Fixed error pulling doc with unchanged attachments from CouchDB

Nasty edge case where the attachment is unchanged, but the parent rev
isn't available (doc was changed multiple times remotely), _and_ the
attachment metadata doesn't contain a usable digest (CouchDB's digests
are MD5 not SHA-1.)
Fixes #802

Source/CBLDatabase+Attachments.h

@@ -30,7 +30,7 @@ typedef enum {
 /** Scans the rev's _attachments dictionary, adding inline attachment data to the blob-store
     and turning all the attachments into stubs. */
 - (BOOL) processAttachmentsForRevision: (CBL_MutableRevision*)rev
-                             prevRevID: (NSString*)prevRevID
+                              ancestry: (NSArray*)ancestry // 1st item is parent revID, etc.
                                 status: (CBLStatus*)outStatus;
 
 /** Modifies a CBL_Revision's _attachments dictionary by adding the "data" property to all

Source/CBLDatabase+Attachments.m

@@ -260,7 +260,7 @@ - (BOOL) expandAttachmentsIn: (CBL_MutableRevision*)rev
 
 /** Given a revision, updates its _attachments dictionary for storage in the database. */
 - (BOOL) processAttachmentsForRevision: (CBL_MutableRevision*)rev
-                             prevRevID: (NSString*)prevRevID
+                              ancestry: (NSArray*)ancestry
                                 status: (CBLStatus*)outStatus
 {
     *outStatus = kCBLStatusOK;
@@ -276,6 +276,7 @@ - (BOOL) processAttachmentsForRevision: (CBL_MutableRevision*)rev
         return YES;
     }
 
+    NSString *prevRevID = (ancestry.count > 0) ? ancestry[0] : nil;
     unsigned generation = [CBL_Revision generationFromRevID: prevRevID] + 1;
     __block NSDictionary* parentAttachments = nil;
 
@@ -307,12 +308,20 @@ - (BOOL) processAttachmentsForRevision: (CBL_MutableRevision*)rev
                 parentAttachments = [self attachmentsForDocID: rev.docID revID: prevRevID
                                                        status: &status];
                 if (!parentAttachments) {
-                    if (status == kCBLStatusNotFound
-                        && [_attachments hasBlobForKey: attachment.blobKey]) {
-                        // Parent revision's body isn't known (we are probably pulling a rev along
-                        // with its entire history) but it's OK, we have the attachment already
-                        *outStatus = kCBLStatusOK;
-                        return attachInfo;
+                    if (status == kCBLStatusNotFound) {
+                        if ([_attachments hasBlobForKey: attachment.blobKey]) {
+                            // Parent revision's body isn't known (we are probably pulling a rev along
+                            // with its entire history) but it's OK, we have the attachment already
+                            *outStatus = kCBLStatusOK;
+                            return attachInfo;
+                        }
+                        // If parent rev isn't available, look farther back in ancestry:
+                        NSDictionary* ancestorAttachment = [self findAttachment: name
+                                                                         revpos: attachment->revpos
+                                                                          docID: rev.docID
+                                                                       ancestry: ancestry];
+                        if (ancestorAttachment)
+                            return ancestorAttachment;
                     }
                     if (status == kCBLStatusOK || status == kCBLStatusNotFound)
                         status = kCBLStatusBadAttachment;
@@ -343,6 +352,27 @@ - (BOOL) processAttachmentsForRevision: (CBL_MutableRevision*)rev
 }
 
 
+// Looks for an attachment with the given revpos in the document's ancestry.
+- (NSDictionary*) findAttachment: (NSString*)name
+                          revpos: (unsigned)revpos
+                           docID: (NSString*)docID
+                        ancestry: (NSArray*)ancestry
+{
+    for (NSInteger i = ancestry.count - 1; i >= 0; i--) {
+        NSString* revID = ancestry[i];
+        if ([CBL_Revision generationFromRevID: revID] >= revpos) {
+            CBLStatus status;
+            NSDictionary* attachments = [self attachmentsForDocID: docID revID: revID
+                                                           status: &status];
+            NSDictionary* attachment = attachments[name];
+            if (attachment)
+                return attachment;
+        }
+    }
+    return nil;
+}
+
+
 #pragma mark - MISC.:
 
 

Source/CBLDatabase+Insertion.m

@@ -181,7 +181,7 @@ - (CBL_Revision*) putDocID: (NSString*)inDocID
                                                                          deleted: deleting];
         tmpRev.properties = properties;
         if (![self processAttachmentsForRevision: tmpRev
-                                       prevRevID: prevRevID
+                                        ancestry: (prevRevID ? @[prevRevID] : nil)
                                           status: outStatus]) {
             CBLStatusToOutNSError(*outStatus, outError);
             return nil;
@@ -238,9 +238,9 @@ - (CBLStatus) forceInsert: (CBL_Revision*)inRev
     CBLStatus status;
     if (inRev.attachments) {
         CBL_MutableRevision* updatedRev = [inRev mutableCopy];
-        NSString* prevRevID = history.count >= 2 ? history[1] : nil;
+        NSArray* ancestry = [history subarrayWithRange: NSMakeRange(1, history.count-1)];
         if (![self processAttachmentsForRevision: updatedRev
-                                       prevRevID: prevRevID
+                                        ancestry: ancestry
                                           status: &status]) {
             CBLStatusToOutNSError(status, outError);
             return status;

Unit-Tests/DatabaseAttachment_Tests.m

@@ -483,6 +483,41 @@ - (void) test14_FollowingAttachments {
                                         {@"revpos", @1})}));
 }
 
+// Test for inserting a revision with attachments, when the parent of the new revision isn't local
+// and there are attachments that are unchanged in the revision. See issue #802.
+- (void) test15_MissingIntermediateRevs {
+    // Put a revision that includes an _attachments dict:
+    NSData* attach1 = [@"This is the body of attach1" dataUsingEncoding: NSUTF8StringEncoding];
+    NSString* base64 = [CBLBase64 encode: attach1];
+    NSDictionary* attachmentDict = $dict({@"attach", $dict({@"content_type", @"text/plain"},
+                                                           {@"data", base64})});
+    NSDictionary* props = $dict({@"_id", @"X"},
+                                {@"_attachments", attachmentDict});
+    CBL_Revision* rev1;
+    CBLStatus status;
+    NSError* error;
+    rev1 = [db putRevision: [CBL_MutableRevision revisionWithProperties: props]
+            prevRevisionID: nil allowConflict: NO status: &status error: &error];
+    AssertEq(status, kCBLStatusCreated);
+    AssertNil(error);
+    AssertEqual(rev1[@"_attachments"][@"attach"][@"revpos"], @1);
+
+    // Insert a revision several generations advanced but which hasn't changed the attachment:
+    CBL_MutableRevision* rev4 = [rev1 mutableCopy];
+    rev4[@"_rev"] = @"4-4444";
+    rev4[@"foo"] = @"bar";
+    [rev4 mutateAttachments: ^NSDictionary *(NSString *name, NSDictionary *att) {
+        NSMutableDictionary* nuAtt = [att mutableCopy];
+        [nuAtt removeObjectForKey: @"data"];
+        nuAtt[@"stub"] = @YES;
+        nuAtt[@"digest"] = @"md5-deadbeef";     // CouchDB adds MD5 digests!
+        return nuAtt;
+    }];
+    NSArray* history = @[@"4-4444", @"3-3333", @"2-2222", rev1.revID];
+    status = [db forceInsert: rev4 revisionHistory: history source: nil error: &error];
+    AssertEq(status, 200);
+}
+
 
 - (void) test16_FollowWithRevpos {
     NSDictionary* attachInfo = $dict({@"content_type", @"text/plain"},