Completely rework delta algorithm

Using the graph structures that Nagy set up for dependency sorting, we now
do a similar process for deltas. Load up all of the deltas into a graph
object on which we can then apply Dijkstra's algorithm, using the new weight
field of graph struct.
We initialize the nodes weight using the base files that we can use in our
filecache (both filename and md5sum must match). The algorithm then picks
the best path among those that can be resolved.

Note that this algorithm has a few advantages over the old one:
1. It is completely file agnostic. These delta chains do not have to consist
   of package files- this could be adopted to do delta-fied DBs.
2. It does not use the local_db anymore, or even care if a package or file
   is currently installed. Instead, it only looks in the filecache for files
   and packages that match delta chain entries.

Original-work-by: Dan McGee <dan@archlinux.org>
Signed-off-by: Chantry Xavier <shiningxc@gmail.com>

1 files changed, 137 insertions, 95 deletions

diff --git a/lib/libalpm/delta.c b/lib/libalpm/delta.c
index 12fb9bd7..fdb4d99b 100644
--- a/lib/libalpm/delta.c
+++ b/lib/libalpm/delta.c
@@ -21,13 +21,14 @@
 
 #include <stdlib.h>
 #include <string.h>
+#include <limits.h>
 
 /* libalpm */
 #include "delta.h"
+#include "alpm_list.h"
 #include "util.h"
 #include "log.h"
-#include "alpm_list.h"
-#include "alpm.h"
+#include "graph.h"
 
 /** \addtogroup alpm_deltas Delta Functions
  * @brief Functions to manipulate libalpm deltas
@@ -78,129 +79,170 @@ unsigned long SYMEXPORT alpm_delta_get_size(pmdelta_t *delta)
 
 /** @} */
 
-/** Calculates the combined size of a list of delta files.
- * @param deltas the list of pmdelta_t * objects
- * @return the combined size
- */
-unsigned long _alpm_delta_path_size(alpm_list_t *deltas)
+static alpm_list_t *delta_graph_init(alpm_list_t *deltas)
 {
-	unsigned long sum = 0;
-	alpm_list_t *dlts = deltas;
-
-	while(dlts) {
-		pmdelta_t *d = alpm_list_getdata(dlts);
-		sum += d->delta_size;
+	alpm_list_t *i, *j;
+	alpm_list_t *vertices = NULL;
+	/* create the vertices */
+	for(i = deltas; i; i = i->next) {
+		char *fpath, *md5sum;
+		pmgraph_t *v = _alpm_graph_new();
+		pmdelta_t *vdelta = i->data;
+		vdelta->download_size = vdelta->delta_size;
+		v->weight = ULONG_MAX;
+
+		/* determine whether the delta file already exists */
+		fpath = _alpm_filecache_find(vdelta->delta);
+		md5sum = alpm_get_md5sum(fpath);
+		if(fpath && md5sum && strcmp(md5sum, vdelta->delta_md5) == 0) {
+			vdelta->download_size = 0;
+		}
+		FREE(fpath);
+		FREE(md5sum);
+
+		/* determine whether a base 'from' file exists */
+		fpath = _alpm_filecache_find(vdelta->from);
+		md5sum = alpm_get_md5sum(fpath);
+		if(fpath && md5sum && strcmp(md5sum, vdelta->from_md5) == 0) {
+			v->weight = vdelta->download_size;
+		}
+		FREE(fpath);
+		FREE(md5sum);
 
-		dlts = alpm_list_next(dlts);
+		v->data = vdelta;
+		vertices = alpm_list_add(vertices, v);
 	}
 
-	return(sum);
+	/* compute the edges */
+	for(i = vertices; i; i = i->next) {
+		pmgraph_t *v_i = i->data;
+		pmdelta_t *d_i = v_i->data;
+		/* loop a second time so we make all possible comparisons */
+		for(j = vertices; j; j = j->next) {
+			pmgraph_t *v_j = j->data;
+			pmdelta_t *d_j = v_j->data;
+			/* We want to create a delta tree like the following:
+			 *          1_to_2
+			 *            |
+			 * 1_to_3   2_to_3
+			 *   \        /
+			 *     3_to_4
+			 * If J 'from' is equal to I 'to', then J is a child of I.
+			 * */
+			if(strcmp(d_j->from, d_i->to) == 0
+					&& strcmp(d_j->from_md5, d_i->to_md5) == 0) {
+				v_i->children = alpm_list_add(v_i->children, v_j);
+			}
+		}
+		v_i->childptr = v_i->children;
+	}
+	return(vertices);
 }
 
-/** Calculates the combined size of a list of delta files that are not
- * in the cache.
- * @param deltas the list of pmdelta_t * objects
- * @return the combined size
- */
-unsigned long _alpm_delta_path_size_uncached(alpm_list_t *deltas)
-{
-	unsigned long sum = 0;
-	alpm_list_t *dlts = deltas;
-
-	while(dlts) {
-		pmdelta_t *d = alpm_list_getdata(dlts);
-		char *fname = _alpm_filecache_find(d->delta);
+static unsigned long delta_vert(alpm_list_t *vertices,
+		const char *to, const char *to_md5, alpm_list_t **path) {
+	alpm_list_t *i;
+	pmgraph_t *v;
+	while(1) {
+		v = NULL;
+		/* find the smallest vertice not visited yet */
+		for(i = vertices; i; i = i->next) {
+			pmgraph_t *v_i = i->data;
+
+			if(v_i->state == -1) {
+				continue;
+			}
 
-		if(!fname) {
-			sum += d->delta_size;
+			if(v == NULL || v_i->weight < v->weight) {
+				v = v_i;
+			}
+		}
+		if(v == NULL || v->weight == ULONG_MAX) {
+			break;
 		}
 
-		FREE(fname);
-
-		dlts = alpm_list_next(dlts);
-	}
+		v->state = -1;
 
-	return(sum);
-}
+		v->childptr = v->children;
+		while(v->childptr) {
+			pmgraph_t *v_c = v->childptr->data;
+			pmdelta_t *d_c = v_c->data;
+			if(v_c->weight > v->weight + d_c->download_size) {
+				v_c->weight = v->weight + d_c->download_size;
+				v_c->parent = v;
+			}
 
-/** Calculates the shortest path from one version to another.
- * The shortest path is defined as the path with the smallest combined
- * size, not the length of the path.
- * The algorithm is based on Dijkstra's shortest path algorithm.
- * @param deltas the list of pmdelta_t * objects that a package has
- * @param from the version to start from
- * @param to the version to end at
- * @param path the current path
- * @return the list of pmdelta_t * objects that has the smallest size.
- * NULL (the empty list) is returned if there is no path between the
- * versions.
- */
-static alpm_list_t *shortest_delta_path(alpm_list_t *deltas,
-		const char *from, const char *to, alpm_list_t *path)
-{
-	alpm_list_t *d;
-	alpm_list_t *shortest = NULL;
+			v->childptr = (v->childptr)->next;
 
-	/* Found the 'to' version, this is a good path so return it. */
-	if(strcmp(from, to) == 0) {
-		return(path);
+		}
 	}
 
-	for(d = deltas; d; d = alpm_list_next(d)) {
-		pmdelta_t *v = alpm_list_getdata(d);
+	v = NULL;
+	unsigned long bestsize = 0;
 
-		/* If this vertex has already been visited in the path, go to the
-		 * next vertex. */
-		if(alpm_list_find_ptr(path, v)) {
-			continue;
-		}
+	for(i = vertices; i; i = i->next) {
+		pmgraph_t *v_i = i->data;
+		pmdelta_t *d_i = v_i->data;
 
-		/* Once we find a vertex that starts at the 'from' version,
-		 * recursively find the shortest path using the 'to' version of this
-		 * current vertex as the 'from' version in the function call. */
-		if(strcmp(v->from, from) == 0) {
-			alpm_list_t *newpath = alpm_list_copy(path);
-			newpath = alpm_list_add(newpath, v);
-			newpath = shortest_delta_path(deltas, v->to, to, newpath);
-
-			if(newpath != NULL) {
-				/* The path returned works, now use it unless there is already a
-				 * shorter path found. */
-				if(shortest == NULL) {
-					shortest = newpath;
-				} else if(_alpm_delta_path_size(shortest) > _alpm_delta_path_size(newpath)) {
-					alpm_list_free(shortest);
-					shortest = newpath;
-				} else {
-					alpm_list_free(newpath);
-				}
+		if(strcmp(d_i->to, to) == 0
+				|| strcmp(d_i->to_md5, to_md5) == 0) {
+			if(v == NULL || v_i->weight < v->weight) {
+				v = v_i;
+				bestsize = v->weight;
 			}
 		}
 	}
 
-	alpm_list_free(path);
+	alpm_list_t *rpath = NULL;
+	while(v != NULL) {
+		pmdelta_t *vdelta = v->data;
+		rpath = alpm_list_add(rpath, vdelta);
+		v = v->parent;
+	}
+	*path = alpm_list_reverse(rpath);
+	alpm_list_free(rpath);
 
-	return(shortest);
+	return(bestsize);
 }
 
 /** Calculates the shortest path from one version to another.
  * The shortest path is defined as the path with the smallest combined
  * size, not the length of the path.
- * @param deltas the list of pmdelta_t * objects that a package has
- * @param from the version to start from
- * @param to the version to end at
- * @return the list of pmdelta_t * objects that has the smallest size.
- * NULL (the empty list) is returned if there is no path between the
- * versions.
+ * @param deltas the list of pmdelta_t * objects that a file has
+ * @param to the file to start the search at
+ * @param to_md5 the md5sum of the above named file
+ * @param path the pointer to a list location where pmdelta_t * objects that
+ * have the smallest size are placed. NULL is set if there is no path
+ * possible with the files available.
+ * @return the size of the path stored, or ULONG_MAX if path is unfindable
  */
-alpm_list_t *_alpm_shortest_delta_path(alpm_list_t *deltas, const char *from,
-		const char *to)
+unsigned long _alpm_shortest_delta_path(alpm_list_t *deltas,
+		const char *to, const char *to_md5, alpm_list_t **path)
 {
-	alpm_list_t *path = NULL;
+	alpm_list_t *bestpath = NULL;
+	alpm_list_t *vertices;
+	unsigned long bestsize = ULONG_MAX;
+
+	ALPM_LOG_FUNC;
+
+	if(deltas == NULL) {
+		*path = NULL;
+		return(bestsize);
+	}
+
+	_alpm_log(PM_LOG_DEBUG, "started delta shortest-path search\n");
+
+	vertices = delta_graph_init(deltas);
+
+	bestsize = delta_vert(vertices, to, to_md5, &bestpath);
+
+	_alpm_log(PM_LOG_DEBUG, "delta shortest-path search complete\n");
 
-	path = shortest_delta_path(deltas, from, to, path);
+	alpm_list_free_inner(vertices, _alpm_graph_free);
+	alpm_list_free(vertices);
 
-	return(path);
+	*path = bestpath;
+	return(bestsize);
 }
 
 /** Parses the string representation of a pmdelta_t object.