[RFC PATCH] RFC: expand_tilde () for potential future path expansion

[Bijan Chokoufe Nejad]

(Second Try: This time it should come from a mail adress of the mailing list)

Woops. Now we did it twice. I have my implementation directly in
notmuch-config.c which makes it harder to test and to reuse elsewhere (not sure
that this is necessary though).

I tested mine to work with

~
~/
~foo/.mail
~foo/
~foo
~bar/.mail
~bar/
~bar

(where bar is not a user in my system but foo is) and all cases work fine. I
send the patch and then we can discuss how to proceed. For me both versions look
good enough though.

On 16-05-14, Tomi Ollila wrote:
> One implementation how to do this. Output of the "tests".
>
> $ sh expand-tilde.c
> + exec gcc -std=c99 -Wall -Wstrict-prototypes -Winit-self -Wformat=2 -Wcast-align -Wpointer-arith -Wextra -Wwrite-strings -Wcast-qual -Wshadow -Wmissing-include-dirs -Wundef -Wbad-function-cast -Wlogical-op -Waggregate-return -Wold-style-definition -Wmissing-prototypes -Wmissing-declarations -Wredundant-decls -Wnested-externs -Winline -Wvla -Woverlength-strings -Wpadded -O2 -o expand-tilde expand-tilde.c
> $
> $ ./expand-tilde
>
> input '~',  expanded '/home/too',  rest ''
> input '~root',  expanded '/root',  rest ''
>
> $ HOME=/a/b/c/ ./expand-tilde '~' '~'/ "~$USER" "~$USER/" '~'root '~'root/ '~none' '~none/'
>
> input '~',  expanded '/a/b/c/',  rest ''
> input '~/',  expanded '/a/b/c/',  rest '/'
> input '~too',  expanded '/home/too',  rest ''
> input '~too/',  expanded '/home/too',  rest '/'
> input '~root',  expanded '/root',  rest ''
> input '~root/',  expanded '/root',  rest '/'
> input '~none',  expanded '(null)',  rest '~none'
> input '~none/',  expanded '(null)',  rest '~none/'
>
> $ HOME= ./expand-tilde '~' '~'/ "~$USER" "~$USER/"
>
> input '~',  expanded '',  rest ''
> input '~/',  expanded '',  rest '/'
> input '~too',  expanded '/home/too',  rest ''
> input '~too/',  expanded '/home/too',  rest '/'
>
> $ ( unset HOME; ./expand-tilde '~' '~'/ "~$USER" "~$USER/" )
>
> input '~',  expanded '(null)',  rest '~'
> input '~/',  expanded '(null)',  rest '~/'
> input '~too',  expanded '/home/too',  rest ''
> input '~too/',  expanded '/home/too',  rest '/'
> ---
>  util/expand-tilde.c | 102 ++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 102 insertions(+)
>  create mode 100644 util/expand-tilde.c
>
> diff --git a/util/expand-tilde.c b/util/expand-tilde.c
> new file mode 100644
> index 0000000..e3097e6
> --- /dev/null
> +++ b/util/expand-tilde.c
> @@ -0,0 +1,102 @@
> +#if 0 /* -*- mode: c; c-file-style: "stroustrup"; tab-width: 8; -*-
> + set -eu; trg=`exec basename "$0" .c`; rm -f "$trg"
> + WARN="-Wall -Wstrict-prototypes -Winit-self -Wformat=2" # -pedantic
> + WARN="$WARN -Wcast-align -Wpointer-arith " # -Wfloat-equal #-Werror
> + WARN="$WARN -Wextra -Wwrite-strings -Wcast-qual -Wshadow" # -Wconversion
> + WARN="$WARN -Wmissing-include-dirs -Wundef -Wbad-function-cast -Wlogical-op"
> + WARN="$WARN -Waggregate-return -Wold-style-definition"
> + WARN="$WARN -Wmissing-prototypes -Wmissing-declarations -Wredundant-decls"
> + WARN="$WARN -Wnested-externs -Winline -Wvla -Woverlength-strings -Wpadded"
> + case ${1-} in '') set x -O2; shift; esac
> + #case ${1-} in '') set x -ggdb; shift; esac
> + set -x; exec ${CC:-gcc} -std=c99 $WARN "$@" -o "$trg" "$0"
> + exit $?
> + */
> +#endif
> +/*
> + * $ expand-tilde.c $
> + *
> + * Author: Tomi Ollila -- too ät iki piste fi
> + *
> + * Created: Sat 14 May 2016 13:10:35 EEST too
> + * Last modified: Sat 14 May 2016 14:22:10 +0300 too
> + *
> + * *** Public Domain ***
> + */
> +
> +#include <stdlib.h>
> +#include <sys/types.h>
> +#include <pwd.h>
> +
> +/* USER_NAME_MAX_LENGTH is not usually defined (publicly in standard paths). */
> +
> +#ifndef USER_NAME_MAX_LENGTH
> +#define USER_NAME_MAX_LENGTH 32
> +#endif
> +
> +static // for -Wmissing-prototypes
> +/* This is modeled after expand-file-name in emacs sources (fileio.c);
> + *  simplified and using constant buffer for user name.
> + *  neither emacs nor this implementation has restrictions in username chars
> + *  ...we may be looking forward for multibyte usernames...
> + */
> +const char * expand_tilde(const char * path, const char ** rest)
> +{
> +    if (path == NULL || path[0] != '~') {
> +        *rest = path;
> +        return NULL;
> +    }
> +
> +    if (path[1] == '/' || path[1] == '\0') {
> +        const char * home = getenv ("HOME");
> +        *rest = home? path + 1: path;
> +        return home;
> +    }
> +
> +    char username[USER_NAME_MAX_LENGTH + 1];
> +    int namepos = 0;
> +    const char * pathp = path + 1;
> +
> +    while (1) {
> +        username[namepos++] = pathp++[0];
> +        if (pathp[0] == '/' || pathp[0] == '\0')
> +            break;
> +        if (namepos >= USER_NAME_MAX_LENGTH) {
> +            *rest = path;
> +            return NULL;
> +        }
> +    }
> +    username[namepos] = '\0';
> +
> +    struct passwd * pw = getpwnam (username);
> +    if (pw == NULL) {
> +        *rest = path;
> +        return NULL;
> +    }
> +    *rest = path + 1 + namepos;
> +    return pw->pw_dir;
> + }
> +
> +#include <stdio.h>
> +
> +static void print_expanded(const char * path)
> +{
> +    const char * rest;
> +    const char * expanded = expand_tilde(path, &rest);
> +    printf("input '%s',  expanded '%s',  rest '%s'\n",
> +           path, expanded, rest);
> +}
> +
> +int main(int argc, char * argv[])
> +{
> +    printf("\n");
> +    if (argc < 2) {
> +        print_expanded("~\0-- this something not to be seen in output --");
> +        print_expanded("~root\0-- this something not to be seen in output --");
> +    } else {
> +        for (int i = 1; i < argc; i++)
> +            print_expanded(argv[i]);
> +    }
> +    printf("\n");
> +    return 0;
> +}
> --
> 2.8.2
>