From a4b6a14ea524689556e9f9cf927a3519c64c0e24 Mon Sep 17 00:00:00 2001
From: Jose Marcial Vieira Bisneto <marcial.vieirab@gmail.com>
Date: Thu, 1 Dec 2016 06:48:16 -0300
Subject: [PATCH] Initial implementation of path/resolver

---
 include/ipfs/path/path.h |   9 +++
 path/resolver.c          | 128 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 137 insertions(+)
 create mode 100644 path/resolver.c

diff --git a/include/ipfs/path/path.h b/include/ipfs/path/path.h
index f2a97c1..2b3fdbb 100644
--- a/include/ipfs/path/path.h
+++ b/include/ipfs/path/path.h
@@ -35,4 +35,13 @@
    int ParseCidToPath (char *dst, char *txt);
    int ParsePath (char *dst, char *txt);
    int PathIsValid (char *p);
+
+   // Resolver provides path resolution to IPFS
+   // It has a pointer to a DAGService, which is uses to resolve nodes.
+   // TODO: now that this is more modular, try to unify this code with the
+   //       the resolvers in namesys
+   typedef struct s_resolver {
+       DAGService DAG;
+       int (*ResolveOnce)(NodeLink **lnk, Context ctx, DAGService *ds, Node **nd, char *name);
+   } Resolver;
 #endif // IPFS_PATH_H
diff --git a/path/resolver.c b/path/resolver.c
new file mode 100644
index 0000000..15e9e70
--- /dev/null
+++ b/path/resolver.c
@@ -0,0 +1,128 @@
+#include "ipfs/cid/cid.h"
+#include "ipfs/path/path.h"
+
+Resolver* NewBasicResolver (DAGService *ds)
+{
+    Resolver *ret = malloc(sizeof(Resolver));
+    if (!ret) return NULL;
+    ret->DAG = ds;
+    ret->ResolveOnce = ResolveSingle;
+    return ret;
+}
+
+// SplitAbsPath clean up and split fpath. It extracts the first component (which
+// must be a Multihash) and return it separately.
+int SplitAbsPath (struct Cid* cid, char ***parts, char *fpath)
+{
+    *parts = Segments(fpath);
+
+    if (strcmp (**parts, "ipfs") == 0) *parts++;
+
+    // if nothing, bail.
+    if (!**parts) return ErrNoComponents;
+
+    // first element in the path is a cid
+    cid_decode_from_string(**parts, strlen(**parts), cid);
+    return 0;
+}
+
+// ResolvePath fetches the node for given path. It returns the last item
+// returned by ResolvePathComponents.
+int ResolvePath(Node **nd, Context ctx, Resolver *s, char *fpath)
+{
+    int err = IsValid(fpath);
+    Node **ndd;
+
+    if (err) {
+        return err;
+    }
+    err = ResolvePathComponents(&ndd, ctx, s, fpath);
+    if (err) {
+        return err;
+    }
+    if (ndd == NULL) {
+        return ErrBadPath;
+    }
+    while(*ndd) {
+        *nd = *ndd;
+        ndd++;
+    }
+    return 0;
+}
+
+int ResolveSingle(NodeLink **lnk, Context ctx, DAGService *ds, Node **nd, char *name)
+{
+    return ResolveLink(lnk, name);
+}
+
+// ResolvePathComponents fetches the nodes for each segment of the given path.
+// It uses the first path component as a hash (key) of the first node, then
+// resolves all other components walking the links, with ResolveLinks.
+int ResolvePathComponents(Node ***nd, Context ctx, Resolver *s, char *fpath)
+{
+    int err;
+    struct Cid h;
+    char **parts;
+
+    err = SplitAbsPath(&h, &parts, fpath);
+    if (err) {
+        return err;
+    }
+
+    //log.Debug("resolve dag get");
+    //*nd = s->DAG.Get(ctx, h);
+    //if (nd == DAG_ERR_VAL) {
+    //   return DAG_ERR_VAL;
+    //}
+
+    return ResolveLinks(ctx, *nd, parts);
+}
+
+// ResolveLinks iteratively resolves names by walking the link hierarchy.
+// Every node is fetched from the DAGService, resolving the next name.
+// Returns the list of nodes forming the path, starting with ndd. This list is
+// guaranteed never to be empty.
+//
+// ResolveLinks(nd, []string{"foo", "bar", "baz"})
+// would retrieve "baz" in ("bar" in ("foo" in nd.Links).Links).Links
+int ResolveLinks(Node ***result, Context ctx, Node *ndd, char **names)
+{
+    int err, idx = 0;
+    NodeLink *lnk;
+    Node *nd;
+
+    *result = calloc (sizeof(Node*), SegmentsLength(names) + 1);
+    if (!*result) {
+        return -1;
+    }
+    memset (*result, NULL, sizeof(Node*) * (SegmentsLength(names)+1));
+
+    *result[idx++] = ndd;
+    nd = ndd; // dup arg workaround
+
+    while (*names) {
+        //TODO
+        //var cancel context.CancelFunc
+        //ctx, cancel = context.WithTimeout(ctx, time.Minute)
+        //defer cancel()
+
+        // for each of the path components
+        err = ResolveLink(&lnk, *names);
+        if (err) {
+            char msg[51];
+            *result[idx] = NULL;
+            snprintf(msg, sizeof(msg), ErrPath[ErrNoLinkFmt], *names, nd->Cid);
+            if (ErrPath[ErrNoLink]) {
+                free(ErrPath[ErrNoLink]);
+            }
+            ErrPath[ErrNoLink] = malloc(strlen(msg) + 1);
+            if (ErrPath[ErrNoLink]) {
+                strcpy(ErrPath[ErrNoLink], msg);
+            }
+            free (*result);
+            return ErrNoLink;
+        }
+        names++;
+    }
+    return 0;
+}