bpo-32030: Add _Py_FindEnvConfigValue() (#4963)

Add a new _Py_FindEnvConfigValue() function: code shared between
Windows and Unix implementations of _PyPathConfig_Calculate() to read
the pyenv.cfg file.

_Py_FindEnvConfigValue() now uses _Py_DecodeUTF8_surrogateescape()
instead of using a Python Unicode string, the Python API must not be
used early during Python initialization. Same change in Unix
search_for_exec_prefix(): use _Py_DecodeUTF8_surrogateescape().

Cleanup also encode_current_locale(): PyMem_RawFree/PyMem_Free can be
called with NULL.

Fix also "NUL byte" => "NULL byte" typo.

1 files changed, 50 insertions, 0 deletions

diff --git a/Python/pathconfig.c b/Python/pathconfig.c
index acb25b6..9591fcc 100644
--- a/Python/pathconfig.c
+++ b/Python/pathconfig.c
@@ -354,6 +354,56 @@ _PyPathConfig_ComputeArgv0(int argc, wchar_t **argv)
     return PyUnicode_FromWideChar(argv0, n);
 }
 
+
+/* Search for a prefix value in an environment file (pyvenv.cfg).
+   If found, copy it into the provided buffer. */
+int
+_Py_FindEnvConfigValue(FILE *env_file, const wchar_t *key,
+                       wchar_t *value, size_t value_size)
+{
+    int result = 0; /* meaning not found */
+    char buffer[MAXPATHLEN*2+1];  /* allow extra for key, '=', etc. */
+
+    fseek(env_file, 0, SEEK_SET);
+    while (!feof(env_file)) {
+        char * p = fgets(buffer, MAXPATHLEN*2, env_file);
+        wchar_t *tmpbuffer;
+        int n;
+
+        if (p == NULL) {
+            break;
+        }
+        n = strlen(p);
+        if (p[n - 1] != '\n') {
+            /* line has overflowed - bail */
+            break;
+        }
+        if (p[0] == '#') {
+            /* Comment - skip */
+            continue;
+        }
+        tmpbuffer = _Py_DecodeUTF8_surrogateescape(buffer, n, NULL);
+        if (tmpbuffer != NULL) {
+            wchar_t * state;
+            wchar_t * tok = wcstok(tmpbuffer, L" \t\r\n", &state);
+            if ((tok != NULL) && !wcscmp(tok, key)) {
+                tok = wcstok(NULL, L" \t", &state);
+                if ((tok != NULL) && !wcscmp(tok, L"=")) {
+                    tok = wcstok(NULL, L"\r\n", &state);
+                    if (tok != NULL) {
+                        wcsncpy(value, tok, MAXPATHLEN);
+                        result = 1;
+                        PyMem_RawFree(tmpbuffer);
+                        break;
+                    }
+                }
+            }
+            PyMem_RawFree(tmpbuffer);
+        }
+    }
+    return result;
+}
+
 #ifdef __cplusplus
 }
 #endif