{
+    return BufferedIOBase_unsupported("detach");
+}
+
 PyDoc_STRVAR(BufferedIOBase_read_doc,
     "Read and return up to n bytes.\n"
     "\n"
@@ -127,6 +139,7 @@ BufferedIOBase_write(PyObject *self, PyObject *args)
 
 
 static PyMethodDef BufferedIOBase_methods[] = {
+    {"detach", (PyCFunction)BufferedIOBase_detach, METH_NOARGS, BufferedIOBase_detach_doc},
     {"read", BufferedIOBase_read, METH_VARARGS, BufferedIOBase_read_doc},
     {"read1", BufferedIOBase_read1, METH_VARARGS, BufferedIOBase_read1_doc},
     {"readinto", BufferedIOBase_readinto, METH_VARARGS, NULL},
@@ -181,6 +194,7 @@ typedef struct {
 
     PyObject *raw;
     int ok;    /* Initialized? */
+    int detached;
     int readable;
     int writable;
     
@@ -260,15 +274,25 @@ typedef struct {
 
 #define CHECK_INITIALIZED(self) \
     if (self->ok <= 0) { \
-        PyErr_SetString(PyExc_ValueError, \
-            "I/O operation on uninitialized object"); \
+        if (self->detached) { \
+            PyErr_SetString(PyExc_ValueError, \
+                 "raw stream has been detached"); \
+        } else { \
+            PyErr_SetString(PyExc_ValueError, \
+                "I/O operation on uninitialized object"); \
+        } \
         return NULL; \
     }
 
 #define CHECK_INITIALIZED_INT(self) \
     if (self->ok <= 0) { \
-        PyErr_SetString(PyExc_ValueError, \
-            "I/O operation on uninitialized object"); \
+        if (self->detached) { \
+            PyErr_SetString(PyExc_ValueError, \
+                 "raw stream has been detached"); \
+        } else { \
+            PyErr_SetString(PyExc_ValueError, \
+                "I/O operation on uninitialized object"); \
+        } \
         return -1; \
     }
 
@@ -430,6 +454,24 @@ end:
     return res;
 }
 
+/* detach */
+
+static PyObject *
+BufferedIOMixin_detach(BufferedObject *self, PyObject *args)
+{
+    PyObject *raw, *res;
+    CHECK_INITIALIZED(self)
+    res = PyObject_CallMethodObjArgs((PyObject *)self, _PyIO_str_flush, NULL);
+    if (res == NULL)
+        return NULL;
+    Py_DECREF(res);
+    raw = self->raw;
+    self->raw = NULL;
+    self->detached = 1;
+    self->ok = 0;
+    return raw;
+}
+
 /* Inquiries */
 
 static PyObject *
@@ -1101,6 +1143,7 @@ BufferedReader_init(BufferedObject *self, PyObject *args, PyObject *kwds)
     PyObject *raw;
 
     self->ok = 0;
+    self->detached = 0;
 
     if (!PyArg_ParseTupleAndKeywords(args, kwds, "O|n:BufferedReader", kwlist,
                                      &raw, &buffer_size)) {
@@ -1387,6 +1430,7 @@ _BufferedReader_peek_unlocked(BufferedObject *self, Py_ssize_t n)
 
 static PyMethodDef BufferedReader_methods[] = {
     /* BufferedIOMixin methods */
+    {"detach", (PyCFunction)BufferedIOMixin_detach, METH_NOARGS},
     {"flush", (PyCFunction)BufferedIOMixin_flush, METH_NOARGS},
     {"close", (PyCFunction)BufferedIOMixin_close, METH_NOARGS},
     {"seekable", (PyCFunction)BufferedIOMixin_seekable, METH_NOARGS},
@@ -1499,6 +1543,7 @@ BufferedWriter_init(BufferedObject *self, PyObject *args, PyObject *kwds)
     PyObject *raw;
 
     self->ok = 0;
+    self->detached = 0;
 
     if (!PyArg_ParseTupleAndKeywords(args, kwds, "O|nn:BufferedReader", kwlist,
                                      &raw, &buffer_size, &max_buffer_size)) {
@@ -1745,6 +1790,7 @@ error:
 static PyMethodDef BufferedWriter_methods[] = {
     /* BufferedIOMixin methods */
     {"close", (PyCFunction)BufferedIOMixin_close, METH_NOARGS},
+    {"detach", (PyCFunction)BufferedIOMixin_detach, METH_NOARGS},
     {"seekable", (PyCFunction)BufferedIOMixin_seekable, METH_NOARGS},
     {"readable", (PyCFunction)BufferedIOMixin_readable, METH_NOARGS},
     {"writable", (PyCFunction)BufferedIOMixin_writable, METH_NOARGS},
@@ -2089,6 +2135,7 @@ BufferedRandom_init(BufferedObject *self, PyObject *args, PyObject *kwds)
     PyObject *raw;
 
     self->ok = 0;
+    self->detached = 0;
 
     if (!PyArg_ParseTupleAndKeywords(args, kwds, "O|nn:BufferedReader", kwlist,
                                      &raw, &buffer_size, &max_buffer_size)) {
@@ -2128,6 +2175,7 @@ BufferedRandom_init(BufferedObject *self, PyObject *args, PyObject *kwds)
 static PyMethodDef BufferedRandom_methods[] = {
     /* BufferedIOMixin methods */
     {"close", (PyCFunction)BufferedIOMixin_close, METH_NOARGS},
+    {"detach", (PyCFunction)BufferedIOMixin_detach, METH_NOARGS},
     {"seekable", (PyCFunction)BufferedIOMixin_seekable, METH_NOARGS},
     {"readable", (PyCFunction)BufferedIOMixin_readable, METH_NOARGS},
     {"writable", (PyCFunction)BufferedIOMixin_writable, METH_NOARGS},
diff --git a/Modules/_io/textio.c b/Modules/_io/textio.c
index 26fc68d..f201ba7 100644
--- a/Modules/_io/textio.c
+++ b/Modules/_io/textio.c
@@ -28,6 +28,19 @@ _unsupported(const char *message)
     return NULL;
 }
 
+PyDoc_STRVAR(TextIOBase_detach_doc,
+    "Separate the underlying buffer from the TextIOBase and return it.\n"
+    "\n"
+    "After the underlying buffer has been detached, the TextIO is in an\n"
+    "unusable state.\n"
+    );
+
+static PyObject *
+TextIOBase_detach(PyObject *self)
+{
+    return _unsupported("detach");
+}
+
 PyDoc_STRVAR(TextIOBase_read_doc,
     "Read at most n characters from stream.\n"
     "\n"
@@ -93,6 +106,7 @@ TextIOBase_newlines_get(PyObject *self, void *context)
 
 
 static PyMethodDef TextIOBase_methods[] = {
+    {"detach", (PyCFunction)TextIOBase_detach, METH_NOARGS, TextIOBase_detach_doc},
     {"read", TextIOBase_read, METH_VARARGS, TextIOBase_read_doc},
     {"readline", TextIOBase_readline, METH_VARARGS, TextIOBase_readline_doc},
     {"write", TextIOBase_write, METH_VARARGS, TextIOBase_write_doc},
@@ -616,6 +630,7 @@ typedef struct
 {
     PyObject_HEAD
     int ok; /* initialized? */
+    int detached;
     Py_ssize_t chunk_size;
     PyObject *buffer;
     PyObject *encoding;
@@ -759,6 +774,7 @@ TextIOWrapper_init(PyTextIOWrapperObject *self, PyObject *args, PyObject *kwds)
     int r;
 
     self->ok = 0;
+    self->detached = 0;
     if (!PyArg_ParseTupleAndKeywords(args, kwds, "O|zzzi:fileio",
                                      kwlist, &buffer, &encoding, &errors,
                                      &newline, &line_buffering))
@@ -1059,19 +1075,45 @@ TextIOWrapper_closed_get(PyTextIOWrapperObject *self, void *context);
 
 #define CHECK_INITIALIZED(self) \
     if (self->ok <= 0) { \
-        PyErr_SetString(PyExc_ValueError, \
-            "I/O operation on uninitialized object"); \
+        if (self->detached) { \
+            PyErr_SetString(PyExc_ValueError, \
+                 "underlying buffer has been detached"); \
+        } else {                                   \
+            PyErr_SetString(PyExc_ValueError, \
+                "I/O operation on uninitialized object"); \
+        } \
         return NULL; \
     }
 
 #define CHECK_INITIALIZED_INT(self) \
     if (self->ok <= 0) { \
-        PyErr_SetString(PyExc_ValueError, \
-            "I/O operation on uninitialized object"); \
+        if (self->detached) { \
+            PyErr_SetString(PyExc_ValueError, \
+                 "underlying buffer has been detached"); \
+        } else {                                   \
+            PyErr_SetString(PyExc_ValueError, \
+                "I/O operation on uninitialized object"); \
+        } \
         return -1; \
     }
 
 
+static PyObject *
+TextIOWrapper_detach(PyTextIOWrapperObject *self)
+{
+    PyObject *buffer, *res;
+    CHECK_INITIALIZED(self);
+    res = PyObject_CallMethodObjArgs((PyObject *)self, _PyIO_str_flush, NULL);
+    if (res == NULL)
+        return NULL;
+    Py_DECREF(res);
+    buffer = self->buffer;
+    self->buffer = NULL;
+    self->detached = 1;
+    self->ok = 0;
+    return buffer;
+}
+
 Py_LOCAL_INLINE(const Py_UNICODE *)
 findchar(const Py_UNICODE *s, Py_ssize_t size, Py_UNICODE ch)
 {
@@ -2341,6 +2383,7 @@ TextIOWrapper_chunk_size_set(PyTextIOWrapperObject *self,
 }
 
 static PyMethodDef TextIOWrapper_methods[] = {
+    {"detach", (PyCFunction)TextIOWrapper_detach, METH_NOARGS},
     {"write", (PyCFunction)TextIOWrapper_write, METH_VARARGS},
     {"read", (PyCFunction)TextIOWrapper_read, METH_VARARGS},
     {"readline", (PyCFunction)TextIOWrapper_readline, METH_VARARGS},