Read PE exports directly instead of shelling to dumpbin

dumpbin only exists inside a Visual Studio developer environment, which
the CI runner never enters, so the symbol check died with WinError 2
after the example had built and passed its tests.

Parse the PE export name table instead. It needs no toolchain, so the
check keeps working wherever Python runs, and Windows is the platform
this check exists to cover: it is the one that can silently fail to
export a symbol.

Validated against the win_amd64 wheel built from this branch, read on
macOS: 252 exports, of which 219 are ccsp_, matching the 219 declared
symbols exactly. Non-PE input is rejected rather than misparsed.

Signed-off-by: Tim Paine <3105306+timkpaine@users.noreply.github.com>

Author: timkpaine

ci/scripts/check_c_api.py

@@ -18,6 +18,7 @@
 import argparse
 import platform
 import re
+import struct
 import subprocess
 import sys
 import sysconfig
@@ -39,10 +40,55 @@ def declared_symbols() -> set[str]:
     return symbols
 
 
+def pe_exported_symbols(library: Path) -> set[str]:
+    """Read the export name table out of a PE image.
+
+    dumpbin is the obvious tool but only exists inside a Visual Studio developer environment,
+    which the CI runner does not enter, so parse the image directly instead.
+    """
+    data = library.read_bytes()
+    pe = struct.unpack_from("<I", data, 0x3C)[0]
+    if data[pe : pe + 4] != b"PE\0\0":
+        raise ValueError(f"{library} is not a PE image")
+
+    num_sections = struct.unpack_from("<H", data, pe + 6)[0]
+    opt_size = struct.unpack_from("<H", data, pe + 20)[0]
+    opt = pe + 24
+    magic = struct.unpack_from("<H", data, opt)[0]
+    # The export directory is the first data directory entry; PE32+ places it 16 bytes later.
+    export_rva = struct.unpack_from("<I", data, opt + (112 if magic == 0x20B else 96))[0]
+    if not export_rva:
+        return set()
+
+    sections = []
+    sec = opt + opt_size
+    for i in range(num_sections):
+        off = sec + i * 40
+        virt_addr, raw_size, raw_ptr = struct.unpack_from("<III", data, off + 12)
+        sections.append((virt_addr, raw_size, raw_ptr))
+
+    def to_offset(rva: int) -> int:
+        for virt_addr, raw_size, raw_ptr in sections:
+            if virt_addr <= rva < virt_addr + raw_size:
+                return raw_ptr + (rva - virt_addr)
+        raise ValueError(f"RVA {rva:#x} outside every section of {library}")
+
+    export = to_offset(export_rva)
+    num_names = struct.unpack_from("<I", data, export + 24)[0]
+    names_rva = struct.unpack_from("<I", data, export + 32)[0]
+    names = to_offset(names_rva)
+
+    symbols = set()
+    for i in range(num_names):
+        name_rva = struct.unpack_from("<I", data, names + i * 4)[0]
+        start = to_offset(name_rva)
+        symbols.add(data[start : data.index(b"\0", start)].decode("ascii"))
+    return symbols
+
+
 def exported_symbols(library: Path) -> set[str]:
     if platform.system() == "Windows":
-        out = subprocess.run(["dumpbin", "/EXPORTS", str(library)], capture_output=True, text=True, check=True).stdout
-        return set(re.findall(r"\b(ccsp_[A-Za-z0-9_]+)\b", out))
+        return {s for s in pe_exported_symbols(library) if s.startswith("ccsp_")}
 
     out = subprocess.run(
         ["nm", "-gU" if platform.system() == "Darwin" else "-D", "--defined-only", str(library)]