Attempting to get canonical path, for usage in ngspice..

get_windows_canonical_path.c

#include <windows.h>
#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include <errno.h>

/**
 * @brief Resolves a Windows path to its canonical, absolute form using GetFullPathNameW.
 *
 * This function takes a path string (assumed to be UTF-8), converts it to
 * UTF-16, calls the Windows API GetFullPathNameW to resolve '..' and '.'
 * components and make the path absolute, and then converts the result back
 * to a newly allocated UTF-8 string.
 *
 * It handles potential failures during conversion or path resolution.
 * It does NOT automatically add the '\\?\' prefix for long paths, but
 * GetFullPathNameW can produce paths longer than MAX_PATH. The caller
 * might need to add the prefix separately if using the result in APIs
 * that require it for long path support.
 *
 * @param input_path The input path string (UTF-8 encoded). Can be relative or
 *                   absolute, may contain '.' or '..'.
 * @return char* A newly allocated UTF-8 string containing the canonical absolute
 *               path, or NULL on failure. The caller is responsible for
 *               calling free() on the returned string. On failure, errno is
 *               set to indicate the error (e.g., ENOMEM, EINVAL, ENOENT).
 */
char* get_windows_canonical_path(const char* input_path) {
    wchar_t* wPathInput = NULL;
    wchar_t* wPathOutput = NULL;
    char*    utf8PathOutput = NULL;
    DWORD    inputLenW = 0;
    DWORD    outputLenW = 0;
    DWORD    resultLenW = 0;
    int      inputLenMB = 0;
    int      outputLenMB = 0;
    int      original_errno = errno;

    if (input_path == NULL) {
        errno = EINVAL;
        return NULL;
    }

    inputLenMB = (int)strlen(input_path);

    if (inputLenMB == 0) {
        inputLenW = 1;
    } else {
         inputLenW = MultiByteToWideChar(CP_UTF8, 0, input_path, inputLenMB, NULL, 0);
         if (inputLenW == 0) {
             errno = EINVAL;
             return NULL;
         }
         inputLenW++;
    }

    wPathInput = (wchar_t*)malloc(inputLenW * sizeof(wchar_t));
    if (!wPathInput) {
        errno = ENOMEM;
        return NULL;
    }

    if (MultiByteToWideChar(CP_UTF8, 0, input_path, inputLenMB + 1, wPathInput, inputLenW) == 0) {
        free(wPathInput);
        errno = EINVAL;
        return NULL;
    }

    errno = original_errno;
    outputLenW = GetFullPathNameW(wPathInput, 0, NULL, NULL);
    if (outputLenW == 0) {
        DWORD dwError = GetLastError();
        if (dwError == ERROR_FILE_NOT_FOUND || dwError == ERROR_PATH_NOT_FOUND)
            errno = ENOENT;
        else if (dwError == ERROR_ACCESS_DENIED)
            errno = EACCES;
        else
            errno = EINVAL;
        free(wPathInput);
        return NULL;
    }

    wPathOutput = (wchar_t*)malloc(outputLenW * sizeof(wchar_t));
    if (!wPathOutput) {
        free(wPathInput);
        errno = ENOMEM;
        return NULL;
    }

    errno = original_errno;
    resultLenW = GetFullPathNameW(wPathInput, outputLenW, wPathOutput, NULL);
    free(wPathInput);

    if (resultLenW == 0 || resultLenW >= outputLenW) {
        DWORD dwError = GetLastError();
        if (dwError == ERROR_FILE_NOT_FOUND || dwError == ERROR_PATH_NOT_FOUND)
            errno = ENOENT;
        else if (dwError == ERROR_ACCESS_DENIED)
            errno = EACCES;
        else
            errno = EINVAL;
        free(wPathOutput);
        return NULL;
    }

    outputLenMB = WideCharToMultiByte(CP_UTF8, 0, wPathOutput, -1, NULL, 0, NULL, NULL);
    if (outputLenMB == 0) {
        free(wPathOutput);
        errno = EINVAL;
        return NULL;
    }

    utf8PathOutput = (char*)malloc(outputLenMB);
    if (!utf8PathOutput) {
        free(wPathOutput);
        errno = ENOMEM;
        return NULL;
    }

    if (WideCharToMultiByte(CP_UTF8, 0, wPathOutput, -1, utf8PathOutput, outputLenMB, NULL, NULL) == 0) {
        free(wPathOutput);
        free(utf8PathOutput);
        errno = EINVAL;
        return NULL;
    }

    free(wPathOutput);
    errno = original_errno;
    return utf8PathOutput;
}

int main() {
    const char* test_path = "C:/Users/test/some/dir/../../another/../real_dir/./file.txt";
    const char* long_base = "C:\\VeryLongDirectoryNameOftenExceedingLegacyLimits";
    char long_test_path[1024];
    snprintf(long_test_path, sizeof(long_test_path), "%s\\Subdir1\\..\\Subdir2\\.\\FinalFile.data", long_base);
    const char* ngspice_path = "C:/Users/kreij/scoop/apps/msys2/2022-01-28/home/kreij/ok/protodec/examples/juan_temp/sky130A/libs.tech/ngspice/corners/../../../libs.ref/sky130_fd_pr/spice/../../../libs.tech/ngspice/parasitics/sky130_fd_pr__model__parasitic__diode_pw2dn__extended_drain.model.spice";

    char* canonical1 = get_windows_canonical_path(test_path);
    char* canonical2 = get_windows_canonical_path(long_test_path);
    char* canonical3 = get_windows_canonical_path(ngspice_path);
    char* canonical4 = get_windows_canonical_path(".\\relative\\..\\path.txt");
    char* canonical_fail = get_windows_canonical_path("C:\\NonExistent\\..\\Path");

    printf("Input 1:  %s\n", test_path);
    if (canonical1) {
        printf("Output 1: %s\n", canonical1);
        free(canonical1);
    } else {
        perror("Error resolving path 1");
    }
    printf("\n");

    printf("Input 2:  %s\n", long_test_path);
     if (canonical2) {
        printf("Output 2: %s\n", canonical2);
        free(canonical2);
    } else {
        perror("Error resolving path 2");
    }
    printf("\n");

     printf("Input 3:  %s\n", ngspice_path);
     if (canonical3) {
        printf("Output 3: %s\n", canonical3);
        free(canonical3);
    } else {
        perror("Error resolving path 3");
    }
    printf("\n");

    printf("Input 4:  .\\relative\\..\\path.txt\n");
     if (canonical4) {
        printf("Output 4: %s\n", canonical4);
        free(canonical4);
    } else {
        perror("Error resolving path 4");
    }
    printf("\n");

    printf("Input 5:  C:\\NonExistent\\..\\Path\n");
     if (canonical_fail) {
        printf("Output 5: %s\n", canonical_fail);
        free(canonical_fail);
    } else {
        printf("Output 5: NULL\n");
        perror("  Error reported for path 5");
    }
    printf("\n");

    return 0;
}

output.txt

Input 1:  C:/Users/test/some/dir/../../another/../real_dir/./file.txt
Output 1: C:\Users\test\real_dir\file.txt

Input 2:  C:\VeryLongDirectoryNameOftenExceedingLegacyLimits\Subdir1\..\Subdir2\.\FinalFile.data
Output 2: C:\VeryLongDirectoryNameOftenExceedingLegacyLimits\Subdir2\FinalFile.data

Input 3:  C:/Users/kreij/scoop/apps/msys2/2022-01-28/home/kreij/ok/protodec/examples/juan_temp/sky130A/libs.tech/ngspice/corners/../../../libs.ref/sky130_fd_pr/spice/../../../libs.tech/ngspice/parasitics/sky130_fd_pr__model__parasitic__diode_pw2dn__extended_drain.model.spice
Output 3: C:\Users\kreij\scoop\apps\msys2\2022-01-28\home\kreij\ok\protodec\examples\juan_temp\sky130A\libs.tech\ngspice\parasitics\sky130_fd_pr__model__parasitic__diode_pw2dn__extended_drain.model.spice

Input 4:  .\relative\..\path.txt
Output 4: C:\test\path.txt

Input 5:  C:\NonExistent\..\Path
Output 5: C:\Path