Build a minimized Nix with MinGW

At this point many features are stripped out, but this works:

- Can run libnix{util,store,expr} unit tests
- Can run some Nix commands

Co-Authored-By volth <volth@volth.com>
Co-Authored-By Brian McKenna <brian@brianmckenna.org>

src/libutil/windows/file-descriptor.cc

@@ -0,0 +1,148 @@
+#include "file-system.hh"
+#include "signals.hh"
+#include "finally.hh"
+#include "serialise.hh"
+#include "windows-error.hh"
+#include "file-path.hh"
+
+#include <fileapi.h>
+#include <error.h>
+#include <namedpipeapi.h>
+#include <namedpipeapi.h>
+#define WIN32_LEAN_AND_MEAN
+#include <windows.h>
+
+namespace nix {
+
+std::string readFile(HANDLE handle)
+{
+    LARGE_INTEGER li;
+    if (!GetFileSizeEx(handle, &li))
+        throw WinError("%s:%d statting file", __FILE__, __LINE__);
+
+    return drainFD(handle, true, li.QuadPart);
+}
+
+
+void readFull(HANDLE handle, char * buf, size_t count)
+{
+    while (count) {
+        checkInterrupt();
+        DWORD res;
+        if (!ReadFile(handle, (char *) buf, count, &res, NULL))
+            throw WinError("%s:%d reading from file", __FILE__, __LINE__);
+        if (res == 0) throw EndOfFile("unexpected end-of-file");
+        count -= res;
+        buf += res;
+    }
+}
+
+
+void writeFull(HANDLE handle, std::string_view s, bool allowInterrupts)
+{
+    while (!s.empty()) {
+        if (allowInterrupts) checkInterrupt();
+        DWORD res;
+#if _WIN32_WINNT >= 0x0600
+        auto path = handleToPath(handle); // debug; do it before becuase handleToPath changes lasterror
+        if (!WriteFile(handle, s.data(), s.size(), &res, NULL)) {
+            throw WinError("writing to file %1%:%2%", handle, path);
+        }
+#else
+        if (!WriteFile(handle, s.data(), s.size(), &res, NULL)) {
+            throw WinError("writing to file %1%", handle);
+        }
+#endif
+        if (res > 0)
+            s.remove_prefix(res);
+    }
+}
+
+
+std::string readLine(HANDLE handle)
+{
+    std::string s;
+    while (1) {
+        checkInterrupt();
+        char ch;
+        // FIXME: inefficient
+        DWORD rd;
+        if (!ReadFile(handle, &ch, 1, &rd, NULL)) {
+            throw WinError("reading a line");
+        } else if (rd == 0)
+            throw EndOfFile("unexpected EOF reading a line");
+        else {
+            if (ch == '\n') return s;
+            s += ch;
+        }
+    }
+}
+
+
+void drainFD(HANDLE handle, Sink & sink/*, bool block*/)
+{
+    std::vector<unsigned char> buf(64 * 1024);
+    while (1) {
+        checkInterrupt();
+        DWORD rd;
+        if (!ReadFile(handle, buf.data(), buf.size(), &rd, NULL)) {
+            WinError winError("%s:%d reading from handle %p", __FILE__, __LINE__, handle);
+            if (winError.lastError == ERROR_BROKEN_PIPE)
+                break;
+            throw winError;
+        }
+        else if (rd == 0) break;
+        sink({(char *) buf.data(), (size_t) rd});
+    }
+}
+
+
+//////////////////////////////////////////////////////////////////////
+
+
+void Pipe::create()
+{
+    SECURITY_ATTRIBUTES saAttr = {0};
+    saAttr.nLength = sizeof(SECURITY_ATTRIBUTES);
+    saAttr.lpSecurityDescriptor = NULL;
+    saAttr.bInheritHandle = TRUE;
+
+    HANDLE hReadPipe, hWritePipe;
+    if (!CreatePipe(&hReadPipe, &hWritePipe, &saAttr, 0))
+        throw WinError("CreatePipe");
+
+    readSide = hReadPipe;
+    writeSide = hWritePipe;
+}
+
+
+//////////////////////////////////////////////////////////////////////
+
+#if _WIN32_WINNT >= 0x0600
+
+std::wstring handleToFileName(HANDLE handle) {
+    std::vector<wchar_t> buf(0x100);
+    DWORD dw = GetFinalPathNameByHandleW(handle, buf.data(), buf.size(), FILE_NAME_OPENED);
+    if (dw == 0) {
+        if (handle == GetStdHandle(STD_INPUT_HANDLE )) return L"<stdin>";
+        if (handle == GetStdHandle(STD_OUTPUT_HANDLE)) return L"<stdout>";
+        if (handle == GetStdHandle(STD_ERROR_HANDLE )) return L"<stderr>";
+        return (boost::wformat(L"<unnnamed handle %X>") % handle).str();
+    }
+    if (dw > buf.size()) {
+        buf.resize(dw);
+        if (GetFinalPathNameByHandleW(handle, buf.data(), buf.size(), FILE_NAME_OPENED) != dw-1)
+            throw WinError("GetFinalPathNameByHandleW");
+        dw -= 1;
+    }
+    return std::wstring(buf.data(), dw);
+}
+
+
+Path handleToPath(HANDLE handle) {
+    return os_string_to_string(handleToFileName(handle));
+}
+
+#endif
+
+}