[pacman-dev] [PATCHv2] add.c: refactor backup file modification checks

[Dave Reisner]

On Mon, May 13, 2013 at 04:03:54PM -0400, Andrew Gregory wrote:
> The previous implementation was overly complex with unnecessary checks
> and nested conditionals.  By reordering the tests and changing them to
> all be checks for positive hash matches rather than non-matches, we can
> collapse several cases and make the process much more linear.  This
> removes the need to set hash_orig = "" just to reach some of the checks
> and corrects a faulty assumption that files are equivalent when the
> hashing process fails.
> 
> Signed-off-by: Andrew Gregory <andrew.gregory.8 at gmail.com>
> ---
> 
> Turns out we can do even better.  Reordered the tests to collapse two more
> cases and updated a few of the comments to better reflect the more linear
> layout.
> 
>  lib/libalpm/add.c | 114 ++++++++++++++++++++++++------------------------------
>  1 file changed, 50 insertions(+), 64 deletions(-)
> 
> diff --git a/lib/libalpm/add.c b/lib/libalpm/add.c
> index 3ef81e3..ba808a5 100644
> --- a/lib/libalpm/add.c
> +++ b/lib/libalpm/add.c
> @@ -273,8 +273,6 @@ static int extract_single_file(alpm_handle_t *handle, struct archive *archive,
>  				/* check newpkg first, so that adding backup files is retroactive */
>  				backup = _alpm_needbackup(entryname, newpkg);
>  				if(backup) {
> -					/* if we force hash_orig to be non-NULL retroactive backup works */
> -					hash_orig = "";
>  					needbackup = 1;
>  				}
>  
> @@ -332,83 +330,71 @@ static int extract_single_file(alpm_handle_t *handle, struct archive *archive,
>  		_alpm_log(handle, ALPM_LOG_DEBUG, "new:      %s\n", hash_pkg);
>  		_alpm_log(handle, ALPM_LOG_DEBUG, "original: %s\n", hash_orig);
>  
> -		if(!oldpkg) {
> -			if(hash_local && hash_pkg && strcmp(hash_local, hash_pkg) != 0) {
> -				/* looks like we have a local file that has a different hash as the
> -				 * file in the package, move it to a .pacorig */
> -				char *newpath;
> -				size_t newlen = strlen(filename) + 9;
> -				MALLOC(newpath, newlen,
> -						errors++; handle->pm_errno = ALPM_ERR_MEMORY; goto needbackup_cleanup);
> +		if(hash_local && hash_pkg && strcmp(hash_local, hash_pkg) == 0) {
> +			/* local and new files are the same, no sense in installing the file
> +			 * over itself, regardless of what the original file was */
> +			_alpm_log(handle, ALPM_LOG_DEBUG,
> +					"action: leaving existing file in place\n");
> +			unlink(checkfile);
> +		} else if(hash_orig && hash_pkg && strcmp(hash_orig, hash_pkg) == 0) {

Mini-rant: Why can't we have hash methods which return int
representations of the hashes instead of strings? It would save us from
needing to use strcmp to compare them.

> +			/* original and new files are the same, leave the local version alone,
> +			 * including any user changes */
> +			_alpm_log(handle, ALPM_LOG_DEBUG,
> +					"action: leaving existing file in place\n");
> +			unlink(checkfile);
> +		} else if(hash_orig && hash_local && strcmp(hash_orig, hash_local) == 0) {
> +			/* installed file has NOT been changed by user,
> +			 * update to the new version */
> +			_alpm_log(handle, ALPM_LOG_DEBUG, "action: installing new file: %s\n",
> +					entryname_orig);
> +			if(try_rename(handle, checkfile, filename)) {
> +				errors++;
> +			}
> +		} else {
> +			/* none of the three files matched another, unpack the new file alongside
> +			 * the local file */
> +			char *newpath;
> +			size_t newlen = strlen(filename) + 9;
> +			MALLOC(newpath, newlen,
> +					errors++; handle->pm_errno = ALPM_ERR_MEMORY; goto needbackup_cleanup);
> +
> +			if(oldpkg) {
> +				_alpm_log(handle, ALPM_LOG_DEBUG,
> +						"action: keeping current file and installing"
> +						" new one with .pacnew ending\n");
> +				snprintf(newpath, newlen, "%s.pacnew", filename);
> +				if(try_rename(handle, checkfile, newpath)) {
> +					errors++;
> +				} else {
> +					_alpm_log(handle, ALPM_LOG_WARNING, _("%s installed as %s\n"),
> +							filename, newpath);
> +					alpm_logaction(handle, ALPM_CALLER_PREFIX,
> +							"warning: %s installed as %s\n", filename, newpath);
> +				}
> +			} else {
> +				_alpm_log(handle, ALPM_LOG_DEBUG,
> +						"action: saving existing file with a .pacorig ending"
> +						" and installing a new one\n");
>  				snprintf(newpath, newlen, "%s.pacorig", filename);
>  
>  				/* move the existing file to the "pacorig" */
>  				if(try_rename(handle, filename, newpath)) {
> -						errors++;
> -					errors++;
> +					errors++;   /* failed rename filename  -> filename.pacorig */
> +					errors++;   /* failed rename checkfile -> filename */
>  				} else {
>  					/* rename the file we extracted to the real name */
>  					if(try_rename(handle, checkfile, filename)) {
>  						errors++;
>  					} else {
> -						_alpm_log(handle, ALPM_LOG_WARNING, _("%s saved as %s\n"), filename, newpath);
> +						_alpm_log(handle, ALPM_LOG_WARNING,
> +								_("%s saved as %s\n"), filename, newpath);
>  						alpm_logaction(handle, ALPM_CALLER_PREFIX,
>  								"warning: %s saved as %s\n", filename, newpath);
>  					}
>  				}
> -				free(newpath);
> -			} else {
> -				/* local file is identical to pkg one, so just remove pkg one */
> -				unlink(checkfile);
>  			}
> -		} else if(hash_orig) {
> -			/* the fun part */
> -
> -			if(hash_local && strcmp(hash_orig, hash_local) == 0) {
> -				/* installed file has NOT been changed by user */
> -				if(hash_pkg && strcmp(hash_orig, hash_pkg) != 0) {
> -					_alpm_log(handle, ALPM_LOG_DEBUG, "action: installing new file: %s\n",
> -							entryname_orig);
>  
> -					if(try_rename(handle, checkfile, filename)) {
> -						errors++;
> -					}
> -				} else {
> -					/* no sense in installing the same file twice, install
> -					 * ONLY if the original and package hashes differ */
> -					_alpm_log(handle, ALPM_LOG_DEBUG, "action: leaving existing file in place\n");
> -					unlink(checkfile);
> -				}
> -			} else if(hash_pkg && strcmp(hash_orig, hash_pkg) == 0) {
> -				/* originally installed file and new file are the same - this
> -				 * implies the case above failed - i.e. the file was changed by a
> -				 * user */
> -				_alpm_log(handle, ALPM_LOG_DEBUG, "action: leaving existing file in place\n");
> -				unlink(checkfile);
> -			} else if(hash_local && hash_pkg && strcmp(hash_local, hash_pkg) == 0) {
> -				/* this would be magical.  The above two cases failed, but the
> -				 * user changes just so happened to make the new file exactly the
> -				 * same as the one in the package... skip it */
> -				_alpm_log(handle, ALPM_LOG_DEBUG, "action: leaving existing file in place\n");
> -				unlink(checkfile);
> -			} else {
> -				char *newpath;
> -				size_t newlen = strlen(filename) + 8;
> -				_alpm_log(handle, ALPM_LOG_DEBUG, "action: keeping current file and installing"
> -						" new one with .pacnew ending\n");
> -				MALLOC(newpath, newlen,
> -						errors++; handle->pm_errno = ALPM_ERR_MEMORY; goto needbackup_cleanup);
> -				snprintf(newpath, newlen, "%s.pacnew", filename);
> -				if(try_rename(handle, checkfile, newpath)) {
> -					errors++;
> -				} else {
> -					_alpm_log(handle, ALPM_LOG_WARNING, _("%s installed as %s\n"),
> -							filename, newpath);
> -					alpm_logaction(handle, ALPM_CALLER_PREFIX,
> -							"warning: %s installed as %s\n", filename, newpath);
> -				}
> -				free(newpath);
> -			}
> +			free(newpath);
>  		}
>  
>  needbackup_cleanup:
> -- 
> 1.8.2.3
> 
>